Presentation on Climate Change

The National Park service in Yosemite organizes a wonderful monthly lecture series called “The Croaking Toad” where scientists present the results of their research. This month, Michael Dettinger of the US Geological Survey and Climate Research Division/ Scripps Institution of Oceanography visited the park and shared with us his models that predict the impact of global warming on the Sierra Nevada.

His provocative (and downright scary) theory asserts that the Sierra Nevada in general—and Yosemite specifically—are situated at ground zero for some of the possible consequences of increasing average temperatures. As most Californians know (or should know), the “snowmelt’s the thing” The water cycle, which we all learn in third grade, is pretty basic—snow falls in the Sierra Nevada in the winter and as the spring and summer progresses, it melts gradually, flows into the rivers, and ultimately into our water taps.

Mr. Dettinger’s data suggests that as temperatures rise, rain will replace snow in higher frequencies, and the snowmelt will peak in February instead of April. Why? Since Sierra Nevada weather is more moderate than many other colder regions in the US (where else can you ski in shorts?) even a slight 2-3 degree difference could mean the shift from snow to rain. As a result, in the future the rivers—and our taps—could run dry before spring even begins! We already have some convincing evidence to suggest that the peak snowmelt has been shifting to earlier in the year.