Climate Impacts From a Removal of Anthropogenic Aerosol Emissions

Abstract

Limiting global warming to 1.5 or 2.0°C requires strong mitigation of anthropogenic greenhouse gas (GHG) emissions. Concurrently, emissions of anthropogenic aerosols will decline, due to coemission with GHG, and measures to improve air quality. However, the combined climate effect of GHG and aerosol emissions over the industrial era is poorly constrained. Here we show the climate impacts from removing present‐day anthropogenic aerosol emissions and compare them to the impacts from moderate GHG‐dominated global warming. Removing aerosols induces a global mean surface heating of 0.5–1.1°C, and precipitation increase of 2.0–4.6%. Extreme weather indices also increase. We find a higher sensitivity of extreme events to aerosol reductions, per degree of surface warming, in particular over the major aerosol emission regions. Under near‐term warming, we find that regional climate change will depend strongly on the balance between aerosol and GHG forcing.

Robust changes in tropical rainy season length at 1.5 °C and 2 °C

“…Changes in modelled rainy season characteristics, are also influenced by forcings other than CO 2 , in particular other greenhouse gases, aerosols, ozone concentration as well as land use and land cover; these other forcings are identical for the 1.5 • C and 2.0 • C experiments (Mitchell et al 2017). Thereby, we cannot rule out that a substantial share of the projected changes between the historical period and 1.5 • C and 2.0 • C is also influenced by changes in non-GHG factors (Wang et al 2017, Samset et al 2018. Furthermore, both HAPPI experiments are forced by an end-of-century ocean that may also lead to a northward shift of the ITCZ as the result of northern high latitude warming in a climate with an Atlantic meridional overturning circulation showing signs of recovery (Schleussner et al 2014).…”

How Uneven Are Changes to Impact‐Relevant Climate Hazards in a 1.5 °C World and Beyond?

“…However, there are open questions about (1) how the impacts of an N-degree increase in global mean temperatures are influenced by the emissions pathway taken to reach that threshold, such as regional changes to aerosol emissions (Samset et al, 2018;Wang et al, 2017), as well as (2) whether reaching a global temperature threshold in a transient scenario will generate the same climate impacts as for a case where temperatures stabilize at that threshold (James et al, 2017). Our analysis has made use of the high-emissions RCP8.5 scenario as there is a necessary requirement for the future climate trajectory to span as wide a range of temperature thresholds as possible.…”

“…Our analysis has made use of the high-emissions RCP8.5 scenario as there is a necessary requirement for the future climate trajectory to span as wide a range of temperature thresholds as possible. However, there are open questions about (1) how the impacts of an N-degree increase in global mean temperatures are influenced by the emissions pathway taken to reach that threshold, such as regional changes to aerosol emissions (Samset et al, 2018;Wang et al, 2017), as well as (2) whether reaching a global temperature threshold in a transient scenario will generate the same climate impacts as for a case where temperatures stabilize at that threshold (James et al, 2017). These remain open questions which could influence the TE index for some individual locations and for some types of impacts and should thus be a priority for future research.…”

The Role of Anthropogenic Aerosol Forcing in Interdecadal Variations of Summertime Upper‐Tropospheric Temperature Over East Asia

“…Our results show that a decreased anthropogenic aerosol burden will lead to a rise of 0.05°C per decade in the JA mean UTT averaged over East Asia for the period 2010-2050 under the RCP8.5 scenario. This will likely have significant effects on the spatial distribution of summer precipitation over East Asia (Lin et al, 2018;Samset et al, 2018;Z. L. Wang, Lin, Zhang, et al, 2017).…”

“…Therefore, the rising trend of JA mean UTT over East Asia in the future can be stronger than that in the RCP8.5_FixG simulation ( Figure S4). This reversal in the UTT trend will likely result in significant changes to the spatial distribution of summer precipitation over East Asia in the future (Lin et al, 2018;Samset et al, 2018;Z. L. Wang, Zhang, & Zhang, 2016).…”