Improved air quality has accelerated global warming in recent decades

Chemistry and physics of the atmosphere (2022). DOI: 10.5194/acp-22-12221-2022″ width=”800″ height=”346″/>

Linear trends (2000-2019) of (a) Aerosol Optical Depth (AOD) extracted from the Multi-Angle Imaging Spectroradiometer (MISR; Garay et al., 2017) on board the Terra satellite, where colored circles show AOD trends of the AERONET ground-based solar photometer network (Holben et al., 1998; Giles et al., 2019) where data since 2000 are available. Panel (b) is the same as (a), but for fine mode AOD, i.e. AOD due to aerosols with radii less than 1 µm. Panels (c) and (d) are the same as for (a) and (b), but with recoveries from the MODerate Resolution Imaging Spectroradiometer (MODIS; Levy et al., 2013) (fine mode AOD not available on earth) from the Terra satellite, averaged (from 2002) with MODIS recoveries from the Aqua satellite; (e) AOD of polar multisensor aerosol product (PMAp) extracted from the Global Ozone Monitoring Experiment-2 (GOME-2) instrument on board EUMETSAT’s Metop-A satellite, available only from 2008 to 2017. Chemistry and physics of the atmosphere (2022). DOI: 10.5194/acp-22-12221-2022

An international research team led by the University of Leipzig has used satellite data to demonstrate that concentrations of polluting particles have decreased significantly since the year 2000. This is necessary because of their impact on health. But it is also of great importance because it has reduced the cooling effect of particles on the climate. The results of the study have been published in the journal Chemistry and physics of the atmosphere.

Global warming is caused by the emission of greenhouse gases. According to the Intergovernmental Panel on Climate Change (IPCC), in 2019 the temperature had risen by 1.1 degrees Celsius above pre-industrial levels. However, at the same time, the combustion of fossil fuels emits aerosols, in the form of polluting particles such as soot or sulfuric acid, which cool our climate.

They reflect sunlight and also increase cloud reflectivity. According to the IPCC, the presence of aerosols in the atmosphere made the climate 0.5 degrees Celsius cooler in 2019 than without them. Other effects such as land use change also play a role.

Study documents widespread evidence of reduced climate effect on cooling

In a new international analysis, Professor Johannes Quaas, a meteorologist at the University of Leipzig, and his colleagues from across Europe, China and the United States have now documented strong evidence of this effect on the climate of the improvement in air quality.

“We analyzed data from NASA’s Terra and Aqua satellites. They have been providing comprehensive satellite observations of Earth since the year 2000, measuring incoming and outgoing radiation, but also clouds and aerosol pollution. The latter has declined significantly in North America, Europe and East Asia since 2000,” says Professor Johannes Quaas, lead author of the study, which was launched at a meeting by the two research projects European CONSTRAIN and FORCES.

Reduced aerosol-induced cooling increases CO warming2 since 2000 up to 50%

This also reduced the cooling effect of aerosols. Compared to the year 2000, it has led to an increase in the warming effect which accounts for up to 50% of that of CO2 increases in the same period. This means an acceleration of the drivers of global warming compared to the previous period.

“Our study should not be taken to mean that we should now emit more aerosols to cool the climate. On the contrary: aerosols are harmful to human health and the environment, which is why we must continue to reduce emissions. emissions,” concludes Quaas. And that is why air quality legislation has become increasingly strict since the 1970s and is being implemented by more and more countries.

Professor Quaas and his colleagues in the new study point to the increasingly urgent need for rapid and deep reductions in greenhouse gas emissions.

Cloud study debunks aerosol impact

More information:
Johannes Quaas et al, Strong Evidence for Reversing the Trend of Effective Aerosol Climate Forcing, Chemistry and physics of the atmosphere (2022). DOI: 10.5194/acp-22-12221-2022

Provided by the University of Leipzig

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Teresa H. Sadler