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In the Sierra, John Muir's famous "range of light," changes are already being observed. At Reno's Desert Research Institute, scientists have been tracking rising temperatures in the Sierra and across California as part of that state's efforts to confront climate change.
Researchers have compiled temperature records from nearly 200 stations statewide that indicate mean temperatures have risen about 2 degrees over the last 30 years, said Kelly Redmond of DRI's Western Regional Climate Center. Changes have been particularly striking when one looks at nighttime minimum temperatures, which have risen more than 2 degrees. It was certainly noticeable in Reno last June, when nighttime low temperatures stayed in the 70s for an unusually long span. "That was unheard of in Reno's history until 10 or 15 years ago," Redmond said. "Reno has had a great deal of very warm nights, nights that we would never have expected to see around here."
At Tahoe City, where historic temperatures often dipped below zero, Redmond said subzero temperatures weren't experienced for 12 years straight. The span was broken by a cold snap last January, when temperatures dipped to 2 below zero for a single night. The January event, which burst water pipes across the region, is not a surprise, Redmond said. Exceptions to a gradual warming trend that started roughly 50 years ago and significantly accelerated in the mid-1970s are to be expected, he said.
Worldwide, the winter of 2006-2007 was the warmest on record, according to the National Oceanic and Atmospheric Administration. March was the second-warmest on record across the U.S. and the fifth warmest on record worldwide, the NOAA reported. In a process that Redmond compared to piecing together evidence at a crime scene, researchers have documented warming trends in different ways. Weather balloons launched by the National Weather Service in Reno indicate the atmosphere is heating up at "roughly the same rate" as the surface, Redmond said. Bore holes drilled into the ground indicate the heating is occurring downward from the surface and into the rock as well, he said. "Most of the pieces of evidence are pointing in the same direction," Redmond said. "If we have multiple lines of evidence that all fit together, that tells us something is going on."
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http://news.rgj.com/apps/pbcs.dll/article?AID=/20070513/NEWS/705130354&theme=WARMING_SIERRA