Sensitivity of historical climate simulations to uncertain aerosol forcing
The role of anthropogenic aerosol forcing in driving historical climate variations is currently a topic of ongoing scientific debate, owing to large uncertainties in the magnitude of historical forcing due to anthropogenic aerosol. The computational cost of running climate model simulations has steadily declined in recent years, making it possible to run a large number of ensemble members designed to investigate the roles of internal variability and aerosol forcing in shaping surface climate variability. Here, we present results from a novel historical ensemble of simulations conducted with the HadGEM3- GC3.1 climate model for the period 1850-2014. In this ensemble, the anthropogenic aerosol emissions are scaled to sample a wide range in historical aerosol forcing. Multiple ensemble members sampling different ocean initial conditions are run for each scaling factor to enable the differences between the forced responses to be reliably estimated. As expected, a wide range of historical global mean temperature changes are simulated, depending on the aerosol scaling factors.
Ed Hawkins is a Professor of Climate Science at the National Centre for Atmospheric Science (NCAS) at the University of Reading. He is a contributing author to the IPCC's Assessment Reports and is one of the world's most effective climate science communicators having developed novel ways to visualise increasing global temperatures - including the famous 'climate spirals' and 'climate stripes'.