Climate effects of changing aerosol emissions over the coming decades

2021 ◽  
Author(s):  
Bjorn H. Samset ◽  
Camilla W. Stjern ◽  
Marianne T. Lund
Keyword(s):  
Global Scale ◽  
Mitigation Strategies ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Surface Temperature Change ◽  
Temperature And Precipitation ◽  
Large Ensembles ◽  
Near Term ◽  
Aerosol Emissions

<div>Emissions of anthropogenic aerosols strongly influence the climate, by modulating global and regional temperature, and by affecting precipitation, extremes, circulation patterns and other local-to-global scale features. This influence has been continually changing over previous decades, and will continue to change at least until 2050. It is also highly heterogeneous, in space and time. Hence, a deeper look at the potential role of anthropogenic aerosol emissions in shaping climate change over the coming decades is crucial for both adaptation and mitigation strategies. </div><div> </div><div>Here, we discuss three techniques to bound the potential near-term role of aerosols: (i) The influence on local and global rates of warming, relative to natural variability, using simplified models in combination with Large Ensembles, (ii) an overall constraint on the precipitation influence of absorbing aerosols, combining recent emission projections with results from several multi-model intercomparison projects, and (iii) changes to regional distributions of daily temperature and precipitation as function of the level of aerosol emissions and global warming, leveraging the statistics available through Large Ensembles. </div><div> </div><div>Overall, we find that while greenhouse gas emissions will continue to dominate the global mean climate evolution, by driving surface temperature change and its associated feedbacks, aerosol emissions may still hold a key - or even dominating - influence on changes to regional weather and climate. </div>

scholarly journals A continued role of short-lived climate forcers under the Shared Socioeconomic Pathways

2020 ◽  
Vol 11 (4) ◽  
pp. 977-993
Author(s):  
Marianne T. Lund ◽  
Borgar Aamaas ◽  
Camilla W. Stjern ◽  
Zbigniew Klimont ◽  
Terje K. Berntsen ◽  
...  
Keyword(s):  
Climate Impact ◽  
Mitigation Strategies ◽  
Decision Makers ◽  
Detailed Knowledge ◽  
Agriculture Waste ◽  
Development Goals ◽  
Near Term ◽  
Temperature Responses

Abstract. Mitigation of non-CO2 emissions plays a key role in meeting the Paris Agreement ambitions and sustainable development goals. Implementation of respective policies addressing these targets mainly occur at sectoral and regional levels, and designing efficient mitigation strategies therefore relies on detailed knowledge about the mix of emissions from individual sources and their subsequent climate impact. Here we present a comprehensive dataset of near- and long-term global temperature responses to emissions of CO2 and individual short-lived climate forcers (SLCFs) from 7 sectors and 13 regions – for both present-day emissions and their continued evolution as projected under the Shared Socioeconomic Pathways (SSPs). We demonstrate the key role of CO2 in driving both near- and long-term warming and highlight the importance of mitigating methane emissions from agriculture, waste management, and energy production as the primary strategy to further limit near-term warming. Due to high current emissions of cooling SLCFs, policies targeting end-of-pipe energy sector emissions may result in net added warming unless accompanied by simultaneous methane and/or CO2 reductions. We find that SLCFs are projected to play a continued role in many regions, particularly those including low- to medium-income countries, under most of the SSPs considered here. East Asia, North America, and Europe will remain the largest contributors to total net warming until 2100, regardless of scenario, while South Asia and Africa south of the Sahara overtake Europe by the end of the century in SSP3-7.0 and SSP5-8.5. Our dataset is made available in an accessible format, aimed also at decision makers, to support further assessment of the implications of policy implementation at the sectoral and regional scales.

scholarly journals Anthropogenic aerosol drives uncertainty in future climate mitigation efforts

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
E. J. L. Larson ◽  
R. W. Portmann
Keyword(s):  
Climate Models ◽  
Ghg Emissions ◽  
Paris Agreement ◽  
Climate Mitigation ◽  
Mathematical Framework ◽  
Emission Rates ◽  
Anthropogenic Aerosol ◽  
Greenhouse Gasses ◽  
Near Term ◽  
Aerosol Emissions

