The climate models that project greater amounts of warming this century are the ones that best align with observations of the current climate, according to a new paper from Carnegie’s Patrick Brown and Ken Caldeira published by Nature. Their findings suggest that the models used by the Intergovernmental Panel on Climate Change, on average, may be underestimating future warming.
Climate model simulations are used to predict how much warming should be expected for any given increase in the atmospheric concentration of carbon dioxide and other greenhouse gases.
“There are dozens of prominent global climate models and they all project different amounts of global warming for a given change in greenhouse gas concentrations, primarily because there is not a consensus on how to best model some key aspects of the climate system,” Brown explained.
Raw climate model results for a business-as-usual scenario indicate that we can expect global temperatures to increase anywhere in the range of 5.8 and 10.6 degrees Fahrenheit (3.2 to 5.9 degrees Celsius) over preindustrial levels by the end of the century—a difference of about a factor of two between the most- and least-severe projections.
Brown and Caldeira set out to determine whether the upper or lower end of this range is more likely to prove accurate. Their strategy relied on the idea that the models that are going to be the most skillful in their projections of future warming should also be the most skillful in other contexts, such as simulating the recent past. Brown and Caldeira’s study eliminates the lower end of this range, finding that the most likely warming is about 0.9 degrees Fahrenheit (0.5 degrees Celsius) greater than what the raw model results suggest.
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