CL2.1 | Earth radiation budget, radiative forcing and climate change

CL2.1

EDI
Earth radiation budget, radiative forcing and climate change
Co-organized by AS3
Convener: Martin Wild | Co-conveners: Jörg Trentmann, Maria Z. HakubaECSECS, Paul Stackhouse
Orals
| Thu, 27 Apr, 08:30–12:30 (CEST), 14:00–15:45 (CEST)
 
Room 0.49/50
Posters on site
| Attendance Thu, 27 Apr, 16:15–18:00 (CEST)
 
Hall X5
Posters virtual
| Attendance Thu, 27 Apr, 16:15–18:00 (CEST)
 
vHall CL
Orals |
Thu, 08:30
Thu, 16:15
Thu, 16:15
The radiation budget of the Earth is a key determinant for the genesis and evolution of climate on our planet and provides the primary energy source for life. Anthropogenic interference with climate occurs first of all through a perturbation of the Earth radiation balance. We invite observational and modelling papers on all aspects of radiation in the climate system. A specific aim of this session is to bring together newly available information on the spatial and temporal variation of radiative and energy fluxes at the surface, within the atmosphere and at the top of atmosphere. This information may be obtained from direct measurements, satellite-derived products, climate modelling as well as process studies. Scales considered may range from local radiation and energy balance studies to continental and global scales. In addition, related studies on the spatial and temporal variation of cloud properties, albedo, water vapour and aerosols, which are essential for our understanding of radiative forcings, feedbacks, and related climate change, are encouraged. Studies focusing on the impact of radiative forcings on the various components of the climate system, such as on the hydrological cycle, on the cryosphere or on the biosphere and related carbon cycle, are also much appreciated.

Orals: Thu, 27 Apr | Room 0.49/50

Chairpersons: Martin Wild, Jörg Trentmann, Paul Stackhouse
Surface Energy Budget
08:30–08:50
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EGU23-8365
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CL2.1
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solicited
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Highlight
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On-site presentation
John Augustine

Multidecadal dimming and brightening of solar radiation at Earth’s surface has been shown to occur over all continents. Trends have been especially well documented over the Northern Hemisphere (NH) with dimming from the 1950s through the middle 1980s followed by brightening through the first decade of the 2000s in the United States, Europe, and parts of Asia. Trends in Europe and China have been attributed to both aerosols and clouds, but in the U.S. cloud variability has been dominant. A recent analysis shows that U.S. brightening of 7.4 Wm-2/decade peaked in 2012 and then dramatically dropped to near normal values in 2013. Since then, surface solar radiation in the U.S. has remained within 1 Wm-2 of the long-term average. However, in Europe surface solar radiation has remained high, at least through 2017.

 

It has been shown that the direct effect of aerosols cannot account for the magnitude of the latest brightening in the U.S. It has also been shown that the second indirect effect of aerosols may explain brightening into the first decade of the 2000s, but is in opposition to the observed dimming after 2012. High aerosol content does explain perpetual dimming in India and industrial parts of China, but, given that the magnitude and period of dimming and brightening trends from the 1950s through the first decade of the 2000s are similar over North America, Europe, and parts of Asia, I speculate the primary cause is meteorological. A recent study documents a strong association between multidecadal surface solar radiation trends over NH continents and long-term North Pacific and North Atlantic sea surface temperature (SST) patterns. For example, the reversal of the Pacific Decadal Oscillation (PDO) index in the mid-1980s is nearly simultaneous with the change from dimming to brightening over NH continents. A similar association is shown between Atlantic SST patterns and continental surface solar radiation trends but with a decade lag. Using reanalysis and observed SST patterns it is demonstrated that persistent warm SST anomalies support overlying semipermanent geopotential height ridges at tropospheric mid-levels that dynamically induce persistent troughs downstream over adjacent continents, if positioning is favorable. Semipermanent troughs over the continents cause greater than average cloud cover and dimming. Conversely, long-term cool SSTs produce the opposite scenario and yield less clouds and brightening downstream over the continents. Further, marine heat waves on either side of North America are shown to be associated with the recent dimming in the midcontinent from 2013 to the present, and warm SSTs in the Mediterranean and North Seas in the last decade are likely responsible for a persistent midlevel geopotential ridge pattern and continued high surface solar radiation there. Recent studies present evidence that the observed increase in frequency and variability of marine heat waves in the past few decades may be associated with global warming, possibly linking warming to trends in surface solar radiation.

How to cite: Augustine, J.: Contributors to multidecadal dimming and brightening of surface solar radiation over Northern Hemisphere continents, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8365, https://doi.org/10.5194/egusphere-egu23-8365, 2023.

08:50–09:00
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EGU23-5155
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CL2.1
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ECS
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On-site presentation
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Boriana Chtirkova, Doris Folini, Lucas Ferreira Correa, and Martin Wild

We investigate potential reasons for decadal-scale internal variability of surface solar radiation (SSR) using model data from the Coupled Model Intercomparison Project - Phase 6. We compare unforced coupled atmosphere-ocean (piControl) to atmosphere-only (piClim) simulations with prescribed climatological sea surface temperatures (SSTs) to access the relevance of SSTs for unforced SSR inter-annual variability. Further, the connection between SSTs and known climate modes of variability is exploited. We focus on coupled and ocean-only modes of variability such as El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). Using the climate indices which describe these modes, we relate the SST field to SSR trends in different regions and we find a relationship between periods with strongly changing SSTs and decadal SSR depending on the regions. Unforced clear-sky SSR trends appear to mimic the SST trend pattern, while all-sky trends show a complex spatial structure with trends opposite in sign in different regions. These results are based only on pre-industrial control simulations (CMIP6 piControl) and can be used to infer in which direction internal variability has affected SSR in the historical period and whether it has enhanced or suppressed the anthropogenic signal from aerosols.

How to cite: Chtirkova, B., Folini, D., Ferreira Correa, L., and Wild, M.: Low-frequency modes in internal variability of surface solar radiation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5155, https://doi.org/10.5194/egusphere-egu23-5155, 2023.

09:00–09:10
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EGU23-4469
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CL2.1
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ECS
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On-site presentation
Lucas Ferreira Correa, Doris Folini, Boriana Chtirkova, and Martin Wild

Sea Surface Temperature (SST) plays a major role in the unforced variability of the climate system on decadal scales via the interplay between ocean and atmosphere, and associated changes in cloud cover and water vapor. The ocean modes, such as El Nino Southern Oscillation (ENSO) and Interdecadal Pacific Oscillation (IPO), are major coherent manifestations of SST variability. This means that the impacts of the ocean modes might be reflected in several components of the climate system, such as the energy budget. At the surface, this can be observed in the decadal trends in surface solar radiation (SSR). In this study we investigated the impacts of IPO and ENSO and associated cloud cover and water vapor variability on the decadal trends in SSR at 6 island stations scattered in the western Pacific (two stations in Fiji, one in New Caledonia, Nauru, Papua New Guinea and Marshall Islands). We combined between 15 and 40 years of daily SSR observations (depending on the station) with cloud cover from ERA5 reanalysis, aerosol optical depth (AOD) from CAMS reanalysis, and time series of IPO and ENSO. The comparison between clear-sky and all-sky SSR trends show that the all-sky trends strongly dominate in 5 out of the 6 stations. The exception is New Caledonia, where the clear-sky seems to also play an important role in the overall trend. This is the least cloudy station, and also the closest station to eastern Australia, an important source of aerosols in the region. Maps of cloud cover trends show two distinct regions which can be approximately separated by the average climatological position of the South Pacific Convergence Zone (SPCZ): one where cloud cover trends follow the phase of the IPO (positive IPO phase = positive cloud cover trend; N-NE of the SPCZ) and one where the opposite happens (positive IPO phase = negative cloud cover trend; S-SW of the SPCZ). The direct comparison between annual time series of all-sky SSR and IPO shows correlations stronger than 0.5 at two stations in Fiji and the one in New Caledonia (SW of the SPCZ). At the station in Nauru (North of the SPCZ) there is a negative correlation stronger than -0.5. When comparing annual all-sky SSR to the ENSO index, significant negative correlations are found at Momote-Papua New Guinea (-0.41) and at Nauru (-0.96), both located in the Western Pacific Warm Pool, near the Equator. In all cases strong negative correlations (<-0.7) between SSR and cloud cover using both annual and 11-year moving means time series support the hypothesis of strong cloud control over SSR interannual and decadal variability. The results indicate that IPO and ENSO play a major role in the SSR variability over the Western Pacific by controlling different cloud cover regimes in the region. This reveals a real world case of the importance of unforced internal variability to the SSR decadal and sub decadal changes.

How to cite: Ferreira Correa, L., Folini, D., Chtirkova, B., and Wild, M.: Impacts of the Ocean Modes on the Surface Solar Radiation decadal variability over the western Pacific, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4469, https://doi.org/10.5194/egusphere-egu23-4469, 2023.

09:10–09:20
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EGU23-15351
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CL2.1
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Highlight
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On-site presentation
Paul Glantz

Unmasking the Effects of Aerosols on Greenhouse Warming Over Europe

P. Glantz1, O. G. Fawole2, J. Ström1, M. Wild3 and K. J. Noone1

1Department of Environmental Science, Stockholm University, Stockholm, Sweden

2Dept. of Physics and Engineering Physics, Obafemi Awolowo University, Ile-Ife, Nigeria

3Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

 

This work with corresponding publication in Journal of Geophysical Research: Atmospheres, 127, e2021JD035889. https://doi.org/10.1029/2021JD035889 is supported by FORMAS, grant 2018-01291.

 

Aerosol optical thickness (AOT) has decreased substantially in Europe in the summer half year (April–September) since 1980, with almost a 50% reduction in Central and Eastern Europe, according to Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis. At the same time, strong positive trends in ERA5 reanalysis surface solar radiation downward for all-sky and clear-sky conditions (SSRD and SSRDc, respectively) and temperature at 2 m are found for Europe in summer during the period 1979–2020. The Global Energy Balance Archive (GEBA) observations show as well strong increases in SSRD during the latest four decades. Estimations of changes in SSRDc, using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model, show similarly strong increases when fed by MERRA-2 AOT. The estimates of warming in this study, caused by increases in SSRD and SSRDc, are based on energy budget approximations and the Stefan Boltzmann law. The increases in near surface temperature, estimated both for clear-sky and all-sky conditions, are up to about 1°C for Central and Eastern Europe. The total warming over large parts of this region for clear-sky conditions is however nearly double the global mean temperature increase of 1.1°C, while somewhat less for all-sky conditions. Although the largest effects from aerosols on the radiation balance occurred in the 1980s and 1990s, the total warming has continued to increase more or less at the same rates during the latest four decades over large parts of Europe, considering both all-sky and clear-sky situations. Thus, decline in aerosols can certainly not explain all warming observed and particularly not considering the southern Iberian Peninsula where the aerosol effects on warming are weaker compared to countries further north. The largest increases in sensible heat flux at the expense of latent heat flux have occurred in Iberian Peninsula, which is probably a result of drier surface conditions. This means a positive feedback associated with reduced evaporate cooling and warming of the lowest air layers. Decline in water vapor in combination with the warming may have contributed to decreased cloud cover, which is found for large parts of Europe in the summer half year during the latest four decades. Anthropogenic aerosols over large parts of Europe have thus temporarily masked, until around 1980, parts of rapid warming from increases in greenhouse gases. CO2 from fossil fuels is of particularly serious concern, since it can continue to affect climate for thousand years.

How to cite: Glantz, P.: Unmasking the Effects of Aerosols on Greenhouse Warming Over Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15351, https://doi.org/10.5194/egusphere-egu23-15351, 2023.

09:20–09:30
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EGU23-11280
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CL2.1
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ECS
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On-site presentation
Gabriel Chesnoiu, Nicolas Ferlay, Frédérique Auriol, Maxime Catalfamo, Isabelle Jankowiak, and Isabelle Chiapello

The absorption and scattering by aerosols and clouds greatly affect surface solar irradiance and the Earth's energy budget. Large uncertainties still remain on the current estimates of these radiative effects because of an incomplete knowledge of their spatial and temporal variabilities.

