Welcome to the California Climate change Portal

Global Climate Change Background

Climate change refers to long-term changes in temperature, precipitation, wind patterns, and other elements of the earth's climate system. The Intergovernmental Panel on Climate Change (IPCC) (link) defines climate change as "any change in climate over time, whether due to natural variability or as a result of human activity." An ever-increasing body of scientific research attributes recent climatological changes to greenhouse gases (GHGs), particularly those generated from the human production and use of fossil fuels.

The term climate change has become synonymous with "global warming," which is defined as a gradual increase in the overall near surface temperature of the earth.

Below are the basic facts regarding climate change and its impacts on California. Please also see the Frequently Asked Questions (FAQs) page.

Please click here if you are interested in the History of California's Climate Change Activities.


Rising Concentrations Of Greenhouse Gases

Trends in Atmospheric Concentrations and Anthropogenic Emissions of Carbon Dioxide from US EIA
  • Up until the last two hundred years, atmospheric CO2 concentration had stayed between 265 parts per million (ppm) and 280 ppm according to analyses of gases obtained from ice cores that reflect the past 10,000 years.
  • Atmospheric CO2 concentration at the beginning of the 21st Century is approximately 365 ppm.
  • Atmospheric concentrations of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) have increased 31 percent, 151 percent, and 17 percent respectively since the year 1750.
  • Humans added more than 270 billion metric tons of carbon (GtC) to the atmosphere since the nineteenth century.
  • The natural carbon cycle emits about 60-90 GtC per year, while current levels of human-caused emissions are greater than 6 GtC per year.
  • About three-quarters of human emissions of CO2 to the global atmosphere during the past 20 years is due to fossil fuel burning.

Rising Global Average Temperatures

NASA graphic depicting 2007 surface temperature anamolies with link to NASA movie file showing temperatures from 1884 to 2007
  • Global average surface temperature increased over the last 100 years by about 1.1 degrees Fahrenheit.
  • There is at least a 90 percent chance that the 1990s was the warmest decade for the planet, since 1861 and the beginning of instrumental records .
  • There is strong evidence that most of the warming observed over the last 50 years is attributable to human activities.
  • 2006 had an annual average temperature of 55°F in the United States, which is 2.2°F (1.2°C) above the 20th Century mean.
  • Each of the last nine years (1998-2007) has earned a spot in the rankings of the 25 warmest years on record.
  • 2007 tied with 1998 as the second warmest year in a century, behind 2006.
  • Of the four hottest years in the last century (1934, 1998, 2006, and 2007), the only year without a true regional concentration of warmth was 2006. The entire United States was warm all over; no state was near or below average for 2006.

Changes Are Being Documented

graphic depicting shrinkage of Arctic summer ice in 2005 and 2007
  • Global average sea level has risen between 4 and 8 inches over the last 100 years.
  • Arctive summer ice is disappearing faster than expected.
  • There has been widespread retreat of mountain glaciers during the twentieth century.
  • The frost season in the United States has shortened by an average of 1.1 days per decade.
  • Total annual precipitation has increased five to ten percent over the continental United States.
  • Heavy or severe precipitation events in the United States show a slight increasing trend.
  • Loss of permafrost in Alaska is damaging roads, housing and pipeline structures.
  • Loss of 60 percent of tropical corals is threatening barrier reefs.

Potential Effects Of Global Warming On California Water And Forest Resources

graphic depicting greenland surface melt 1992-2002-2005
  • Precipitation is the most important hydrologic variable and most difficult to forecast.
  • Warming would raise the elevation of snow levels with reduced spring snowmelt and more winter runoff.
  • Added winter runoff is generally not storable because of flood control needs.
  • Less snowmelt runoff would mean lower early summer storage at major foothill reservoirs with less hydroelectricpower production.
  • Lower summer reservoir levels would adversely affect recreation.
  • Higher temperatures and reduced snowmelt will compound the problem of providing suitable cold water habitat for salmon species.
  • Sea level rise would affect the Sacramento/San Joaquin Delta worsening existing levee problems and causing more saltwater intrusion.
  • Rising sea levels would adversely affect many coastal marshes and wildlife reserves.
  • Increase the demand for water by plants due to higher temperatures.
  • Climate change in California will result in a higher frequency of large damaging fires.
  • Regional climates that are hotter and drier will result in increased pest and insect epidemics within California's forests.