With successive generations of the Coupled Model Intercomparison Project (CMIP)—a prominent multimodel experiment based on an ensemble of global climate model simulations—new models are added and old models are adapted and expanded with the goal of improving simulations of Earth’s climate and projections of how it will change in the future.
Scientists have observed that in the latest generation, CMIP6, the models appear to be more sensitive on a global scale to changes in atmospheric carbon dioxide concentrations than in the preceding version, CMIP5, suggesting that future warming could be even greater than previously thought for a given carbon dioxide level. However, the extreme weather caused by climate change that humans experience happens at regional and local scales, and scientists are keen to understand where extreme temperature and precipitation events will increase and decrease.
In a new study, Seneviratne and Hauser analyze the regional climate sensitivity of climate extremes—in other words, how regional extremes change as a function of global warming—in CMIP6 versus CMIP5. They find little change overall between the two generations of models, in contrast to the reported differences in global climate sensitivity. However, the model spread, or the difference between the highest and lowest estimates of projected regional climate extremes, within the ensembles is more strongly affected by the regional climate sensitivities in the models than by uncertainty in global climate sensitivity. This suggests that reducing spread in regional climate sensitivity among models may be the best way to derive more precise estimates of future changes in climate extremes.
The authors say their results suggest that regional climate sensitivity is a distinct property of climate models compared with global climate sensitivity, which has received more attention in the past. Many of the variables that drive climate impacts at regional scales are themselves regional in scale: The authors cite soil moisture content and snow feedbacks as examples. These types of variables are included in global climate models, but their influences are far more pronounced at regional rather than global scales. In the same vein, the researchers suggest that global climate sensitivity is more heavily tied to exchanges between the atmosphere and the ocean.
Ultimately, regional responses result from the combination of both measures, regional and global climate sensitivity, and distinguishing and better quantifying these two model properties will help to constrain projections of extremes in a warming climate. (Earth’s Future, https://doi.org/10.1029/2019EF001474, 2020)
—David Shultz, Science Writer