 

We analyze coincident daytime ground-based measurements of aerosol optical properties from AERONET photometer and of direct and diffuse horizontal surface irradiances from a set of pyrheliometer and pyranometer routinely performed at the ATOLL (Atmospheric Observations in LiLle) platform in north of France over the period 2010-2020. The site is located in a highly populated area greatly influenced by clouds and aerosol pollution. In order to isolate the radiative effect of aerosols from that of cloud occurences, a separation between cloudy-sun, clear-sun with surrounding clouds and clear-sky moments is performed using two cloud detection algorithms at 1-min resolution. The measurements are further analyzed using a radiative transfer code to simulate the spectrally integrated solar global horizontal irradiance and its components in clear-sky conditions with and without aerosols (pristine like conditions).

 

Our analysis shows that on average in ATOLL over the period 2010-2020, the sky is cloudy 89% of the time with around 67% of cloudy-sun situations and 22% of clear-sun with clouds moments. The proportion of clear-sky conditions is relatively low (11%) with a minimum in winter (6%) and a maximum in spring (15%).

 

In summer, we observe over the period a robust increasing trend in measured total irradiances in all-sky conditions of +5.2 ± 1.8 W/m²/year. This evolution is mainly explained by a positive trend in the occurrence of clear-sky situations (+0.7 ± 0.3% per year) to the detriment of cloudy-sun moments.

 

In spring, we highlight a high variability of cloud occurences and mean solar irradiances. Indeed, the mean proportion of clear-sky moments varies more than fourfold between 2013 (8%) and 2020 (35%), leading to corresponding all-sky irradiance extrema of 285 and 389 W/m² respectively. Moreover, in clear-sky conditions, an important variability is observed between the maximum of seasonal global irradiance of spring 2018 (522 W/m²) and the minimum of spring 2014 (435 W/m²). The latter variability is emphasised by a significative positive trend in direct irradiances observed for springtime clear-sky conditions of +5.3 ± 2.3 W/m²/year. A sensitivity analysis based on our radiative simulations shows that it is partly explained by a significant decrease in measured AOD440 nm (-0.006 ± 0.002 per year) and a change in the proportion of high aerosol loads over 2010-2020. This is also consistent with a negative trend of the diffuse component (-1.2 ± 0.4 W/m²/year) observed for clear-sky conditions in spring.

 

Finally, besides showing the highest proportion of clear-sky moments, spring is also the most polluted season in aerosol, with more than 80% of AOD440 nm higher than 0.1. This translates to an average seasonal maximum of aerosol direct radiative effect in spring of -22.6 W/m² (-6.1%), with a loss of -69.3 W/m² (-19.2%) of direct irradiance partially compensated by an increase of the diffuse radiation of +46.6 W/m² (101.0%).

How to cite: Chesnoiu, G., Ferlay, N., Auriol, F., Catalfamo, M., Jankowiak, I., and Chiapello, I.: Contribution of cloudy/clear-sky partitions and aerosol variability to the solar irradiance measured over 2010-2020 in Northern France, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11280, https://doi.org/10.5194/egusphere-egu23-11280, 2023.

09:30–09:40
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EGU23-6217
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CL2.1
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On-site presentation
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Quentin Bourgeois, Anke Tetzlaff, Reto Stöckli, Nicolas Christen, John Viju, William Moutier, Nicolas Clerbaux, Françoise Gellens-Meulenberghs, Jörg Trentmann, and Isabel Trigo

During the Third Continuous Development and Operations Phase (CDOP-3) of EUMETSAT, the Satellite Application Facility (SAF) on Climate Monitoring (CM SAF) extends its product portfolio with a Thematic Climate Data Record (TCDR) of Regional Land Fluxes based on two sensors of the Meteosat suite of geostationary satellites: the Meteosat Visible and InfraRed Imager (MVIRI) and the Spinning Enhanced Visible and InfraRed Imager (SEVIRI). The Regional Land Fluxes TCDR will provide various parameters depicting the surface states and radiation fluxes, including the Surface Radiative Balance (SRB), the Cloud Fractional Cover (CFC), the Land Surface Temperature (LST), the Evapotranspiration (ET) and the Latent (LE) and Sensible (H) Heat Fluxes. The TCDR is achieved by consolidating and unifying previously separated developments in CM SAF, LSA SAF and the EUMETSAT Secretariat, and running them in a joint retrieval using the Meteosat Fundamental Climate Data Record. This unique concept ensures consistency among the TCDR parameters.

We focus here on the SRB product of the Regional Land Flux TCDR. All components of the SRB - including the Surface Incoming Solar radiation (SIS, or solar irradiance), the Surface Albedo (SAL), the Surface Outgoing Longwave radiation (SOL) and the Surface Downward Longwave radiation (SDL) - are jointly retrieved using the CM SAF software “GeoSatClim” over the period 1983-2020. The SRB data record covers area up to 65°N/S and 65°W/E. The TCDR consists in hourly, daily and monthly means with a spatial resolution of 0.05 degree.

In this presentation, we show the detailed concept of the SRB algorithm. The SRB product and its single components are validated with BSRN, GEBA, ASRB and SwissMetNet ground based stations and they are compared with other global SRB products such as ERA5-Land, ISCCP-FH and CLARA. Overall, the SRB monthly mean absolute bias reaches the target accuracy of 15 W.m-2, and the SRB stability falls below the requirement of 2 W/m2/decade.

How to cite: Bourgeois, Q., Tetzlaff, A., Stöckli, R., Christen, N., Viju, J., Moutier, W., Clerbaux, N., Gellens-Meulenberghs, F., Trentmann, J., and Trigo, I.: Concept and validation of a Meteosat based dataset for Surface Radiative Balance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6217, https://doi.org/10.5194/egusphere-egu23-6217, 2023.

09:40–09:50
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EGU23-2608
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CL2.1
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ECS
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On-site presentation
Francisco José Cuesta-Valero and Jian Peng

Ground heat flux constitutes the conductive component of the surface energy budget. Quantifying this energy component is important to close the surface energy balance and to understand the energy exchanges between the lower atmosphere and the shallow subsurface. Furthermore, ground heat storage accounts for approximately 90 % of the continental heat storage, and 4-5 % of the total Earth heat storage. Therefore, monitoring changes in ground heat flux at global scale is of critical importance to quantify and understand the evolution of the Earth heat inventory, and thus climate change. However, the main sources of information about past and present ground heat flux are measurements of subsurface temperature profiles and micrometeorological observations, which are incomplete records biased towards northern extratropical latitudes.

Here, we present preliminary estimates of global ground heat flux derived from remote sensing products from the European Space Agency (ESA) Climate Change Initiative (CCI). Estimates from four land surface temperature (LST) products (MODIS-Terra, MODIS-Aqua, ENVISAT-AATSR, and SSMI-SSMIS) are evaluated against FLUXNET observations, obtaining a range of root mean squared errors from 3.8 to 5.2 W m-2 at monthly resolution. Nevertheless, there are some spatial inconsistencies among estimates from different LST products, as well as in long-term trends during the period 2003-2013. Several factors affecting the estimated ground heat flux are analyzed, with soil water and land cover having the largest effect on the retrieved values. These results suggest that land surface temperature from satellite observations may be able to provide global long-term ground heat flux estimates, although some issues still need to be solved.

How to cite: Cuesta-Valero, F. J. and Peng, J.: Global ground heat flux from remote sensing data: preliminary results and evaluation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2608, https://doi.org/10.5194/egusphere-egu23-2608, 2023.

09:50–10:00
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EGU23-8463
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CL2.1
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ECS
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On-site presentation
Norman Julius Steinert, Jesús Fidel González-Rouco, Philipp de Vrese, Francisco José Cuesta-Valero, Félix García Pereira, and Camilo Andrés Melo Aguilar

Under current climate-change conditions, the energy imbalance at the top of the atmosphere results in an uptake of energy by the Earth system. Previous efforts have identified the magnitude and proportions of this energy excess and how it is distributed among the different components of the climate system. However, the bulk of the Earth System Models (ESMs) participating in CMIP5/6 deliver Earth energy inventory estimates that differ substantially from recent observations. Particularly for the land component, there is a significant underestimation of simulated continental energy uptake, which was hypothesized to be caused by too shallow land surface model components in current-generation ESMs. Support for the latter was given by previous modeling estimates based on analytical heat conduction models and standalone land surface model simulations. Here we use a suite of current-generation fully-coupled CMIP6 ESMs and a version of the MPI-ESM that includes a deep land model component, accommodating the required space for increased terrestrial energy storage. The simulations show that a sufficiently deep land model leads to more realistic subsurface energy storage - correlating with model depth rather than climate sensitivity, and an adjusted estimate of energy uptake ratios among the Earth system components compared to observational estimates. However, the impact of changes in the land energy budget from the perspective of the entire Earth system appears to have only a marginal influence due to its relatively small fraction of the Earth energy inventory.

How to cite: Steinert, N. J., González-Rouco, J. F., de Vrese, P., Cuesta-Valero, F. J., García Pereira, F., and Melo Aguilar, C. A.: Global energy budget changes from underestimated land heat uptake in CMIP6 models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8463, https://doi.org/10.5194/egusphere-egu23-8463, 2023.

10:00–10:10
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EGU23-12
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CL2.1
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On-site presentation
William Collins and Daniel Feldman

In this study, we examine whether the interhemispheric symmetry observed
in broadband shortwave albedos also applies to the
hemispheric-mean visible and near-infrared albedos.  While
several recent exploratory studies have examined this question
using climate models, we explore this
question using direct observations of the visible and
near-infrared albedos collected by the Nimbus-7 satellite. This
study builds upon earlier intercomparisons of cloud spectral
albedos from Nimbus-7 and from climate models using the same
combinations of Nimbus-7 measurements used here (Collins, 1998).

We find that the hemispheric-mean spectral partitioning of albedo is
consistently and statistically significantly different between the two
hemispheres.  Consistent with prior studies, the origin of these
differences is due to interhemispheric differences in cloud cover.
Over oceans, the regional daily-mean differences between visible and
near-IR albedos are closely correlated with cloud amount.  The
relative differences are maximized for clear-sky conditions and
minimized for overcast conditions.

Background: The shortwave broadband albedo is a weighted sum of the albedos
in the visible and near-infrared bands.  Under condensate-free
conditions, the interactions of solar insolation in these bands
with the atmosphere and surface are quite different.  To an
excellent approximation, the condensate-free atmosphere is a
conservative Rayleigh-scattering medium in the visible.  Solar
radiation that is not reflected back to space is, to leading
order, transmitted to the surface.  In the near-infrared, the
interactions of sunlight with the atmosphere are dominated by
absorption, primarily with water vapor.  Additional absorption is
contributed by well-mixed greenhouse gases, oxygen, and other
gaseous constituents. The solar radiation
reaching the surface has therefore been reduced both by
reflection to space (from atmospheric condensates and the surface
albedo) and by absorption in the atmosphere. Hence, the relative
partitioning of net TOA insolation between the visible and
near-infrared bands will affect the relative partitioning between
atmospheric absorption and transmission to the surface.

 

How to cite: Collins, W. and Feldman, D.: Evidence for Hemispheric Spectral Albedo Inequality, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12, https://doi.org/10.5194/egusphere-egu23-12, 2023.

