In the News

How Will Climate Change Affect the Sierra?
date posted: December 22 2005

Lake Tahoe Report #96
Dec. 10, 2004
By John Cobourn and Heather Segale

While some skeptics continue to question whether “global warming” is occurring, most climatologists now agree that human activities are causing natural increases in global temperatures to accelerate. In May 2001, the Bush Administration asked the National Research Council (NRC) to review the research findings of the Intergovernmental Panel on Climate Change (IPCC). In its report, “Climate Change Science: an Analysis of Some Key Questions,” the NRC expert panel confirmed that climate change is occurring, and that during the 20th century, global mean surface air temperature warmed between 0.7 and 1.5 degrees Fahrenheit.

Carbon dioxide is the primary “greenhouse” or heat-trapping gas produced through human activities. Carbon dioxide (CO2) levels in earth’s atmosphere had remained steady for close to 10,000 years before the industrial revolution. Since 1750, however, CO2 levels have risen 32 percent worldwide.

The Sierra Nevada Alliance, a regional nonprofit organization, has gathered research findings on the effects climate change will have on the Sierra, and recently released these findings in a report, “Troubled Water of the Sierra.” In the report, a study by researchers at the Lawrence Berkeley National Laboratory and the National Weather Service’s California-Nevada River Forecast Center is referenced. The study states that higher temperatures and a higher percentage of rain versus snow will result in fewer days of below-freezing temperatures and less snowpack coverage.

California’s Department of Water Resources has established a Joint Agency Climate Team to predict what impact climate change will have on the state’s water supply. The State Water Plan is using climate change models that assume a 3-degree Celsius rise in temperature during this century. The snow line in the Sierra is expected to move up in elevation 500 feet for every 1-degree Celsius rise in temperature. Different climate models show different rates of change, with two models used by the National Oceanic and Atmospheric Administration showing a 2-degree Celsius rise in temperature in the next 25 years, and a 4.5- to 6-degree rise by the 2090s.

Studies by the U.S. Geological Survey and Scripps Institute of Oceanography report that changes in the timing of the spring snowmelt and runoff have already been documented in the Sierra. For example, in the Yuba watershed, during the first half of the twentieth century, only 30.1 percent of the annual runoff occurred from November through February. However, in the second half of the century, 37.5 percent of the runoff occurred during these months. Conversely, less water came down in the usual, later runoff period of April to July over the last 50 years (42.1 percent) than did during the same period in the first half of the century (51.2 percent). If these kinds of changes in timing continue as expected, there likely will be a push for construction of more water supply reservoirs to meet water needs on both sides of the Sierra during the summer dry season.

Another research organization, the U.S. Global Change Research Program, predicts that the number, extent and severity of extreme events will rise during this century due to climate change. Events such as rain-on-snow floods, droughts, and wildfires, which negatively affect lives and property, the economy, and the survival of plant and animal communities, will be more common.

So, what can we do about global warming? We can think globally and act locally to try to minimize our impact on climate. At Lake Tahoe, many regional planners are looking at further improving public transportation to get people to use their polluting vehicles less often. Reducing air pollution from transportation and home heating can have beneficial affects on reducing water pollution in Lake Tahoe, as well as reducing the rate of greenhouse gas buildup. With our Mediterranean climate (wet winters and dry summers) and an average of over 300 days of sunshine each year, entrepreneurs in our building industry could fill an economic niche by designing more passive and active solar structures for the Sierra and its surrounding communities.

To view the Sierra Nevada Alliance report “Troubled Water of the Sierra,” visit http://www.sierranevadaalliance.org/publications/TroubledWatersReport.pdf.