It is vital and informative to understand the lifetime and timescales of tropospheric O3 so that we can predict the impact of changing O3 sources on its abundance throughout the troposphere, and thence its climate and pollution damage.  As an example, current model intercomparison projects (MIPs) diagnose the impact of stratosphere-troposphere exchange (STE) flux of O3 into the troposphere by assuming that loss of this added O3 occurs through 3 specific reactions (O(1D)+H2O, HO2+O3, OH+O3) and is linear in O3, and that production through XO2+NO reactions is a constant.  A linearization of the full chemistry with respect to O3 clearly shows these assumptions are wrong (see ATom data, shown here).  Another example is the effort made to define odd-oxygen by a chemical family grouping (e.g., O3+O+NO2+…) to better understand the timescales for O3 loss, yet the true pattern of the odd-oxygen family should be apparent from the eigenvectors of the system. 

Here we define and test a new protocol for model experiments designed to understand how the coupling of O3 with the full chemistry can change the accumulation and the pattern of decay depending on the O3 source (stratosphere, surface pollution, aviation).  We take a full chemistry-transport model (UCI CTM) and generate a control run for the present day, then add direct O3 emissions (not in the control run) from (i) a large industrial region, (ii) aviation, and (iii) the mid-latitude tropopause where most STE occurs. These perturbation runs produce a seasonally varying additional O3 burden – which gives us the seasonally varying lifetime for such sources – and then we cut emissions and watch the decay pattern in terms of e-fold timescale and patterns of key species to derive the odd-oxygen family pattern.   Due to the large latitudinal and seasonal variation in reactivity rates (see ATom data: Guo et al. ACP, 23, 99–117, 2023), we expect lifetimes and timescale to vary with location and timing of O3 emissions.

How to cite: Prather, M. and Zhu, X.: Lifetimes and timescales of tropospheric ozone , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9839, https://doi.org/10.5194/egusphere-egu23-9839, 2023.

Long-term exposure to ambient ozone is linked with respiratory-related mortality, while the emerging climate change is projected to pose double-edged challenges for ozone air quality. Here, we calculate the impact of emissions- and climate-change under SSP3-7.0 scenario on ozone-related mortality on a global scale, using historical (experiment histSST) and future simulations (experiments ssp370SST and ssp370pdSST) from three CMIP6 Earth System Models (ESMs) (GFDL-ESM4, EC-Earth3-AerChem, and UKESM1-0-LL). The ssp370SST experiment follows time-varying SSTs, while the SSP370pdSST follows a present-day climatology for SSTs. The chronic obstructive pulmonary disease mortality attributable to ozone pollution is estimated following the Global Burden Disease (GBD) 2019 approach, by using the ozone season daily maximum 8-hour mixing ratio (OSDMA8), the baseline mortality rate (from the GBD), and the SSP3-7.0 present and future gridded population. An increase in ozone-related mortality of approximately 2.5 million people per year globally is projected at the end of the century (2090) with respect to 2000 due to emissions and population changes. The climate-change footprint on ozone-related mortality exhibits large variability among the ESMs; yet, over India and China all ESMs project an increase of ozone-related mortality in the future, highlighting the importance of the ozone penalty due to global warming in regions with strong anthropogenic sources.

How to cite: Akritidis, D., Bacer, S., Zanis, P., Georgoulias, A. K., Horowitz, L. W., Naik, V., O'Connor, F. M., Keeble, J., Le Sager, P., van Noije, T., Zhou, P., and Pozzer, A.: Future projection of ozone-related mortality under SSP3-7.0 scenario based on CMIP6 simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5642, https://doi.org/10.5194/egusphere-egu23-5642, 2023.

