Cover of the report Global Climate Change Impacts in the United States.

Washington — The first U.S. report in nearly a decade to assess the impacts of climate change in different regions of the United States confirms and extends research that describes rising sea and air temperatures and sea levels, melting ice, intensified hurricanes and many other changes that are happening now. Such changes will continue into the future, affecting water resources, agriculture, coastal areas and health.

Global Climate Change Impacts in the United States, called a state-of-knowledge report, was released June 16 during a briefing at the White House by John Holdren, assistant to the president for science and technology and director of the White House Office of Science and Technology Policy, and Jane Lubchenco, administrator of the U. S. National Oceanic and Atmospheric Administration (NOAA).

The report, in development for more than a year, “tells us why remedial action is needed sooner rather than later,” Holdren said in a statement. It shows “why that action must include both global emissions reductions to reduce the extent of climate change and local adaptation measures to reduce the damage from the changes that are no longer avoidable.”

Findings are based largely on results of the U.S. Global Change Research Program (USGCRP), which began as a presidential initiative in 1989 and that Congress included in the Global Change Research Act of 1990. Thirteen federal agencies participate in the work of the USGCRP.

CHANGES HAPPENING NOW, REPORT FINDS

In the United States, rising water temperatures and ocean acidification — caused by the ocean’s uptake of carbon dioxide from the atmosphere — threaten coral reefs and the rich ecosystems they support. These and other climate-related impacts on coastal and marine ecosystems have major implications for fisheries and tourism.

Insect infestations and wildfires are increasing and are projected to increase further in a warming climate. Heat waves will become more frequent and intense, increasing threats to human health and quality of life. Extreme heat will affect transportation, energy systems and crop and livestock production.

Over time, local sea-level rise on the order of 1 meter in addition to storm surges will increasingly threaten homes and other coastal infrastructure. Coastal flooding will become more frequent and severe, and coastal land will increasingly be lost to rising seas.

Increased heavy downpours will lead to more flooding and waterborne diseases, negative effects on agriculture, and disruptions to energy, water and transportation systems. Reduced summer runoff and increasing water demands will create greater competition for water supplies in some regions, especially the West.

For the new report, USGCRP integrated its research with that from around the world, including the findings of the Intergovernmental Panel on Climate Change (IPCC), whose main activity is to provide regular assessments of the state of knowledge on climate change.

The latest report was “Climate Change 2007,” the Fourth IPCC Assessment Report. The IPCC is now outlining its Fifth Assessment Report, to be finalized in 2014.

THE RESPONSE

Climate change is a global phenomenon but its impacts are local and regional, affecting farmers and fishers, local and public health officials, water resource managers, emergency responders, business owners and citizens.

In the United States over the past 50 years, for example, average temperature has risen more than 2 degrees Fahrenheit, precipitation has increased an average of about 5 percent and sea level has risen along most of the U.S. coast. Such impacts, according to the report, are expected to become increasingly severe for more people and places as the amount of warming increases.

The report classifies the actions that society can take in response to climate change in two categories — mitigation and adaptation.

Mitigation refers to options for limiting climate change by, for example, reducing heat-trapping emissions of carbon dioxide, methane, nitrous oxide and halocarbons, or by removing some of the heat-trapping gases from the atmosphere.

The report does not evaluate mitigation technologies or analyze the effectiveness of different approaches. The U.S. government’s Climate Change Technology Program is studying these issues, along with NOAA, the Environmental Protection Agency and the departments of Agriculture, Energy and Transportation.

Adaptation refers to changes made to better respond to climatic and other environmental conditions, reducing harm or taking advantage of opportunity. These can range from a farmer growing a crop variety better suited to warmer or drier conditions, a company relocating key business centers away from coastal areas vulnerable to sea-level rise and hurricanes, and a community changing its zoning and building codes to put fewer structures in harm’s way.

INTO THE FUTURE

Choices made about emission reductions now and over the next few decades will have far-reaching consequences for climate-change impacts, the report says.

No matter how aggressively heat-trapping emissions are reduced, because of gases that have already been released, some climate change will occur. But reducing emissions of carbon dioxide would reduce warming over this century and beyond.

Implementing sizable and sustained reductions in carbon dioxide emissions as soon as possible would significantly reduce the pace and the overall amount of climate change and would be more effective than reductions of the same size initiated later.

Reducing emissions of some shorter-lived greenhouse gases, such as methane, and some types of particles, such as soot, would begin to reduce the warming influence within weeks to decades.

See the related “Spotlight on the Colorado River.”

More information about the U.S. Global Change Research Program, the U.S. Climate Change Technology Program and NOAA are available at their respective Web sites.

The complete report is available for download at the USGCRP Web site.