Impact of differences in recent emission inventories on regional and global aerosol trends and radiative forcing

Over recent decades, anthropogenic emissions of aerosols and their precursor gases has been changing rapidly, and with substantial spatiotemporal heterogeneity, particularly in Asia. The regional climate effects likely to result from such rapid aerosol changes remains insufficiently quantified. One factor contributing to uncertainty is the substantial differences, in both magnitudes and trends, that exist between current emission inventories. In particular, the Community Emission Data System (CEDS) developed for the CMIP6 is now understood to underestimate the decline in Chinese SO2 and NOx emissions and overestimate carbonaceous aerosol emissions in Asia and Africa compared to observations and more recent inventories.

Here we investigate the implications of discrepancies between recent anthropogenic emission inventories for estimates of the global and regional aerosol loading and radiative forcing over the 1990-2019 period. Using the chemical transport model OsloCTM3, we perform time slice simulations with the first and most recent releases of the CEDS (CEDS16 and CEDS21), and the ECLIPSE version 6b (ECLv6) emissions.

We find that, apart for nitrate, the CEDS21 and ECLv6 result in lower global aerosol burdens than CEDS16. Total AOD is 3% (6%) lower with CEDS21 (ECLv6), respectively, compared to CEDS in 2014, with regional difference up to 30% over Asia. A negative linear trend in global mean AOD from 2005 to 2017 is estimated with all three inventories, but increasingly stronger with CEDS21 and ECLv6. A factor 3(5) stronger positive net global mean radiative forcing is estimated in 2014 relative to 1990 with CEDS21 (ECLv6) compared to CEDA16. Evaluation against MODIS and AERONET AOD retrievals reveals regionally improved model performance, but also new discrepancies possibly related to natural aerosols. Our findings are discussed in the context of conclusions from the sixth IPCC assessment report.