Near-term climate forcers (NTCF) are a group of chemically and radiatively active constituents that have a relatively short lifetime in the atmosphere (<20 years). They can exert effects on the climate, important for the future rate of climate warming, and in elevated concentrations at the lowest most levels of the atmosphere can lead to poor air quality and detrimental impacts on human health. Two important NTCFs that are considered in this study are tropospheric O₃ and fine particulate matter (with a diameter less than 2.5 microns – PM_2.5). Future climate mitigation scenarios that seek to limit future temperature increases, and include reductions in air pollutant emissions, need to consider the impact on climate, air quality and human health from changes in NTCFs. Here we use results from UKESM1 (an Earth system model with interactive chemistry and aerosols) in different future sensitivity scenarios that consider air pollutant emission mitigation, future climate change and land-use change, conducted as part of the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP). We assess the impact on climate (in terms of effective radiative forcing), air pollutants (in terms of change in ambient surface concentrations) and human health (in terms of long-term adult mortality from exposure to ambient air pollutants) by comparing the results from these sensitivity scenarios to the future reference scenario ssp370, a scenario that involves low mitigation of climate and air pollutants.

Scenarios that involve combined strong mitigation of aerosols and O₃ precursors, including large reductions in global CH₄ concentrations, produce the largest benefits to climate (an ERF of -1.2 Wm^-2), air quality (10-25% reduction in O₃ and PM_2.5 concentrations) and human health (>25% reduction in the rate of long-term premature mortality). Benefits to health are largest across Asia for these scenarios (a 44% reduction in the mortality rate). If global CH₄ concentrations are not reduced or aerosol precursors emissions are reduced in isolation, then there is a detrimental impact to future climate but there are still improvements to future air quality and a reduction in the long-term air pollutant health burden. If climate and air quality mitigation measures are not enacted on top of ssp370 then there is a penalty to global climate, a detrimental impact on air pollutant concentrations and an increase in the long-term air pollutant health burden across certain regions (e.g. by 20% over Africa). Considering only the impacts from climate change show increases in air pollutant concentrations over some continental regions and also an increase in the long-term rate of premature mortality by more than 10% over Europe and parts of Asia, offsetting some of the benefits achieved from emission mitigation measures. Quantifying co-benefits and trade-offs between climate, air quality, and human health together in this way, enables policy makers to understand the outcomes of different mitigation strategies and to identify pathways with maximum benefits across all three axes.

How to cite: Turnock, S., Reddington, C., and O'Connor, F.: The Climate, Air Quality and Health co-benefits and trade-offs from different future mitigation scenarios involving Near-Term Climate Forcers in UKESM1, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2685, https://doi.org/10.5194/egusphere-egu23-2685, 2023.

Air quality co-benefits are expected to occur with greater climate mitigation, however climate mitigation is not expected to occur in isolation of other socio-economic changes. Although modelling studies investigating these co-benefits are common, limited work uses the recently developed “Shared Socioeconomic Pathways” which factor in the different patterns of climate mitigation, socioeconomic development and pollution control. Additionally, as the SSPs were designed for climate model ensembles, such as CMIP6, existing work usually uses global climate or earth system models with interactive chemistry simulated at relatively coarse horizontal resolution. These computational trade-offs may impact how effectively they model air quality at human exposure-relevant scales and may miss differing trends seen only at subregional scales.

We have used the anthropogenic emissions inputs from different SSPs which have different mitigation patterns applied to climate change and air pollution in 2050 to drive a specialised Atmospheric Chemistry model (WRF-Chemv4.2) at 30km resolution over Europe. We compare these to a 2014 control simulation. We present the validation of this model setup, which suggests an overestimation of surface PM2.5 concentrations, largely driven by overestimated NO3 aerosol, but good agreement with O3 observations. We find that while significant potential for air quality co-benefits exists, these effects are non-linear, with both PM2.5 and O3 worsening in some locations and scenarios despite increased pollution control compared to the present. We also find notable spatial heterogeneity in the change of PM2.5 and O3 across Europe in some scenarios.  Overall, however the results show that across Europe, scenarios with greater mitigation of climate change and air pollution show improvements in air quality that could lead to benefits to human health. 

