Confronting Climate Change in California (1999)
To read UCS's most recent work on the impacts of climate change in California, please visit www.climatechoices.org/ca.
Executive Summary
Over the past century, human activities have dramatically altered the natural landscape of California. Our historical legacy includes severe shrinkage and isolation of natural habitats, altered flows in streams and rivers, extensive introductions of non-native plants and animals, and pollution of the air, land, and water. As we enter the 21st century, a powerful new agent -- global climate change -- will increasingly interact with the human pressures that continue to stress California's ecosystems. In the future, direct impacts generated by the state's rapidly growing human population will be intensified by the impacts of climate change. Confronting Climate Change in California provides the California public and policy makers with insights drawn from the best available science—insights that may help us safeguard both our ecological heritage and our economic future. This summary highlights key findings.
What is the likely climate future for California?
It is highly probable that California winters will become warmer and wetter during the next century. Summers will also become warmer, but the temperature increase will not be as great as the winter increase. Most of California's precipitation falls in winter, and in the future more of it is likely to fall as rain, less as snow, a change that is likely to lead to increased winter runoff and decreased summer stream flow. The consequences for spring and summer soil moisture are difficult to predict, but the state's summers are likely to remain hot and dry, and perhaps become even hotter and drier. Such a consequence, combined with decreased summer stream flow, would exacerbate demands for water in the state.
El Niños, with their dramatic effects on California's weather and economy, may increase in intensity and/or frequency as the climate changes. Sea level is expected to rise by 8 to 12 inches, which is two to three times the increase experienced at San Francisco over the past 150 years. The impact of a rise in sea level on coastal wetlands, housing, and agriculture, as well as on roads, levees, and other public works, will be amplified by any increases in the frequency and/or intensity of major storms.
What might these changes mean for California ecosystems?
California's natural ecosystems—communities of plants and animals interacting in a physical environment—span 10 different biological categories, ranging from the cool, wet redwood forests of the North Coast to the hot, dry Mojave and Colorado deserts of the southeast. Many of these natural ecosystems—as well as agricultural ones—are highly sensitive to the availability of water. Thus changes in the timing or amount of precipitation over the next century are likely to have a greater impact than changes in temperature. For example,
* Decreased summer stream flows would intensify competing demands for water to meet the needs of agriculture, industry, and urban areas, and to sustain the health of California's aquatic and streamside ecosystems.
* Intensified competition for an already oversubscribed water supply could lower the profitability of water-intensive crops, including alfalfa, cotton, and grapes.
* Reduced summer runoff of fresh water would increase summer salinity in San Francisco Bay, leading to changes in water circulation and quality and complex changes in the food web, including impacts on fish and invertebrates that use the bay as a nursery ground.
* Increases in the amount of winter rains could intensify flooding and landslide hazards.
The highly diverse California landscape includes ecosystem types ranging from desert to temperate rainforest, from largely pristine to intensively managed, and stretching from coastline to mountain ridges. Climate change will inevitably shift the suitable range for each type of ecosystem, as well as the mix of plants and animals and the vital flows of energy and nutrients that occur within them. Some of these changes are already occurring, providing a first glimpse of the kinds of processes and problems that are likely to intensify as climate change continues. For example,
* One species of butterfly, Edith's Checkerspot, is shifting from the southern to the northern limits of its range and from low-elevation to high-elevation sites, a likely consequence of rising temperatures.
* Warming of the California Current in recent decades has been linked to population declines of zooplankton and seabirds known as sooty shearwaters. On the rocky shores of Monterey Bay, southern animal species have increased in the warmer waters while native northern species have declined.
* In kelp forests off the Southern California coast, the proportion of northern, cold-water fish species—e.g., greenspotted rockfish—has dropped by half since the 1970s, and the proportion of southern warm-water fish species—e.g., Garibaldi—has increased nearly 50%.
Other shifts are likely in the future:
* Expanding grasslands will likely encroach on the foothill shrublands of the coastal ranges and the Sierra Nevada.
* At higher elevations, shrubs could proliferate at the expense of forests, and, where the peaks are high enough, forests could expand into the areas now occupied by tundra. In many cases, however, plant and animal species will not be able to shift northward or upslope because the potential habitat has been claimed by development, captured by non-native species, or contains unsuitable soils or other physical limitations.
* In California's agricultural ecosystems, important perennial crops such as fruit, nuts, and grapes will be most vulnerable, because it can take years for farmers to bring more suitable tree and vine cultivars into production to adapt to shifting conditions.
