California goes nuts over declining winters.

• Position: Agriculture

Winter chill, a vital climatic trigger for many tree crops, is likely to decrease by more than 50% during this century as global climate warms, making California no longer suitable for growing many fruit and nut crops, maintain researchers from the University of California, Davis. In some parts of California's agriculturally rich Central Valley, winter chill already has declined by nearly 30%.

This study is the first to map winter chill projections for all of California, which is home to nearly 3,000,000 acres of fruit and nut trees that require chilling. The combined production value of these crops was more than $8,000,000,000 last year, according to the California Department of Food and Agriculture.

"Our findings suggest that California's fruit and nut industry will need to develop new tree cultivars with reduced chilling requirements and new management strategies for breaking dormancy in years of insufficient winter chill," explains Eike Luedeling, a postdoctoral fellow in the Department of Plant Sciences.

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Most fruit and nut trees from non-tropical locations avoid cold injury in the winter by losing their leaves in the fall...