Weather Window: Tahoe Climate Change
July 22, 2010
TAHOE, Calif. – According to the National Oceanic and Atmospheric Administration, not only was June 2010 the hottest sixth month on record worldwide, but this year’s January to June period was also the warmest ever recorded. NOAA’s analysis is based on weather records going back to 1880. Scientists blame warmer than normal sea surface temperatures caused by last winter’s El Nino event for some of the heat, but global land surface temperatures in June were nearly two degrees Fahrenheit above the 20th century average.
Global warming and rapid climate change are making headline news with persistent heat waves and images of melting glaciers and shrinking Arctic sea ice. The evidence for climate change is substantial and encapsulates what some scientists have been warning of for decades. Despite a small percentage of so called “contrarians” who don’t believe the planet’s atmosphere is warming, or whatever warming may be occurring is within the bounds of a natural cycle, most professionals now agree that increasing concentrations of human-caused greenhouse gas is driving rising temperatures in many regions around the world.
Have you ever thought about how, or if, climate change is affecting Lake Tahoe? Scientists at the University of California in Davis have been studying Lake Tahoe for more than 40 years and in recent years researchers with the Tahoe Environmental Research Center have published their findings and the trends that they are observing in an annual “Tahoe: State of the Lake Report.” Until recently, only one indicator of Lake Tahoe’s health status was widely available; the yearly clarity report. This new comprehensive report on the conditions at Tahoe covers a wide range of topics, including invasive species, physical properties, nutrients and particles, biology and water clarity.
Virtually every environmental aspect of the Lake Tahoe Basin is likely to be affected by climate change, but a statistical analysis of changing weather and climate at lake level by UC Davis scientist Dr. Robert Coats has revealed some undeniable trends in lake level temperatures, snowfall and snowmelt. During the past century, the average temperature at Tahoe City has warmed significantly, with the daily minimum temperature up more than 4 degrees F and the daily maximum less than two degrees. The Tahoe City weather station is located near the Tahoe dam and is situated near a paved parking lot and tennis courts, which led me to believe the urban heat island effect was the culprit for the rising overnight lows. But Dr. Coats blames the higher rate of increase in minimum temperatures on increasing concentrations of greenhouse gases which suppress nocturnal re-radiation of long wave radiation.
Another impact of the warming temperatures at lake level is the changing ratio of snow as a fraction of annual precipitation. (Precipitation is the rainfall and the liquid content of any snowfall added together.) During the past 100 years, snowfall as a percentage of annual precipitation has declined fairly dramatically, from an average of 52 percent in 1910 to just 34 percent today. (The winter of 2008 was a stark departure from this trend with snow representing 65 percent of the precipitation.) Dr. Coats has determined this changing ratio statistically by assuming that precipitation falls as snow whenever the average daily air temperature is below freezing. Dr. Coats admits that the methodology is a bit crude but not biased and accurately reflects the warming trend and increasing proportion of rain at lake level. Other indicators of a changing climate regime include an earlier snowmelt and warming surface temperatures in regional lakes, but we’ll have to cover them in a future column.
– Tahoe historian Mark McLaughlin is a nationally published author and professional speaker. His award-winning books are available at local stores or at http://www.thestormking.com. You can reach him at firstname.lastname@example.org