Regional Impacts Poorly Constrained by Climate Sensitivity

Abstract

Climate risk assessments must account for a wide range of possible futures, so scientists often use simulations made by numerous global climate models to explore potential changes in regional climates and their impacts. Some of the latest-generation models have high effective climate sensitivities (EffCS). It has been argued these “hot” models are unrealistic and should therefore be excluded from analyses of climate change impacts. Whether this would improve regional impact assessments, or make them worse, is unclear. Here we show there is no universal relationship between EffCS and projected changes in a number of important climatic drivers of regional impacts. Analyzing heavy rainfall events, meteorological drought, and fire weather in different regions, we find little or no significant correlation with EffCS for most regions and climatic drivers. Even when a correlation is found, internal variability and processes unrelated to EffCS have similar effects on projected changes in the climatic drivers as EffCS. Model selection based solely on EffCS appears to be unjustified and may neglect realistic impacts, leading to an underestimation of climate risks.


Key Points

Future changes in climatic drivers of floods, droughts, and wildfires are generally not correlated with climate sensitivity in Sixth Coupled Model Intercomparison Project models

Model selection for impacts solely based on climate sensitivity is not justified and may lead to an underestimation of climate risks

Model internal variability plays an important role in future projections of climate impact drivers


Plain Language Summary

Climate impact researchers often must decide which of the many available global climate models to use for their analyses. It has been suggested models with very high climate sensitivities should be excluded from impact analyses, because their global mean temperature projections are unrealistic. However, we show that projected future changes in climatic drivers of floods, droughts, and wildfires, across many regions of the world, are not correlated with model climate sensitivity. Regional impacts depend on numerous processes and phenomena many of which are unrelated to climate sensitivity. Excluding models solely on the basis of their climate sensitivity is thus not justified, and can lead to important impacts being ignored by policymakers, with serious consequences for society.