To prepare for extreme events, we need to have a better idea about the likelihood an event will occur in the future and what the magnitude of that event will be. For example, if it’s going to be rainier in the fall, how many more intense bursts of rainfall will happen? Scientists at the IPCC (International Panel on Climate Change) have designed mathematical models to help policymakers and citizens understand what types of changes in climate are predicted, the timescale for those predictions, and how reductions in greenhouse gas emissions can impact those predictions. While past models were based on greenhouse gas emission rates, the newer models also account for social, economic, and technological advances that may alter future GHG emission rates.
Emissions Levels Determine Temperature Rises. Source: Third National Climate Assessment Report (2014).
The IPCC models help us visualize the range of change that could be expected under several emissions scenarios. The chart below illustrates the range of global surface temperature change predicted by 2100. The red scenario (RCP 8.5) reflects the highest rate of GHG emissions (the rate at which emissions are now occurring); the blue scenario (RCP 2.6) reflects a rapid decrease in GHG emissions. Depending on the scenario, we can expect an average increase of 2.5°F to 8°F by 2100. While the models vary widely in their predictions about the amount of change that will occur, the overall trend of increasing average global temperature is consistent (1).
Regional and local policymakers have to make decisions based on their understanding about how climate change will affect the communities they represent. Information from the IPCC models can help them revise building codes, improve flood maps, and develop stronger emergency preparedness plans for extreme weather events. But how can the global models be used to address regional changes in climate?
Climate scientists use a process called downscaling to modify the global models and make regional predictions. For larger areas, like the Northeast or the Midwest, downscale predictions for future temperature and rainfall patterns are fairly robust. Recent research suggests that downscaling to the state level or to compare future impacts between cities is more uncertain, particularly for precipitation models (2).
Climate Change Impacts in the US. The Third National Climate Asessment. 2014.
Zhang, F., W. Li* and M. E. Mann, 2016: Scale-dependent Regional Climate Predictability over North America Inferred from CMIP3 and CMIP5 Ensemble Simulations. Advances in Atmospheric Sciences, 33, 905-918