10:10–10:15
Coffee break
Chairpersons: Jörg Trentmann, Paul Stackhouse, Martin Wild
Forcing / Feedbacks / Clouds
10:45–11:05
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EGU23-11930
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CL2.1
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solicited
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Highlight
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On-site presentation
Chris Rentsch and Gunnar Myhre

We use 19 years of continuous near-global land and ocean direct AIRS satellite measurements combined with detailed atmospheric radiative transfer modelling to demonstrate strong strengthening in the greenhouse effect caused by CO2 and detectable, but comparatively smaller strengthening, by CH4 and N2O. An increase in the outgoing longwave radiation is found in the 800-1000 cm−1 atmospheric window resulting from the Planck response to surface heating. The combined use of satellite measurements and the radiative transfer model also demonstrate that reductions in concentrations of prohibited ozone depleting substances have weakened the greenhouse effect in the spectral region where these gases absorb thermal infrared radiation. The strong greenhouse effect strengthening signal in the satellite data in the spectral region 710-720 cm−1 is a fingerprint of CO2 increase since we demonstrate that other factors could not cause such a robust spectral feature. We show how the spectral clear sky instantaneous change in TOA flux relates to the greenhouse gas radiative forcing over the 19-year period.

How to cite: Rentsch, C. and Myhre, G.: Fingerprint of CO2 and other gases on the greenhouse effect from direct satellite observation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11930, https://doi.org/10.5194/egusphere-egu23-11930, 2023.

11:05–11:15
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EGU23-1015
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CL2.1
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On-site presentation
Brian Soden, Haohe He, Ryan Kramer, and Nadir Jeevanjee

Instantaneous radiative forcing (IRF) is a fundamental metric for measuring the extent to which anthropogenic activities and natural events perturb the Earth's energy balance. This perturbation initiates all other forced climate responses. Among all the anthropogenic forcing agents, CO2 is the dominant driver of warming over the past century and the defining forcing variable for quantifying climate sensitivity. When evaluating the effect of CO2 changes on the earth’s climate, it is universally assumed that the IRF from a doubling of a given CO2 concentration (IRF2×CO2) is constant and that variances in climate sensitivity arise from differences in radiative feedbacks, or a dependence of these feedbacks on the climatological base-state. In this paper, we show that the IRF2×CO2 is not constant, but also depends on the climatological base-state, increasing by ~25% for every doubling of CO2, and has increased by ~10% since the pre-industrial era, implying a proportionate increase in climate sensitivity. This base-state dependence also explains about half of the intermodel spread in IRF2×CO2, a problem that has persisted among climate models for nearly three decades. It may also have important implications for elucidating the causes and consequences of deep-time paleoclimates, where changes in the climatological base-state can strongly modulate the magnitude of the CO2 IRF.

How to cite: Soden, B., He, H., Kramer, R., and Jeevanjee, N.: State Dependence of CO2 Forcing and Its Implications for Climate Sensitivity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1015, https://doi.org/10.5194/egusphere-egu23-1015, 2023.

11:15–11:25
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EGU23-8983
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CL2.1
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On-site presentation
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Ragnhild Bieltvedt Skeie and Gunnar Myhre

In this study, radiative forcing time series on a component basis from the historical experiment in CMIP6 are presented. For each aerosol component (sulphate, black carbon, organic aerosols, nitrate) aerosol radiative forcing for aerosol-radiation interaction (RFari) is calculated from 1850 to 2014 using a radiative kernel and modelled changes in aerosol mass. The radiative kernel has been generated using the DISORT radiative transfer model. Aerosol radiative forcing for aerosol-cloud interaction (RFaci) is calculated offline based on the monthly fields from CMIP6 and simulate changes in the effective radius. For the individual models the time development of total aerosol radiative forcing is compared to aerosol effective radiative forcing (ERF) time series calculated within RFMIP, that take into account the adjustments. The radiative forcing trend will be presented on a global and a regional scale. The calculations are also done for the AeroCom phase III historical experiment. Both the AeroCom phase III and CMIP6 historical experiment use the CMIP6 CEDS emissions. These emissions are recently updated and extended. Using results from a chemistry transport model (OsloCTM3) we show how the updated emissions have changed the radiative forcing trends in the model. The emissions used to drive the models play an important role for determining the time development of the aerosol radiative forcing. At the end we will discuss uncertainties in the trend based on available historical global emission inventories for aerosol and aerosol precursors.

How to cite: Skeie, R. B. and Myhre, G.: Aerosol Radiative Forcing time development in the CMIP6 historical experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8983, https://doi.org/10.5194/egusphere-egu23-8983, 2023.

11:25–11:35
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EGU23-5727
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CL2.1
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ECS
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On-site presentation
Shreya Srivastava, Sushovan Ghosh, and Sagnik Dey

Aerosols directly affect Earth’s radiation budget by scattering and absorbing incoming solar radiation and outgoing terrestrial radiation. While the uncertainty in aerosol radiative forcing (ARF) has decreased over the years, it is still higher than that of greenhouse gas forcing, particularly in the South Asian region, due to high heterogeneity in aerosols’ chemical properties. India has been identified as an aerosol hotspot. Understanding the Spatiotemporal heterogeneity of aerosol composition is critical in improving ARF estimation.                            

In this study, we have taken aerosol data from Multi-angle Imaging Spectro-Radiometer (MISR) level-2 version 23 aerosol products retrieved at 4.4 km and radiation data from Clouds and the Earth’s Radiant Energy System (CERES, spatial resolution=1ox1o), for 21 years (2000-2021) over the Indian subcontinent. MISR aerosol product includes size and shapes segregated aerosol optical depth (AOD), Angstrom exponent (AE), and single scattering albedo (SSA). Additionally, 74 aerosol mixtures included in version 23 data are used for aerosol speciation. In addition, we have used CERES radiation data in four different atmospheric conditions: all-sky (AS), clear-sky (CS), pristine (PR) and no aerosol (NAER), for estimating aerosol radiative forcing in different aerosol-cloud conditions.

We have seasonally mapped aerosol optical and microphysical properties from MISR for India at quarter degrees resolution. Results show strong Spatio-temporal variability, with a constant higher value of AOD for the Indo-Gangetic Plain (IGP). The fractional contribution of small-size particles to AOD is higher (>0.4) throughout the year, spatially during post-monsoon and winter seasons (October to February). SSA is found to be overestimated by MISR, where absorbing particles are present. The climatological map of short wave (SW) ARF at the top of the atmosphere (TOA) shows a strong cooling except in only a few places (values ranging from +2.5W/m2 to -22.5 W/m2). Cooling due to aerosols is higher in the absence of clouds. Higher aerosol cooling is found over the IGP region, given the high aerosol concentration over the region. Aerosols are causing a surface cooling effect over our study domain, which is higher in clear conditions. The results strongly correlate with AOD from MISR and ARF from CERES. 

How to cite: Srivastava, S., Ghosh, S., and Dey, S.: Aerosol Radiative Forcing Over Indian Subcontinent for 2000-2021 using satellite observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5727, https://doi.org/10.5194/egusphere-egu23-5727, 2023.

11:35–11:45
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EGU23-7090
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CL2.1
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ECS
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On-site presentation
Jorma Rahu and Velle Toll

Anthropogenic aerosol particles affect clouds by serving as cloud condensation nuclei, thus significantly influencing Earth’s energy balance. The magnitude of aerosol-induced changes in cloud properties is still uncertain. This is primarily due to the meteorological covariability between aerosols and clouds, which hinders inferring causal relationships. Industrial air pollution sources serve as natural experiments to study strong anthropogenic cloud perturbations (Toll et al. 2019 Nature https://doi.org/10.1038/s41586-019-1423-9) and allow us to infer causal relationships between aerosols and clouds.

 

We use geostationary satellite observations to study the temporal evolution of polluted clouds. Polluted clouds are usually thinner than nearby unpolluted clouds. But in some cases, the polluted clouds grow much thicker in the afternoon than the nearby unpolluted clouds. We find that continental polluted cloud tracks are relatively long-lived, with a median lifetime of 18 hours. Moreover, there are many cases where polluted cloud tracks are visible for multiple consecutive days. This means polluted cloud tracks live long enough for clouds to fully adjust to aerosol-increased cloud droplet numbers. Future work is needed to combine geostationary and polar orbiting satellite observations of polluted cloud tracks to develop stronger observational constraints for aerosol-cloud interactions.

How to cite: Rahu, J. and Toll, V.: Novel insights into aerosol-cloud interactions enabled by analysing the temporal evolution of strong anthropogenic cloud perturbations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7090, https://doi.org/10.5194/egusphere-egu23-7090, 2023.

11:45–11:55
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EGU23-14718
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CL2.1
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ECS
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On-site presentation
Jean Lac, Hélène Chepfer, Michael R. Gallagher, and Assia Arouf

Greenland Ice Sheet (GrIS) melt plays a major role in the global sea level rise. Surface melting is driven by changes in the radiative budget at the surface which is modulated by clouds. However, relatively little is known on the influence of local atmospheric processes on the fragile GrIS coast. Here we used space based lidar cloud profile observations with complementary data to show that low clouds formed in response to the Arctic sea ice retreat in September are transported over the GrIS west coast and warm radiatively the GrIS surface. Previous works have shown that low liquid clouds are formed in response to arctic sea ice retreat in September. We first showed the existence of continuous stratiform low liquid clouds between the Baffin Sea and the GrIS west coast in September using 12 years space lidar data at full resolution (instantaneous time scale and less than 500m spatial scale). Secondly, we analyzed wind profiles from re-analyis and from recent Doppler wind space lidar data and found that westerlies transport these stratiform clouds from the Baffin Sea to the GrIS west coast. Then, we used Surface LongWave Cloud Radiative Effect data derived from space-based active sensors for days that correspond to these specific situations where clouds are transported from the Baffin Sea, to quantify how much they warm radiatively the GrIS coast. We found that clouds coming from the Baffin Sea warm radiatively the GrIS west coast surface by +80W/m2 during the month of September. This contributes to an increase of +10W/m2 of cloud surface warming in average between July and September on the GrIS west coast. Overall, this study suggests that processes independent from large-scale circulation also influence the GrIS mass balance. 

How to cite: Lac, J., Chepfer, H., Gallagher, M. R., and Arouf, A.: Low opaque clouds formed over Baffin Sea enhances Greenland's west coast surface cloud warming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14718, https://doi.org/10.5194/egusphere-egu23-14718, 2023.

11:55–12:05
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EGU23-2448
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CL2.1
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ECS
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On-site presentation
Chongxing Fan, Yi-Hsuan Chen, Xiuhong Chen, Wuyin Lin, Xianglei Huang, and Ping Yang

Climate models often ignore cloud scattering and surface emissivity in the longwave (LW) for computational efficiency. Such approximations can cause biases in radiative fluxes and affect simulated climate, especially in the Arctic because of its large sensitivity to perturbations. We implemented treatments to both physics into the Energy Exascale Earth System Model (E3SM) version 2 by DoE and assessed their impacts on the simulated mean-state global climate as well as climate feedback and sensitivity.

By turning on and off the switches in the modified E3SMv2 model, we studied the changes in mean-state climate due to cloud LW scattering and surface emissivity effects by comparing four 35-year fully-coupled simulations. Cloud LW scattering warms the entire global troposphere by ~0.4 K on average; the warming is stronger in the Arctic (~0.8 K) than in the tropics, which is a manifestation of the polar amplification phenomenon. When realistic emissivity is incorporated into the model, the surface skin temperature increases by 0.36 K instantaneously on a global average, especially in the Sahara Desert (~0.7 K) where the surface emissivity is low. Surface skin temperature, as well as surface air temperature and tropospheric temperature, further increases by 0.19 K due to the inclusion of surface spectral emissivity. The mean-state climate changes due to both effects are linearly additive. The latitudinal and seasonal pattern of surface air temperature warming resulting from both effects is very similar to the response due to CO2 increase in the standard E3SMv2 model.

We also carried out four 35-year simulations under the abrupt 4xCO2 scenario, with cloud LW scattering and/or surface emissivity effects on and off. Based on standard radiative kernel analysis, we found that total global-mean climate feedback does not change significantly after including either or both physics. Nevertheless, lapse rate feedback, water vapor feedback, and cloud feedbacks in the tropics have changes by up to 10%. They are primarily associated with high cloud fraction response in the upper troposphere. Our study suggests that both the cloud LW scattering effect and the surface spectral emissivity effect should be included in climate models for a faithful representation of the radiative process in the atmosphere, especially at regional scales.