Abstract The 2016 Paris agreement set a global mean surface temperature (GMST) goal of not more than 2 degrees Celsius above preindustrial. This is an ambitious goal that will require substantial decreases in emission rates of long-lived greenhouse gasses (GHG). This work provides a mathematical framework, based on current state of the art climate models, to calculate the GHG emissions consistent with prescribed GMST pathways that meet the Paris agreement goal. The unique capability of this framework, to start from a GMST timeseries and efficiently calculate the emissions required to meet that temperature pathway, makes it a powerful resource for policymakers. Our results indicate that aerosol emissions play a large role in determining the near-term allowable greenhouse gas emissions that will limit future warming to 2 °C, however in the long term, drastic GHG emissions reductions are required under any reasonable aerosol scenario. With large future aerosol emissions, similar to present day amounts, GHG emissions need to be reduced 8% by 2040 and 74% by 2100 to limit warming to 2 °C. Under a more likely low aerosol scenario, GHG emissions need to be reduced 36% and 80% by 2040 and 2100, respectively. The Paris agreement Intended Nationally Determined Contributions are insufficient to meet this goal.

scholarly journals Comparison of Climate Response to Anthropogenic Aerosol versus Greenhouse Gas Forcing: Distinct Patterns

2016 ◽  
Vol 29 (14) ◽  
pp. 5175-5188 ◽  
Author(s):  
Hai Wang ◽  
Shang-Ping Xie ◽  
Qinyu Liu
Keyword(s):  
Northern Hemisphere ◽  
Radiative Forcing ◽  
Climate Model ◽  
East Asian Monsoon ◽  
Climate Response ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Asian Monsoon Region ◽  
Surface Temperature Change ◽  
Aerosol Forcing

Abstract Spatial patterns of climate response to changes in anthropogenic aerosols and well-mixed greenhouse gases (GHGs) are investigated using climate model simulations for the twentieth century. The climate response shows both similarities and differences in spatial pattern between aerosol and GHG runs. Common climate response between aerosol and GHG runs tends to be symmetric about the equator. This work focuses on the distinctive patterns that are unique to the anthropogenic aerosol forcing. The tropospheric cooling induced by anthropogenic aerosols is locally enhanced in the midlatitude Northern Hemisphere with a deep vertical structure around 40°N, anchoring a westerly acceleration in thermal wind balance. The aerosol-induced negative radiative forcing in the Northern Hemisphere requires a cross-equatorial Hadley circulation to compensate interhemispheric energy imbalance in the atmosphere. Associated with a southward shift of the intertropical convergence zone, this interhemispheric asymmetric mode is unique to aerosol forcing and absent in GHG runs. Comparison of key climate response pattern indices indicates that the aerosol forcing dominates the interhemispheric asymmetric climate response in historical all-forcing simulations, as well as regional precipitation change such as the drying trend over the East Asian monsoon region. While GHG forcing dominates global mean surface temperature change, its effect is on par with and often opposes the aerosol effect on precipitation, making it difficult to detect anthropogenic change in rainfall from historical observations.

scholarly journals Impacts of the 1900–74 Increase in Anthropogenic Aerosol Emissions from North America and Europe on Eurasian Summer Climate

2018 ◽  
Vol 31 (20) ◽  
pp. 8381-8399 ◽  
Author(s):  
S. Undorf ◽  
M. A. Bollasina ◽  
G. C. Hegerl
Keyword(s):  
Twentieth Century ◽  
Large Scale ◽  
Coupled Model ◽  
Temporal Variations ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Near Surface ◽  
Summer Climate ◽  
Aerosol Emissions ◽  
The Impact

The impact of North American and European (NAEU) anthropogenic aerosol emissions on Eurasian summer climate during the twentieth century is studied using historical single- and all-forcing (including anthropogenic aerosols, greenhouse gases, and natural forcings) simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Intermodel agreement on significant linear trends during a period of increasing NAEU sulfate emissions (1900–74) reveals robust features of NAEU aerosol impact, supported by opposite changes during the subsequent period of decreasing emissions. Regionally, these include a large-scale cooling and associated anticyclonic circulation, as well as a narrowing of the diurnal temperature range (DTR) over Eurasian midlatitudes. Remotely, NAEU aerosols induce a drying over the western African and northern Indian monsoon regions and a strengthening and southward shift of the subtropical jet consistent with the pattern of temperature change. Over Europe, the temporal variations of observed temperature, pressure, and DTR tend to agree better with simulations that include aerosols. Throughout the twentieth century, aerosols are estimated to explain more than a third of the simulated interdecadal forced variability of European near-surface temperature and more than half between 1940 and 1970. These results highlight the substantial aerosol impact on Eurasian climate, already identifiable in the first half of the twentieth century. This may be relevant for understanding future patterns of change related to further emission reductions.

