California 

-- An overview prepared by Susanne Moser, Ph.D. (Union of Concerned Scientists) --
 

Climate and changes in it – regardless of their cause – matter to people, communities and businesses. Global warming is likely to bring many changes to the nation. The United States as a whole is in a strong economic position to adapt to many of these changes, but adaptation is often expensive, not always possible or successful, and during transitions ecosystems, communities, and individuals could suffer. Moreover, national impact summaries disguise local dislocations and disruptions to the ways we live, work and recreate. Climate change adds a serious stress to our already threatened resources and treasured places. Overall impact statements also mask significant opportunities. To minimize the negative changes and make the most of the positive changes we need to take a close look at how climate change will affect each region. How will California experience the effects of global warming? And how can we respond?

California’s remarkable quality of life and economic strength is built on a rich and diverse base of natural capital. From a vast array of ecosystems and species to bountiful resources and a unique geography, California is endowed with natural assets that underpin its success and wealth.  National treasures like Yosemite and the redwoods share the land with major metropolitan areas and some of the most productive agriculture in the world. Changes in climate will impact California in important ways.  The specific impacts are dependent on climate changes that are not fully understood or predictable, but it is possible to identify potential impacts based on possible futures as outlined by the science.

Climate Projections for California
The climate scenarios used in the National Assessment suggest temperature increases of 3-4° F by 2030 and 8-11° F by the 2090s, as well as a more vigorous hydrologic cycle, resulting both in more and heavier rain and more evaporation. A warmer climate will also cause more precipitation to fall as rain rather than snow at higher elevations, fundamentally affecting the state’s reliance on snow as a vital water storage system. Already, the length of the snow season decreased notably from 1950-1998.  Reduced snowpack combined with an increase in the intensity of rainfall events is expected to result in higher runoff in winter and lower runoff in summer, reducing water availability in summer. 

Klamath Mountain still snow-covered.

While the total rainfall may rise in some areas, it may not be distributed evenly. Thus, drought may also increase in some areas. The northern portions of the state are currently much wetter than the southern and inland regions.  Climate change may result in intensifying these conditions rather than increasing rainfall equally over the state, or it could shift the patterns.  Current models suggest the possibility of significant increases in precipitation in the southern part of the state.

In addition, glacial melting and thermal expansion of the oceans is projected to cause a global average sea-level rise of 6 to 37 inches by 2100.  Sea-level change in California is expected to be 8-12 inches, i.e., below the global average due to uplifting of the land. However, even this amount of sea-level rise leads to an increased risk of erosion, coastal inundation during storms, and saltwater intrusion into coastal aquifers and agricultural areas like the Sacramento-San Joaquin Delta.

Key Findings
 

Global warming adds a significant stress to those environments already experiencing intense development and population pressures. The regional assessment for California identified several key impact areas, some of which are reflected in the National Assessment synthesis. These are thought to pose the most important challenges to the state: effects on water systems; impacts on communities and cities; coastal impacts from sea-level rise; impacts on agriculture; and changes in ecosystems and biodiversity.

Water resources and systems
Water is the key climate issue for the state as the economic well-being of its agricultural sector and urban areas is so closely linked to water. The main water sources for the state – the Colorado River and the Sierra Nevada mountain range – are very likely to be effected by climate change. If more precipitation falls as rain instead of snow as is expected, the result would be more runoff during the winter and early spring season when floods are already common, and lower streamflow during the summer when it is most needed.
The sea-level rise expected to accompany global warming can cause saltwater to intrude into coastal aquifers, making it unsuitable for drinking or irrigation.
 

Levee break in the Sacramento-San Joaquin Delta.

Communities and cities
Over 93% of Californians live in cities and their surrounding metropolitan areas. The increasing temperatures will add to the heat stress in built-up, urban areas. Higher temperatures and droughts also further stress the energy and water supply systems, and could result in more wild fires at the urban/wildland interface. Other vulnerabilities include impacts on coastal infrastructure from sea-level rise, coastal erosion, and flooding and landslides from storms, as well as increased risk of spreading disease. 

Coastal impacts from sea-level rise
Sea-level rise is likely to have widespread effects on coastal structures, infrastructure, beaches, wetlands, and agricultural lands. Coastal erosion, flooding, and saltwater intrusion have been threatening coastal areas and water resources for decades already. 

