An official website of the United States government
Abstract The distribution of anthropogenic aerosols’ climate effects depends on the geographic distribution of the aerosols themselves. Yet many scientific and policy discussions ignore the role of emission location when evaluating aerosols’ climate impacts. Here, we present new climate model results demonstrating divergent climate responses to a fixed amount and composition of aerosol—emulating China’s present-day emissions—emitted from 8 key geopolitical regions. The aerosols’ global-mean cooling effect is fourteen times greater when emitted from the highest impact emitting region (Western Europe) than from the lowest (India). Further, radiative forcing, a widely used climate response proxy, fails as an effective predictor of global-mean cooling for national-scale aerosol emissions in our simulations; global-mean forcing-to-cooling efficacy differs fivefold depending on emitting region. This suggests that climate accounting should differentiate between aerosols emitted from different countries and that aerosol emissions’ evolving geographic distribution will impact the global-scale magnitude and spatial distribution of climate change.
more »
« less
Anthropogenic aerosol changes disproportionately impact the evolution of global heatwave hazard and exposure
Abstract Understanding and predicting heatwave risk is a societal imperative in the face of climate change. Anthropogenic aerosol emissions impact heat extremes more strongly per unit of mean warming than do greenhouse gases, but the influence of aerosols’ evolving spatial pattern on time-varying heatwave hazard and resulting population exposure has been largely ignored. Aerosols’ spatially heterogeneous forcing is often co-located with population centers due to aerosols’ industrial sources and short atmospheric lifetime, potentially resulting in amplified exposure to aerosol-driven climate effects. Here, we quantify the influence of historical and projected future changes in aerosol emissions through 2100 on global patterns of heatwave hazard (i.e. the frequency of heatwave days) and exposure (i.e. population-weighted hazard) using the NCAR Community Earth System Model v1 single forcing large ensemble (LE). Our results show that increased aerosol emissions since 1920 have suppressed heatwave frequency (HWF) over populated regions by roughly half through present-day—a trend that is now reversing with shifting emission patterns and net global declining emissions. This may already be leading to an aerosol-driven acceleration in HWF, a signal that is amplified in populated regions. Aerosols’ influence on heatwaves is strongly co-located with population, creating out-sized exposure, which evolves through time with aerosols’ evolving emissions pattern within this LE. Our results suggest that near-term changes in aerosol emissions will be a disproportionate driver of trends in heatwave exposure, meriting dedicated future study, and that aerosols’ evolving spatial pattern should be considered in attempts to attribute recent heatwave trends to human activity.
more »
« less
- Award ID(s):
- 2235177
- PAR ID:
- 10611791
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Environmental Research Letters
- Volume:
- 20
- Issue:
- 8
- ISSN:
- 1748-9326
- Format(s):
- Medium: X Size: Article No. 084023
- Size(s):
- Article No. 084023
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract. Even though the Arctic is remote, aerosol properties observed there arestrongly influenced by anthropogenic emissions from outside the Arctic. Thisis particularly true for the so-called Arctic haze season (January throughApril). In summer (June through September), when atmospheric transportpatterns change, and precipitation is more frequent, local Arctic sources,i.e., natural sources of aerosols and precursors, play an important role.Over the last few decades, significant reductions in anthropogenic emissionshave taken place. At the same time a large body of literature shows evidencethat the Arctic is undergoing fundamental environmental changes due toclimate forcing, leading to enhanced emissions by natural processes that mayimpact aerosol properties. In this study, we analyze 9 aerosol chemical species and 4 particleoptical properties from 10 Arctic observatories (Alert, Kevo, Pallas,Summit, Thule, Tiksi, Barrow/Utqiaġvik, Villum, and Gruvebadet and ZeppelinObservatory – both at Ny-Ålesund Research Station) to understand changesin anthropogenic and natural aerosol contributions. Variables includeequivalent black carbon, particulate sulfate, nitrate, ammonium,methanesulfonic acid, sodium, iron, calcium and potassium, as well asscattering and absorption coefficients, single scattering albedo andscattering Ångström exponent. First, annual cycles are investigated, which despite anthropogenic emissionreductions still show the Arctic haze phenomenon. Second, long-term trendsare studied using the Mann–Kendall Theil–Sen slope method. We find in total41 significant trends over full station records, i.e., spanning more than adecade, compared to 26 significant decadal trends. The majority ofsignificantly declining trends is from anthropogenic tracers and occurredduring the haze period, driven by emission changes between 1990 and 2000.For the summer period, no uniform picture of trends has emerged. Twenty-sixpercent of trends, i.e., 19 out of 73, are significant, and of those 5 arepositive and 14 are negative. Negative trends include not only anthropogenictracers such as equivalent black carbon at Kevo, but also natural indicatorssuch as methanesulfonic acid and non-sea-salt calcium at Alert. Positivetrends are observed for sulfate at Gruvebadet. No clear evidence of a significant change in the natural aerosolcontribution can be observed yet. However, testing the sensitivity of theMann–Kendall Theil–Sen method, we find that monotonic changes of around 5 % yr−1 in an aerosol property are needed to detect a significanttrend within one decade. This highlights that long-term efforts well beyonda decade are needed to capture smaller changes. It is particularly importantto understand the ongoing natural changes in the Arctic, where interannualvariability can be high, such as with forest fire emissions and theirinfluence on the aerosol population. To investigate the climate-change-induced influence on the aerosolpopulation and the resulting climate feedback, long-term observations oftracers more specific to natural sources are needed, as well as of particlemicrophysical properties such as size distributions, which can be used toidentify changes in particle populations which are not well captured bymass-oriented methods such as bulk chemical composition.more » « less