How to cite: Clayton, C. J., McQuaid, J. B., Marsh, D. R., Turnock, S. T., Graham, A. M., Pringle, K. J., and Kumar, R.: High Resolution Simulations of European Air Quality in 2050 Following Different CMIP6 Climate Change Mitigation Pathways, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4217, https://doi.org/10.5194/egusphere-egu23-4217, 2023.

Methane plays a central role in the atmosphere, affecting the atmospheric oxidising capacity through its reaction with OH, air quality through its role as an ozone precursor, and climate through its greenhouse gas properties.  

Methane emissions-driven models provide an opportunity to study the Earth system within a global model that features the most accurate representation of the methane cycle. Here we use the methane emissions-driven configuration of the UK Earth System Model, UKESM1-CH4. 

Previously we explored a zero anthropogenic methane scenario, which focused on attributing the composition, air quality and climate impacts of future anthropogenic methane emissions. Here, we study the potential co-benefits of methane mitigation: reducing NOx and CO emissions. We use SSP1-2.6 emissions pathways for CO and NO in these scenarios. 

The complex interactions between methane, CO, OH and NOx are represented more completely in the emissions-driven model. We calculate the sensitivity of ozone and OH to the CO and NO emissions changes, and their dependence on the methane burden. We also show the impacts on other near-term climate forcers such as aerosols and ozone. 

Global reductions in CO and NO emissions have disproportionate effects in different regions. We present analysis of the regional differences in ozone and OH response, based on the HTAP regions. We demonstrate much greater effects in South and East Asia than in the Europe and North America.

How to cite: Staniaszek, Z., Griffiths, P. T., Folberth, G. A., O'Connor, F. M., and Archibald, A. T.: Regional impacts of CO and NOx mitigation in a methane emissions-driven model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1291, https://doi.org/10.5194/egusphere-egu23-1291, 2023.

Reforestation is widely proposed for carbon dioxide (CO₂) removal but the impact on climate, via atmospheric composition and surface albedo changes, remains relatively unexplored. Using two Earth System models, UKESM1 and CESM2, we compare scenarios where existing forests expand to a near biophysical limit (with croplands fixed at 2015 to preserve food production) with SSP1-2.6 and SSP3-7.0 at 2050 and 2095.  

In the reforestation scenario, global BVOC emissions are 18% (35%) higher than SSP3-7.0 at 2050 (2095) and 8% (12%) higher than SSP1-2.6. The resulting increases to secondary organic aerosols and aerosol scattering, from BVOC emission changes, drive a negative radiative forcing (RF). However, this is outweighed by the positive RF from increases to methane and ozone and decreases to surface albedo.

The net RF is equivalent to CO₂ increases of 13 (32) ppm relative to SSP3-7.0 at 2050 (2095) and 3 (8) ppm relative to SSP1-2.6. These indirect factors offset ~25% of the additional CO₂ removal arising from reforestation relative to SSP3-7.0 and ~10% relative to SSP1-2.6. This highlights the importance of assessing the full response of the Earth System to reforestation, rather than just the potential CO₂ removal.  

How to cite: Weber, J., King, J. A., Abraham, N. L., Grosvenor, D. P., Beerling, D. J., Lawrence, P., and Val Martin, M.: Chemistry-albedo feedbacks from reforestation partially offset CO2 removal benefits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8236, https://doi.org/10.5194/egusphere-egu23-8236, 2023.

Water vapor plays an important role in many aspects of the climate system, by affecting radiation, cloud formation, atmospheric chemistry and dynamics. Even the low stratospheric water vapor content provides an important climate feedback, but current climate models show a substantial moist bias in the lowermost stratosphere. Here we report crucial sensitivity of the atmospheric circulation in the stratosphere and troposphere to the abundance of water vapor in the lowermost stratosphere. We show from a mechanistic climate model experiment and inter-model variability that lowermost stratospheric water vapor decreases local temperatures, and thereby causes an upward and poleward shift of subtropical jets, a strengthening of the stratospheric circulation, a poleward shift of the tropospheric eddy-driven jet and regional climate impacts. The mechanistic model experiment in combination with atmospheric observations further shows that the prevailing moist bias in current models is likely caused by the transport scheme, and can be alleviated by employing a less diffusive Lagrangian scheme. The related effects on atmospheric circulation are of similar magnitude as climate change effects. Hence, lowermost stratospheric water vapor exerts a first order effect on atmospheric circulation and improving its representation in models offers promising prospects for future research.

