Warming Climate Changing U.S. Fields and Forests

The Climate Change Science Program integrates the federal research efforts of 13 agencies on global change change. The U.S. Department of Agriculture, USDA, is the lead agency for this report and coordinated its production.

The report describes the effects of climate change on agriculture, land resources, water resources, and biodiversity in the United States.

"The report issued today provides practical information that will help land owners and resource managers make better decisions to address the risks of climate change," said Joe Glauber, chief economist with the the USDA.

The report was written by 38 authors from universities, national laboratories, nongovernmental organizations, and federal agencies. It was subject to peer review by 14 scientists through a Federal Advisory Committee formed by the USDA. The National Center for Atmospheric Research assisted in coordinating production of the report.

The report concludes that climate change is already affecting U.S. water resources, agriculture, land resources, and biodiversity, and will continue to do so.

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.

There is a trend toward reduced mountain snowpack and earlier spring snowmelt runoff in the western United States, the report finds.

A continuation of the trend toward increased water use efficiency could help mitigate the impacts of climate change on water resources, the authors advise.

The growing season has increased by 10 to 14 days over the last 19 years across the temperate latitudes. Species' distributions have also shifted.

Barley harvest in Washington state's Palouse Hills. (Photo courtesy USDA)

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.

Weeds grow more rapidly under conditions of elevated atmospheric carbon dioxide, CO2, the main greenhouse gas emitted by burning fossil fuels. Under projections reported in the assessment, weeds migrate northward and are less sensitive to herbicide applications.

Horticultural crops such as tomato, onion, and fruit are more sensitive to climate change than grains and oilseed crops.

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.

But not all plants will experience negative effects as the climate warms. 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.

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 report finds. The U.S. Department of the Interior earlier this month declared the polar bear to be Threatened under the Endangered Species Act.

Agencies within the USDA already are responding to the risks of climate change, the report states, saying, "For example, the Forest Service is incorporating climate change risks into National Forest Management Plans and is providing guidance to forest managers on how to respond and adapt to climate change."

The Natural Resources Conservation Service and Farm Services Agency are encouraging actions to reduce greenhouse gas emissions and increase carbon sequestration through conservation programs.

The USDA's Risk Management Agency has prepared tools to manage drought risks and is conducting an assessment of the risks of climate change on the crop insurance program.

The report, "Synthesis and Assessment Product 4.3 (SAP 4.3): The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States," is posted on the Climate Change Science Program website. To access it, click here.

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