How to cite: Fan, C., Chen, Y.-H., Chen, X., Lin, W., Huang, X., and Yang, P.: Including Ice-Cloud Longwave Scattering and Surface Spectral Emissivities in Climate Models Leads to More Impacts on Mean-State Climate than Climate Feedbacks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2448, https://doi.org/10.5194/egusphere-egu23-2448, 2023.

12:05–12:15
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EGU23-5372
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CL2.1
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ECS
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On-site presentation
Florian E. Roemer, Stefan A. Buehler, Manfred Brath, Lukas Kluft, and Viju O. John

The spectral longwave feedback parameter λν represents how Earth’s outgoing longwave radiation adjusts to temperature changes and is thus the detailed fingerprint of all longwave feedbacks, directly impacting Earth’s climate sensitivity. Most research so far has focused on the spectral integral of λν. Spectrally resolving λν permits inferring information about the vertical distribution of longwave feedbacks, thus gaining a better understanding of the underlying processes. However, investigations of λν have so far been largely limited to model studies, and no observational study we are aware of has inferred the global all-sky λν.

Here we show that it is possible to directly observe the global all-sky λν using satellite observations of seasonal and interannual variability taken by the Infrared Atmospheric Sounding Interferometer (IASI). We find that spectral bands subject to strong water vapour absorption exhibit a substantial stabilising net feedback. We demonstrate that this stabilising feedback is partly caused by changes in relative humidity with warming, the radiative fingerprints of which can be directly observed. Therefore, our findings emphasise the importance of better understanding processes affecting future trends in relative humidity. This first observational constraint on the global all-sky λν can be used as a powerful tool to evaluate the representation of longwave feedbacks in global climate models and to better constrain Earth’s climate sensitivity.

How to cite: Roemer, F. E., Buehler, S. A., Brath, M., Kluft, L., and John, V. O.: Direct observation of Earth’s spectral longwave feedback parameter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5372, https://doi.org/10.5194/egusphere-egu23-5372, 2023.

12:15–12:25
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EGU23-3896
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CL2.1
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ECS
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On-site presentation
Brett McKim, Sandrine Bony, Marion Saint-Lu, and Jean-Louis Dufresne

An outstanding question in climate science is how much the change in tropical anvil cloud clover with warming influences Earth's climate sensitivity. Here, we construct a simple model of cloud radiative effects to obtain an analytical equation for the tropical anvil area “iris” feedback. Our equation shows how the feedback is constrained by the fractional change in anvil cloud area, the anvil cloud radiative effect, and the radiative masking of low clouds that live beneath anvils.  We then look at satellite observations to diagnose these quantities. We find that the inferred values of anvil cloud radiative effect and low cloud masking effects sum to 1 Wm-2. Owing to this small radiative effect, the observed changes in anvil cloud cover in interannual variability implies an iris feedback that is wholly insufficient to strongly influence climate sensitivity. We then extend our equation to address whether anvil clouds might affect climate sensitivity through their masking of other forcings  or feedbacks.

How to cite: McKim, B., Bony, S., Saint-Lu, M., and Dufresne, J.-L.: Constraining the tropical anvil cloud "iris" feedback, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3896, https://doi.org/10.5194/egusphere-egu23-3896, 2023.

12:25–12:30
Lunch break
Chairpersons: Paul Stackhouse, Martin Wild, Jörg Trentmann
TOA Energy Budget
14:00–14:20
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EGU23-2962
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CL2.1
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solicited
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Highlight
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On-site presentation
Norman Loeb, Tyler Thorsen, Sueng-Hee Ham, Fred Rose, and Seiji Kato

Observations from the Clouds and the Earth’s Radiant Energy System (CERES) show a marked increase in Earth’s energy imbalance (EEI) since 2000. At the same time, we’ve seen marked changes in numerous geophysical variables that influence EEI. While observations alone cannot quantify the anthropogenic and natural contributions to changes in these quantities, they can provide insight into how changes in different components of the climate system have led to the observed EEI trend. Using additional data from MODIS, CALIPSO, Cloudsat, and reanalysis, we find the increase in EEI to be due to decreased reflection by clouds and sea-ice, which cause a pronounced increase absorbed solar radiation (ASR), and a decrease in outgoing longwave radiation (OLR) due to increases in trace gases and water vapor. The ASR increases are largest over the subtropics and mid-latitudes in regions with decreases in low and middle cloud fraction, which likely occur in response to observed increases in sea-surface temperature (SST) in those locations. We diagnose the SST changes by performing an ocean mixed layer energy budget analysis at regional, hemispheric, and global scales using TOA and surface radiation observations from CERES, SST and temperature/humidity fields from ERA-5, and ocean mixed layer depth from ocean reanalysis. This analysis suggests that heating of the mixed layer and the subsequent increase in SST stems from ocean mixing/advection rather than from surface forcing. 

How to cite: Loeb, N., Thorsen, T., Ham, S.-H., Rose, F., and Kato, S.: Observational Assessment of Changes in Earth’s Energy Imbalance Since 2000, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2962, https://doi.org/10.5194/egusphere-egu23-2962, 2023.

14:20–14:30
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EGU23-2796
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CL2.1
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ECS
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On-site presentation
Bernd Uebbing, Kristin Vielberg, Bene Aschenneller, Roelof Rietbroek, Armin Köhl, and Jürgen Kusche

Earth Energy Imbalance (EEI) results from a net positive radiative flux at the top of atmosphere. Over 90% of this excess energy is stored as heat in the ocean causing present day ocean heat content (OHC) change. This in turn leads to volumetric or steric expansion of the water column and sea level rise. Utilizing observed bias-corrected short- and long-wave energy fluxes from the CERES project, it is possible to estimate EEI at the top of atmosphere. However, bias corrections rely on reanalysis OHC, potentially resulting in overestimation of ocean heat uptake (OHU).

Combining GRACE(-FO) and altimetry observations and constructing global sea level budgets allows to derive (thermo-)steric sea level change and convert this to OHU; the latter is generally achieved considering a literatute-based ocean-mean expansion efficiency of 0.52 [W/m^2 / mm/yr]. Nonetheless, this approach is valid for global mean steric sea level change only and it is unclear to what extent one can use it for investigating regional OHU.

Here, we develop a novel approach for deriving global and regional observation based OHC and OHU, which consists of three steps. (1) Fitting mass and steric spatial patterns, so called fingerprints, to GRACE(-FO) and altimetry data in a joint least-squares inversion. (2) Projecting reanalysis OHC onto the same spatial patterns that we use to explain steric variability. (3) Rescaling reanalysis OHC based on the observed steric sea level changes and reconstruction of spatial maps of OHC. These can then be further analyzed in order to derive global and regional OHU.

Based on preliminary results for years 2005-01 till 2015-12, we find ~1.2 mm/yr (thermo-)steric sea level change. Global-mean OHU of 0.62 [W/m^2] can be derived from the literature expansion efficiency above, while we find 0.63 [W/m^2] from the novel rescaling approach and 0.87 [W/m^2] based on ORAS5 ocean model data only. Regionally analyzing these results regarding individual ocean contributions reveals that the ocean model seems to significantly overestimate the uptake of the Atlantic and Pacific oceans, while slightly underestimating the Indian ocean contribution.

How to cite: Uebbing, B., Vielberg, K., Aschenneller, B., Rietbroek, R., Köhl, A., and Kusche, J.: A novel approach for assessing regionally differentiated ocean contributions to Earth Energy Imbalance from GRACE(-FO) and multi-mission altimetry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2796, https://doi.org/10.5194/egusphere-egu23-2796, 2023.

14:30–14:40
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EGU23-14330
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CL2.1
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Highlight
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On-site presentation
Øivind Hodnebrog, Gunnar Myhre, Hailing Jia, Johannes Quaas, Caroline Jouan, and Piers M. Forster

The Earth’s energy imbalance (EEI) is the difference in the net solar radiative flux and outgoing longwave radiative flux at the top-of-atmosphere. It has been shown that the positive EEI trend in the previous two decades is unexplained by internal variability and caused by anthropogenic forcing and response, such as that resulting from anthropogenic CO2 emissions. In this work we apply two state-of-the-art global climate models, the CESM2 and ICON-HAM, forced with observed (evolving) sea-surface temperature fields for the period 2000-2019 and with multiple ensemble members, to explore causes for the positive trend in EEI. Both models are able to reproduce the observed EEI trend from the CERES satellite product relatively well. Sensitivity simulations with aerosol emissions kept constant at year 2000 values indicate a relatively strong influence of recent aerosol emission reductions on the EEI trend. Preliminary results further indicate a considerable effect of using the latest CEDS emission version, as opposed to the CMIP6 CEDS version, on the EEI trend.

How to cite: Hodnebrog, Ø., Myhre, G., Jia, H., Quaas, J., Jouan, C., and Forster, P. M.: Earth’s energy imbalance trend strengthened by recent aerosol emission reductions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14330, https://doi.org/10.5194/egusphere-egu23-14330, 2023.

14:40–14:50
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EGU23-3268
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CL2.1
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On-site presentation
Steven Dewitte

The long term global temperature rise caused by increased greenhouse gas radiative forcing is partially masked by temporary aerosol radiative cooling, which remains poorly known.

I present a new purely observation based estimate of Aerosol Radiative Forcing (ARF) due solely to the direct radiative effect of aerosols over clear sky ocean, and its time variation over the period 2003-20204 from combined MODIS and CERES aerosol, cloud, and radiation measurements. The resulting mean 2003-2020 ARF is -1.16 +/- 0.39 W/m2 , with no significant trend within an uncertainty of +/- 0.025 W/m2dec.

Combining this ARF with the best estimate of the greenhouse gas and solar radiative forcing, and the most likely value of the Equilibrium Climate Sensitivity, produces a plausible Earth Energy Imbalance as a residual of the energy balance equation at the top of the atmosphere.

How to cite: Dewitte, S.: Aerosol Radiative Forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3268, https://doi.org/10.5194/egusphere-egu23-3268, 2023.

14:50–15:00
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EGU23-13064
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CL2.1
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ECS
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Virtual presentation
Michael Stamatis, Nikolaos Hatzianastassiou, Marios Bruno Korras Carraca, Christos Matsoukas, Martin Wild, and Ilias Vardavas

The Earth’s energy balance and radiation budget, which play a key role in the Earth’s climate system, are driven by the incident solar radiation at surface (surface solar radiation, SSR). Over the past few decades, changes in the SSR (ΔSSR) have been observed that are dependent on the transparency of the terrestrial atmosphere. This phenomenon, called global dimming and brightening (GDB), is a significant factor in climate change and modulates global warming. This study examines the interdecadal variability of SSR based on computations of the FORTH radiative transfer model, using as input data cloud optical properties taken from the International Satellite Cloud Climatology Project H Series (ISCCP-H) and aerosol optical properties and meteorological data taken from the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) Reanalysis. Ground-based measurements of SSR from the Global Energy Balance Archive (GEBA) and Baseline Surface Radiation Network (BSRN) networks are utilized to evaluate the FORTH’S SSR fluxes and GDB. The FORTH RTM computations are made on a monthly basis from 01/1984 - 12/2018 at 51 atmospheric levels and a spatial horizontal resolution of 0.5°×0.625° (with a conversion of the original input data to the same spatio-temporal resolution). Firstly, the FORTH SSR fluxes are evaluated against ground measurements from GEBA and BSRN. This comparison reveals a general underestimation of the FORTH SSR fluxes, with a satisfactory evaluation metrics, such as the relative bias, which is equal to –2.9% and –7.7% against GEBA and BSRN, respectively or the correlation coefficient values, computed using deseasonalized SSR anomalies, being equal to 0.72 and 0.8 against GEBA and BSRN, respectively. Then, the SSR changes (or GDB) for each pixel, also calculated using deseasonalized SSR anomalies, were compared with the GDB from the corresponding GEBA/BSRN station, lying in that pixel, for their common time period. This comparison reveals an agreement between the sign of the FORTH’s pixels and the corresponding stations’ GDB equal to 63.5% for the GEBA and 54.5% for the BSRN sites. Finally, the GDB was also calculated on global (land & ocean), hemispherical and regional scales, either for the entire period and for sub-periods too. The computed GDB for the period 01/1984-12/2018 is equal to –2.22 ± 0.38 W/m2 for the Globe, -0.48 ± 0.39 W/m2 for the Northern Hemisphere and -2.73 ± 0.54 W/m2 for the Southern Hemisphere. Larger GDB values are estimated over oceans than land (-2.56 ± 0.44 versus -1.04 ± 0.47 W/m2, respectively), suggesting that the atmosphere over oceans got less transparent than over continents during the 35-year study period. During this period, a brightening has taken place over Europe, Middle East, Mexico against a dimming over India, Maritime Continent, Australia and Southern Ocean.