How to cite: Charlesworth, E., Plöger, F., Birner, T., Baikhadzhaev, R., Abalos, M., Abraham, L., Akiyoshi, H., Bekki, S., Dennison, F., Jöckel, P., Keeble, J., Kinnison, D., Morgenstern, O., Plummer, D., Rozanov, E., Strode, S., Zeng, G., and Riese, M.: Stratospheric water vapor affecting atmospheric circulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14506, https://doi.org/10.5194/egusphere-egu23-14506, 2023.

The ICOsahedral Non-hydrostatic (ICON) modelling system was originally developed by DWD and MPI-M for a range of weather (forecast) and climate applications. An Aerosols and Reactive Tracers (ART) module was added by KIT to enable a comprehensive assessment of composition interactions within the atmospheric domain. Recognising that atmospheric processes happen on a multitude of temporal and spatial scales, flexible horizontal and vertical grid options are a key element of versatile model configurations in use. Here, we present a selection of results from different ICON-ART configurations that explore (stratospheric) ozone-climate interactions and stratosphere-troposphere coupling – e.g. regional climatic impacts of the ozone hole (and ozone losses in other regions) and global warming induced changes in jet-streams – in different types of integrations. In addition, we explore the potential to forecast “chemical weather” with ICON-ART, including environmental (UV) indices.

Starting with time-slice experiments, we provide a range of examples using the ICON-ART modelling system to investigate (idealised) climate change scenarios with respect to different threshold temperatures (reached under global warming) and the climatic impact of the ozone hole (and ozone losses in other regions). For the latter, halogen induced depletion of (stratospheric) ozone can be switched on and off in our modelling world. We illustrate how such integrations allow the unambiguous attribution of certain climate change effects, e.g. the contribution of the ozone hole (and other regional ozone losses) to regional surface warming in Antarctica and changes to regional and global “effective radiative forcing”, and the change of jet stream variability under global warming. Moving on, we explore the capability of ICON-ART to work with regionally nested grids to capture accurately smaller spatial scales and to provide “meaningful” forecasts of environmental (UV) indices, thus, demonstrating comprehensively the seamless philosophy regarding processes, scales and applications with the flexible ICON-ART modelling system.

How to cite: Braesicke, P., Hanft, V., Kusakova, K., Ruhnke, R., Satitkovitchai, K., Sinnhuber, B.-M., Versick, S., and Weimer, M.: Beyond ozone hole impacts: Seamless composition-climate interactions explored with ICON-ART, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8610, https://doi.org/10.5194/egusphere-egu23-8610, 2023.

The Asian summer monsoons are globally significant meteorological features, creating a strongly seasonal pattern of precipitation, with the majority of the annual precipitation falling between June and September. The stability of such a strongly seasonal hydrological cycle is of extreme importance for a vast range of ecosystems and for the livelihoods of a large share of the world’s population.

Simulations are performed with an intermediate complexity climate model, PLASIM, in order to assess the future response of the Asian monsoons to changing concentrations of aerosols and greenhouse gases. The radiative forcing associated with aerosol loading consists of a mid-tropospheric warming and a compensating surface cooling, which is applied to India, Southeast Asia and East China, both concurrently and independently. The primary effect of increased aerosol loading is a decrease in summer precipitation in the vicinity of the applied forcing, although the regional responses vary significantly. The decrease in precipitation is only partially ascribable to a decrease in the precipitable water, and instead derives from a reduction of the precipitation efficiency, due to changes in the stratification of the atmosphere.

