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News from the National Academies

Date: July 16, 2010
Contacts: Molly Galvin, Senior Media Relations Officer
Sara Frueh, Media Relations Officer
Christopher White, Media Relations Assistant
Office of News and Public Information
202-334-2138; e-mail <news@nas.edu>


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FOR IMMEDIATE RELEASE

NEAR-TERM EMISSIONS CHOICES COULD LOCK IN CLIMATE CHANGES FOR CENTURIES TO MILLENNIA; REPORT ESTIMATES IMPACTS FROM VARIOUS LEVELS OF WARMING

WASHINGTON — Choices made now about carbon dioxide emissions reductions will affect climate change impacts experienced not just over the next few decades but also in coming centuries and millennia, says a new report from the National Research Council. Because CO2 in the atmosphere is long lived, it can effectively lock the Earth and future generations into a range of impacts, some of which could become very severe.

Policy choices about emissions can be informed by recent advances in climate research that quantify the relationships between atmospheric CO2 and warming levels, and between warming levels and future impacts. Drawing upon this research, the report estimates changes in precipitation, streamflow, wildfires, crop yields, and sea level rise that can be expected with different degrees of warming. It also estimates the average temperature increases that would be likely if CO2 were stabilized in the atmosphere at various target levels. However, the report does not recommend any particular stabilization target, noting that choosing among different targets is a policy choice rather than strictly a scientific one because of questions of values regarding how much risk or damage to people or to nature might be considered too much.

Increased Confidence About Future Impacts

Although some important future effects of climate change are difficult to quantify, there is now increased confidence in how global warming of various levels would relate to several key impacts, says the report. It lists some of these impacts per degree Celsius (or per 1.8 degrees Fahrenheit) of global warming, for example (these apply for 1 C to 4 C of warming):

  • 5 percent to 10 percent less total rain in southwest North America, the Mediterranean, and southern Africa per degree Celsius of warming.
  • 5 percent to 10 percent less streamflow in some river basins, including the Arkansas and Rio Grande, per degree Celsius of warming.
  • 5 percent to 15 percent lower yields of some crops, including U.S. and African corn and Indian wheat, per degree Celsius of warming.

While total rain is expected to decrease in some areas, more of the rain that does occur is expected to occur in heavy falls in most land areas (3 percent to 10 percent more heavy rain per degree Celsius). In addition, warming of 1C to 2 C (1.8 F to 3.6 F) could be expected to lead to a twofold to fourfold increase per degree in the area burned by wildfire in parts of western North America, the report says. Warming of 3 C (5.4 F) would put many millions more people at risk of coastal flooding and lead to the loss of about 250,000 square km of wetlands and drylands. And warming of 4 C (7.2 F) would lead to far warmer summers; about nine out of 10 summers would be warmer than the warmest ever experienced during the last decades of the 20th century over nearly all land areas.

Stabilizing Atmospheric CO2 Requires Deep Emissions Cuts

Currently the concentration of CO2 in the atmosphere is about 390 parts per million volume (ppmv), the highest level in at least 800,000 years. Depending on emissions rates, that level could double or nearly triple by the end of the century, greatly amplifying future human impacts on climate, the report says.

Because the amount of human-caused CO2 emissions already far exceeds the amount that can be removed through natural carbon "sinks" such as oceans, keeping emissions rates the same will not stabilize the concentration of CO2 in the atmosphere. Even if emissions held steady, the CO2 concentration in the atmosphere would increase, much like the water level in a bathtub when water is coming in faster than it is draining. Emissions reductions larger than about 80 percent, relative to whatever peak global emissions rate may be reached, would be required to approximately stabilize carbon dioxide concentrations for a century or so at any chosen target level.

Further, stabilizing atmospheric concentrations does not mean that temperatures will stabilize immediately. Warming that occurs in response to a given increase in the CO2 concentration is only about half the total warming that will ultimately occur. For example, if the CO2 concentration stabilizes at 550 ppmv, the Earth would warm about 1.6 C on the way to that level; but even after the CO2 level stabilizes, the warming would continue to grow in the following decades and centuries, reaching a best-estimate global "equilibrium" warming of about 3 C (5.4 F). Waiting to observe impacts before choosing a stabilization target would therefore imply a lock-in to about twice as much eventual crop loss, rainfall changes, and other impacts that increase with warming.

The report offers likely ranges and best estimates of the equilibrium warming that can be expected from various levels of CO2 in the atmosphere:

Table 1: Relationship of Atmospheric Concentrations of Carbon Dioxide to Temperature

The report was sponsored by the Energy Foundation and the U.S. Environmental Protection Agency. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies. They are independent, nonprofit institutions that provide science, technology, and health policy advice under an 1863 congressional charter. Committee members, who serve pro bono as volunteers, are chosen by the Academies for each study based on their expertise and experience and must satisfy the Academies' conflict-of-interest standards. The resulting consensus reports undergo external peer review before completion. For more information, visit http://national-academies.org/studycommitteprocess.pdf. A committee roster follows.

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Copies of Climate Stabilization Targets: Emissions, Concentrations, and Impacts Over Decades to Millennia are available from the National Academies Press; tel. 202-334-3313 or 1-800-624-6242 or on the Internet at http://www.nap.edu. Reporters may obtain a copy from the Office of News and Public Information (contacts listed above).

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[ This news release and report are available at http://national-academies.org ]

NATIONAL RESEARCH COUNCIL

Division on Earth and Life Studies
Board on Atmospheric Sciences and Climate
Committee on Stabilization Targets for Atmospheric Greenhouse Gas Concentrations

Susan Solomon* (chair)
Senior Scientist
National Oceanic and Atmospheric Administration
Boulder, Colo.

David S. Battisti
Tamaki Endowed Chair
Department of Atmospheric Sciences
University of Washington
Seattle

Scott C. Doney
Senior Scientist
Department of Marine Chemistry and Geochemistry
Woods Hole Oceanographic Institution
Woods Hole, Mass.

Katharine Hayhoe
Research Associate Professor
Department of Geosciences
Texas Tech University
Lubbock

Isaac M. Held*
Senior Scientist
Geophysical Fluid Dynamics Laboratory
National Oceanic and Atmospheric Administration
Princeton, N.J.

Dennis P. Lettenmaier
Robert and Irene Sylvester Professor of Civil and Environmental Engineering
University of Washington
Seattle

David Lobell
Assistant Professor
Program on Food Security and Environment
Stanford University
Stanford, Calif.

Damon Matthews
Assistant Professor
Department of Geography, Planning and Environment
Concordia University
Montreal

Raymond T. Pierrehumbert
Professor
Department of Geophysical Sciences
Hinds Geological Laboratory
University of Chicago
Chicago

Marilyn Raphael
Professor
Department of Geography
University of California
Los Angeles

Richard Richels
Senior Technical Executive
Electric Power Research Institute Inc.
Washington, D.C.

Terry L. Root
Professor

Center for Environmental Science and Policy
Institute for International Studies
Stanford University
Stanford, Calif.

Konrad Steffen
Professor
Cooperative Institute for Environmental Research
University of Colorado
Boulder

Claudia Tebaldi
Research Scientist
Adjunct Professor

University of British Columbia-Vancouver
British Columbia, Canada

Gary W. Yohe
Woodhouse/Sysco Professor
Department of Economics
Wesleyan University
Middletown, Conn.

STAFF

Toby M. Warden
Study Director

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* Member, National Academy of Sciences