Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling
21 September 2020

Characterization of Long Period Return Values of Extreme Daily Temperature and Precipitation in the CMIP6 Models: Part 2, Projections of Future Change.

Science

Using a non-stationary Generalized Extreme Value statistical method, projected future changes in selected extreme daily temperature and precipitation indices and their 20-year return values from the CMIP5 and CMIP6 climate models are calculated and compared. Projections are framed in terms of specified global warming target temperatures rather than at specific times and under specific emissions scenarios. The change in framing shifts projection uncertainty due to differences in model climate sensitivity from the values of the projections to the timing of the global warming target. At their standard resolutions, there are no meaningful differences between the two generations of models in their projections of simulated extreme daily temperature and precipitation at specified global warming targets.

Impact

The IPCC WG1 AR6 report and possibly the 5th US National Climate Assessment will present future climate change projections as functions of “global warming levels” instead of and/or in addition to the more standard scenario and time frames. This effectively removes differences in models’ climate sensitivity with an apparent reduction in uncertainty. I find no substantial differences between CMIP5 and CMIP6 future changes in extreme precipitation and temperature when presented at various global warming levels. This is part 2 of a two-part study, the other one evaluating simulated extreme temperature and precipitation of the recent past. Taken together, regarding extreme weather we conclude that the CMIP5 and CMIP6 models are indistinguishable, in large part because the model resolution in the standard configurations is unchanged.

Summary

There are no meaningful differences in projected changes in extreme temperature and precipitation between the standard CMIP6 and CMIP5 simulations when framed as functions of global warming level.

Contact
Michael Wehner
Lawrence Berkeley National Laboratory