When the aerosol loading is added in all regions simultaneously, precipitation in East China is most strongly affected, with a quite distinct transition to a low precipitation regime as the radiative forcing increases beyond 60 W/m². The response is less abrupt as we move westward, with precipitation in South India being least affected. By applying the aerosol loading to each region individually, we are able to explain the mechanism behind the lower sensitivity observed in India, and attribute it to aerosol forcing over East China. Additionally, we note that the effect on precipitation is approximately linear with the forcing.

The impact of doubling carbon dioxide levels is to increase precipitation over the region, whilst simultaneously weakening the circulation. When the carbon dioxide and aerosol forcings are applied at the same time, the carbon dioxide forcing partially offsets the surface cooling and reduction in precipitation associated with the aerosol response.

How to cite: Reccchia, L. and Lucarini, V.: Modelling the effect of aerosol and greenhouse gas forcing on the Asian monsoons with an intermediate complexity climate model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3339, https://doi.org/10.5194/egusphere-egu23-3339, 2023.

Aerosol emissions have a wide range of impacts on the climate both near to and far from emission sources. Impacts span from local changes in surface solar warming to large-scale modifications of atmospheric circulation patterns and monsoonal precipitation. They have also been found to have an outsized near-term influence on extreme events in recent climate model studies. Consequently, future aerosol emission changes are likely to contribute to climate related risk in many highly populated regions, some of which are particularly vulnerable, for instance, to shifts in precipitation patterns or timing with respect to growing seasons. However, aerosol climate impacts generally follow patterns and time evolutions that are markedly different to those from greenhouse gas driven global surface warming, and our understanding of them is still plagued by high scientific uncertainty.

Given the urgent need for improved knowledge about the near-term influences of changes in aerosol emissions, we here introduce SyRAP-FORTE – a tool for understanding and decomposing the local and remote climate effects of regional aerosol emissions. SyRAP – a set of Systematic Regional Aerosol Perturbations – is developed using FORTE2.0, a Reduced Complexity (RC) climate model developed in the UK. Current and expected future aerosol emission changes are particularly strong in East and South Asia, where high population densities imply high potential climate risk. In the initial version of SyRAP, presented here, we therefore perturb absorbing and scattering aerosols, separately, over India and East China, to assess their separate influence on local responses in a range of climate parameters.

We document and validate the climate responses in FORTE to the regional aerosol perturbations, showing for instance that removing emissions of absorbing aerosols over both East China and will cause a local drying, but a range of more widespread effects. We find that SyRAP is able to reproduce the overall aerosol responses documented in the literature, and also that it allows us to decompose the influences of different aerosol species from the two regions on the climate near to, and far from, the emission sources.

Finally, we show how SyRAP can be used as input to emulators and tunable simple climate models, and as a ready-made tool for projecting the effects of near-term changes in Asian aerosol emissions.

How to cite: Stjern, C. W., Samset, B. H., Wilcox, L., and Joshi, M.: Climate influences of Asian anthropogenic aerosols decomposed using a Reduced Complexity Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7319, https://doi.org/10.5194/egusphere-egu23-7319, 2023.

After years of rapid growth, India has become a hotspot for emissions of aerosols and their precursors, recently surpassing China in terms of magnitude of SO₂ emissions. The resulting high air pollution levels influence climate through interactions with solar radiation, clouds, and the hydrological cycle, and pose one of the greatest environmental threats to public health. Model estimates of these impacts are influenced by the substantial spread that exists between current emission inventories, in terms of both trend and magnitude. Activity and fuel data is heterogeneous and can be challenging to compile, and many emission sources are highly region specific. Hence, inventories need to be based on up-to-date national statistics and detailed sectoral information.

