April 14, 2009

CO2 Cuts Could Spare Worst Of Global Warming’s Impact

The threat of global warming can still be greatly diminished if nations cut emissions of heat-trapping greenhouse gases by 70 percent this century, according to a new analysis led by scientists at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado.

Although global temperatures would rise, the most dangerous aspects of climate change, including enormous losses of Arctic sea ice and permafrost and a significant rise in sea levels, could be partially avoided, the study found.

"This research indicates that we can no longer avoid significant warming during this century," said NCAR scientist Warren Washington, the study's lead author.

"But if the world were to implement this level of emission cuts, we could stabilize the threat of climate change and avoid catastrophe."

Average global temperatures have warmed nearly 2 degrees Fahrenheit since the pre-industrial era.  Much of that is due to human-produced emissions of greenhouse gases, predominantly carbon dioxide (CO2). This heat-trapping gas has increased from about 284 parts per million (ppm) in the atmosphere during pre-industrial times to more than 380 ppm today.

With research showing that additional warming of 1.8 degrees Fahrenheit may be the threshold for dangerous climate change, the European Union has called for significant reductions in emissions of carbon dioxide and other greenhouse gases.  Debate on the matter is also underway within the U.S. Congress.

To analyze the impact of such cuts on the global climate, Washington and his team conducted a series of global supercomputer studies with the NCAR-based Community Climate System Model. They assumed that CO2 levels could be held to 450 ppm at the end of this century based on figures from the U.S. Climate Change Science Program.  The program has cited 450 ppm as an achievable target if the world quickly enacts conservation practices and new green technologies to dramatically reduce emissions.  By comparison, emissions are now on track to reach about 750 ppm by 2100 if left unchecked.

The study's results showed that if CO2 were held to 450 ppm, global temperatures would increase by about 1 degree Fahrenheit by the end of the century.  In contrast, temperatures would rise by almost four times that amount if emissions continue on their present course.

The climate modeling study showed that maintaining carbon dioxide levels to 450 ppm would have other impacts as well, such as:

  • Rising sea levels due to thermal expansion by warming water temperatures would be about 5.5 inches instead of 8.7 inches.  Substantial additional sea level rise would be expected in either scenario from melting glaciers and ice sheets.
  • Summer Arctic ice would be reduced by about a quarter in volume and stabilize by 2100, as opposed to shrinking more than three-quarters and continuing to melt.  Separate research has suggested that summertime ice will disappear altogether this century if emissions are not reduced.
  • Arctic warming would be reduced by nearly half, helping preserve Arctic mammals, fisheries and sea birds in areas such as the northern Bering Sea. "¨
  • Considerable regional changes in precipitation, including decreased precipitation in the U.S. Southwest and an increase in the U.S. Northeast and Canada, would be reduced by half if emissions were maintained at 450 ppm.
  • The overall climate system would stabilize by about 2100, rather than continuing to warm.

The researchers used supercomputer simulations to compared a "present course" scenario in which no emissions reductions are made to one with dramatic cuts in CO2 emissions beginning in roughly 10 years. The scientists emphasized that they were not examining how such cuts could be achieved nor advocating a particular policy.

"Our goal is to provide policymakers with appropriate research so they can make informed decisions," said Washington.

"This study provides some hope that we can avoid the worst impacts of climate change--if society can cut emissions substantially over the next several decades and continue major cuts through the century."

The study, funded by the U.S. Department of Energy and the National Science Foundation, will be published next week in Geophysical Research Letters.


Image 2: New computer simulations show the extent that average air temperatures at Earth's surface could warm by 2080-2099 compared to 1980-1999, if (top) greenhouse gases emissions continue to climb at current rates, or if (bottom) society cuts emissions by 70 percent. In the latter case, temperatures rise by less than 2°C (3.6°F) across nearly all of Earth's populated areas. However, unchecked emissions could lead to warming of 3°C (5.4°F) or more across parts of Europe, Asia, North America, and Australia. (Graphic courtesy Geophysical Research Letters, modified by UCAR.) 


On the Net: