Examining the role of aerosol forcing in driving global climate variations using a novel large ensemble of historical simulations

The role of anthropogenic aerosol forcing in driving historical climate variations is currently a topic of ongoing scientific debate. Poor model representation of aerosol processes and large inter-model differences in aerosol and its climate effects mean that there is currently a large uncertainty in the magnitude of historical forcing due to anthropogenic aerosol. This uncertainty needs to be understood and constrained in order for us to have confidence in projections of future climate.

Here, we present results from a novel large 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. We also explore how historical aerosol forcing has shaped hiatus and surge events in the twentieth and early twenty-first century and discuss how the spatial patterns of warming are related to regional differences in the time evolution of aerosol forcing.