CL4.18

The climate system is heating up, causing warming at the surface and changes in the global water cycle. Updated reconstructions of Earth’s energy budget since the 1980s are presented and show how heat uptake is unevenly distributed across the northern and southern hemisphere. Heating is closely associated with ocean heat content changes and sea level rise while surface warming depends on partitioning between the upper mixed layer and deeper levels, leading to decadal variability. CMIP6 simulations are used to illustrate how global precipitation and evaporation are constrained by the Earth's energy balance to increase at ∼2–3%/°C and how this rate of increase is suppressed by rapid atmospheric adjustments in response to greenhouse gases and absorbing aerosols that directly alter the atmospheric energy budget. Rapid adjustments to forcings, cooling effects from scattering aerosol, and observational uncertainty can explain why observed global precipitation responses are currently difficult to detect but are expected to emerge and accelerate as warming increases and aerosol forcing diminishes.

How to cite: Allan, R. and Liu, C.: Global-scale changes in Earth’s energy budget and implications for the water cycle, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1335, https://doi.org/10.5194/egusphere-egu21-1335, 2021.

The Earth’s surface energy balance is heavily affected by incoming solar radiation and how it propagates through our atmosphere. How the sunlight propagates towards the surface depends on the atmospheric presence of aerosols, gases, and clouds. 

Surface temperature evolution according to earth system models (ESMs) in the historical experiment from the coupled model intercomparison project phase 6 (CMIP6) suggests that models may be overly sensitive to aerosol forcing. Other studies have found that ESMs do not recreate observed decadal patterns in surface shortwave radiation - suggesting the models inaccurately underestimate the shortwave impact of atmospheric aerosols. These contradictory results act as a basis for our study.
Our study decomposes what determines both all sky and clear sky downwelling shortwave radiation at the surface in ESMs, using different experiments of CMIP6. We try to determine the respective role of aerosols, clouds and gases in the shortwave energy balance at the surface, and assess the effect of seasonality and regional differences.

How to cite: Moseid, K. O.: Disentangeling the shortwave surface energy balance in earth system models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15200, https://doi.org/10.5194/egusphere-egu21-15200, 2021.

As solar energy share is showing a significant growth in the European electricity generation system, assessments regarding long-term variation of this variable related to climate change are becoming more and more relevant for this sector. Several studies analysed the impact of climate change on the solar energy sector in Europe (Jerez et al, 2015) finding light impact (-14%; +2%) in terms of mean surface solar radiation. The present study focuses on extreme values, namely on the distribution of low surface solar radiation (overcast situation) and high surface solar radiation (clear sky situation), since the frequencies of these situations have high impact on electricity generation.

The study considers 11 high-resolution (0.11 deg) bias-corrected climate projections from the EURO-CORDEX ensemble with 5 Global Climate Models (GCMs) downscaled by 6 Regional Climate Models (RCMs).

Changes in extreme surface solar radiation frequencies show different regional patterns over Europe.

The study also includes a case study determining the changes in solar power generation induced by the extreme situations.

Jerez et al (2015): The impact of climate change on photovoltaic power generation in Europe, Nature Communications 6(1):10014, 10.1038/ncomms10014

How to cite: Bartok, B.: Changes in extreme surface solar radiation in EURO-CORDEX Regional Climate Models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16536, https://doi.org/10.5194/egusphere-egu21-16536, 2021.

The annual mean surface solar radiation (SSR) trends under all-sky, clear-sky, all-sky-no-aerosol, and clear-sky-no-aerosol conditions as well as their possible causes are analyzed during 2005-2018 over China based on different satellite-retrieved datasets to determine the likely drivers of the trends. The results confirm clouds and aerosols as the major contributors to such all-sky SSR trends over China but playing different roles over sub-regions. Aerosol variations during this period result in a widespread brightening, while cloud effects show opposite trends from south to north. Moreover, aerosols contribute more to the increasing all-sky SSR trends over northern China, while clouds dominate the SSR declines over southern China. A radiative transfer model is used to explore the relative contributions of cloud cover from different cloud types to the all-types-of-cloud-cover-induced (ACC-induced) SSR trends during this period in four typical sub-regions over China. The simulations point out that the decreases in low-cloud-cover (LCC) over the North China Plain are the largest positive contributor of all cloud types to the marked annual and seasonal ACC-induced SSR increases, and the positive contributions from both high-cloud-cover (HCC) and LCC declines in summer and winter greatly contribute to the ACC-induced SSR increases over East China. The contributions from medium-low-cloud-cover (mid-LCC) and LCC variations dominate the ACC-caused SSR trends over southwestern and South China all year round, except for the larger HCC contribution in summer.