Infrastructure impacts may potentially include flooding of low-lying airports, roads, and structures. Rail lines, pipelines for oil, gas, and water, and major roadways located along coastal areas are vulnerable to increased rates of cliff erosion. Increased erosion rates may alter sediment transport rates and impact coastal port facilities (e.g., dredging operations in ports and harbors). Wastewater systems designed for present sea levels would be significantly affected by sea-level changes (e.g., a number of municipal systems treat wastewater at facilities near sea level whose collection system and treatment processes could be impacted by salt water intrusion). Already diminished coastal wetlands currently protected by natural barriers such as sand beaches will be affected by more frequent or permanent inundation, salinity changes (e.g., including the San Francisco Bay-Delta area), and sediment flow changes impacting river-mouth areas and coastal wetlands. The species dependent on estuaries at one time or another in their life cycles and already suffering from environmental pressures could decline further.

Agriculture
California has produced the highest agricultural crop value in the U.S. for over 50 consecutive years. It is the leading dairy state, the number two cotton producer, and it grows more than half the nation’s fruits, nuts, and vegetables. Moreover, California wineries produce three-quarters of the wine sold in the U.S.

Agriculture will perhaps be the sector most susceptible to climate changes. Direct climate variability and change impacts may include: increased frequency of extreme heat/cold events; increased frequency of extreme wet/dry years; pattern shifts for first and last frost in the year and unseasonable precipitation (e.g., extended rain in late summer can be devastating for many crops including vineyards, and certain tree and field crops).  Increased productivity due to warmer temperatures in certain areas is possible, although variability and secondary impacts like increased pests and diseases could cancel out these benefits.  For example, increased average temperatures in certain areas could increase yields and options for crop types, but extreme hot / cold and wet / dry events compromise the potential benefits. The necessary shifts in the agricultural sector to cope with climate variability and change will likely produce winners and losers in the state.

Ecosystems and biodiversity-
California’s spectacular variety of ecosystems is one of its biggest treasures: the redwood forests of the Coastal Range, alpine meadows of the Sierra, the offshore waters teeming with marine life, the salt marshes of San Francisco Bay, and the deserts and saline lakes inland draw millions of tourists, local residents, and industries based on natural resources. Yet these treasured ecosystems are particularly vulnerable to climate change. 

The combination of water and temperature changes poses problems for plants and animals, including threatened and endangered species. While wildlife, forests, and grasslands will tend to shift north and upward to more suitable habitats, human development or other obstacles can prevent migration or reduce suitable areas for new colonization. The species with the least ability to colonize new habitats will have the biggest problems. The study finds that there are already major shifts in California’s ocean life, including decreases in zooplankton, sea bird populations, and northern cold-water species, but increases in southern warm-water species.

How can Californians prepare for the potential impacts of global warming?
 

Climate scientists agree that further climate change may be inevitable and will therefore require adaptation, although most scientists also think that the pace of climate change can be slowed by substantially reducing greenhouse gas emissions. This would give governments, businesses, and ecosystems around the world more time to respond and adapt to climate change as well as reducing the overall severity of climate change-related impacts, thereby buying "insurance" for an uncertain future.  Another way to buy insurance now is to incorporate climate change into all long-term decisions about natural resources, thereby providing greater resilience.

The National Synthesis report and regional assessment effort for California have sought to identify strategies to build resilience in critical systems and to provide information useful to those who must adapt to and cope with climate changes that already appear to be occurring.  A number of useful strategies have been identified, including 

• watershed restoration to buffer variations in precipitation patterns;


• efficiency improvements in water use in all sectors, diversification of the water delivery system, and possibly development of additional water storage facilities;


• land-use changes and building design changes to avoid impacts of flooding, coastal erosion, and fire;


• an increase in local capacity for power generation and water storage in urban areas, improvement of land use policies and practices to reduce sprawl, amelioration of  building designs etc.;


• maintenance and increase of agricultural crop diversity, and shift to different crop varieties better adapted to heat and water stress;

Additional Information
Confronting Climate Change in California, a comprehensive report by the Union of Concerned Scientists and the Ecological Society of America on the potential impacts of climate change in California.

For more detailed information on the potential impacts of global warming on California, several experts are available to answer your questions:

Robert Wilkinson, Ph.D., University of California – Santa Barbara
 Tel.: (805) 569-2590   Email: wilkinso@envst.ucsb.edu
Walter Oechel, Ph.D., San Diego State University, Director of the Global Change 
Research Group, Department of Biology 
 Tel.: (619) 594-4818   Email: oechel@sunstroke.sdsu.edu
 Susanne Moser, Ph.D., Union of Concerned Scientists
 Tel.: (617) 547-5552   Email: smoser@ucsusa.org