U.S. Geological Survey: Warmer Springs Causing Loss Of Snow Cover Throughout The Rocky Mountains

May 19, 2013

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http://feedproxy.google.com/~r/climateprogress/lCrX/~3/NpkoaivZIvs/story01.htm

A new U.S. Geological Survey study finds, “Warmer spring temperatures since 1980 are causing an estimated 20 percent loss of snow cover across the Rocky Mountains of western North America.” The USGS explains, “The new study builds upon a previous USGS snowpack investigation which showed that, until the 1980s, the northern Rocky Mountains experienced large snowpacks when the central and southern Rockies experienced meager ones, and vice versa. Yet, since the 1980s, there have been simultaneous snowpack declines along the entire length of the Rocky Mountains, and unusually severe declines in the north.” We reported on that previous work in 2011 — see “USGS: Global Warming Drives Rockies Snowpack Loss Unrivaled in 800 Years, Threatens Western Water Supply.” The USGS explained back then: The warming and snowpack decline are projected to worsen through the 21st century, foreshadowing a strain on water supplies. Runoff from winter snowpack – layers of snow that accumulate at high altitude – accounts for 60 to 80 percent of the annual water supply for more than 70 million people living in the western United States. What’s most worrisome is that we now have three major trends driven by human emissions of greenhouse gases that threaten to significantly worsen drought and water problems in the West and Southwest: Less precipitation in many areas (see here) Less snowpack, as the USGS studies have found Hotter temperatures (see “We’re Already Topping Dust Bowl Temperatures — Imagine What’ll Happen If We Fail To Stop 10°F Warming“). Assuming the anti-science crowd continue to block any serious action, these catastrophic changes will last a long, long time (see NOAA: Climate change “largely irreversible for 1000 years,” with permanent Dust Bowls in Southwest and around the globe). For the record, it was the possibility of losing the Sierra snowpack in the second half of the century that led then Energy Secretary Chu to warn in 2009, “Wake up,” America, “we’re looking at a scenario where there’s no more agriculture in California.” Geophysical Research Letters published the new research, “Regional patterns and proximal causes of the recent snowpack decline in the Rocky Mountains” (subs. req’d). Here are the key points from the USGS news release: The new study has teased apart and quantified the different influences of winter temperature, spring temperature, and precipitation on historic snowpack variations and trends in the region. To distinguish those varying influences, the researchers implemented a regional snow model that uses inputs of monthly temperature and precipitation data from 1895 to 2011. “Each year we looked at temperature and precipitation variations and the amount of water contained within the snowpack as of April,” said USGS scientist Greg Pederson, the lead author of the study. “Snow deficits were consistent throughout the Rockies due to the lack of precipitation during the cool seasons during the 1930s – coinciding with the Dust Bowl era. From 1980 on, warmer spring temperatures melted snowpack throughout the Rockies early, regardless of winter precipitation. The model in turn shows temperature as the major driving factor in snowpack declines over the past thirty years.” … The timing of snowmelt affects not only when water is available for crop irrigation and energy production from hydroelectric dams, but also the risk of regional floods and wildfires. Earlier and faster snowmelt could have repercussions for water supply, risk management, and ecosystem health in western watersheds. … [Greg] McCabe, co-author of the study, explains that “recent springtime warming also reduced the extent of snow cover at low to middle elevations where temperature has had the greatest impact.” What’s particularly worrisome is that we’ve seen these dramatic and harmful changes already — and we’ve only warmed about a degree and a half Fahrenheit in the past century. The problem for our children and grandchildren is that if we continue anywhere near our current greenhouse gas emissions pathway, we are on track to warm five times times that or more this century (see “An Illustrated Guide to the Science of Global Warming Impacts: How We Know Inaction Is the Gravest Threat Humanity Faces“). Another 2011 study, “The Last Drop: Climate Change and the Southwest Water Crisis,” found that drought and reduced precipitation in the U.S. SW alone could cost up to $1 trillion by century’s end. The time to act was a long time ago, but now is still better than later.

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