According to an August 2013 report by the California Environmental Protection Agency titled “Indicators of Climate Change in California,” regional climate change has profoundly impacted the state’s natural physical and biological systems.

Annual average air temperatures in California have increased by approximately 1.5 degrees since 1895. As a result of an increasing presence of greenhouse gases including carbon dioxide, methane and nitrous oxide, most regions of the state have seen accelerated warming over the past three decades, with minimum temperatures increasing nearly twice as fast as maximum temperatures.

According to the report, impacts of climate change on the state’s physical systems include:

• Ocean and lake temperature increase. Lake Tahoe has seen an average water temperature increase of nearly 1 degree in the past 30 years, while sea surface temperatures along the California coast have increased by about 1.8 degrees over the past century -- around twice the global rate. Warmer ocean waters contribute to global sea level rise and extreme weather events.
• Glacier change. Glaciers in the Sierra Nevada have decreased in area over the past century. A 2004 study found the areal extents of seven glaciers to have ranged from 22 to 69 percent of their 1900 areas. This shrinkage will result in earlier peak water runoff, drier summer conditions, and global sea rise.
• Sea level rise. Sea levels measured at stations in San Francisco and La Jolla have risen at respective rates of 8 and 6 inches over the past century. Experts warn that this rise could lead to flooding of low-lying areas, loss of coastal wetlands, erosion of cliffs and beaches, saltwater contamination of drinking water, and impacts on roads and bridges.

Climate change has also affected natural biological systems, as shifts in habitat elevation, changes in timing of growth stages, and increased vulnerability to wildfires or pathogens have threatened species’ abilities to survive. These biological impacts include:

• Heat-related mortality. The July 2006 heat wave, “unprecedented in its magnitude and geographic extent,” resulted in 140 California deaths. Heat-related illness and death is expected to increased as a result of continued warming and more frequent and intense heat waves.
• Large wildfires. The annual acreage burned in statewide wildfires has increased in California since 1950, the three largest fire years occurring within the last ten years.
• Tree mortality. Tree deaths in California have increased with rising temperatures and drought, most notably in the Sierra Nevada and southern Cascade Mountains.
• Vegetation patterns. In Southern California, the distribution of plant species across a slope in the Santa Rosa Mountains has moved upward in the past 30 years by 213 feet. Experts believe warmer and drier climates have stressed plants at lower elevations and provided more favorable conditions for plants at higher elevations.

The report warns that emerging climate change issues may include an increase in frequency, severity and duration of harmful algal blooms in all aquatic environments. Changes in the climate may also lead to a reduced duration and extent of winter fog in the Central Valley, an increased survival and spread of disease-causing pathogens and insects, and changes in the frequency of droughts and floods.