News•February 7, 2013

Climate Change Set to Batter U.S. Agriculture, Forests

By Lauren Morello

Climate change is likely to transform U.S. agriculture by mid-century, reducing yields of many staple crops and the productivity of livestock operations, according to a new government analysis.

Rising temperatures and shifting precipitation patterns will also harm the nation’s forests, increasing their vulnerability to fires, insect infestations and disease.

Those are some of the dramatic projections outlined in a pair of analyses released Tuesday by the Agriculture Department. The documents, written by agency and academic scientists, are USDA’s contribution to the National Climate Assessment the government will finalize later this year.

Global warming will also exert growing stress on livestock, reducing the productivity of herds, which will lead to higher costs for meat and milk.
Credit: USDA

Researchers examined more than 1,000 scientific studies as they compiled the two reports, which are intended to help the federal government to devise new strategies to cope with climate change in its forests and advise the nation’s farmers and ranchers.

At stake is the country's annual $300 billion agricultural output, as well as a far-reaching network of federal lands that range from lush Puerto Rican rainforest to scrubby Alaskan tundra.

Both are likely to suffer as climate change intensifies, the new reports warn.

For agriculture, the USDA’s analysis predicts that climate change will end a 150-year period of relatively stable climate that has contributed to the industry’s “remarkable capacity to adapt to a wide diversity of growing conditions and dynamic social and economic changes.”

By mid-century, temperatures will rise between 1.8°F and 5.4°F and yields of major crops will begin to decline. Shifting rain and snowfall patterns will also work to reduce crop productivity, outweighing any benefit that rising atmospheric carbon dioxide levels might have on plant growth.

Jerry Hatfield, director of USDA’s National Laboratory for Agriculture and the Environment, said that climate change could mean that a staple crop like corn spends more growing days in temperatures outside the range that produces optimal yields.

And perennial crops like cherries may have a harder time as warming reduces the number of cold winter days the plants need to experience to properly flower and set fruit once spring comes.

The Forest Service conducts a prescribed burn in the Desoto National Forest in Mississippi.
Credit: Jan Boykin/Forest Service

“Cherries need 1,000 hours of temperature below 43 degrees Fahrenheit,” Hatfield said. “If those hours now go from 1,000 to 500 in a season because of warming at a certain location, cherry production is going to be greatly affected.”

Warming will also exert growing stress on livestock, reducing the productivity of herds and flocks and causing production costs for meat, eggs and milk to increase.

As climate change intensifies, many adaptation measures will become less effective and more expensive, the report said.

A second USDA analysis examined climate change’s likely effects on lands managed by the U.S. Forest Service.

“By the end of the 21st century, forest ecosystems in the United States will differ from those of today as a result of changing climate,” the report says.

The “most rapidly visible and most significant” short-term effects from warming are likely to include increased wildfires, insect infestations, erosion and flooding, and drought-induced tree death.

By mid-century, the area burned by wildfires is set to double, the report said. Insect infestations, like the bark beetle outbreaks that have ravaged western forests, will grow to affect an even larger area each year than wildfires.

Forests will begin to shift northward and upward, seeking cooler temperatures in the face of warming, but they may not be able to keep up with the pace of that temperature change.

Higher temperatures have already decreased snow cover depth, duration and extent, increasing drying in some forests, especially in the Western U.S.

The cumulative effect of those changes could be devastating for many Forest Service lands, said the agency’s climate change advisor, Dave Cleaves.

“If trees and forests are under stress from gradual effects like long-term drought or changes in the moisture situation, then they are more susceptible to episodic agents like fire and disease,” he said. “Their immune system is less geared up, if you will.”

But Cleaves said that the situation “is not all gloom and doom.”

“Some species of trees, if they’re tolerant to a changing climate, might actually thrive on warmer temperatures and more carbon dioxide in the air and more rain,” he said. “We’ve actually seen in some regions of the country, like the Northeast, rainfall increase. We’ll probably see forests there that grow faster, though the species mix may change. There’s some opportunity for new kinds of forest.”