Climate change science and research have advanced substantially in recent years. These key messages highlight selected findings from California’s Fifth Climate Change Assessment and illustrate how the latest climate science can inform decisions about California’s future. More detail on these key messages, including citations, can be found in the sections below. Additional context about these climate issues can be found throughout the Assessment portfolio of research and data.
■ California will experience rising temperatures across the century. Average temperatures
in California are increasing at an unprecedented rate, projected to rise by 3.5–4.3°F (1.9–2.4°C) by 2050 relative to the 1981–2010 baseline. By 2100, projected temperature increases range between 5.7°F (3.2°C) under an intermediate emission scenario to 8°F (4.4°C) under a high emission scenario.
■ California will experience greater precipitation variability and more “climate whiplash.”
California’s weather will feature greater swings between wet and dry extremes. Storms are
expected to intensify and deliver a greater share of total precipitation.
■ California’s snowpack will decline substantially, affecting downstream water systems,
local economies, and ecosystems. Early April snowpack is projected to decrease by
approximately 40% by mid-century (2041–2070) and approximately 60% by the end of the
century (2071–2100) compared to the 1981–2010 average. Snowpack decline is due to rising temperatures and a greater amount of precipitation falling as rain.
■ Climate change is reshaping California’s seasons, altering the timing, duration, and
intensity of seasonal conditions. As summer periods lengthen, winters shorten, and seasonal conditions become more variable, natural and human systems that depend on the reliability of seasonal patterns will be affected and forced to adapt.
■ Wildfire smoke exposure and associated health risks are increasing. Models project that
California will experience the highest increase in annual excess deaths from wildfire smoke
of any US state by 2050, reaching over 5,000 excess deaths per year compared to 2011–2020.
Farmworkers alone are projected to experience a 190% increase in smoke exposure days
considered “unhealthy for sensitive groups” by mid-century.
■ Extreme heat events are growing longer and more frequent, resulting in prolonged heat
waves and more days above important temperature thresholds. By end-of-century, the average longest heat wave of the year is projected to lengthen across all regions of the state, with durations ranging from six days in the Bay Area to as long as 19 days across the Sierra Nevada under a high emissions scenario.
■ Climate risks are not distributed equally across California communities. Communities
differ in their exposure, sensitivity, and capacity to prepare for, respond to, and recover from
climate impacts. For example, people living unsheltered (0.5% of California’s population) make up 13% of all hospitalizations for heat-related illness. Many disadvantaged communities are particularly sensitive to place-based risks, ranging from drying of domestic wells during droughts to exposure to toxic substances from sea level rise near contaminated sites.
■ Marine and coastal ecosystems are being reshaped by marine heat waves, ocean
acidification, and hypoxia. Ocean acidification along the California coast is occurring at twice the global rate due to upwelling. Combined with severe marine heat waves and low oxygen levels in California coastal waters, marine ecosystems and wildlife are facing devastating threats.
■ With 3.3 feet of sea level rise $78 billion worth of property and 201,000 people could be
exposed to coastal flooding by 2100. This means five times the exposure expected in 2050.
A 100-year storm could raise these estimates to 310,000 people and $122 billion in property
exposed by 2100.
■ California Native American tribes face disproportionate impacts from climate change
yet are leading effective climate adaptation solutions. Historical land dispossession and
criminalization of traditional practices have heightened tribal vulnerability to shifting seasons
and climate-related hazards. Nonetheless, California Native American tribes are implementing strategies such as ecocultural restoration and cultural burning which can reduce the likelihood of catastrophic wildfires by up to 92% for a decade post-treatment. These practices strengthen ecosystems, communities, and California’s overall adaptive capacity.
■ Climate hazards are increasingly interconnected, creating cascading and compounding
risks. Major climate hazards in California are most destructive when they occur sequentially
or simultaneously. For example, an exceptionally hot summer and fall in 2024 exacerbated fire conditions leading into the 2025 Los Angeles Fires, one of the most expensive natural disasters in US history. Multi-benefit solutions can help address the complex and intersecting nature of climate hazards.
■ Climate change will have significant economic impacts across California, particularly
through the effects on health and labor. For example, recent extreme heat events have led to billions of dollars in losses through premature death, lost work hours, and more, while rising global temperatures are increasing the pace of inflation.
■ The future is not predetermined. The decisions made today can help California adapt to changing climate and strengthen resilience for generations to come.