-
Abstract. Changes in anthropogenic aerosol emissions have strongly contributed to global and regional trends in temperature, precipitation, and other climate characteristics and have been one of the dominant drivers of decadal trends in Asian and African precipitation. These and other influences on regional climate from changes in aerosol emissions are expected to continue and potentially strengthen in the coming decades. However, a combination of large uncertainties in emission pathways, radiative forcing, and the dynamical response to forcing makes anthropogenic aerosol a key factor in the spread of near-term climate projections, particularly on regional scales, and therefore an important one to constrain. For example, in terms of future emission pathways, the uncertainty in future global aerosol and precursor gas emissions by 2050 is as large as the total increase in emissions since 1850. In terms of aerosol effective radiative forcing, which remains the largest source of uncertainty in future climate change projections, CMIP6 models span a factor of 5, from −0.3 to −1.5 W m−2. Both of these sources of uncertainty are exacerbated on regional scales. The Regional Aerosol Model Intercomparison Project (RAMIP) will deliver experiments designed to quantify the role of regional aerosol emissions changes in near-term projections. This is unlike any prior MIP, where the focus has been on changes in global emissions and/or very idealised aerosol experiments. Perturbing regional emissions makes RAMIP novel from a scientific standpoint and links the intended analyses more directly to mitigation and adaptation policy issues. From a science perspective, there is limited information on how realistic regional aerosol emissions impact local as well as remote climate conditions. Here, RAMIP will enable an evaluation of the full range of potential influences of realistic and regionally varied aerosol emission changes on near-future climate. From the policy perspective, RAMIP addresses the burning question of how local and remote decisions affecting emissions of aerosols influence climate change in any given region. Here, RAMIP will provide the information needed to make direct links between regional climate policies and regional climate change. RAMIP experiments are designed to explore sensitivities to aerosol type and location and provide improved constraints on uncertainties driven by aerosol radiative forcing and the dynamical response to aerosol changes. The core experiments will assess the effects of differences in future global and regional (Africa and the Middle East, East Asia, North America and Europe, and South Asia) aerosol emission trajectories through 2051, while optional experiments will test the nonlinear effects of varying emission locations and aerosol types along this future trajectory. All experiments are based on the shared socioeconomic pathways and are intended to be performed with 6th Climate Model Intercomparison Project (CMIP6) generation models, initialised from the CMIP6 historical experiments, to facilitate comparisons with existing projections. Requested outputs will enable the analysis of the role of aerosol in near-future changes in, for example, temperature and precipitation means and extremes, storms, and air quality.more » « less
-
Abstract The regional climate impacts of anthropogenic aerosol emissions and irrigation growth in South Asia have conventionally been studied separately. These forcings have overlapping influences on surface temperature and atmospheric stability, but detection and attribution simulations typically quantify the impact of individual time‐evolving climate forcings, which does not account for nonlinear interactions between forcings or their impacts, when forcings evolve in tandem. Using transient simulations in GISS ModelE 2.1‐G, we assess the summertime surface energy balance in five different sub‐regions of South Asia by comparing the linear addition of anthropogenic aerosol and land use single‐forcing historical simulations with novel dual‐forcing simulations. We find that the combination of aerosol emissions and irrigation changes between preindustrial and present‐day increases aerosol hydration and cloud cover more strongly than does the linear addition of the individual forcings. This results in a strong nonlinear decrease in downwelling shortwave radiation, which drives subsequent nonlinearities in the surface energy balance through a relative suppression of energy availability at the surface. While aerosols and irrigation are each credited with suppressing monsoon winds and delaying onset, combined simulations of both forcings suggest that surface pressure is nonlinearly reduced over the northern Indian Subcontinent. This results in a net increase in 850 mb winds from the Bay of Bengal toward northwest India and Pakistan in combined simulations, suppressing the weakening of summer monsoon winds from single forcing results. The nonlinearities identified in our study suggest that the current framework for detection and attribution may not adequately account for potential interactions between forcings.more » « less
-
Biomass burning can affect climate via the emission of aerosols and their subsequent impact on radiation, cloud microphysics, and surface and atmospheric albedo. Biomass burning emissions (BBEs) over the boreal region have strongly increased during the last decade and are expected to continue increasing as the climate warms. Climate models simulate aerosol processes, yet historical and future Coupled Model Intercomparison Project (CMIP) simulations have no active fire component, and BBEs are prescribed as external forcings. Here, we show that CMIP6 used future boreal BBEs scenarios with unrealistic near-zero trends that have a large impact on climate trends. By running sensitivity experiments with ramped up boreal emissions based on observed trends, we find that increasing boreal BBEs reduces global warming by 12% and Arctic warming by 38%, reducing the loss of sea ice. Tropical precipitation shifts southward as a result of the hemispheric difference in boreal aerosol forcing and subsequent temperature response. These changes stem from the impact of aerosols on clouds, increasing cloud droplet number concentration, cloud optical depth, and low cloud cover, ultimately reducing surface shortwave flux over northern latitudes. Our results highlight the importance of realistic boreal BBEs in climate model simulations and the need for improved understanding of boreal emission trends and aerosol–climate interactions.more » « less