Many California ecosystems are effectively isolated, either as islands surrounded by human developments or as remnant ecosystems hemmed in by contrasting soils, geographical features such as mountains, invading non-native species, or other factors. Isolation increases the vulnerability of these communities in the face of even modest climate changes, because it limits the ability of species to persist in place or to migrate in response to shifting conditions. Some of these isolated or "museum" ecosystems are likely to become more biologically impoverished and eventually to disappear if we fail to recognize that persistence in the short term is no guarantee of long-term success. For example,
* Individual redwoods may survive for centuries, even millennia-long past the point where climate changes make growth of new seedlings impossible. The same longevity of individuals that can mask the slow degradation of these landmark California forests can also provide time for restoration efforts.
* Isolated patches of unique grassland, marsh, and aquatic habitats -- such as the Serpentine outcrops of Northern California and vernal pools in the Central Valley, which often harbor rare or spectacular species -- are so poorly connected with other patches that migrations required by climate change may be difficult or impossible without human intervention.
A large proportion of the effects of climate change on California ecosystems will be indirect; climate change may alter the frequency and/or intensity of extreme weather events such as severe storms, winds, droughts, and frosts in still-uncertain ways. Similarly, the frequency and/or magnitude of some ecologically important processes such as wildfires, flooding, and disease and pest outbreaks is likely to alter as climate changes occur. Altogether, these difficult-to-predict phenomena, driven by shifts in climate patterns, may be more important for the future of California ecosystems than changes in average temperature and precipitation. For example,
* Any increase in Santa Ana wind conditions, combined with warmer, drier summers, could escalate economic and environmental loss to wildfires in California.
* An increase in the number or intensity of now-infrequent thunderstorms, which form over land and pick up more acids and other pollutants than Pacific frontal storms, may mean more acid rain and increased murkiness (from nutrient enrichment) for Sierra lakes.
* Pests such as pine bark beetles could become more prominent or more destructive if shifts in climate stress trees.
* El Niño warming may encourage toxic algal blooms in bays and estuaries and depress ocean productivity offshore.
* On shore, heavier and/or more frequent El Niño rains could increase the frequency of the rodent population booms that precede hantavirus outbreaks.
Although many California ecosystems are adapted for quick recovery from extreme events, increases in the frequency of such events could push some systems beyond their potential to recover. For example,
* Unlike redwood forests, coastal marine communities such as kelp forests can be destroyed in only a few seasons by disturbances such as severe El Niños. Yet they can also recover much more rapidly than terrestrial forests.
* Chaparral and closed-cone pine forests are adapted to fire and regenerate rapidly from fires that recur at certain intervals; however, fires in these habitats are a major threat to human property and lives in California.
How can Californians address the challenges of a shifting climate?
The impacts of climate change on California can best be appreciated in the context of the state's burgeoning population and how its residents currently use their natural resources. With a population exceeding 30 million, the state's landscape has been considerably transformed -- from urban sprawl to intensive agriculture. Overall, the impacts of climate change on California ecosystems will exacerbate the consequences of these intensive human land-use practices and the pressures of a growing population. Fortunately, there are many actions the California public and policy makers can take now to safeguard and restore vulnerable ecosystems.
The steps that will provide the greatest protection for California's ecosystems from avoidable damage during climate change will also yield positive benefits for public safety, recreation, agriculture, fisheries, and our unique natural heritage -- even without significant changes to the climate. One key step involves limiting the footprint of development on the landscape, particularly in vulnerable habitats such as wetlands and areas subject to fires, floods, and landslides. Another prudent step is designing nature reserves on land and in coastal waters that will provide California's unique plant and animal communities with room to adapt to the changing conditions created by a shifting climate.
Although Californians cannot act alone to stabilize the state's climate, they have the opportunity to make a large contribution to worldwide efforts to minimize the pace and intensity of greenhouse warming. For one thing, since Californians are substantial contributors of global greenhouse gases -- emitting, for example, over 400 million tons of CO2 a year -- their individual actions as consumers and producers can be globally important. Another opportunity arises from California's stature as a bellwether for new attitudes and innovative practices, including many that help reduce emissions of greenhouse gases. Today's Californians can continue to be models for the nation and the world by encouraging and embracing the development of novel energy, transportation, and land-use solutions to the problem of global climate change. Taking the lead in effective action to slow climate change and protect California's natural and human resources can help secure our economic and ecological future for many generations.
