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Climate Change and Utah: The Scientific Consensus

Summary

As directed by Governor Jon Huntsman’s Blue Ribbon Advisory Council on Climate Change (BRAC), this report summarizes present scientific understanding of climate change and its potential impacts on Utah and the western United States. Prepared by scientists from the University of Utah, Utah State University, Brigham Young University, and the United States Department of Agriculture, the report emphasizes the consensus view of the national and international scientific community, with discussion of confidence and uncertainty as defined by the BRAC.

News

There is no longer any scientific doubt that the Earth’s average surface temperature is increasing and that changes in ocean temperature, ice and snow cover, and sea level are consistent with this global warming. In the past 100 years, the Earth’s average surface temperature has increased by about 1.3°F, with the rate of warming accelerating in recent decades. Eleven of the last 12 years have been the warmest since 1850 (the start of reliable weather records). Cold days, cold nights, and frost have become less frequent, while heat waves have become more common. Mountain glaciers, seasonal snow cover, and the Greenland and Antarctic ice sheets are decreasing in size, global ocean temperatures have increased, and sea level has risen about 7 inches since 1900 and about 1 inch in the past decade.

Based on extensive scientific research, there is very high confidence that human-generated increases in greenhouse gas concentrations are responsible for most of the global warming observed during the past 50 years. It is very unlikely that natural climate variations alone, such as changes in the brightness of the sun or carbon dioxide emissions from volcanoes, have produced this recent warming. Carbon dioxide concentrations are now more than 35% higher than pre-industrial levels and exceed the highest natural concentrations over at least the last several hundred thousand years.

It is likely that increases in greenhouse gas concentrations are contributing to several significant climate trends that have been observed over most of the western United States during the past 50 years. These trends are: (1) a several day increase in the frost-free growing season, (2) an earlier and warmer spring, (3) earlier flower blooms and tree leaf out for many plant species, (4) an earlier spring snowmelt and run off, and (5) a greater fraction of spring precipitation falling as rain instead of snow.

In Utah, the average temperature during the past decade was higher than observed during any comparable period of the past century and roughly 2oF higher than the 100 year average. Precipitation in our state during the 20th century was unusually high; droughts during other centuries have been more severe, prolonged, and widespread. Declines in low-elevation mountain snowpack have been observed over the past several decades in the Pacific Northwest and California. However, clear and robust long-term snowpack trends have yet to emerge in Utah’s mountains.

Climate models estimate an increase in the Earth’s average surface temperature of about 0.8°F over the next 20 years. For the next 100 years, the projected increase is between 3° and 7°F, depending on a range of credible estimates of future greenhouse gas emissions. These projections, combined with extensive scientific research on the climate system, indicate that continued warming will take place over the next several decades as a result of prior greenhouse gas emissions. Ongoing greenhouse gas emissions at or above current levels will further alter the Earth’s climate and very likely produce global temperature, sea level, and snow and ice changes greater than those observed during the 20th century.

What does this mean for Utah? Utah is projected to warm more than the average for the entire globe and the expected consequences of this warming are fewer frost days, longer growing seasons, and more heat waves. Studies of precipitation and runoff over the past several centuries and climate model projections for the next century indicate that ongoing greenhouse gas emissions at or above current levels will likely result in a decline in Utah’s mountain snowpack and the threat of severe and prolonged episodic drought in Utah is real. Preparation for the future impacts of climate variability and change on Utah requires enhanced monitoring and knowledge of Utah’s climate, as well as better understanding of the impacts of weather and climate on the state’s water availability, agriculture, industry, and natural resources.

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