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« Uncertainties in the causal chain from human activities to climate change: A brief history of emissions scenarios and the uncertainties in using them. »

By Michael Prather, University of California, Irvine, Visiting Scientist at Cerfacs

Abstract:

Trying to understand what humans have done to the climate system up to now, and what climate change awaits us, comes down to the fundamentals of: Just what are people emitting to the atmosphere? How that has changed greenhouse gases and aerosols? And then how much climate change is driven by those gases? The Intergovernmental Panel on Climate Change (IPCC) was initiated by scientists to act as the conduit for vetted scientific information to be delivered to the UN Framework Convention on Climate Change (UNFCCC). The IPCC has been doing assessments since 1990 and there are a range of bewilderingly different scenarios developed for past and future emissions of greenhouse gases. This talk presents a brief history of the IPCC emissions scenarios and their increasing realism (or perhaps just increasing complexity). Because of the political desire to attribute climate damage to a nation's historical greenhouse gas emissions (a.k.a. the Brazil Proposal), we then follow the causal chain from emissions to climate change with a full propagation of errors. The case of greenhouse gases nitrous oxide and methane highlights the problems of natural emissions and atmospheric chemistry.