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Lake Tahoe: Barometer For Climate Change

Four times a month, as the sun breaks over snow-covered peaks, researchers from the Tahoe Environmental Research Center (TERC) board a research vessel. They glide across the lake to the same two places, where they lower a line with a weight and a white, plastic disc down into the water, watching until it fades from sight.

In recent years, it has started to fade from sight sooner than it used to.

TERC researchers use the rope and disc, called the Secchi test, as a means to determine lake health. Over the last 38 years, the clarity of the lake has decreased from an average of 102.4 feet as measured in 1968 to 67.7 feet in 2006.

On August 15, 2007, Geoff Schladow of the University of California Davis and his team of investigators released the "Tahoe: State of the Lake 2007” report to an online audience, making Lake Tahoe a barometer for climate change. This new report represents hundreds of hours of data collection, hundreds of hours of analysis, and tens of thousands of scientific observations all depicted in easy to read charts and graphs.

Since 1968, the average surface temperature of the lake has risen more than one degree to 52.6 degrees Fahrenheit. Surface temperatures in the summer have risen five degrees to an average of 67.8 degrees F., and the highest temperature recorded was 78 degrees F.

Meteorological data show that the air in the Lake Tahoe basin is getting warmer. Since 1911, low temperatures at night have risen four degrees. Furthermore, fewer days with a temperature below freezing have been recoded, reducing the amount of precipitation in the form of snow that falls each year. Higher air temperatures and more precipitation in the form of rain contribute to earlier and higher rates of runoff into the lake, decreasing clarity.

Less snowfall and more runoff affect stakeholders in the Tahoe basin. Currently, local water companies draw water from the lake, and because of the water's purity, the water companies do not filter or purify it. If the lake health continues to decline, a relatively inexpensive water source would no longer be available.

"The Tahoe basin is a very unique ecosystem,” says Schladow. Although it is not possible to make sweeping claims about global warming based on the Tahoe data, the extensive nature of the report offers insight into how changing environmental factors affect large ecosystems.

Data from the Tahoe report will inform researchers all over the world about warming and the impact on ecosystems.

Because the Tahoe basin spans Nevada and California and includes thousands of acres of federal land, the U.S. Congress created the Tahoe Regional Planning Agency to oversee the area. The lake report includes data from local, state, and federal sources, including NASA, which maintains four permanently moored buoys there, according to Simon Hook of NASA's Jet Propulsion Laboratory. NASA uses the buoys to collect data about surface temperature and the behavior of light beneath the surface. The NASA satellites also use the buoys to validate surface temperatures collected by the satellite's infrared cameras. Because NASA calibrates on the surface temperature of Lake Tahoe, their satellites can then be used to collect data about lake temperatures all over the world, assessing the affects of global warming in other places.

Bret Norris is a writer and doctoral student in Education at the University of Washington.


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