California and climate change
California, home to the largest population and most diverse economy in the United States, faces significant challenges related to climate change. The state, which contributed approximately 6.2% of U.S. carbon dioxide emissions in 2021, has a complex relationship between its climate, population, and economic activities, particularly in agriculture, which relies heavily on water resources. With nearly 39 million residents, expected to reach 50 million by 2025, California’s water supply is under increasing pressure due to both population growth and climate variability, leading to concerns about droughts, floods, and agricultural productivity.
Climate projections indicate warming of up to 1.1° Celsius over the next thirty years, which may exacerbate issues such as reduced snowpack, increased flooding, and heightened wildfire risks. In response, California has implemented strict greenhouse gas emission standards and ambitious renewable energy initiatives, aiming to reduce emissions to 80% below 1990 levels by 2050. The state's position as a global leader in clean technology and renewable energy development underscores its critical role in addressing climate change, not just locally but also on a global scale. The interplay of environmental, social, and economic factors creates a unique set of challenges and opportunities for California in the context of climate change adaptation and mitigation.
California and climate change
California has the largest population, most vehicles, most diverse economy, and most productive agricultural sector of any US state. It produced about 6.2 percent of total US carbon dioxide emissions in 2021.
Background
California’s climate, population, economy, and agriculture share a complex relationship with global warming. The state has a highly productive and diverse industrial complex, ranging from manufacturing and oil production to biotechnology and telecommunications. Population and industry are concentrated in the state’s southern and coastal regions, where the water supply is limited. An expansive agricultural sector supports a food production capacity important for California, the United States, and the world, but it depends on irrigation water and a workforce of more than 1 million. California has led the United States in food and agricultural production for over fifty years and leads the nation in exporting agricultural products.
Population and the Water Supply
California’s 39 million people represent 12 percent of the nation’s population, and the state’s population is expected to approach 50 million by 2025. Nearly 60 percent of the populace is concentrated in Southern California, and 90 percent resides in metropolitan areas. Population growth is expected to be greater in inland counties, but coastal counties containing the major metropolitan areas will continue to account for over 60 percent of the population. Population growth has critical implications for almost every area of public policy, but issues particularly relevant for California are social services, education, transportation, the environment, the water supply, and loss of agricultural land.
Contrasting seasonal precipitation and temperature patterns, the influence of topography, and proximity to the coast create a variety of climates within California. However, the population favors the water-limited regions of southern and coastal California, while the mountains of northern and central California produce an abundant but variable water supply. California also relies on pumping water from underground sources, though this often occurs at a rate faster than these sources can be naturally replenished, resulting in groundwater overdraft. The time and space mismatch between the water supply and the water needed by the population and agriculture is overcome by a statewide water storage and conveyance system. California’s water system is a collection of constructed facilities and natural features blended by a mixture of overlapping agencies and jurisdictions from all levels of government.
Vulnerability to Climate Change
California’s climate is expected to warm by as much as 1.1° Celsius over thirty years, with greater summer than winter warming likely. Precipitation changes are uncertain, but the seasonal precipitation pattern is expected to continue. The warmer climate will produce a reduced winter snowpack; an earlier start of spring snowmelt; an increase in winter runoff as a fraction of total runoff; an increase in winter flooding frequency; decreases in total runoff; increased stress on drinking water and irrigation water supplies; increased droughts, floods, and wildfires; decreased agricultural productivity; and increased threats to human health. California was in a state of drought from 2011 into 2017, and again from 2020 through 2022 and in 2024. California’s 2050 global warming impacts could approach total annual costs and revenue losses of $15 billion.
The impact of warmer temperatures on the winter snowpack has major consequences. Snow accounts for up to 50 percent of California’s stored water, but this figure may be reduced to 12 to 42 percent in a warmer climate. More precipitation occurring as rain rather than snow increases immediate runoff and heightens chances for more severe and frequent floods. Protecting against floods requires lower reservoir levels that reduce the water supply capacity of reservoirs, reduce available irrigation water, and reduce the ability of reservoirs to offset drought. Furthermore, summer hydropower generation is reduced when reservoir levels are lowered.
Most crops and forests will benefit from increased atmospheric carbon dioxide (CO2) concentrations, but warmer temperatures may aggravate ozone pollution, which makes plants more susceptible to diseases and pests. Higher and more extreme temperatures increase the likelihood of air pollution episodes, which are a public health threat, and over 90 percent of California’s current population lives in areas that violate the state’s air quality standards for ozone or particulate matter. Warmer temperatures will increase the wildfire risk to homes and forests by 11 to 55 percent and will contribute to air quality problems.
Reducing Climate Change Contributions
California is the world’s twelfth-largest emitter of greenhouse gases (GHGs), producing 500 million metric tons, or 13.5 metric tons per capita. However, the state has reduced per capita GHG emissions by 10 percent. Transportation is California’s largest source of GHG emissions, but the state has a long history of adopting rigorous vehicle GHG emission standards beyond federal Environmental Protection Agency requirements. Beginning in 2009, all new vehicles sold in California have an environmental performance sticker, rating the car on smog emissions and the amount of GHG emissions per mile, including emissions related to the production and distribution of the fuel.
The California Global Warming Solutions Act of 2006 is the United States’ first comprehensive regulatory and market-mechanisms program. The legislation, along with related initiatives that include penalties for noncompliance, are designed to achieve quantifiable, cost-effective GHG emissions equal to 1990 levels by 2020—a goal the state was able to reach by 2016. By 2050, GHG emissions are to be reduced to 80 percent of their 1990 levels.
Electric power generation accounts for 28 percent of California’s GHG emissions, and natural gas accounts for 56 percent of annual power generation. However, California has aggressively pursued renewable energy, which currently accounts for 14 percent of California’s annual energy use. Geothermal is California’s largest renewable source of electric power. Small hydroelectric, wind, and biomass contribute about equal shares, and solar provides about 0.2 percent. Nearly half of the nationwide venture capital investment in clean technology is in California.
Context
California’s role in global warming extends well beyond its position as an individual state. If California were a nation, in 2022 it would have had roughly the thirty-seventh-largest population and the fifth-largest economy in the world. It is a world leader in developing energy-efficient technology, in implementing new technology, and in efforts to shift energy production to renewable resources. California’s gross domestic product (GDP) was around 14.6 percent of the US GDP in 2022.
Projected temperature increases for California are smaller than estimated global temperature increases, but even small temperature increases are significant for California’s population, agriculture, and economy, because they alter the character of a water supply that is already approaching its limits. The challenge of providing a reliable water supply is magnified by global warming and the uncertainty of its effects on California’s climate.
Key Concepts
- geothermal energy: energy generated from heat stored in the Earth
- greenhouse gases (GHGs): atmospheric trace gases that absorb and emit infrared radiant energy and warm the atmosphere and the Earth’s surface
- ozone: a molecule of three oxygen atoms that can form in the lower atmosphere by photochemical reaction of sunlight with hydrocarbons and nitrogen oxides
- runoff: precipitated water that flows into rivers, lakes, streams, oceans, and other water bodies
- snowpack: accumulated snow in mountainous areas that melts during warmer months
Bibliography
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