How to cite: Wang, Q., Zhang, H., and Wild, M.: Potential Driving Factors on Surface Solar Radiation Trends over China in Recent Years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5264, https://doi.org/10.5194/egusphere-egu21-5264, 2021.

The incoming surface solar radiation has been defined as an essential climate variable 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.

The EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) is deriving climate data records (CDRs) from geostationary and polar-orbiting satellite instruments. Within the CM SAF these CDRs are accompanied by operational data at a short time latency to be used for climate monitoring. All data from the CM SAF are freely available via www.cmsaf.eu.

Here we present the regional and global climate data records of surface solar radiation from the CM SAF. The regional SARAH-2.1 climate data record (Surface Solar Radiation Dataset – Heliosat, doi: 10.5676/EUM_SAF_CM/SARAH/V002_01) is based on observations from the series of Meteosat satellites. SARAH-2.1 provides high resolution data (temporal and spatial) of the surface solar radiation (global and direct) and the sunshine duration from 1983 to 2017 for the full view of the Meteosat satellite (i.e, Europe, Africa, parts of South America, and the Atlantic ocean). The global climate data record CLARA (CM SAF Clouds, Albedo and Radiation dataset from AVHRR data, doi: 10.5676/EUM_SAF_CM/CLARA_AVHRR/V002_01) is based on observations from the series of AVHRR instruments onboard polar-orbiting satellites. CLARA provides daily- and monthly-averaged global data of the solar irradiance (SIS) from January 1982 to June 2019 with a spatial resolution of 0.25°. In addition to the solar surface radiation, also the longwave surface radiation as well as surface albedo and numerous cloud properties are provided in CLARA. The high accuracy and stability of these data record allows the assessment of the spatial and temporal variability and trends as well as a number of other applications that require high-resolution surface irradiance data.

Both Thematic Climate Data Records (TCDR) are accompanied and temporally-extended by consistent data records, so-called Interim Climate Data Records (ICDR), which are provided with a latency of 5 days to support applications that require more recent surface irradiance data, e.g., operational climate monitoring.

In late 2021 / early 2022 new versions of both data records, SARAH and CLARA, will be provided by the CM SAF. The quality of these data records will be improved, e.g, by a better treatment of snow-covered surfaces, and temporally extended to cover the WMO climate reference period 1991 to 2020. Here, first results of the updated data records and their improvements will be presented.

How to cite: Trentmann, J., Pfeifroth, U., Drücke, J., and Cremer, R.: Global and Regional Satellite-based Surface Solar Radiation data sets provided by the CM SAF, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8167, https://doi.org/10.5194/egusphere-egu21-8167, 2021.

Solar radiation incident on the Earth's surface is important for the functioning of tropical forests, as it affects the availability of light and water. Due to the lack of in-situ data in tropical forest environments, satellite products and reanalyses are the only ways to estimate solar radiation on a regional scale. An intercomparison of five satellite databases including CERES-EBAF, CERES-SYN1deg, CMSAF-SARAH, CMSAF-CLARA, CAMS-JADE as well as the ERA5 reanalysis, is carried out for the Atlantic coast of Central Africa by evaluating them against two in-situ data sets: the monthly FAOCLIM2 database and original infra-daily data from meteorological stations set up within the framework of ecoclimatic projects. From this inter-comparison we show the differences between these six products and with in-situ data from monthly to daily scales. We also show that the Atlantic coast of Central Africa receives the least amount of solar radiation in all products compared to other regions of Central Africa.

How to cite: Ouhechou, A., Philippon, N., and Morel, B.: Validation and comparison of incoming solar radiation satellite databases on the Atlantic coast of Central Africa., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3493, https://doi.org/10.5194/egusphere-egu21-3493, 2021.

The radiation budget of the earth and its climate system is driven by the solar radiation, which interacts with gases, aerosol particles and clouds. Focusing on aerosol, a fundamental measure is the radiative forcing resulting from aerosol-radiation interactions (RFari) which is also known as the aerosol direct radiative effect. Quantifying the surface RFari on regional scales aids the understanding of the role of aerosol in the climate system and is important for the planning of solar energy systems.

