Energy Budget Constraints on the Time History of Aerosol Forcing and Climate Sensitivity

Abstract

Aerosol effective radiative forcing (ERF) remains one of the most uncertain components of the present-day climate . Uncertainty in present-day forcing reduces our ability to confidently predict the future climate response to emissions (Forster et al., 2013) and the level of historical greenhouse gas warming masked by the cooling effect of aerosols (Samset et al., 2018). Aerosol forcing is the largest uncertainty governing future committed warming (Matthews & Zickfeld, 2012;Smith et al., 2019) and remaining carbon budgets consistent with Paris Agreement targets (Mengis & Matthews, 2020). In most future socio-economic scenarios, aerosol forcing is projected to become less negative over the 21st century (Gidden et al., 2019;Huppmann et al., 2018;Rogelj et al., 2018), promoting an increase in the rate of warming unless there is a concurrent reduction in greenhouse gas emissions (Shindell & Smith, 2019). The time history of aerosol ERF is a necessary input to many reduced-complexity climate models (Nicholls et al., 2020), which