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Continued global warming will worsen conditions for bad air quality. Meet Central Valley residents concerned about the effect of global warming on their health in the video, Ozone Alert.


As temperatures rise from global warming, the frequency and severity of heat waves will grow—as will the potential for bad air days. The risk of illness and death due to dehydration, heart attack, stroke, and respiratory disease will increase as a result. Those most likely to suffer are children, the elderly, and other vulnerable populations.

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Unhealthy Air Made Worse

More than 90 percent of California's population lives in areas that fail to meet the state's air quality standards for ground-level ozone ("smog") or particulate matter ("soot"). Exposure to these pollutants can cause or exacerbate acute respiratory diseases, decreased lung function in children, asthma, and other serious health problems.

Continued global warming is expected to exacerbate air quality problems by increasing the frequency, duration, and intensity of conditions conducive to air pollution formation. If temperatures rise to the medium warming range (5.5 to 8°F), the number of days with weather conducive to smog formation is expected to rise by 75 to 85 percent in Los Angeles and the San Joaquin Valley—areas where the air is already the dirtiest in the nation. This is more than twice the increase expected if temperature rise is kept to the lower warming range (3 to 5.5 °F). Furthermore, if temperatures rise into the medium warming range the risk of wildfires is expected to increase by as much as 50 percent, which would further worsen air quality by elevating soot levels.

Extreme Heat

If global warming continues unabated, causing temperatures to rise into the higher warming range, statewide summer temperatures in California are projected to rise as much as 9 to 18°F, heat waves will become more common and more severe, and the number of days with temperatures above 90°F in Los Angeles and 95°F in Sacramento are expected to increase by about 100 days toward the end of the century.

As temperatures rise, California's population will face greater risk of death from dehydration, heat stroke/exhaustion, heart attack, stroke, and respiratory distress. By mid-century, extreme heat events in urban centers such as Sacramento, Los Angeles, and San Bernardino are projected to cause two to three times as many heat-related deaths as there are today.

Those most vulnerable to heat-related problems include people who are already ill, the elderly, and the poor, who may lack the sufficient access to air conditioning and medical assistance. Paradoxically, while expanding air conditioner use can help improve society's ability to cope with extreme heat, it will also lead to increased costs as well as increased energy consumption, which—based on today's energy mix—would contribute to further global warming and worsening air quality.



Dreschler, D.M., N. Motallebi, M. Kleeman, D. Cayan, K. Hayhoe, L. Kalkstein, N. Miller, S. Sheridan, and J. Jin. 2006. Public health-related impacts of climate change. Draft report. Sacramento, CA: California Climate Change Center. Online at www.energy.ca.gov/2005publications

Westerling, A. and B. Bryant 2006. Climate change and wildfire in and around California: Fire modeling and loss modeling. Draft report. Sacramento, CA: California Climate Change Center. Online at www.energy.ca.gov/2005publications


See the warming projectionsTo learn more about the effects of global warming on California under different emissions scenarios, see the Impacts Overview.


chart showing increased risk of poor air quality
chart key

Chart data source: Kleeman and Cayan 2006.


chart showing increase in extreme heat
chart key

Chart data source: Dreschler et al. 2006.


ucsusa.org: Global warming and public health fact sheet (PDF)

energy.ca.gov: "Public health related impacts of climate change in California" California Climate Change Center 2006 (PDF)

ucsusa.org: Find out more about UCS's work on clean vehicles and global warming in California.

ucsusa.org: Vehicles, Health, and Global Warming section of the UCS Clean Vehicles program

Union of Concerned Scientists