Study: Crop Yields Down as Temp. Rises

    Global warming will have severe negative impacts on California crop yields in the coming years, according to a new study by researchers at the UC-managed Lawrence Livermore National Laboratory.

    LLNL’s study, published in the journal Agricultural and Forest Methodology, showed the effects of rising temperatures on six major Californian crops: wine grapes, almonds, table grapes, oranges, walnuts and avocados.

    Historically, each of these crops is typically planted only once every 25 to 40 years, so climates have the potential capability to change considerably in the lifetime of individual vines or trees. To investigate the effects of temperature on the crops, scientists put them in 20 different climate settings, each with 2 to 4 degrees Celsius difference in temperature.

    The team found that the varied temperatures had little influence on wine grape yields but spurred notably lower yields for the remaining crops in the study. Considering the current harvesting locations and conditions of almonds, table grapes, oranges and walnuts, researchers projected a potential 20 percent decrease in yields by mid-century.

    Researchers’ temperature intervals mirrored separate findings from the Intergovernmental Panel on Climate Change’s third assessment report, which predicted that Earth’s average surface temperature will increase between 1.4 degrees Celsius and 5.8 degrees Celsius due to global warming between 1990 and 2100.

    “”We were interested in how the production of crops that are most valuable in California will be helped or hurt by climate change,”” lead study author David Lobell said in a statement. “”So we developed models to simulate how crops respond to the amount of climate change we expect in California.””

    LLNL spokesperson Anne M. Stark did not respond to requests for comment.

    Overall, the team found that unless California’s farming techniques adapt to the rising temperatures, most crops will be less productive in a warmer climate. For example, by 2020, Californians can expect yields of almonds and avocados to be about 10 percent lower than they would have been without an increase in warmth.

    Ninety-five percent of the United States’ avocados are grown in California, 80 percent of which are from San Diego County. The study, which was funded by the U.S. Department of Energy’s Office of Science, Biological and Environmental Research Program, projected an overall 40 percent decrease in avocado harvests, which could lead to a potentially severe negative impact on local farmers.

    The research did not include potential effects of rising atmospheric carbon dioxide or farming modifications due to increasing temperatures and less rainfall. However, the team did take into account multiple factors that can influence yields in a changing climate, including plant physiological processes and the climate-related effects of crop pests, pathogens and air pollution.

    According to Lobell, the results put concrete numbers on the potential cost of climate change for these particular crops, so Californians know what is at stake in a warmer world. For example, a 10 percent loss on a $1.5 billion crop – such as almonds – translates to $150 million. These numbers can then be compared to the cost of reducing climate change or adapting the crops to the new climate.

    The study also noted that although the crops can be grown in cooler regions, it would take time for the orchards and vineyards to mature and become harvestable. There is also the issue of finding fertile soil and conditions suitable for farming.

    “”The impacts are based on the assumption that farmers do not move to other locations with more favorable climates,”” Lobell said. “”With long-lived perennial plants, moving to another region within California is somewhat limited.””

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