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Meet California fruit and wine-grape growers and other experts witnessing global warming's impact on agriculture in the video, Growing Concern.

IMPACTS Agriculture

Global warming threatens California's multibillion-dollar agriculture and forestry industries—and the livelihoods of the more than one million people who work in them.

Why? As temperatures continue to rise, crops will require more water and become more susceptible to pests and disease. Meanwhile, the water supply will become less reliable and pests and disease outbreaks are likely to increase.

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Less Fruit Production

A minimum number of chill hours (the hours per year where temperatures drop below 45°F) are necessary for proper bud setting for many fruit and nut trees. Chill hours are rapidly decreasing in many areas of the state and are approaching levels insufficient for proper plant growth. If average statewide temperatures rise more than 5.5°F, the entire Central Valley is expected to approach, and in some cases surpass, critical thresholds for some fruit trees.

Shrinking Timber Yields

Global warming is expected to have widespread effects on the productivity and health of California's forests. Forestlands cover 45 percent of the state, and commercial forests such as pine plantations cover 16 percent of the state. If average statewide temperatures rise between 5.5 and 8°F, the productivity of mixed conifer forests is expected to shrink 18 percent by the end of the century. The reductions in yield from pine plantations are expected to be even more severe, declining by 31 percent by the end of the century.

Less Productive Dairies

California's $3 billion dairy industry supplies nearly a fifth of the entire country's milk products. Heat stress in dairy cows can lead to poor feeding, weight loss, and reduced milk production, which begins to decline at temperatures at low as 77°F and can drop substantially as temperatures climb above 90°F. Toward the end of the century, a temperature increase of 8 to 10°F is expected to reduce milk production by up to 20 percent, more than twice the reduction expected if temperatures do not rise more than 5.5°F.

Lower Quality Wine Grapes

California is renowned for its high-quality wines, produced throughout Napa and Sonoma Valleys and along the northern and central coasts. Temperature is one of the most important and controlling factors in wine grape development. Higher temperatures are expected to cause wine grapes to ripen as much as one to two months earlier toward the end of the century, reducing grape quality. If temperatures rise 8 to 10°F, grape growing conditions are expected to be impaired throughout the state by the end of the century.



Baldocchi, D., S. Wong, and A. Gutierrez. 2005. An assessment of impacts of future CO2 and climate on agriculture. Draft report. Sacramento, CA: California Climate Change Center. Online at www.energy.ca.gov/2005publications

Battles, J., T. Robards, A. Das, K. Waring, J.K. Gilless, F. Schurr, J. LeBlanc, G. Biging, and C. Simon, 2006. Climate change impact on forest resources. Sacramento, CA: California Climate Change Center. Online at www.energy.ca.gov/2005publications

Hayhoe, K., D. Cayan, C.B. Field, P.C. Frumhoff, E.P. Maurer, S.C. Moser, S.H. Schneider, K.N. Cahill, E.E. Cleland, L.L. Dale, R. Drapek, W.M. Hanemann, L.S. Kalkstein, J. Lenihan, C.K. Lunch, R.P. Neilson, S.C. Sheridan, and J.H. Verville. 2004. Emissions pathways, climate change, and impacts on California. Proceedings of the National Academy of Sciences 101:12422-12427.


ucsusa.org: Global warming and California agriculture fact sheet. (PDF)

energy.ca.gov: "Assessment of the impacts of future CO2 and climate on California agriculture," California Climate Change Center. (PDF)

energy.ca.gov: "Climate affects on agricultural systems," California Climate Change Center. (PDF)

energy.ca.gov: "Climate change: Challenges and aolutions for california agricultural landscapes," California Climate Change Center. (PDF)

energy.ca.gov: ""Climate change impacts on forest resources," California Climate Change Center. (PDF)


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


key to all charts


chart showing decreasing chill hours

Chart data source: Baldocchi et al. 2006.


chart showing decreasing forest yields

Chart data source: Battles et al. 2006.


chart showing decreasing dairy productiony

Chart data source: Hayhoe et al. 2004.


chart showing decreasing wine grape quality

Chart data source: Hayhoe et al. 2004.

Union of Concerned Scientists