California is already experiencing the impacts of a changing climate, including observable shifts in the frequency and severity of extreme weather events, such as more frequent and severe heat waves and wildfires, more variable precipitation, and a succession of droughts that have increased as temperatures warm.
While the impacts vary in different regions of California, the evidence is clear – every corner of the state is already experiencing the impacts of climate change, requiring sustained commitment to ambitious emissions reductions and proactive implementation of climate adaptation and resilience efforts. While we don’t have answers to every question about what these changes mean for California, this strategy provides a clear framework for action that also allows for adjustments and course corrections as our understanding evolves.
Statewide trends are elaborated below. For more information on the impacts of climate change in California and for insight into region-specific variations, explore CA’s Fourth Climate Change Assessment and the Indicators for Climate Change in California report.
The latest IPCC report included relevant regional projections that reaffirm the findings from the CA Fourth Assessment highlighted below; California faces increased temperatures, drought, fire weather, and more extreme flooding.
Annual temperature increases experienced over most of California have already exceeded 1°F, 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 better predict 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.
California is known for its highly variable precipitation and has the highest variability of year-to-year precipitation in the contiguous United States. California’s variable precipitation is also characterized by multi-year wet or dry periods. As a result, future average precipitation is difficult to predict, but may likely not change substantially when measured by annual precipitation. However, there is high confidence in projections that even if precipitation remains stable or increases, drought severity and the number of dry years will increase, even as more extreme precipitation events may occur. Warming air temperatures will increase moisture loss from soils, which will lead to drier seasonal conditions even if precipitation increases. The snowpack in California’s mountains is a key source of surface and groundwater in the state, and rising temperatures will cause a decline in snowpack by more than a third by 2050 and more than half by 2100, even if precipitation levels remain stable.
Wildfires are driven by multiple, complex, and interacting factors such as the environment, land use, and human activity, all of which make future wildfires difficult to predict. In recent years, the area burned by wildfire in California has dramatically increased and unprecedented fires are occurring in sensitive ecosystems like higher elevations and along the coast. In addition, many of California’s wildfires are burning hotter and more intensely than observed in recent history. Fires are concentrating in upper watersheds, further compounding crises like drought. The 2020 wildfires resulted in the largest wildfire season recorded in California’s modern history, with nearly 10,000 fires that burned over four million acres in total. However, fewer than 40 fires accounted for the vast majority of the area burned, pointing to the accelerating severity and frequency of extreme fires. In 2021, California experienced 4 of the 20 largest wildfires in our history, with 8,000 wildfires burning over 2.5 million acres across the state. The 2021 fire season also marks the first time that fire crossed the granite crest of the Sierra, California’s largest natural fuel break. 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.
Sea-level rise, coastal flooding, and erosion
Sea-level rise is already accelerating along the California coast and will continue to rise substantially over the 21st century, threatening coastal communities, natural resources, cultural sites, and infrastructure. The current best available science predicts that the state’s coastline could experience between 1.1–1.9 feet of sea-level rise by 2050 (with a low-probability, but high impact extreme of 2.7 feet) and between 2.4–6.9 feet by 2100 (with a low-probability, but high impact extreme of 10.2 feet). Though we may be uncertain the exact amount of sea-level rise for a certain location at a certain year, we know that water levels are rising and communities need to be prepared. Coastal wave events and king tides, in combination with current and rising sea levels, will increase flood impacts on land, which will exacerbate the impact on coastal assets. Rising sea levels may also salinate coastal groundwater aquifers and raise groundwater tables, causing increased flooding leading to impacts that will further damage buried and low-lying infrastructure. Finally, rising water levels and increased storm activity will increase coastal erosion, impacting beaches and cliffs throughout the state. For example, a projected 31–67 percent of Southern California beaches are projected to be lost by the end of the century if adaptation actions are not implemented.
Ocean warming, hypoxia, and acidification
The world’s oceans absorb excess heat (~90%) and CO2 (~30%) from greenhouse gas emissions, the former contributing to ocean warming and the latter to ocean acidification. Both warming and acidification can be catastrophic to marine ecosystems (e.g. disease, degradation, bleaching) and the coastal communities and industries that rely on them. Relatedly, deoxygenation or hypoxia of surface waters can lead to dead zones that further challenge marine habitats and species and cause cascading impacts for our coastal economies and communities.
Climate change is considered the greatest global public health threat of the 21st century and affects virtually all aspects of health and well-being, including access to clean air, food, water, shelter, and physical safety. Communities across California are experiencing health impacts associated with the climate crisis today. Examples include injury, illness, and death from wildfires and wildfire smoke, extreme heat, drought, landslides, extreme weather events, vector-borne diseases, and associated mental health impacts. Climate-driven disasters directly result in injuries, deaths, and displacement, but also loss of livelihoods, businesses, crops, and homes - contributing to unemployment, poverty, and the housing crisis. Direct impacts and subsequent cascading effects increase chronic diseases, infectious diseases, mental health challenges, and heat- and smoke-related illnesses. Climate change affects every Californian, but the most climate vulnerable communities and populations experience worse health impacts from the crisis than others.