Why do climate models vary so much?
It may be a sign we're close to one or more tipping points The latest report from the Intergovernmental Panel on Climate Change is known as Assessment Report 6, or IPCC AR6 for short. Rather than contain new research, AR6 summarizes the latest work of climate scientists, and synthesizes thousands of papers. An important element of this are the climate models. The climate models examined by AR6 are called CMIP6 models, for Coupled Model Intercomparison Project v6. Climate models can provide answers to "what if?" questions. Some of these What Ifs are described by the IPCC in their Shared Socioeconomic Pathways, or SSPs for short. But these What Ifs combine questions about physics (how the Earth will respond) with assumptions about our future behaviour. What we would like is to be able to factor out the human influence and get a single number that measures just how sensitive the Earth's climate is to CO2? That's where Equilibrium Climate Sensitivity (ECS) com