How to cite: Stamatis, M., Hatzianastassiou, N., Korras Carraca, M. B., Matsoukas, C., Wild, M., and Vardavas, I.: The Global Dimming & Brightening based on FORTH radiative transfer model during 1984-2018 and its evaluation against GEBA & BSRN ground-based networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13064, https://doi.org/10.5194/egusphere-egu23-13064, 2023.

15:00–15:10
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EGU23-10455
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CL2.1
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ECS
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On-site presentation
Han Huang and Yi Huang

The outgoing longwave radiation (OLR) at the top of the atmosphere is a critical component of the Earth's radiation energy budget. A substantial portion of the OLR energy lies in the far-infrared (FIR) spectrum, which has not been directly measured for understanding weather and climate variations. Several satellite projects under development, including the Thin Ice Cloud in Far Infrared Experiment (TICFIRE, Blanchet et al. 2011) funded by the Canadian Space Agency, the Polar Radiant Energy in the Far Infrared Experiment (PREFIRE, L’Ecuyer et al., 2021) of U.S. NASA, and the Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM, Palchetti et al., 2020) of the European Space Agency, are being developed to fill this observation gap. Given that the FIR observation data is not available yet, we use simulations to acquire prior knowledge of the climatological mean distribution of the OLR in FIR, by using a rapid radiative transfer model, RRTMG, to simulate spectrally decomposed OLR in different spectral bands from global instantaneous atmospheric profiles of the fifth generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5). Based on the radiative transfer equation, we dissect the OLR by attributing its distribution and variation to spectrally and vertically decomposed contributions of the atmosphere and Earth surface. Our results disclose that the relatively higher far-infrared fraction of the OLR in polar region is due to stronger surface contribution and identify a minimum atmospheric contribution layer around the tropopause. On the other hand, the variability of the spectrally decomposed OLR field is dissected with the aid of a new set of radiative sensitivity kernels. This analysis discovers that the non-cloud longwave climate feedback, as well as its inter-climate model discrepancy, mainly results from the upper tropospheric thermodynamic fields (temperature and water vapor) and their effects on the FIR radiation.

How to cite: Huang, H. and Huang, Y.: The spectrally and vertically decomposed outgoing longwave radiation and its climate trends in the far-infrared, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10455, https://doi.org/10.5194/egusphere-egu23-10455, 2023.

15:10–15:20
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EGU23-1078
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CL2.1
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On-site presentation
Ming Cai, Jie Sun, Feng Ding, Wanying Kang, and Xiaoming Hu

The slope of the quasi-linear relation between planetary outgoing longwave radiation (OLR) and surface temperature (TS) is an important parameter measuring the sensitivity of the Earth climate system. The main goal of this study is to seek a general explanation for the quasi-linear OLR-TS relation that does not require the narrowing of “atmospheric window” of planetary thermal radiation. The physical understanding on the quasi-linear OLR-TS relation and its slope is gained from observation analysis, climate simulations with radiative-convective equilibrium and general circulation models, and a series of online feedback suppression experiments.

The observed quasi-linear OLR-TS relation manifests a climate footprint of radiative (such as greenhouse effect) and non-radiative processes (poleward energy transport). The former acts to increase the meridional gradient of surface temperature and the latter decreases the meridional gradient of atmospheric temperatures, causing the flattening of the meridional profile of the OLR. Radiative processes alone can lead to a quasi-linear OLR-TS relation that is more steeply sloped. The atmospheric poleward energy transport alone can also lead to a quasi-linear OLR-TS relation by rerouting part of the OLR to be emitted from the warmer place to colder place. The combined effects of radiative and non-radiative processes make the quasi-linear OLR-TS relation less sloped with a higher degree of linearity. In response to anthropogenic radiative forcing, the slope of the quasi-linear OLR-TS relation would be further reduced via stronger water vapor feedback and enhanced poleward energy transport.

How to cite: Cai, M., Sun, J., Ding, F., Kang, W., and Hu, X.: The quasi-linear relation between planetary outgoing long wave radiation and surface temperature: a climate footprint of radiative and non-radiative processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1078, https://doi.org/10.5194/egusphere-egu23-1078, 2023.

15:20–15:30
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EGU23-2384
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CL2.1
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ECS
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On-site presentation
Sanjeevani Panditharatne, Helen Brindley, Caroline Cox, and Richard Siddans

Theoretical models suggest that ∼55% of the outgoing longwave radiation from Earth is within the far-infrared region, 100-666 cm−1. Nevertheless, the top-of-atmosphere radiation spectrum in this region has never been measured, something that will change with ESA’s Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission, launching in 2027. Studies have indicated that absorption within this region is dominated by tropospheric water vapour, significantly impacting Earth’s radiation budget. Quantifying these concentrations plays a vital role in estimating its radiative effects and associated feedbacks.

The Infrared and Microwave Sounding (IMS) retrieval scheme developed at RAL Space is an optimal estimation scheme currently using channels within the mid- and near-infrared as well as the microwave region to obtain simultaneous retrievals of the vertical atmospheric profile and cloud properties. Current retrievals using this scheme have been performed on observations from Infrared Atmospheric Sounding Interferometer (IASI), Microwave Humidity Sounder (MHS) and the Advanced Microwave Sounding Unit (AMSU) onboard the MetOp satellites. Temperature and water vapour retrievals using this framework have been validated against radiosonde data with biases within 1 K and 10% of the reference respectively.

This work seeks to extend IMS into the far-infrared and exploit the known sensitivity of upwelling radiation within this region to improve current retrievals of water vapour. This would enhance our understanding of the spatial and temporal variations of water vapour within the atmosphere, and its role in Earth's radiation budget. Unique clear-sky airborne measurements will be used to analyse channel sensitivity within this region and maximise the information content for the retrieval. This retrieval capability would be the first of its kind to be thoroughly validated in this way and would be available for use on FORUM observations.

How to cite: Panditharatne, S., Brindley, H., Cox, C., and Siddans, R.: Optimising water vapour retrievals by exploiting sensitivity within the far-infrared: A study in support of the ESA FORUM mission., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2384, https://doi.org/10.5194/egusphere-egu23-2384, 2023.

15:30–15:40
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EGU23-17097
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CL2.1
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On-site presentation
Peter Pilewskie, Maria Hakuba, and Graeme Stephens

The Libera Mission, named for the daughter of Ceres in Roman mythology, will provide continuity of the Clouds and the Earth’s Radiant Energy System (CERES) Earth radiation budget (ERB) observations from space. Libera’s attributes enable a seamless extension of the current 23-year ERB climate data record from CERES. Libera will acquire spectrally integrated radiance over the CERES FM6-heritage broad spectral bands in the shortwave (0.3 – 5 μm), longwave (5 – 50 μm) and total (0.3 – beyond 100 μm) and adds a split-shortwave band (0.7 – 5 μm) to provide deeper insight into shortwave energy deposition. Libera leverages advanced detector technologies using vertically aligned black-carbon nanotubes with closed-loop electrical substitution radiometry to achieve radiometric uncertainty of approximately 0.2%. Libera will also employ a wide field-of-view camera to provide scene context and accelerate the development of the split-shortwave angular distribution models.

Libera’s stewardship of the ERB record begins in the latter part of this decade, at an important juncture in the monitoring of climate trends. Libera is currently slated for a launch aboard JPSS-3 in December 2027, when the probability of a CERES data gap will be approaching 50%. The Libera science objectives associated with continuity and extension of the ERB data record are to identify and quantify processes responsible for ERB variability on various times scales. Beyond data continuity, Libera’s new and enhanced observational capabilities will advance our understanding of spatiotemporal variations of radiative energy flow in the visible and near-infrared spectral regions in addition to facilitating the rapid development of new angular distribution models for near-infrared and visible radiance-to-irradiance conversion.

This talk provides an overview of the Libera’s observational strategy, its measurements, science goals and objectives. We discuss the importance of climate data record continuity in the context of the current climate state and anticipated changes over the next decade and beyond.

How to cite: Pilewskie, P., Hakuba, M., and Stephens, G.: The Future of Earth Radiation Budget Observations Beyond CERES: Libera and Continuity of the ERB Climate Data Record, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17097, https://doi.org/10.5194/egusphere-egu23-17097, 2023.

15:40–15:45

Posters on site: Thu, 27 Apr, 16:15–18:00 | Hall X5

Chairpersons: Martin Wild, Jörg Trentmann, Paul Stackhouse
X5.185
|
EGU23-6
|
CL2.1
William van Wijngaarden, Cornelis de Lange, James Ferguson, and Will Happer

Higher concentrations of atmospheric nitrous oxide are expected to slightly warm Earth's surface because of an increase in radiative forcing.  For current concentrations of greenhouse gases, the radiative forcing per added N2O molecule, is about 230 times larger than the forcing per added carbon dioxide molecule.  This is due to the heavy saturation of the absorption band of the relatively abundant greenhouse gas, CO2, compared to the much smaller saturation of the absorption bands of the trace greenhosue gas N2O.  But the rate of increase of CO2 molecules, about 2.5 ppm/year is about 3000 times larger than the rate of increase of N2O molecules, which has held steady at around 0.85 ppb/year since 1985.  So the contribution of nitrous oxide to the annual increase in forcing is 230/3000 or about 1/13 that of CO2.  If the main greenhouse gases, CO2, CH4 and N2O have contributed about 0.1 K/decade of the warming observed over the past few decades, this would correspond to about 0.00064 K per year or 0.064 K per century of warming from N2O.  This rather small warming does not support placing harsh restrictions on nitrous oxide emissions, which could seriously jeopardize world food supplies.

How to cite: van Wijngaarden, W., de Lange, C., Ferguson, J., and Happer, W.: Nitrous Oxide and Climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6, https://doi.org/10.5194/egusphere-egu23-6, 2023.

X5.186
|
EGU23-2
|
CL2.1
Miklos Zagoni

We announced a public challenge at the EGU 2020 General Assembly against CMIP6 models predicting an increase of downward longwave radiation (DLR) in the range of 10 – 40 Wm-2 during the 21st century as a result of human greenhouse gas emissions. We based our challenge on observed facts, supported by long-known but rarely referred theoretical constraints. 22 years of CERES data show +0.11 Wm-2/decade increase in DLR, equivalent to +0.36 Wm-2 increase (+0.06 °K) until 2050 (in contrast to IPCC AR6, predicting +2 Wm-2/decade).