Here we use one such inventory for Indian anthropogenic emissions, the recently developed, bottom up SNEII (Sabe National Emission Inventory for India) dataset to simulate and evaluate regional air pollution levels for 2018. SNEII includes a more detailed spatial allocation of point sources of emissions and sectoral disaggregation than many global inventories. The results are compared to estimates using the Community Emission Data System (CEDS) emissions, version 2021, also placing them in the context of the trend over the past decades. For most species, SNEII estimates higher emissions, and we explore the resulting impact of these differences on simulated aerosol abundances, as well as implications for radiative forcing and premature mortality. Finally, we quantify the sectoral contribution to air pollution with a finer breakdown than previously provided, including sectors unique for Indian/South Asian region.  

How to cite: Lund, M. T., Sahu, S. K., Mangaraj, P., Samset, B. H., Chowdhury, S., Myhre, G., and Johansen, A. N.: Quantifying effects of Indian aerosol emissions on regional aerosol abundances, energy balance, and health impacts, using a novel national emission inventory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1597, https://doi.org/10.5194/egusphere-egu23-1597, 2023.

This study investigates the effect of aerosol changes on regional climate in East Asia. Especially, we focus on the recent decreasing trend of aerosol concentrations in China from 2011 to 2018. We conduct climate sensitivity simulations using the Community Earth System Model (CESM) atmospheric general circulation model (AGCM) with observed monthly sea surface temperatures (SST) and sea ice concentrations (SIC) and coupled general circulation model (CGCM) with its own predicted SST and SIC from the coupled ocean and sea ice models. We prescribe the observed monthly aerosol optical depths from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra and Aqua satellite for the base simulations and period-averaged monthly aerosol optical depths for the sensitivity simulations. Comparisons of 50 ensemble averages between the base and sensitivity simulations for the AGCM and CGCM models show that the decreasing aerosols in East Asia warm up the region due to increased net shortwave radiation. We also found that the CGCM simulations show much stronger and more extensive warming in East Asia due to decreasing aerosols than the AGCM simulations, implying the importance of the aerosol-ocean-atmosphere feedback.

How to cite: Lee, S., Park, R., Yeh, S.-W., and Jeong, Y.-C.: Effect of aerosol changes on regional climate in East Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10054, https://doi.org/10.5194/egusphere-egu23-10054, 2023.

The world has changed: You can feel it in the air as temperatures rise, you can feel it in the water as precipitation patterns change. Much of what has once been our daily weather is lost. It began with humankind emitting greenhouse gases and aerosols. However, there is a growing resistance that wants to limit theses emissions. 

Daily variability can be described by probability density functions (PDF). Change can manifest as changes of the mean properties of weather-related variables, and/or changes in the chape of their PDFs. In this study, we examine how regional PDF shapes change due to increasing temperature, driven primarily by greenhouse gas emissions, and due to emissions of different aerosols species (black carbon and sulfate). Our main questions are: (1) How do shapes of regional daily PDFs evolve with global warming? (2) How do these changes differ in response to aerosol and greenhouse gas emissions? (3) And which aerosol-related teleconnections induce these changes in PDF shapes?  As changes in shape affect low and high extremes differently, we aim to link changes in PDF shape to changes in extreme events of daily temperature and precipitation by using parameters describing PDF width and asymmetry.

We use data from PDRMIP single forcer climate model simulations to examine how changes in regional and global aerosol concentrations change the PDF shapes. We also use three CMIP6 large ensembles (MPI-ESM1-2-LR, CanESM5 and ACCESS-ESM1-5) to examine changes in PDF shape at five different levels of global warming, from 1°C to 4 °C. Our main questions are how the shapes of regional daily PDFs evolve with globalwarming, how their changes differ between aerosol and greenhouse gas induced changes, and what teleconnections due to regional aerosol changes induce in PDF shapes.

For the time will soon come when aerosols will shape the near future of our weather.

How to cite: Nordling, K., Samset, B., and Fahrenbach, N.: Change in daily weather variability due to warming and regional aerosols., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1836, https://doi.org/10.5194/egusphere-egu23-1836, 2023.