This study is based on a one year dataset (2015) of shortwave broadband global and diffuse horizontal irradiance measured with shaded and unshaded pyranometers at 26 station across Germany within the German Weather Service (DWD) observational network. A variety of clear-sky models are utilized to quantify RFari with a clear sky fitting technique. Clear sky models used are MMAC, MRM v.6.1, METSTAT, ESRA, Heliosat-1, CEM and the simplified Solis model. As these models have not been designed to estimate the clear sky irradiance without the presence of aerosol, we evaluated the accuracy of RFari with an reference simulation.

The reference RFari is simulated using the TROPOS (Leibniz Institute of Tropospheric Research) Cloud and Aerosol Radiative Simulator (T-CARS) utilizing the offline version of the ECMWF radiation scheme (ecRad) with input data of meteorological state of the atmosphere, trace-gases and aerosol from CAMS reanalysis.

The clear sky fitting approach for this set of clear sky models agrees well with T-CARS, showing an RMSE of 6.7 Wm^-2 and an correlation of 0.75. The annual mean of surface RFari over the observation stations in Germany shows a value of -13.2 Wm^-2 as an average over all clear sky models, compared to -13.4 Wm^-2 from T-CARS. Out of this set of clear sky models, best performance is shown by the ESRA and MRM v6.1 models. Although, the accuracy of the annual mean RFari from the clear sky fitting approach is strongly depended on the number available clear-sky irradiance measurements and its distribution over the year. Therefore, this approach is not recommended for climatological studies, but may serve as valuable information for e.g. the evaluation of power generation and the influence by aerosol of photo-voltaic power plants.

How to cite: Witthuhn, J., Hünerbein, A., Deneke, H., Filipitsch, F., and Wacker, S.: Evaluation of clear sky models to estimate the surface direct aerosol radiative effect over Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7294, https://doi.org/10.5194/egusphere-egu21-7294, 2021.

IPCC announced that the WGI contribution to AR6 will be dedicated to the memory of leading climate scientist Sir John Houghton. Sir John died of complications from COVID-19 one year ago. He helped creating the IPCC in 1988, and served as Chair and Co-Chair of WGI from 1988 to 2002. In this presentation we focus on two aspects of his work: radiation transfer and cloud radiative forcing. — His book “The Physics of Atmospheres” (third edition, 2002) says: “The equation of radiative transfer through the slab, which includes both absorption and emission, is sometimes known as Schwarzschild’s equation” (Eq. 2.3, p.11). Introducing a constant Ф net flux (Eq. 2.5) being equal to the outgoing radiation, the black-body function B of the atmosphere is given as a function of Ф and the optical depth as B = Ф(χ* + 1)/2π (Eq. 2.12). He says, “it is easy to show that there must be a temperature discontinuity at the lower boundary”: B_g – B₀ = Ф/2π (Eq. 2.13). Fig. 2.4 displays the net flux at the boundary as half of the outgoing radiation, independently of the optical depth. He notes: “Such a steep lapse rate will soon be destroyed by the process of convection”, and continues: “Combining (2.12) and (2.13) we find Bg = Ф(χ* + 2)/2π ” (Eq. 2.15, section 2.5 The greenhouse effect). We controlled Eq. (2.13) on 20 years of clear-sky CERES EBAF Ed4.1 global mean data and found it satisfied with a difference of -2.28 Wm^-2. The validity of this equation casts constraint on the surface net radiation and on the corresponding non-radiative fluxes in the hydrological cycle by connecting them unequivocally to half of the outgoing longwave radiation. We constructed the all-sky version of the equation by separating atmospheric radiation transfer from longwave cloud effect, and found it valid within 2.84 Wm^-2. We computed Eq. (2.15) with a special optical depth of χ* = 2 for clear-sky; it is justified with a difference of -2.88 Wm^-2. We also created its all-sky version; the difference is 2.46 Wm^-2. Altogether, the four equations are satisfied on 20-yr of CERES data with a mean bias of 0.035 Wm^-2. We show that the four equations together determine a clear-sky and an all-sky greenhouse factor as 1/3 and 0.4. Data from Wild et al. (2018) and IPCC AR5 (2013) show g(clear) = (398 – 267)/398 = 0.33 and g(all) = (398 – 239)/398 = 0.3995. The IPCC reports predict an enhanced greenhouse effect from human emissions. According to the above arithmetic solutions, Earth’s observed greenhouse factors are equal to the theoretical ones without any deviation or enhancement. — The first IPCC report states that cloud radiative forcing is governed by cloud properties as cloud amount, reflectivity, vertical distribution and optical depth. Here we show that the TOA net CRF (= SWCRF + LWCRF) in equilibrium is equivalent to TOA net clear-sky imbalance, hence to determine its magnitude only clear-sky fluxes are needed.