Supporting our prediction, we repeat here the deduction of the constraint equations, and control them on the recently available data sets. — Our best tool the compute the transfer of radiation in the atmosphere is Schwarzschild’s (1914) equation; its early, two-stream form is given in Schwarzschild (1906, Eq. 11), appropriate for global-mean energy flow computations. The equation consists of three terms; the difference of the second and first terms gives the net radiation at the surface as constrained to half of the outgoing longwave radiation (OLR), independently of the optical depth.  In the literature it was observed early (Emden 1913) that there is a discontinuity at the surface in radiative equilibrium, balanced by the turbulent fluxes in radiative-convective equilibrium. The formula for this net radiation is given for example in the textbook of Goody (1964, Atmospheric radiation: theoretical basis); repeated by Houghton (1977, Eq. 2.13), graphically represented in Chamberlain (1979, Fig. 1.4); and verified by the data (without explicitly describing the equation) of Hartmann (1994, pp. 61-63) within 0.3 Wm-2. The equation is verified by the CERES EBAF Ed2.8 (16 years of clear-sky global mean data) within 0.6 Wm-2. We use the second term of Schwarzschild (1906, Eq.11) with a particular optical depth of τ = 2 to compute the total energy absorption (and emission) at the surface, verified by the same satellite data product within the same difference (0.6 Wm-2) in the clear-sky annual global mean. — We created the all-sky versions of these two equations by introducing longwave cloud radiative effect (LWCRE), and justified the four individual equations on the most recent 22 years of CERES EBAF Edition 4.1 global mean data within ±3 Wm-2; while the mean bias of the four equations together is 0.0007 Wm-2. These equations form the boundary conditions of every valid climate prediction.

Reference:
Zagoni, M.: Challenging CMIP6 model predictions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1, https://doi.org/10.5194/egusphere-egu2020-1

 

How to cite: Zagoni, M.: State of a challenge – Third annual review, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2, https://doi.org/10.5194/egusphere-egu23-2, 2023.

X5.187
|
EGU23-6759
|
CL2.1
|
Martin Wild, Doris Folini, and Donghao Li

A plausible simulation of the global energy balance is a first-order requirement for a credible climate model. Therefore we investigate the representation of the global energy balance in the latest generation of global climate models (CMIP6). In the multi-model global mean, the magnitudes of the energy balance components of the CMIP6 models are often in better agreement with our reference estimates (Wild et al. 2015, 2019 Clim Dyn) as well as those from CERES/EBAF and NASA/NEWS than in earlier model generations (Wild 2020). However, the inter-model spread in the representation of many of the components remains substantial, often on the order of 10-20 Wm-2 globally, except for the shortwave clear-sky budgets, which are now more consistently simulated by the CMIP6 models. The substantial inter-model spread in the simulated global mean latent heat fluxes in the CMIP6 models, exceeding 20% (18 Wm-2), further implies also large discrepancies in their representation of the global water balance. From a historic perspective of model development over the past decades, the largest adjustments in the magnitudes of the simulated present-day global mean energy balance components occurred in the shortwave atmospheric clear-sky absorption and the surface downward longwave radiation. Both components were gradually adjusted upwards over several model generations, on the order of 10 Wm-2, to reach 73 and 344 Wm-2, respectively in the CMIP6 multi-model means. Thereby, CMIP6 has become the first model generation that largely remediates long-standing model deficiencies related to an overestimation in surface downward shortwave and compensational underestimation in downward longwave radiation in its global multi-model mean. There are also indications for an overall improvement in the representation of the energy budgets in the CMIP6 models compared to CMIP5 on regional scales (regions considered here as defined by the NASA/NEWS project). Still substantial spreads between the energy balance components of individual CMIP6 models appear also on regional scales (Li et al. 2022).

 

Related references:

Wild, M., 2020: The global energy balance as represented in CMIP6 climate models. Clim Dyn., 55, 553–577

Li, D., Folini D., Wild, M., 2022: Assessment of regional energy budgets in CMIP6 models, submitted

 

 

How to cite: Wild, M., Folini, D., and Li, D.: The Global Energy Balance as represented in CMIP6 climate models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6759, https://doi.org/10.5194/egusphere-egu23-6759, 2023.

X5.188
|
EGU23-2563
|
CL2.1
|
Jörg Trentmann and Uwe Pfeifroth

The incoming surface solar radiation is an essential climate variable as defined by GCOS. Long term monitoring of this part of the earth’s energy budget is required to gain insights on the state and variability of the climate system. In addition, climate data sets of surface solar radiation have received increased attention over the recent years as an important source of information for solar energy assessments, for crop modeling, and for the validation of climate and weather models.

Gridded regional and global data records of the surface irradiance are available based on satellite measurements as well as derived from numerical models, e.g., reanalysis systems. For climatological analyses, long-term data records, covering about multiple decades, are required. Recently generated satellite-based climate data records from the EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF), i.e., SARAH-3 and CLARA-A3, as well as the GEWEX SRB data set, fulfill this requirement. Corresponding reanalysis data are also available, i.e., ERA-5, MERRA-2.

Here we will assess the quality of these satellite-based and reanalysis-derived climate data records of the surface irradiance by comparison with monthly surface reference data from the Global Energy Balance Archive (GEBA). The quality assessment will include the accuracy of the gridded data as well as their ability to realistically reproduce the anomalies and temporal trends as derived from the surface observations. The inter-comparison of the gridded data records allows to identify regions of high / low confidence in our knowledge of the surface irradiance and the surface radiation budget.  

How to cite: Trentmann, J. and Pfeifroth, U.: Assessing the quality of gridded Climate Data Records of the Surface Irradiance using global Reference Data Sets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2563, https://doi.org/10.5194/egusphere-egu23-2563, 2023.

X5.189
|
EGU23-12198
|
CL2.1
Paul Stackhouse, Stephen Cox, J. Colleen Mikovitz, and Taiping Zhang

The NASA Langley Research Center (LaRC) Surface Radiation Budget (SRB) project produced 3-hourly shortwave and longwave surface and top of atmosphere radiative fluxes for the 1983-2017 in its most recent version, Release 4 Integrated Product (IP) in collaboration with other GEWEX collaborators (Kummerow et al., 2019, Stackhouse et al., 2020, ATBD). This version uses the newly recalibrated and processed ISCCP HXS product as its primary input for cloud and radiance data, replacing ISCCP DX with a ninefold increase in pixel count (10 km instead of 30 km).  Previous work showed comparisons to BSRN and to ocean buoy measurements showed ensemble agreement for monthly averaged shortwave (SW or solar) wavelengths to be ~1 W m-2 bias with an RMS of 14.7 W m-2 RMS and longwave (LW or thermal infrared) ~+1 W m-2 bias with a 15.9 W m-2 RMS.  However, we also found that utilizing the Tselioudis (2020) weather state analysis with ISCCP to partition fluxes by cloud state over the BSRN sites showed that particular cloud states, such as the convective cloud state, showed much larger biases, particularly in the SW.

To address such issues, and to better resolve surface radiative flux spatial variability, this talk describes advances to the SRB inputs and algorithms towards the next release, referred to as LaRC SRB future Release 5. Since the resolution of ISCCP HXS is 10 km (excluding pixels within 25 km of coast lines), the ISCCP data products have enough sampling to grid cloud properties at the 0.5°x0.5°on a global basis.  In the shortwave, the Pinker-Laszlo lookup table approach with a forward call to the Fu-Liou radiative transfer model as modified by the CERES team (Rose et al., 2006).  In addition to being a proven radiation code, Fu-Liou allows the calculation of fluxes at different atmospheric levels and spectral bands, which will provide more insight into the surface radiation budget, its variability and attribution.  Updates to various inputs are described such as surface spectral albedos, emissivities, surface skin and near-surface temperatures, atmospheric profiles, and aerosols optical properties.  

This talk presents the results of early versions of the new products from grid boxes containing BSRN and ocean buoy measurement sites and compare these surface fluxes to the previous version and also to other prominent available data products in the literature.  Key regional differences over oceans and land are assessed to evaluate the changes in the resolving the flux variability.  Although the Tselioudis “weather states” are classified for a 1°x1° resolution, an initial flux partitioning is made at both full and a degraded 1°x1° resolution to assess the new algorithms under different cloud state conditions. The newer algorithms rely on the Fu-Liou based radiative transfer for both the SW and LW providing fluxes within the atmosphere and at the surface and for spectral band fluxes. 

How to cite: Stackhouse, P., Cox, S., Mikovitz, J. C., and Zhang, T.: Advances in ISCCP-based Surface Fluxes at Higher Spatial Resolution from the Surface Radiation Budget Project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12198, https://doi.org/10.5194/egusphere-egu23-12198, 2023.

X5.190
|
EGU23-15880
|
CL2.1
|
ECS
Rachael Byrom and Gunnar Myhre

Addressing the cause of intermodel spread in carbon dioxide (CO2) radiative forcing is essential for reducing uncertainty in estimates of climate sensitivity. Recent studies demonstrate that a large proportion of this spread arises from variance in model base state climatology, particularly the specification of stratospheric temperature, which itself plays a dominant role in determining the magnitude of CO2 forcing.

Here we investigate the significance of intermodel differences in stratospheric ozone (O3) as a cause of intermodel differences in stratospheric temperature, and hence its role as a contributing factor to intermodel spread in CO2 radiative forcing. We use the Community Earth System Model 2 and the Norwegian Earth System Model 2 to analyse the impact of systematic increases/decreases in stratospheric O3 on the magnitude of 2xCO2 and 4xCO2 effective radiative forcing (ERF). Corresponding rapid adjustments and instantaneous radiative forcing (IRF) are diagnosed using radiative kernels and the Parallel Offline Radiative Transfer code, respectively.

We demonstrate that differences in base state stratospheric O3 lead to significant differences in base state stratospheric temperature, ranging from +6 K to -8 K given a 50% increase and decrease in stratospheric O3 concentration. However, this does not result in a correspondingly large spread in CO2 IRF and ERF due to the compensating greenhouse effect of CO2 and O3. Intermodel differences in stratospheric O3 concentration are therefore not predominantly responsible for intermodel spread in CO2 IRF and ERF.

How to cite: Byrom, R. and Myhre, G.: Investigating the relationship between stratospheric temperature and intermodel CO2 radiative forcing spread, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15880, https://doi.org/10.5194/egusphere-egu23-15880, 2023.

X5.191
|
EGU23-14393
|
CL2.1
|
ECS
|
Amit Kumar Sharma and Dilip Ganguly

Aerosols are known to play an important role in regulating the Earth’s energy budget, by directly interacting with solar and terrestrial radiation and modifying the cloud properties. Radiative forcing is commonly used as an index for quantifying such imbalances in the Earth’s radiation budget by any factor. Quantifying aerosol radiative forcing is an initial step towards understanding the response of the Earth’s climate system to changes in emissions of aerosols from anthropogenic sources from pre-industrial (year 1850) to present day.

Our present study is designed to understand implications of changing emissions of aerosols over the historical period (1985-2014) on the evolution of aerosol and cloud radiative forcing using a state of art global chemistry-climate model named CAM6. The estimates of evolution of aerosol radiative forcing and its decomposition into direct radiative forcing (DRF or ERFARI), cloud radiative forcing (CRF or ERFACI) and surface albedo radiative forcing (SARF) on a global scale with special emphasis over the Indian region is being investigated. For this purpose, simulations are performed by CAM6 model for the 30-year period from 1985 to 2014 with model meteorology nudged towards the ERA5 reanalysis data using CMIP6 global emission inventory. We are trying to understand the implications of changing emissions of aerosols on the estimates of ERFARI, ERFACI and SARF to understand the contribution of each pathway through which changes in emissions of aerosols from PI to PD perturb the radiation budget of the earth-atmosphere system. We follow the methodology of Ghan et al. (2012) and use various combinations of additional radiative diagnostics with neglected absorption and scattering of aerosols and clouds along with all sky fluxes of shortwave (SW) and longwave (LW) radiation at top of the atmosphere (TOA) to decompose the total aerosol radiative forcing into ERFARI, ERFACI, and SARF.

