Abstract

Complex Earth system models that are used to make global climate projections are computationally expensive to run, and simpler models have become an important tool in assessing climate responses to a wide range of emissions pathways. Two distinct advantages of simple models, arising from their low resource demands, are (1) large probabilistic ensembles can be run, and (2) hundreds of future emissions pathways can be modelled, as is done in the IPCC ’s Special Report on Global Warming of 1.5°C (SR1.5) and Working Group 3 assessments on climate change mitigation. We have developed a simple open-source Earth system model emulator (FaIR) which projects temperature responses as a function of input emissions and effective radiative forcing. This talk explains how simple climate models can be used for a range of applications, such as: calculation of the remaining carbon budget to 1.5°C; constraining the historical aerosol forcing; and determining committed warming from historical emissions. Simple models find utility in being coupled to integrated assessment models of the population and economy, and are now being extended to report climate impacts and other metrics of interest beyond global mean temperature changes, allowing for the full emissions to climate impacts process chain to be determined.