How to cite: Zagoni, M.: Sir John Houghton (30 December 1931 — 15 April 2020) and radiation transfer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1, https://doi.org/10.5194/egusphere-egu21-1, 2021.

The Earth's Outgoing Longwave Radiation (OLR) is a key component in the study of climate. As part of the Earth's radiation budget, it reflects how the Earth-atmosphere system compensates the incoming solar radiation at the top of the atmosphere. At equilibrium, the two quantities compensate each other on average. Any variation of the climate drivers (e.g. greenhouse gases) causes an energy imbalance which leads to a climate response (e.g. surface temperature increase), with the effect of bringing the radiation budget back to equilibrium. Considerable improvements in our understanding of the Earth-atmosphere system and of its long-term changes have been achieved in the last four decades through the exploitation of measurements from dedicated broadband instruments. However, such instruments only provide spectrally integrated OLR over a broad spectral range and are therefore not well suited for tracking separately the impact of the different parameters affecting the OLR.

Better constraints can, in principle, be obtained from spectrally resolved OLR (i.e. the integrand of broadband OLR, in units of W m^-2 cm^-1) derived from infrared hyperspectral sounders. Recently, a dedicated algorithm was developed to derive clear-sky spectrally resolved OLR from the Infrared Atmospheric Sounding Interferometer (IASI) at the 0.25 cm^-1 native spectral sampling of the L1C spectra (Whitburn et al. 2020).  Here, we analyze the changes in 10 years (2008-2017) of the IASI-derived OLR and we relate them to known changes in greenhouse gases concentrations (CO₂, CH₄, H₂O, …) and climate phenomena activity such as El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO).

Whitburn, S., Clarisse, L., Bauduin, S., George, M., Hurtmans, D., Safieddine, S., Coheur, P. F., and Clerbaux, C. (2020). Spectrally Resolved Fuxes from IASI Data: Retrieval algorithm for Clear-Sky Measurements. Journal of Climate. doi: 10.1175/jcli-d-19-0523.1

How to cite: Whitburn, S., Clarisse, L., Delcloo, A., Dewitte, S., Bouillon, M., George, M., Safieddine, S., Coheur, P., and Clerbaux, C.: Trends in spectrally resolved OLR from 10 years of IASI measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11304, https://doi.org/10.5194/egusphere-egu21-11304, 2021.

The recently selected NASA mission Libera, 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.

Seamless extension of the ERB climate data record is achieved by acquiring integrated radiances over the CERES FM6-heritage broad spectral bands in the shortwave (0.3 to 5 μm), longwave (5 to 50 μm) and total (0.3 to beyond 100 μm). To gain deeper insight into shortwave energy deposition, Libera adds a split-shortwave band (0.7 to 5 μm) that allows to provide deeper insight into shortwave energy deposition.

Libera’s advanced detector technologies is based on vertically aligned black-carbon nanotubes with closed-loop electrical substitution radiometry to achieve radiometric uncertainty of approximately 0.2%. Additionally, a wide field-of-view camera is employed to provide scene context and explore pathways for separating future ERB missions from complex imagers.

This presentation will summarize Libera’s attributes and mission goals, as well as some of the applications of the camera radiances, and the role of the additional split-shortwave channel that splits the shortwave band into its visible and near-IR contributions. This split is vital for the better understanding of shortwave absorption, feedbacks, and planetary albedo variability. The hemispheric symmetry of planetary albedo, as observed by CERES, is not achieved by most state-of-the-art climate models and is associated with long-standing biases in circulation and cloud properties. We will exemplify the study of processes relevant to albedo symmetry by means of CMIP6 simulations that provide the visible and near-IR fluxes.

How to cite: Hakuba, M. Z., Pilewskie, P., and Stephens, G. and the Libera Science Team: Libera – Observing and Understanding Earth’s Energy Budget, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13961, https://doi.org/10.5194/egusphere-egu21-13961, 2021.