scholarly journals Understanding the Rapid Precipitation Response to CO2 and Aerosol Forcing on a Regional Scale*

2016 ◽  
Vol 29 (2) ◽  
pp. 583-594 ◽  
Author(s):  
Thomas B. Richardson ◽  
Piers M. Forster ◽  
Timothy Andrews ◽  
Doug J. Parker
Keyword(s):  
Surface Temperature ◽  
Spatial Pattern ◽  
Land Surface ◽  
Regional Scale ◽  
Anthropogenic Aerosols ◽  
Abrupt Increase ◽  
Anthropogenic Aerosol ◽  
Surface Temperature Change ◽  
Precipitation Response

Abstract Precipitation exhibits a significant rapid adjustment in response to forcing, which is important for understanding long-term climate change. In this study, fixed sea surface temperature (SST) simulations are used to analyze the spatial pattern of the rapid precipitation response. Three different forcing scenarios are investigated using data obtained from phase 5 of CMIP (CMIP5): an abrupt quadrupling of CO2, an abrupt increase in sulfate, and an abrupt increase in all anthropogenic aerosol levels from preindustrial to present day. Analysis of the local energy budget is used to understand the mechanisms that drive the observed changes. It is found that the spatial pattern of the rapid precipitation response to forcing is primarily driven by rapid land surface temperature change, rather than the change in tropospheric diabatic cooling. As a result, the pattern of response due to increased CO2 opposes that due to sulfate and all anthropogenic aerosols, because of the opposing surface forcing. The rapid regional precipitation response to increased CO2 is robust among models, implying that the uncertainty in long-term changes is mainly associated with the response to SST-mediated feedbacks. Increased CO2 causes rapid warming of the land surface, which destabilizes the troposphere, enhancing convection and precipitation over land in the tropics. Precipitation is reduced over most tropical oceans because of a weakening of overturning circulation and a general shift of convection to over land. Over most land regions in the midlatitudes, circulation changes are small. Reduced tropospheric cooling therefore leads to drying over many midlatitude land regions.

Attribution of the relative contributions of anthropogenic aerosols and decadal variability to the mid-20th century global “cooling”: a focus on tropospheric temperature latitudinal gradient

2021 ◽  
Author(s):  
Chenrui Diao ◽  
Yangyang Xu
Keyword(s):  
20Th Century ◽  
Temperature Trend ◽  
Cmip5 Models ◽  
Anthropogenic Emissions ◽  
Tropospheric Temperature ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Continuous Increase ◽  
Cooling Period ◽  
Aerosol Emissions

<p>The global mean surface temperature went through a cooling period during the mid-20th century despite the continuous increase in greenhouse gas concentration. This generates a renewed interest to look at the multi-decadal climate variabilities across the 20th century, which are often believed to be related to the internal variabilities caused by ocean-atmosphere interaction.</p><p>At the same time, an obvious interhemispheric tropospheric temperature trend asymmetry is found in both reanalysis datasets and model simulations during this time. Considering the rapid increase of industrial activities in North America and Europe, it generates another possibility that anthropogenic emissions play a role during this period. And if anthropogenic emissions do have significant effects, then the relative contributions of anthropogenic emissions and internal variabilities to the mid-20th-century cooling is worth understanding because of the increasing importance of human activities to the natural environment.</p><p>To test this hypothesis, we did a detailed analysis on the global temperature trend and the interhemispheric temperature trend asymmetry from the surface to the mid-troposphere based on Coupled Model Intercomparison Project phase 5 (CMIP5) multi-model ensemble and multiple reanalysis datasets. Our results show that the anthropogenic aerosol emissions contribute to global cooling and particularly asymmetry during the mid-20th century, and the fingerprint of anthropogenic emissions is more obvious in the mid-troposphere compared with the surface.</p><p>By different attribution methods (such as multi-linear regression and pattern correlation), we quantified the relative contributions of Anthropogenic Emissions and Internal variabilities based on single forcing simulations of seven CMIP5 models. We conclude that a superposition of Internal Variabilities originating from the Atlantic Ocean and anthropogenic aerosol emissions overwhelms the warming influence of GHGs and lead to the mid-20th century cooling period.</p>

scholarly journals Uncertainty in aerosol radiative forcing impacts the simulated global monsoon in the 20th century