Our results show that although the overall effect of changing emissions aerosols and their precursors from anthropogenic sources is to produce a negative radiative forcing at the top of atmosphere (TOA) thereby resulting in cooling over the south Asian region, we find that the aerosol-radiation interaction (ari) leads to warming while aerosol-cloud interaction (aci) results in cooling over the same region. The results from our CAM6 simulations show that the annual mean shortwave aerosol direct radiative forcing (DRF or ERFARI) averaged across the Indian land mass due to major aerosol species has increased from 0.46 W/m2 to 0.76 W/m2 during the 30-year period from 1985 to 2014. More results with greater details on the contribution of individual aerosol towards the temporal evolution of ERFARI and ERFACI will be presented.

 

Keywords: aerosols, Radiative forcing, ARI, ACI, CAM6

 

How to cite: Sharma, A. K. and Ganguly, D.: Temporal evolution of the aerosol radiative forcing due to changing emissions of individual aerosol species and their precursors over the Indian region as estimated using a global climate model CAM6., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14393, https://doi.org/10.5194/egusphere-egu23-14393, 2023.

X5.192
|
EGU23-13198
|
CL2.1
Omaira García, Rosa Delia García, Emilio Cuevas-Agulló, África Barreto, Victoria Eugenia Cachorro, Carlos Marrero, Fernando Almansa, Ramón Ramos, Óscar Álvarez, and Mario Pó

By injecting aerosols and gases into the atmosphere, volcanoes significantly affect global climate, force changes in atmospheric dynamics, and influence many distinct cycles such as hydrological, carbon, and biogeochemical cycles. However, the irregular temporal and spatial distributions of volcanic processes and their effects are still poorly characterised. The volcanic eruption on La Palma (Canary Islands, Spain), which occurred in the autumn of 2021, presented an outstanding opportunity to improve the current understanding of these natural phenomena. The special conditions at the Izaña Observatory (IZO, Tenerife) and its proximity to La Palma (∼140 km) make it a strategic site for the comprehensive study of the almost unperturbed volcanic plume including the climate effects.

In this context, the present work deals with the experimental estimation of the solar spectral direct radiative forcing (ΔF) and efficiency (ΔFEff) during the volcanic eruption based on radiation measurements performed with an EKO MS-711 grating spectroradiometer during three events characterised by the presence of different types of aerosols: fresh volcanic aerosols, Saharan mineral dust, and a mixture of volcanic and Saharan dust aerosols. Three case studies were identified using ground-based (lidar) data, satellite-based (Sentinel-5P Tropospheric Monitoring Instrument, TROPOMI) data, reanalysis data (Modern-Era Retrospective Analysis for Research and Applications, version 2, MERRA-2), and backward trajectories (Flexible Trajectories, FLEXTRA), and subsequently characterised in terms of optical and micro-physical properties using ground-based sun-photometry measurements. Despite the ΔF of the volcanic aerosols being greater than that of the dust events (associated with the larger aerosol load present), the ΔFEff was found to be lower. The spectral ΔFEff values at 440 nm ranged between −1.9 and −2.6 Wm−2nm−1AOD−1 for the mineral dust and mixed volcanic and dust particles, and between −1.6 and −3.3 Wm−2nm−1AOD−1 for the volcanic aerosols, considering solar zenith angles between 30 and 70, respectively.

How to cite: García, O., García, R. D., Cuevas-Agulló, E., Barreto, Á., Cachorro, V. E., Marrero, C., Almansa, F., Ramos, R., Álvarez, Ó., and Pó, M.: Spectral Aerosol Radiative Forcing and Efficiency of the La Palma Volcanic Plume over the Izaña Observatory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13198, https://doi.org/10.5194/egusphere-egu23-13198, 2023.

X5.193
|
EGU23-1130
|
CL2.1
|
ECS
|
|
Jaswant Moher, Vimlesh Pant, and Sagnik Dey

Clouds cover 67% of the earth's surface hence they play an essential role in governing the energy balance of the earth. The combined effect of two properties, i.e., emissivity and albedo of clouds, defines the net radiative effect and their relative importance changes from day to night. In this study, we analyze four decades (1979-2018) of high-resolution (0.25°×0.25°) hourly cloud data from ECMWF fifth-generation reanalysis ERA5 dataset to study the long-term changes in Spatio-temporal variability of clouds over the Arabian Sea. The rationale behind choosing the ERA5 data is that, unlike any other climate variables, the long-term ground truth data for clouds do not exist, and satellite datasets have discrepancies. Ship-observation compiled Extended Edited Synoptic Cloud Reports Archive (EECRA) is a multidecadal data but has a coarse resolution (10°×10°) and suffers from human observational error. In this study, we used a combination of wind speed, air temperature, sea surface temperature (SST), and cloud cover data from ERA5  to explain the observed diurnal behavior and long-term changes in diurnal amplitude and local time of maximum clouds. The clouds over the Arabian Sea show two distinct diurnal peaks during June - August (JJA), but a single diurnal peak is found during the rest of the year. The seasonal and spatial variability in the diurnal behavior of clouds can be characterized in terms of the local thermodynamics of the Arabian Sea. The diurnal amplitude and local time of a maximum of low, mid, and high-level clouds have changed from 1979 to 2018, and the changes are spatially heterogeneous across all seasons. The diurnal amplitude of high-level clouds has increased through all seasons except during JJA. During the JJA season, the entire Arabian Sea shows a decrease in the diurnal amplitude of high-level clouds, with the largest decrease, observed in the eastern Arabian Sea along the west coast of India.

How to cite: Moher, J., Pant, V., and Dey, S.: Analyzing Spatio-temporal variability of clouds over the Arabian Sea using ERA5 reanalysis dataset, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1130, https://doi.org/10.5194/egusphere-egu23-1130, 2023.

X5.194
|
EGU23-14872
|
CL2.1
Piia Post and Margit Aun

In the Baltic Sea region, a significant decrease and subsequent increase in solar radiation have been detected during the past half-century. But the rise in shortwave irradiance is not seen for all seasons; significant changes appear in the seasonality of the cumulative sum of daily shortwave irradiance and the sea surface temperature of the Baltic Sea. Kahru et al. (2016) show that the accumulated surface incoming shortwave (SIS) energy has decreased in winter and increases during the spring and summer. The cumulative thresholds of surface incoming shortwave irradiance up to 1000 W/m2 are reached later in the season, but higher thresholds are reached earlier. The shift from later towards earlier cumulative thresholds occurs in spring, around March 15.

Changes in shortwave irradiance are associated with atmospheric transparency and cloudiness parameters like cloud fraction and albedo. The more substantial factor here is cloudiness, and therefore, we concentrate on reasons for changes in cloud properties. One of the most important reasons here is the synoptic-scale atmospheric circulation. The satellite-based cloud climate data record CLARA-A2 has been used to analyse regional time series and trends in the Baltic Sea region, from 1982-2019. The investigated cloud parameters were total fractional cloud cover (CFC) and SIS.

In March the interannual variability in CFC is high. The Increasing trend in incoming shortwave radiation could be explained by the decrease in CFC. The decrease in CFC is due to a smaller number of overcast days, that vary in the same rhythm with “cloudy” circulation patterns. This shows, that the shift in seasons that is connected to the earlier accumulated sums of SIS is at least partly explained by the changes in synoptic-scale atmospheric circulation.

 

How to cite: Post, P. and Aun, M.: Changes in cloudiness cause a changing seasonality in the Baltic Sea region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14872, https://doi.org/10.5194/egusphere-egu23-14872, 2023.

X5.195
|
EGU23-12792
|
CL2.1
|
ECS
Julie Carles, Jean-Louis Dufresne, and Nicolas Bellouin

The aviation sector contributes to anthropogenic radiative forcing via impacts from well-known CO2 effects and more uncertain non-CO2 effects. The largest contributor to aviation radiative forcing is one of the non-CO2 effects: induced cirrus cloudiness evolved from contrails generated by aircrafts that persist in the atmosphere. The latest assessment of the impacts of aviation on climate attributes a forcing of 149.1 (90% confidence range: 70, 229) mW/m² to global aviation, including 111.4 (33, 189) mW/m² from contrail cirrus (Lee et al, 2021). Those estimations are based on results from global climate models which use approximations for the description of clouds and radiative transfer, resulting in uncertainties of about 70% in aviation induced cloudiness radiative forcing. As of today, the 3D nature of clouds and the corresponding 3D radiative effects are neglected in climate models, as well as the size and shape of ice crystals in contrails.

In this poster, we present work aimed at improving the estimation of the radiative effect of ice clouds and contrail cirrus by studying its dependence on cloud geometry and size. This work uses a Monte Carlo radiative transfer code that takes into account the full 3D interactions between clouds and radiation (Villefranque et al 2019). Results are compared to a 1D, plane parallel calculation, which is the common assumption in climate models used to estimate radiative forcing.

Results show that 3D effects play a substantial role in the radiative effect of cirrus clouds. The plane parallel calculations always under-estimate cloud radiative effect compared to Monte Carlo calculations when the Sun is at zenith. We discuss the dependence of the results to solar angle. We find that the optical depth of the contrail is not the only driver of its radiative forcing, contrary to behavior in plane parallel calculations. This work contributes to reducing uncertainty in the radiative forcing of aviation, and may over ways to correct estimates of contrail cirrus radiative forcing and high clouds radiative effect in climate models.

How to cite: Carles, J., Dufresne, J.-L., and Bellouin, N.: Investigating the role of 3D radiative effects in contrail cirrus and ice clouds., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12792, https://doi.org/10.5194/egusphere-egu23-12792, 2023.

X5.196
|
EGU23-9084
|
CL2.1
|
ECS
yuan zhang, Shengshan Bi, and Steven Dewitte

Observing the Earth radiation budget (ERB) at top of the atmosphere (TOA) from space is crucial for monitoring and understanding Earth’s climate. The accurate estimation of Earth’s outgoing radiative flux is of critical importance to studying ERB at TOA. The Moon-based wide field-of-view radiometer (MWFVR) can provide long-term, continuous full-disk broadband irradiance measurements, which provides an important data source for studying the ERB. Within this context, the lunar surface site 0° E 0° N is selected as the position of the Moon-based wide field-view radiometer, and based on the radiation transfer function, the entrance pupil irradiances time series are obtained by utilization of the CER_SYN1deg-1Hour_Edition4 data products and ERBE ADMs, which is used as the substitute for the truth of the measurements. In this work, the Earth outgoing radiative flux estimating model from the MWFVR measurements is established, and according to the framework, the entrance pupil irradiances are converted to full-disk LW and daytime SW outgoing radiative fluxes. By comparing the results from Moon-based radiometer measurements with those from NISTAR data and CERES SYN1deg data, the results show the moon-based data a much better agreement with those from the satellite data. Besides, The Moon-based SW fluxes oscillate around 194 and 205 W∙m-2, and the range of LW fluxes is 251 ~ 287 Wm−2. Therefore, the complementary advantages and cooperative work of platforms at different altitudes will be an important way for future research on the ERB.

 

 

How to cite: zhang, Y., Bi, S., and Dewitte, S.: Determining Earth’s outgoing radiative flux from a Moon-Based Wide Field-of-view Radiometer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9084, https://doi.org/10.5194/egusphere-egu23-9084, 2023.

X5.197
|
EGU23-10334
|
CL2.1
|
ECS
Yinglin Tian, Axel Kleidon, Sarosh Alam Ghausi, Deyu Zhong, and Guangqian Wang

Downwelling longwave radiation (Rld) is a dominant term in the surface energy balance and is central to global warming. It is influenced by the radiative properties in the whole atmospheric column, particularly greenhouse gases, water vapor, clouds, and atmospheric heat storage. To reveal the leading terms responsible for the spatiotemporal climatological variations in Rld, we use the semi-empirical equation derived by Brutsaert (1975, “B75”), which only needs near-surface observations of air temperature and humidity. We first evaluated B75 and its extension by Crawford and Duchon (1999, "C&D99") with FLUXNET observations, NASA-CERES satellite data, and ERA5 reanalysis. We found a strong agreement, with R2 being 0.87, 0.97, and 0.99, respectively. We then used the equations to show that diurnal and seasonal variations in Rld are predominantly controlled by changes in atmospheric heat storage. Variations in atmospheric emissivity form a secondary contribution to the variation of Rld, and are mostly controlled by anomalies in cloud cover. We also found that with increased aridity, the contributions by changes in atmospheric heat storage and emissivity acted to compensate each other (20~30 W/m2 and ~-40 W/m2, respectively), thus explaining the relatively little variation in Rld with aridity (-20~-10 W/m2). The equations further indicate that under global warming, the amplification of water vapor is stronger in arid regions because clear-sky conditions are more sensitive to an increase in greenhouse gases. These equations thus provide a firm, physical basis to understand the spatiotemporal variability of downwelling longwave radiation at the surface. This should be helpful to better understand and interpret climatological changes, for instance those associated with global warming and extreme events.