The incoming solar radiation at the top of the atmosphere (TOA), and especially at the Earth’s surface, determines the energy balance of our planet and regulates its climate. During the last decades, variations in the incoming surface solar radiation (SSR) have been observed, which depend on the atmosphere’s transparency. This phenomenon, known as global dimming and brightening (GDB), plays an important role in climate change and global warming. The present study examines the variability and changes of both SSR and the outgoing solar radiation at the TOA (OSR) based on long-term satellite data and ground truth measurements, but also reanalysis data, also with an aim to inter-compare and validate the changes of SSR (ΔSSR or GDB) and OSR (ΔOSR) in order to ensure the highest accuracy of the findings. For this analysis, mean monthly SSR and OSR fluxes are used at the global scale and over the last several decades. More specifically, SSR and OSR solar fluxes are used from the Modern-Era Retrospective Analysis for Research and Applications v.2 (MERRA-2) reanalysis data for the 40-year period 01/1980 - 12/2020 and from the satellite Clouds and the Earth's Radiant Energy System Energy Balanced and Filled (CERES-EBAF) database for the 20-year period 03/2000 - 07/2020. The spatial resolution of CERES-EBAF dataset is 1°×1° latitude and longitude. MERRA-2 data, originally provided on a 0.5°×0.625° horizontal grid, are regridded on the CERES-EBAF spatial resolution (1°×1°). The SSR and ΔSSR fluxes from MERRA-2 and CERES are compared to each other, and they are both assessed through comparisons against ground measurements from the two major reference station networks, namely the Global Energy Balance Archive (GEBA), and the Baseline Surface Radiation Network (BSRN). The OSR and ΔOSR fluxes from MERRA-2 are assessed through comparison against corresponding fluxes from the CERES satellite measurements. The data analysis examines the spatio-temporal distribution and the trends of SSR (ΔSSR or GDB) and OSR, using both radiation fluxes and their deseasonalized anomalies. Special emphasis is given to the accurate estimation of GDB and the associated uncertainty, while attempting to reduce this uncertainty using the results of the analysis at the top of the atmosphere.

How to cite: Stamatis, M., Hatzianastassiou, N., Korras Carraca, M. B., Matsoukas, C., Wild, M., and Vardavas, I.: Comparative analysis of the incoming surface and outgoing top of atmosphere solar radiation based on MERRA-2 & CERES data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13200, https://doi.org/10.5194/egusphere-egu21-13200, 2021.

A plausible simulation of the global energy balance is a first-order requirement for a credible climate model. In the present study I investigate the representation of the global energy balance in 40 state-of-the-art global climate models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6). In the CMIP6 multi-model mean, the magnitudes of the energy balance components are often in better agreement with recent reference estimates compared to earlier model generations  such as CMIP5 on a global mean basis. 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 aspects of 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 multi-model mean (Wild 2020).

Published in: Wild, M., 2020: The global energy balance as represented in CMIP6 climate models. Clim Dyn 55, 553–577. https://doi.org/10.1007/s00382-020-05282-7

How to cite: Wild, M.: The Global Energy Balance as represented in CMIP6 climate models , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1416, https://doi.org/10.5194/egusphere-egu21-1416, 2021.

Equilibrium climate sensitivity (ECS) and transient climate response (TCR) are some of the most fundamental properties characterising the future climate. Progress in estimating climate sensitivity over the last three decades has been hampered by a large climate model spread of ECS and TCR estimates, and more recently by a large increase in ECS predicted by several models in the latest generation of the Climate Model Intercomparison Project 6 (CMIP6). Clouds have been identified as the major source of this uncertainty and the recent increase in estimated ECS. A "too few, too bright" model cloud problem has been found in several regions of the globe, including tropical latitudes and the Southern Ocean. Southern Ocean has also been a major focus of changes in model microphysics in an effort to simulate more realistic supercooled liquid clouds. Here, we focus on the too few, too bright problem in the Southern Ocean in CMIP6 models and its possible relation to climate sensitivity. We explore the possibility of applying new emergent constraints on climate sensitivity based on metrics of the too few, too bright problem. We use satellite and and ship-based observational datasets such as lidar and radiometer observations for constraining climate sensitivity and evaluation of clouds in this region across generations of CMIP models.

