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New Colorado Climate Projections

The Rocky Mountain Climate Organization on August 29, 2014, posted a fact sheet documenting projected changes in Colorado statewide temperature and precipitation using the latest climate models and emissions scenarios. Whether emissions of heat-trapping pollution are rapidly reduced or continue increasing could make a difference of about 2 degrees Fahrenheit in how much hotter Colorado gets by the middle of this century. Just two decades later, the difference could grow to about 4.5°, according to the new projections.

With a scenario assuming rapid global reductions in emissions, Colorado’s statewide average temperature in 2035–2064 is projected to be 1.5° to 4.5° hotter than in 1971–2000. If instead emissions continue increasing as in recent years, the projected increase is 3.5° to 6.5°—another two degrees higher.

Twenty years later, in 2055–2084, the projected inceases are 1.5° to 5° with rapid emission reductions and 5.5° to 9.5° with continued increases. In other words, in just two decades, a 2° difference between the low and high emissions scenarios could grow to at about 4.5°.

By contrast, the first years of this century averaged 1.2° hotter than in 1971-2000 -- hot enough to already lead to substantial climate change impacts, but far short of the changes that are expected if emissions continuing increasing.

These new projections are from the supplemental online information accompanying an August 2014 report by Western Water Assessment at the University of Colorado for the Colorado Water Conservation Board (the supplemental information and report are both available here). The analysis of historical Colorado temperatures is by RMCO. The RMCO fact sheet includes information not only historical and projected statewide average temperatures but also historical and projected rates of extreme temperatures (taken from our report on extreme heat in Fort Collins) and a short summary of how changes in average and extreme temperatures may lead to Colorado impacts, including increases in heat waves, wildfires, and flooding, and impacts on water supplies and forests.

The figure above shows historical and projected average Colorado statewide temperatures compared to 1971–2000, in degrees Fahrenheit. The historical temperatures, included for context, show that temperatures in 2000–2013 averaged 1.2° higher than in 1971–2000. The projections are for two alternative futures: a low-emissions future with rapid reductions in heat-trapping pollution, and a high-emissions future reflecting a continuation of recent increases. The solid colors show the ranges from the 10th to the 90th percentiles of the projections (from 23 climate models for RCP 2.6 and 34 for RCP 8.5) and the black lines show the averages of all such projections. If emissions continue increasing as in recent years, future temperature increases could be several times greater than those so far in this century.

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