What Is Climate Change?

In California and throughout western North America, signs of a changing climate are evident. During the last 50 years, winter and spring temperatures have been warmer, spring snow levels in lower- and mid-elevation mountains have dropped, snowpack has been melting one to four weeks earlier, and flowers are blooming one to two weeks earlier. These regional changes are consistent with global trends. During the past 100 years, average temperatures have risen more than one degree Fahrenheit worldwide.

Research indicates that much of this warming is due to human activities, primarily burning fossil fuels and clearing forests, that release carbon dioxide (CO2) and other gases into the atmosphere, trapping heat that would otherwise escape into space. Once in the atmosphere, these heat-trapping emissions remain there for many years—CO2, for example, lasts about 100 years. As a result, atmospheric concentration of CO2 has increased more than 30 percent above pre-industrial levels. If left unchecked, by the end of the century CO2 concentrations could reach levels three times higher than pre-industrial times, leading to dangerous global warming that threatens our public health, economy and environment.

For additional information, please download and review the document from which this short summary was obtained:  Our Changing Climate, Assessing the Risks to California (2006) (1.8 MB).

California Climate Action Team (CAT), 2009 Biennial Report >>