How to cite: Kuma, P. and Bender, F.: Climate sensitivity and the Southern Ocean: the effect of the "too few, too bright" model cloud problem, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14733, https://doi.org/10.5194/egusphere-egu21-14733, 2021.

Energy budget estimates of the effective climate sensitivity (effCS) are derived based on estimates of the historical forcing and of observations of the sea surface temperature variations and the ocean heat uptake. Recent revisions to Greenhouse gas forcing and aerosol forcing estimates are included and the data is extended to 2018. We consider two different approaches to derive the effCS from the energy budget: 1) a difference of the energy budget between the recent period 2005-2018 and a base period 1861-1880 (following Sherwood 2020) and 2)  a regression of the differential form of energy budget over the period 1955-2017 (following Gregory et al. 2020). These estimates of the effCS over the historical period are representative of the climate feedback experienced by the climate during the historical period. When accounting for the uncertainty in the forcing, the surface temperature and the ocean heat uptake estimates plus the uncertainty due to the internal variability we find a range of effCS of [1.0;9.7] (at the 95%CL) with a median of 2.0 K with approach (1) and [1.2;2.7] with a median of 1.7 K with approch (2). We find that the lower and the upper tail of the distribution in effCS arise dominantly from the uncertainty in the historical forcing, particularly for the regression method, and at a lower extent for the difference method. This is consistent with previous studies (e.g. Lewis and Curry 2018 and Sherwood et al. 2020).

Using the same approach based on historical observations but accounting for the pattern effect and the temperature dependence of the feedback estimated with climate model simulations, we derive new estimates of the effECS that should encompass the equilibrium climate sensitivity (assuming that climate model simulate properly the pattern effect and the temperature dependence of feedback). We find that adding the pattern effect and the temperature dependence of the feedbacks shifts upwards the median of the effECS and increases significantly the uncertainty range. For the difference method, the median is now 2.5 K and the uncertainty range [1.1;17.2]. For the regression method the median is now 2.0 K and the uncertainty range is [1.2;4.7] K ((5-95%). On the overall, we find that the regression method performs better to constraint the equilibrium climate sensitivity and that the major source of uncertainties comes from the differences in the simulation of the pattern effect among climate models rather than the uncertainties on the historical forcing.

How to cite: Chenal, J. and Meyssignac, B.: Estimate of equilibrium climate sensitivity and uncertainties by using observations and CMIP6 global coupled climate models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14682, https://doi.org/10.5194/egusphere-egu21-14682, 2021.

We study how the vertical distribution of relative humidity (RH) affects climate sensitivity (CS), even if it remains unchanged with warming. Using a one-dimensional radiative-convective equilibrium model, konrad, we show that the climate sensitivity depends on the shape of the vertical distribution of humidity, an effect we call humidity-dependence: Moister atmospheres were shown to have a larger CS, increasingly so with warmer temperature, consistent with our understanding of how water vapor influences the transmissivity of the atmospheric window (Nakajima et al., 1992; Koll & Cronin, 2018). CS is further shown to increase with increasing humidity in the upper troposphere but decreases with increases in humidity in the lower mid-troposphere. We interpret these effects in terms of the effective emission height of water vapor. Differences in the vertical distribution of RH are shown to explain a large part of the 10 to 30% differences in clear-sky sensitivity seen in climate and storm-resolving models. The results imply that convective aggregation reduces climate sensitivity, even when the degree of aggregation does not change with warming. Combining our findings with relative humidity trends in reanalysis data shows a tendency toward Earth becoming more sensitive to forcing over time. These trends and their height variation merit further study.

How to cite: Bourdin, S., Kluft, L., and Stevens, B.: Humidity-dependence of Climate Sensitivity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1197, https://doi.org/10.5194/egusphere-egu21-1197, 2021.

Solar radiation modification (SRM), an artificial intervention to reduce the amount of solar radiation reaching the surface, has been proposed as a potential option to ameliorate some undesired consequences of global warming. Marine cloud brightening (MCB) and ocean albedo modification (OAM) are two proposed SRM approaches. MCB aims to cool the planet by increasing marine cloud albedo that might be achieved by injecting sea salt into low marine cloud.  OAM aims to cool the planet by increasing surface ocean albedo that might be achieved by using highly reflective microbubbles over ocean. There is speculation that climate effect of OAM and MCB would be similar as forcing is applied only over ocean in both cases.