2020 ◽  
Author(s):  
Andrew Turner ◽  
Jonathan Shonk ◽  
Laura Wilcox ◽  
Andrea Dittus ◽  
Ed Hawkins
Keyword(s):  
Radiative Forcing ◽  
Monsoon Rainfall ◽  
Strong Relationship ◽  
Dynamical Response ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Global Monsoon ◽  
Monsoon Area ◽  
Hemispheric Temperature ◽  
Aerosol Emissions

<div> <div> <div> <p>Anthropogenic aerosols are dominant drivers of historical monsoon rainfall change.  However, large uncertainties in the radiative forcing associated with anthropogenic aerosol emissions, and the dynamical response to this forcing, lead to uncertainty in the simulated monsoon response.  We use historical simulations in which aerosol emissions are scaled by factors from 0.2 to 1.5 to explore the monsoon sensitivity to aerosol forcing uncertainty (−0.3 W m−2 to −1.6 W m−2).  Hemispheric asymmetry in emissions generates a strong relationship between scaling factor and both hemispheric temperature contrast and meridional location of tropical rainfall.  Increasing the  scaling from 0.2 to 1.5 reduces the global monsoon area by 3% and the global monsoon intensity by 2% over 1950–2014, and changes the dominant influence on the 1950–1980 monsoon rainfall trend from greenhouse gas to aerosol.   Regionally, aerosol scaling has a pronounced effect on Northern Hemisphere monsoon rainfall.</p> </div> </div> </div>

scholarly journals Disentangling the impacts of anthropogenic aerosols on terrestrial carbon cycle during 1850-2014

2021 ◽  
Author(s):  
Yuan Zhang ◽  
Philippe Ciais ◽  
Olivier Boucher ◽  
Fabienne Maignan ◽  
Ana Bastos ◽  
...  
Keyword(s):  
Land Surface ◽  
Dominant Role ◽  
Diffuse Radiation ◽  
Carbon Fluxes ◽  
Surface Model ◽  
Anthropogenic Aerosols ◽  
Radiation Quality ◽  
Anthropogenic Aerosol ◽  
C Cycle ◽  
Aerosol Emissions

<p>Aerosols have a dimming and cooling effect and change hydrological regimes, thus affecting carbon fluxes, which are sensitive to climate. Aerosols also scatter sunlight, which increases the fraction of diffuse radiation, increasing photosynthesis. Although previous studies have quantified the impacts of some of these factors separately, there remains no clear conclusion whether the physical impacts of aerosols on land carbon fluxes is larger through diffuse radiation change than through changes in other climate variables. In this study, we quantified the overall physical impacts of anthropogenic aerosols on land C fluxes and explored the contribution from each factor using a set of factorial simulations driven by climate and aerosol data from the IPSL-CM6A-LR experiments from 1850 to 2014. A newly-developed land surface model which distinguishes diffuse and direct radiation in canopy radiation transmission, ORCHIDEE_DF, was used. Specifically, a sub-grid scheme was developed to distinguish the cloudy and clear sky conditions. We found that anthropogenic aerosol emissions since 1850 cumulatively enhanced the land C sink by 22.6 PgC. 78% of this C sink enhancement is contributed by aerosol-induced increase in the diffuse radiation fraction, which is much larger than the effect of the aerosol-induced dimming. The cooling of anthropogenic aerosols increases the C sink in low latitudes but decreases the C sink in high latitudes and overall slightly increases the global land C sink. Compared with radiation and temperature changes, aerosol-induced precipitation changes have limited impacts. The dominant role of diffuse radiation changes in affecting historical land C fluxes found in this study implies that future aerosol emissions may have a much stronger impacts on the C cycle through changing radiation quality than through changing climate alone. Earth system models need to take into account the diffuse radiation fertilization effect, in order to better evaluate the impacts of climate change mitigation scenarios.</p>

scholarly journals Quantifying the influence of short-term emission reductions on climate

2021 ◽  
Vol 7 (10) ◽  
pp. eabf7133
Author(s):  
J. C. Fyfe ◽  
V. V. Kharin ◽  
N. Swart ◽  
G. M. Flato ◽  
M. Sigmond ◽  
...  
Keyword(s):  
Regional Climate ◽  
Potential Effect ◽  
Short Term ◽  
Emission Reductions ◽  
Temperature And Precipitation ◽  
Aerosol Emission ◽  
Regional Temperature ◽  
Near Term ◽  
Aerosol Emissions ◽  
The Impact

