Multi-angular polarimetric remote sensing to pinpoint global aerosol absorption and direct radiative forcing

Article https://doi.org/10.1038/s41467-022-35147-y Multi-angular polarimetric remote sensing to pinpoint global aerosol absorption and direct radiative forcing Cheng Chen 1,2 , Oleg Dubovik 1 , Gregory L. Schuster3, Mian Chin 4, Daven K. Henze 5, Tatyana Lapyonok1, Zhengqiang Li6, Yevgeny Derimian1 & Ying Zhang6 Quantitative estimations of atmospheric aerosol absorption are rather uncertain due to the lack of reliable information about the global distribution. Because the information about aerosol properties is commonly provided by single-viewing photometric satellite sensors that are not sensitive to aerosol absorption. Consequently, the uncertainty in aerosol radiative forcing remains one of the largest in the Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC AR5 and AR6). Here, we use multi-angular polari- meters (MAP) to provide constraints on emission of absorbing aerosol species and estimate global aerosol absorption optical depth (AAOD) and its climate effect. Our estimate of modern-era mid-visible AAOD is 0.0070 that is higher than IPCC by a factor of 1.3-1.8. The black carbon instantaneous direct radiative forcing (BC DRF) is +0.33 W/m2 [+0.17, +0.54]. The MAP constraint narrows the 95% confidence interval of BC DRF by a factor of 2 and boosts confidence in its spatial distribution. Atmospheric aerosols scatter and absorb solar and terrestrial radia- tion, thereby cooling and warming the atmosphere-earth system. Current estimates of the global aerosol radiative effect indicate that aerosols have a net cooling effect on our planet, which partially offsets warming effects by greenhouse gases1,2. As a result of the limited understanding of details in the global distribution of aerosol absorp- tion, global climate effects by atmospheric aerosols remain one of the largest forcing uncertainties in the 5th and the recent 6th Inter- governmental Panel on Climate Change (IPCC AR5 and AR6) assessments1,3. Although the aerosol absorption by black carbon (BC) aerosol is known to be one of the largest contributors with carbon dioxide (CO2) and methane (CH4) for heating our planet4–6, there are still significant challenges for pinpointing the effects of absorbing aerosols7. The recent AR68 reports ~50% reduction of BC warming effects by adjusting its rapid climate responses. Nonetheless, the het- erogeneity of global spatial distribution of aerosol absorption has also certainly an impact on the rapid adjustments. Thus, the improved quantification of global spatial heterogeneity of aerosol absorption distribution is still highly demanded. Indeed, the climate models pro- duce a large diversity in simulations of global aerosol absorption9–12, largely because of the scarceness of reliable global long-term obser- vation of aerosol absorption to constrain the models. At present, the aerosol absorption optical depth (AAOD) retrieved from sun-sky measurements at worldwide Aerosol Robotic Network (AERONET) stations13,14 is the main product used to evaluate and constrain climate models15–20, and most models underestimate aerosol absorption sig- nificantly when compared to AERONET AAOD10,11. However, the AERONET-derived aerosol single scatter albedo (SSA), which is the ratio of scattering to total extinction (SSA = 1-AAOD/AOD), is of high uncertainty at low aerosol abundance21,22. Therefore, the highest quality AERONET Level 2 inversion products are provided only when the aerosol optical depth (AOD) at the blue channel is higher than 0.4. Received: 4 April 2022 Accepted: 18 November 2022 Check for updates 1Univ. Lille, CNRS, UMR 8518 - LOA - Laboratoire d’Optique Atmosphérique, F-59000 Lille, France. 2GRASP-SAS, Univ. Lille, Villeneuve d’Ascq 59650, France. 3NASA Langley Research Center, Hampton, VA 23681, USA. 4NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. 5Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309, USA. 6Aerospace Information Research Institute, Chinese Academy of Scienc