In this study, we use NCAR CESM model to compare climate response in  these two SRM approaches under the framework of “fast versus slow response”. The term “fast” refers to climate adjustment that is associated with rapid adjustment of the atmosphere and land surface, and “slow” refers to climate feedbacks that are associated with the slow evolution of sea surface temperature.

In our simulation we find that to offset global warming from a doubling of atmospheric CO₂, OAM requires a stronger negative effective radiative forcing than that of MCB, indicating MCB is more effective in producing cooling per unit of radiative forcing. This is mainly associated with differing fast climate adjustment between OAM and MCB forcing. OAM increases upward shortwave radiation from surface and heats the lower atmosphere, causing low-level clouds to dissipate. A reduction in low cloudiness allows more solar radiation to reach the surface, partly offsetting the negative radiative forcing from increase in ocean albedo. At equilibrium state, however, OAM and MCB produces similar pattern of change in temperature and hydrological cycle, but prominent differences in climate response is observed over the tropical ocean where OAM produces larger reduction in precipitation and evaporation than that of MCB. Our results indicate that there is similarity between climate response to marine cloud brightening and ocean albedo increase, but caution should be exercised when using climate response from one to infer the other. 

How to cite: Zhao, M., Cao, L., Duan, L., Bala, G., and Caldeira, K.: Comparison of climate response to marine cloud brightening and ocean albedo modification: A model study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1877, https://doi.org/10.5194/egusphere-egu21-1877, 2021.

Climate models predict a weakening of the tropical atmospheric circulation, more specifically a slowdown of Hadley and Walker circulations. Many climate models predict that global warming will have a major impact on cloud properties, including their geographic and vertical distribution. Climate feedbacks from clouds, which amplify warming when positive, are today the main source of uncertainty in climate forecasts. Tropical clouds play a key role in the redistribution of solar energy and their evolution will likely affect climate. Therefore, it is crucial to better understand how tropical clouds will evolve in a changing climate. Among cloud properties, the vertical distribution is sensitive to climate change. Active sensors integrated into satellites, such as CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization), make it possible to obtain a detailed vertical distribution of clouds. CALIOP measurements and calibration are more stable over time and more precise than passive remote sensing satellite detectors. CALIOP observations can be simulated in the atmospheric conditions predicted by climate models using lidar simulators such as COSP (CFMIP Observation Simulator Package). Moreover, cloud properties directly drive the Cloud Radiative Effect (CRE). Understanding how models predict cloud vertical distribution will evolve in the future has implications for how models predict the Cloud Radiative Effect (CRE) at the Top of the Atmosphere (TOA) will evolve in the future.

The purpose of our study is to compare, firstly, based on satellite observations (GOCCP) and reanalyzes (ERA5), we will establish the relationship between atmospheric dynamic circulation, opaque cloud properties and TOA CRE. Then, we will compare this observed relationship with the one found in climate model simulations of current climate conditions (CESM1 and IPSL-CM6). Finally, we will identify how model biases in present climate conditions influence the cloud feedback spread between models in a warmer climate.

How to cite: Perpina, M., Noel, V., Chepfer, H., Guzman, R., and Feofilov, A.: Link between opaque cloud properties and atmospheric dynamics in observations and simulations of current climate in the Tropics, and impact on future predictions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4502, https://doi.org/10.5194/egusphere-egu21-4502, 2021.

Radiation measurements at the top of the atmosphere show that the two hemispheres of Earth reflect the same amount of shortwave radiation in the long time average (so-called hemispheric albedo symmetry). Here we try to find the origin of this symmetry by analyzing radiation data directly, as well as cloud properties. The radiation data, while being mostly noise, hint that a hemispheric communication mechanism is likely but do not provide enough information to identify it. Cloud properties allow us to define an effective cloud albedo field, much more useful than the commonly used cloud area fraction. Based on that we first show that extra cloud albedo of the SH exactly compensates the extra surface albedo of the NH. We then identify that this this compensation comes almost exclusively from the storm tracks of the extratropics. We close discussing the importance of approaching planetary albedo as a whole and open questions that remain.

How to cite: Datseris, G. and Stevens, B.: Cloudiness and Earth's hemispheric albedo symmetry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-153, https://doi.org/10.5194/egusphere-egu21-153, 2021.