Trends in AOD, Clouds, and Cloud Radiative Effects in Satellite Data and CMIP5 and CMIP6 Model Simulations Over Aerosol Source Regions. Issue 9 (11th May 2020) - Cherian, Ribu
Abstract: Several regions worldwide have seen significant trends in anthropogenic aerosol emissions during the period of detailed satellite observations since 2001. Over Europe (EUR) and North America (NAM) there were strong declines, over China increases then declines and over India, strong increases. Regional trends in model‐simulated aerosol optical depth (AOD) and cloud radiative effects in both the Fifth and Sixth Coupled Model Intercomparison Projects (CMIP5 and CMIP6) are broadly consistent with the ones from satellite retrievals in most parts of EUR, NAM and India. CMIP6 models better match satellite‐derived AOD trend in western NAM (increasing) and eastern China (decreasing), where CMIP5 models failed, pointing to improved anthropogenic aerosol emissions. Drop concentration trends in both observations and models qualitatively match AOD trends. The result for solar cloud radiative effect in models, however, is due to compensating errors: Models fail to reproduce observed liquid water path trends and show, in turn, opposite trends in cloud fraction. Plain Language Summary: Historically, widespread changes in regional air pollution have occurred, with emission reductions over the United States and Europe in response to air quality controls since the mid‐1980s, and a general increase over Asia since the 1970s. In this study we found that current climate models with improved emission estimates match the regional aerosol and cloud trends derived from satellite observations over United States, Europe, China, and India regions. Further analysis revealed that good representation of regional solar cloud radiative effect trend is due to compensating errors in cloud trend in the models. Key Points: Strong trends in AOD in aerosol source regions during 2001 to 2017 reflected in cloud droplet number concentration trends The CMIP6 multimodel ensemble shows improved results compared to CMIP5 pointing to improved anthropogenic aerosol emissions Model results in LWP inconsistent with data: trends in CRE match observations due to compensating errors in cloud fraction trends