updated 5/28/2008 3:22:49 PM ET 2008-05-28T19:22:49

Climate change is increasing the risk of U.S. crop failures, depleting the nation's water resources and contributing to outbreaks of invasive species and insects, according to a federal report released Tuesday.

Those and other problems for the U.S. livestock and forestry industries will persist for at least the next 25 years, said the report compiled by 38 scientists for use by water and land managers.

"I think what's really eye-opening is the depth and breadth of the impacts and consequences going on right now," said Tony Janetos, a study author and director of the Joint Global Change Research Institute at the University of Maryland.

Scientists produced the report by analyzing research from more than 1,000 publications, rather than conducting new research. It's part of a federal assessment of global warming for the U.S. Climate Change Science Program, sponsored by 13 federal agencies and led by the Department of Agriculture.

"Just to see it all there like that and to realize the impacts are pervasive right now is a little bit scary," said Peter Backlund, director of research relations at the National Center for Atmospheric Research in Boulder, Colo.

Drought-strained forests in the West and Southeast are easy prey for tree-killing insects like bark beetles. Snow in the Western mountains is melting earlier, making it more difficult for managers overseeing a long-established system of reservoirs and irrigation ditches that serves Western states.

The Southeast doesn't have the same kind of storage system because rain historically has been more consistent. Current weather disruptions have the region struggling with drought, Janetos said.

Rising carbon dioxide levels are changing the metabolism of grasses and shrubs on range land, decreasing the protein levels in plants eaten by cattle.

Warmer, drier weather is altering the biodiversity of deserts in the Southwest and the high, colder deserts of Nevada, Utah and eastern Washington, said Steve Archer of the University of Arizona. Plants and animals already living in extreme conditions face threats from wildfires and nonnative species, he said.

"These areas historically support a large ranching industry, wildlife habitat," Archer said. "They are major watersheds and airsheds."

The scientists said longer growing seasons provided by higher temperatures don't necessarily translate into bigger crop yields because plants have certain growth patterns.

Their report focuses on the next 25 to 50 years, rather than the next 100 years as other studies have done.

"Sometimes it's so far out that people just don't grasp that it's a problem. This really brings it home," said Jerry Hatfield, lab director of the National Soil Tilth laboratory in Ames, Iowa.

While the report makes no recommendations, Hatfield said it could help farmers consider planting new crop varieties or varying when they plant to accommodate seasonal changes.

The USDA said the specific findings include:

  • "Grain and oilseed crops will mature more rapidly, but increasing temperatures will increase the risk of crop failures, particularly if precipitation decreases or becomes more variable.
  • "Higher temperatures will negatively affect livestock. Warmer winters will reduce mortality but this will be more than offset by greater mortality in hotter summers. Hotter temperatures will also result in reduced productivity of livestock and dairy animals.
  • "Forests in the interior West, the Southwest, and Alaska are already being affected by climate change with increases in the size and frequency of forest fires, insect outbreaks and tree mortality. These changes are expected to continue.
  • "Much of the United States has experienced higher precipitation and streamflow, with decreased drought severity and duration, over the 20th century. The West and Southwest, however, are notable exceptions, and increased drought conditions have occurred in these regions.
  • "Weeds grow more rapidly under elevated atmospheric CO2. Under projections reported in the assessment, weeds migrate northward and are less sensitive to herbicide applications.
  • "There is a trend toward reduced mountain snowpack and earlier spring snowmelt runoff in the Western United States.
  • "Horticultural crops (such as tomato, onion, and fruit) are more sensitive to climate change than grains and oilseed crops.
  • "Young forests on fertile soils will achieve higher productivity from elevated atmospheric CO2 concentrations. Nitrogen deposition and warmer temperatures will increase productivity in other types of forests where water is available.
  • "Invasion by exotic grass species into arid lands will result from climate change, causing an increased fire frequency. Rivers and riparian systems in arid lands will be negatively impacted.
  • "A continuation of the trend toward increased water use efficiency could help mitigate the impacts of climate change on water resources.
  • "The growing season has increased by 10 to 14 days over the last 19 years across the temperate latitudes. Species' distributions have also shifted.
  • "The rapid rates of warming in the Arctic observed in recent decades, and projected for at least the next century, are dramatically reducing the snow and ice covers that provide denning and foraging habitat for polar bears."

The full report is online at www.climatescience.gov/

Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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