How to cite: Tian, Y., Kleidon, A., Alam Ghausi, S., Zhong, D., and Wang, G.: Using Brutsaert’s Equation to Understand the Spatiotemporal Variations of Downwelling Longwave Radiation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10334, https://doi.org/10.5194/egusphere-egu23-10334, 2023.

X5.198
|
EGU23-11494
|
CL2.1
Ryan Bright and Stephanie Eisner

Downwelling longwave irradiance (LW) is challenging and expensive to measure and is often estimated indirectly with parametric modeling of routinely measured surface-level meteorological variables.  Modeling LW under all-sky conditions typically involves “correcting” a clear- (or non-overcast) sky model estimate using solar-irradiance-based proxies of cloud cover in lieu of actual cloud cover given uncertainties and measurement challenges of the latter.  While such approaches are deemed sound, their application in time and space is inherently limited.  Here, we present a correction model free of cloud variables applicable at the true daily (24-hr.) and global scale that – irrespective of the underlying clear-sky model – yields errors over land that are lower than those from stand-alone models and on par with daytime errors from the prevailing solar-based cloud proxy corrections (rRMSD = ~7%; rMAD = ~5.5%).  We document and critically assess its performance over land and ocean independently, as well as in high elevation and cold environments representing two notoriously challenging conditions.  The cloud-free correction is found to perform better than stand-alone approaches at all subsets; however, within-subset performance differences were evident and attributable to the underlying clear-sky model, reinforcing previous findings surrounding performance thresholds of parametric models with globally-tuned parameters. 

How to cite: Bright, R. and Eisner, S.: Modeling downwelling longwave irradiance at daily resolution under all skies:  A cloud-free approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11494, https://doi.org/10.5194/egusphere-egu23-11494, 2023.

X5.199
|
EGU23-7024
|
CL2.1
|
ECS
Félix García-Pereira, Jesús Fidel González-Rouco, Norman Julius Steinert, Camilo Melo-Aguilar, Philipp de Vrese, Johann Jungclaus, Stephan Lorenz, Stefan Hagemann, and Elena García-Bustamante

Under increased warming from ongoing anthropogenic climate change, the land acts as an energy sink for the climate system, interacting with the atmosphere at a wide range of time scales. Based on CMIP multi-model comparisons, the latest estimates of the global energy budget quantify the land contribution to be 2% in the last six decades, whereas other studies based on borehole temperature profiles scale it up to 5%. This discrepancy is suspected to stem from state-of-the-art CMIP land surface models using a shallow zero flux bottom boundary condition placement (BBCP) that severely constrains land energy storage by halting ground heat flux penetration at the BBCP depth and biasing subsurface thermal structure. A 2000-year-long (past2k) forced simulation using a version of the Max Planck Institute (MPI) Earth System Model (ESM) with a deep BBCP (1417 m) was performed to assess the behavior of subsurface temperature and energy storage at long-term scales. Results show that land energy uptake is 4 times higher in a coupled MPI-ESM simulation with a deep version of the land component compared to standard shallow (~10m) simulations. These estimates are well above those provided by CMIP6 models and are much closer to observations, underlining the importance of BBCP-depth in correctly representing the role of the land component in the global energy budget. The results of the analysis of the past2k simulation also allow for deriving reliable estimates of land energy uptake from other observational and reanalysis products as well as providing corrected estimates for the shallow LSM CMIP6 historical and scenario simulations. Land energy uptake estimates rendered from this new approach are much closer to previous BTP-based estimates and agree with the value derived from MPI-ESM deep simulation.

How to cite: García-Pereira, F., González-Rouco, J. F., Steinert, N. J., Melo-Aguilar, C., de Vrese, P., Jungclaus, J., Lorenz, S., Hagemann, S., and García-Bustamante, E.: Assessment of land energy uptake in the industrial period from observation and simulation-based products, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7024, https://doi.org/10.5194/egusphere-egu23-7024, 2023.

X5.200
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EGU23-16873
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CL2.1
Guy Tau, Yehouda Enzel, Hamish McGowan, Vladimir Lyakhovsky, and Nadav Lensky

Air-water interactions regulate lake-water temperature by balancing the rate of change of water temperature (stored heat) with the incoming and outgoing heat fluxes, which are functions of water temperature and external forcing. Yet, there is a large knowledge gap in quantifying the thermoregulation of a lake, and especially managed lakes, which is hypothesized to be related to both external environmental forcing and management decisions on the lake depth and water discharge. Here we explore the thermoregulation of a restored and managed Mediterranean lake (Agamon Hula, Israel), by direct measurements of all major heat fluxes and interpret the results with a rigorous analysis of the energy balance equation. We provide general solutions of (i) the steady-state water temperature under given constant external conditions and show that it is unrelated to water depth, (ii) the time response of the lake’s temperature to reach a steady-state following an abrupt change in various environmental conditions and show its relation to water depth and thermal properties of water, and (iii) the response of the lake’s temperature to a pre-defined oscillations of the environmental forcing (diurnal, seasonal or other cycles). The amplitude of water temperature fluctuations, and the time delay from steady-state are functions of the environmental conditions oscillations and the ratio of the forcing’s time period over the thermal response time of the lake. The summertime measured CO2 fluxes of Agamon Hula revealed the lake acts as a CO2 source to the atmosphere, overpassing similar water bodies from different climates.

How to cite: Tau, G., Enzel, Y., McGowan, H., Lyakhovsky, V., and Lensky, N.: Understanding Water Temperature Regulating of Lakes Through the Energy Balance Approach: Direct Observations (Agamon Hula, Israel) and Analytical Solutions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16873, https://doi.org/10.5194/egusphere-egu23-16873, 2023.

Posters virtual: Thu, 27 Apr, 16:15–18:00 | vHall CL

Chairperson: Maria Z. Hakuba
vCL.4
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EGU23-1416
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CL2.1
Roger Higgs

Fossil-fuel combustion now outweighs solar variations in driving climate change (Higgs 2022, GSA, www.researchgate.net/publication/362103181). Remarkably, land (near-surface-air) warming is three times faster than ocean-surface warming, and Northern Hemisphere (NH; land-ocean average) three times Southern. This aberrant behavior began abruptly in 1985 (contrast pre-1985 lockstep warming-cooling; data.giss.nasa.gov/gistemp/graphs_v4). Moreover, over land and over the NH, warming is significantly slower at altitude (UAH satellite-measured lower-troposphere average temperature).

These strong lateral- and vertical warming gradients incriminate airborne soot (warms atmosphere by absorbing solar radiation). Soot’s poor dispersal causes strong concentration gradients, both (A) laterally, toward its main sources, which are predominantly on-land and NH (diesel engines, cooking woodfires, coal-fired powerplants/industries), e.g. over intensely industrialized nations (USA, Europe, China, etc.), average atmospheric soot concentration is ~1000% (i.e. 10 times) greater than over adjacent oceans (NASA 2011 global black carbon video https://svs.gsfc.nasa.gov/3844), starkly contrasting with CO2’s 1% difference (NASA global CO2 video); and (B) vertically, e.g. year-round average soot concentration above rural Siberia is ~500% higher at 0.5km than at 3km (doi: 10.3390/atmos12030351), far exceeding CO2’s 4% difference above Tokyo (10.3390/s18114064).

Two further observations implicate diesel- and coal-sourced soot specifically. Firstly, 25 years (y) before the 1985 decouplings (above), world annual oil consumption tripled in 1960, then remained high almost continuously (OurWorldinData, GlobalPrimaryEnergyConsumptionBySource graph). Secondly, coal’s distinctively stepwise growth (same graph) is mimicked, with a similar time-lag (10-20y), by stepwise land-air warming (data.giss.nasa.gov/gistemp/graphs_v4): COAL GROWTH fast 1974-1989 (tripled in 1974, due to 1973 oil crisis), nil 1989-1999, fast 1999-2014 (mainly China; OurWorldinData, CoalConsumptionByRegion graph); LAND WARMING fast 1994-2005, nil 2005-2011 (famed ‘hiatus’), fast since 2011.

CO2 cannot explain the observed strong lateral and vertical warming gradients, because its efficient dispersal produces near-homogenous atmospheric concentration. Even heavily industrial regions barely (<0.5%) exceed the global average (10.1038/s41598-019-53513-7). Furthermore, no leap in CO2 concentration occurred ~1985 or any other time; instead, CO2 grew by gradual acceleration, not stepwise (keelingcurve.ucsd.edu). Evidently, CO2 has negligible effect on climate, implying that its greenhouse effect is nullified by unknown and/or underestimated feedbacks (e.g. 10.1007/978-94-007-6606-8_17). If so, hyper-expensive CO2 capture is misconceived, besides counter-productive (today’s 420ppm is well below ~1,000ppm optimum for crop- and forest growth).

In the literature, the global-warming contribution of soot (‘black carbon’) is very uncertain. According to an influential review (10.1002/jgrd.50171; italic emphasis added here): “The best estimate of industrial-era climate forcing of black carbon ... is +1.1 W m-2 with 90% uncertainty bounds of +0.17 to +2.1 W m-2 (sic) ... We estimate that black carbon ... is the second most important human emission in terms of its climate forcing”. Black carbon’s warming effect was estimated to be 70% as strong as CO2. Recent IPCC estimates are 35% and 12% (2013, Physical Science Basis, Summary for Policymakers, fig.SPM.5; 2021, ditto, fig.SPM.2c). On the contrary, the data presented above suggest black carbon is overwhelmingly the dominant anthropogenic-warming agent. Helping to explain previous underestimates, two additional soot-induced warming mechanisms, via its effects on clouds, were recently recognised (10.1038/s41561-020-0631-0). Moreover, developing-world powerplants possibly emit far more soot (10.1029/1999JD900187) than the review assumed.

How to cite: Higgs, R.: Global land-surface warming much faster than ocean surface, and Northern Hemisphere faster than Southern: incriminates soot from burning oil and coal, exonerates CO2, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1416, https://doi.org/10.5194/egusphere-egu23-1416, 2023.

vCL.5
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EGU23-10502
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CL2.1
Robin Wordsworth, Jacob Seeley, and Keith Shine

Although the scientific principles of anthropogenic climate change are now extremely well-established, all existing descriptions of the physics of global warming are either partly empirical or rely on the results of complex numerical models. Here, we present a description of radiative forcing and climate sensitivity that begins from the basic quantum properties of the CO2 molecule. The shape of the CO2 15 micron band, which is so critical to the strength of CO2 radiative forcing, can be understood in terms of vibrational-rotational states and a quantum resonance effect (Fermi resonance). We discuss how classical analogy to the coupled pendulum experiment can be used to understand the nature of this phenomenon in simple terms. We finish by deriving a new analytic equation for CO2 radiative forcing expressed in terms of basic molecular properties such as bond strength and atomic mass. Our aim is for this analysis to elucidate the fundamental physics of climate change for both climate scientists and for physicists working in other fields.

How to cite: Wordsworth, R., Seeley, J., and Shine, K.: From Quantum Mechanics to Climate Change: Global Warming From First Principles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10502, https://doi.org/10.5194/egusphere-egu23-10502, 2023.