The COVID-19 (coronavirus disease 2019) pandemic has resulted in a marked slowdown in greenhouse gas and aerosol emissions. Although the resulting emission reductions will continue to evolve, this will presumably be temporary. Here, we provide estimates of the potential effect of such short-term emission reductions on global and regional temperature and precipitation by analyzing the response of an Earth System Model to a range of idealized near-term emission pathways not considered in available model intercomparison projects. These estimates reveal the modest impact that temporary emission reductions associated with the COVID-19 pandemic will have on global and regional climate. Our simulations suggest that the impact of carbon dioxide and aerosol emission reductions is actually a temporary enhancement in warming rate. However, our results demonstrate that even large emission reductions applied for a short duration have only a small and likely undetectable impact.

Implication of the reduction in anthropogenic aerosols due to the COVID-19 pandemic and the future recovery scenarios for radiative forcing

2021 ◽  
Author(s):  
Stephanie Fiedler ◽  
Klaus Wyser ◽  
Rogelj Joeri ◽  
Twan van Noije
Keyword(s):  
Radiative Forcing ◽  
Internal Variability ◽  
Climate Response ◽  
Emission Scenarios ◽  
Radiative Effects ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Aerosol Forcing ◽  
Effective Radiative Forcing ◽  
Aerosol Emissions

<p>The COVID-19 pandemic has led to unprecedented reductions in socio-economic activities. Associated decreases in anthropogenic aerosol emissions are not represented in the original CMIP6 emission scenarios. Here we estimate the implications of the pandemic for the aerosol forcing in 2020 and quantify the spread in aerosol forcing associated with the differences in the post-pandemic recovery pathways. To this end, we use new emission scenarios taking the COVID-19 crisis into account and projecting different socio-economic developments until 2050 with fossil-fuel based and green pathways (Forster et al., 2020). We use the new emission data to generate input for the anthropogenic aerosol parameterization MACv2-SP for CMIP6 models. In this presentation, we first show the results for the anthropogenic aerosol optical depth and associated effects on clouds from the new MACv2-SP data for 2020 to 2050 (Fiedler et al., in review). We then use the MACv2-SP data to provide estimates of the effective radiative effects of the anthropogenic aerosols for 2020 and 2050. Our forcing estimates are based on new atmosphere-only simulations with the CMIP6 model EC-Earth3. The model uses MACv2-SP to represent aerosol-radiation and aerosol-cloud interactions including aerosol effects on cloud lifetime. For each anthropogenic aerosol pattern, we run EC-Earth3 simulations for fifty years to substantially reduce the impact of model-internal variability on the forcing estimate. Our results highlight: (1) a change of +0.04 Wm<sup>-2</sup> in the global mean effective radiative forcing of anthropogenic aerosols for 2020 due to the pandemic, which is small compared to the magnitude of internal variability, (2) a spread of -0.38 to -0.68 Wm<sup>-2</sup> for the effective radiative forcing associated with anthropogenic aerosols in 2050 depending on the recovery scenario in MACv2-SP, and (3) a more negative (stronger) anthropogenic aerosol forcing for a strong green than a moderate green development in 2050 due to higher ammonium emissions in a highly decarbonized society (Fiedler et al., in review). The new MACv2-SP data are now used in climate models participating in the model intercomparison project on the climate response to the COVID-19 crisis (Covid-MIP, Jones et al., in review, Lamboll et al., in review).</p><p><strong>References:</strong></p><p>Fiedler, S., Wyser, K., Joeri, R., and van Noije, T.: Radiative effects of reduced aerosol emissions during the COVID-19 pandemic and the future recovery, in review, [preprint] https://doi.org/10.1002/essoar.10504704.1.</p><p>Forster, P.M., Forster, H.I., Evans, M.J. et al.: Current and future global climate impacts resulting from COVID-19. Nat. Clim. Chang. 10, 913–919, 2020, https://doi.org/10.1038/s41558-020-0883-0.</p><p>Jones. C., Hickman, J., Rumbold, S., et al.: The Climate Response to Emissions Reductions due to COVID-19, Geophy. Res. Lett., in review.</p><p>Lamboll, R. D., Jones, C. D., Skeie, R. B., Fiedler, S., Samset, B. H., Gillett, N. P., Rogelj, J., and Forster, P. M.: Modifying emission scenario projections to account for the effects of COVID-19: protocol for Covid-MIP, in review, [preprint] https://doi.org/10.5194/gmd-2020-373.</p>

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