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Climate change is already impacting California. Rising temperatures are causing more frequent and severe extreme weather events, including heat waves, droughts, wildfires, and storms, as well as more variable precipitation and sea level rise.
Climate change is considered the greatest global public health threat of the 21st century and affects virtually all aspects of human health and well-being, including access to clean air, food, water, shelter, physical safety, and mental wellbeing. Changing environmental conditions threaten a multitude of ecosystems and species across the state, in addition to energy, transportation, and water management infrastructure, agricultural production, and cultural resources. All Californians are affected, but the most climate vulnerable communities and populations experience worse impacts from the crisis than others.
While climate impacts vary by region, they are present in every corner of the state. Addressing them requires sustained commitment to ambitious emissions reductions and proactive implementation of climate adaptation and resilience efforts. This Strategy provides a clear framework for action that allows for adjustments as our understanding evolves.
Statewide trends are elaborated below based on California’s Fourth Climate Change Assessment (CCCA4), which references medium and high global emissions scenarios (RCP 4.5 and RCP 8.5 per 2014 IPCC 5th Assessment). For more information on the impacts of climate change in California and for insight into region-specific variation, explore California’s Fourth Climate Change Assessment and the Indicators for Climate Change in California report.
The CCCA4 aligns with the IPCC’s Sixth Assessment Report and the Fifth National Climate Assessment on the findings highlighted below. The message is clear: California faces increased temperatures, drought, fire weather, and more extreme flooding in the years ahead.
Statewide Trends
Extreme Heat
Annual temperature increases have already exceeded 1°F over most of California, with some areas exceeding 2°F. The daily maximum average temperature, an indicator of extreme temperature shifts, is expected to rise 4.4°F–5.8°F by mid-century and 5.6°F–8.8°F by late century. Heat-Health Events (HHEs), which pose particular risk to populations vulnerable to heat, will worsen drastically throughout the state. By midcentury, the Central Valley is projected to experience average HHEs that are two weeks longer, and HHEs could occur four to ten times more often in the Northern Sierra region. High ambient temperatures lead to increased incidences of death and illness, raise exposure to vector-borne diseases, worsen air and water quality, and cause major economic impacts.
Drought
California has the most variable year-to-year precipitation in the contiguous United States and experiences multi-year wet or dry periods. While future annual precipitation may remain relatively stable on average, droughts will grow more frequent, prolonged, and intense. Warming air temperatures will cause moisture loss from soils, which will lead to drier seasonal conditions. Snowpack in California’s mountains will decline more than a third by 2050 and more than half by 2100, significantly reducing surface and groundwater supply. These changes pose substantial danger to ecosystems, human health, and agriculture. They also compound with other water insecurity issues in water-vulnerable areas, particularly for households dependent on domestic wells or state small water systems.
Wildfire
Wildfires are driven by multiple complex and interacting factors, including variation in temperature, moisture, wind, and vegetation as well as land use and human activity, making future wildfires difficult to predict. In recent years, the area burned by wildfire in California has dramatically increased. 2020 and 2021 were the two most destructive wildfire seasons on record with a combined 7 million acres burned, and 15 of California’s 20 most destructive fires on record occurred since 2015, pointing to accelerating severity and frequency of extreme fires. A model developed for California’s Fourth Climate Change Assessment projected up to a 77 percent increase in average area burned and a 50 percent increase in the frequency of fires exceeding 25,000 acres by 2100. These changes cause death, injury, and smoke-related illness; damage ecosystems; threaten critical infrastructure; induce economic losses; and displace people from their homes.
Flooding
California’s increasingly long and intense drought conditions are punctuated by more intense storms and higher flood flows that can overwhelm stormwater and wastewater systems. More precipitation falls as rain instead of snow, leading to higher volumes of runoff, while proliferating wildfires further raise California’s flood risk by reducing water absorption through the soil. The 2022 Central Valley Flood Protection Plan update estimates that lives lost to flooding over the next fifty years will double in the Sacramento River Basin and quadruple in the San Joaquin River Basin without new investments in flood management systems.
Sea Level Rise
Sea level has risen 6-8 inches along the California coast in the past century and will rise at a much faster rate in the coming decades, threatening coastal communities, natural resources, cultural sites, and infrastructure. The current best available science predicts that California sea level will rise between 1.6 feet and 3.1 feet by 2100, with slim potential for a rise as high as 6.6 feet. Sea level rise exacerbates coastal storms and flooding events, causing accelerated cliff and bluff erosion, beach loss, and mobilization of subsurface contaminants. It also causes groundwater rise which threatens underground infrastructure and exposes freshwater aquifers to saltwater intrusion. 31–67 percent of Southern California beaches are projected to be lost by the end of the century if adaptation actions are not implemented.
Cascading and Compounding Impacts
The impacts California faces, including extreme heat, drought, wildfire, flood, and sea level rise, may cascade and compound with each other, resulting in even more dangerous conditions. For example:
- Heavy rainfall following wildfire can lead to landslides that endanger infrastructure and human lives.
- Climate change causes ocean warming and acidification, which occur because the world’s oceans absorb 90% of the excess heat and 30% of the excess carbon dioxide from greenhouse gas emissions. These can be catastrophic to marine ecosystems (e.g. disease, degradation, bleaching) and the coastal communities that rely on them.
- Increased runoff from changes in precipitation also causes harmful algal blooms, which diminish water quality and disrupt tribal and recreational use of California’s waters.
California is taking action to protect people, nature, and our economy against these impacts. The California Climate Adaptation Strategy lays out direct actions the State is taking to improve climate resilience through management of landscapes, infrastructure, and other assets, emphasizing protection of vulnerable communities and supported by the best available climate science. Combined with California’s global leadership in reducing emissions, the State’s adaptation efforts aim to ensure a safe and prosperous future for all Californians.