Black carbon (BC) aerosols absorb solar radiation and thus heat the atmosphere. This process occurs on a short time scale and can influence clouds, precipitation, and boundary layer meteorology. Global climate models (GCMs) strongly disagree in their representation of such rapid adjustments, adding to the uncertainty in the effective radiative forcing (ERF) due to BC. Disagreements are at least partly caused by differences in parametrization of the highly regional and potentially non-linear rapid adjustments, which are poorly resolved in coarse resolution GCMs. Knowledge of how the rapid adjustments depend on model resolution is therefore important.

Here we explore the dependence of rapid adjustments on model resolution by performing a set of idealized experiments using a GCM, the Community Earth System Model version 2 (CESM2) with fixed sea-surface temperatures, downscaled by a regional climate model, the Weather Research and Forecasting (WRF), for five years at 45 km horizontal resolution over East and South Asia and at 15 km resolution covering East China. To ensure a sufficient climate response in the models, we perturb BC emissions by a factor of ten, and compare the results to separate simulations with a fivefold increase in (scattering) sulfate emissions and a doubling of CO₂ concentrations.

Preliminary results indicate similar BC-induced responses between CESM2 and 15 km WRF simulations in terms of tropospheric temperature and humidity, and mean precipitation, but strong dependence on model and/or resolution in the cloud response to BC. Potential differences in seasonal and extreme precipitation will be examined, and we plan to explore finer scales using the WRF model in Large Eddy Simulation (LES) mode down to 100 m horizontal resolution.

How to cite: Hodnebrog, Ø., Stjern, C. W., and Myhre, G.: Aerosol-radiation interactions on global to local scales, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13213, https://doi.org/10.5194/egusphere-egu23-13213, 2023.

Over Fennoscandian mountain birch forest region, there are increased attacks of geometrid moth larvae. These herbivores can change forests from a carbon sink to a carbon source. When moths start to chew on leaves, large quantities of biogenic volatile organic compounds (BVOCs) are released. Herbivory-induced BVOC emissions have been observed and quantified at a few sites over Fennoscandian mountain birch forest, but we know very little of their potential regional implications for atmospheric processes.

In this work, we extracted birch defoliation information based on MODIS leaf area index (LAI) for an outbreak year 2012, and together with field-observed relationship between leaf defoliated level and changes in emissions, we modelled herbivory-induced BVOC emissions at regional scale using MEGAN. Taking a step further, we fed MEGAN-modelled BVOC emission data with or without considering herbivory impacts to a two-way coupled WRF-CMAQ system to dynamically assess the impacts of these emissions on the atmospheric chemistry and climate system .

During the whole growing season of 2012, the defoliation at some MODIS grids can be as high as 90%, and the large defoliation mainly occurs in June and July. For t-β-ocimene, Other Monoterpenes, Stress and Other compound groups, herbivory contributes to more than 30, 8, 5 and 16 times the increase in the seasonal sum for the defoliated regions. For terpenes, herbivory increased monthly emissions up to 3 times for June and July. The reduction of emissions caused by herbivory-caused decrease in LAI is much smaller than the herbivory-induced increase. We also found strong impacts of herbivory-induced BVOC emissions on downward shortwave radiation and cloud radiative forcing.

This is the first time we can link all these components, i.e., satellite monitoring of leaf defoliation, in-situ observation, ecosystem and atmospheric modelling together to answer the research questions related to the regional importance of insect herbivory on atmospheric composition and climate.

How to cite: Tang, J., Wang, H., Cai, Z., Guenther, A., Rinnan, R., Olsson, P.-O., Borchmann, R. L., Davie-Martin, C. L., Schurgers, G., Ren, Z., Rieksta, J., and Li, T.: Insect herbivory have significantly altered BVOC emissions, SOA concentration and radiative forcing over Fennoscandian birch forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12434, https://doi.org/10.5194/egusphere-egu23-12434, 2023.