Climate change could come quickly, study warns

Posted: 15 February 2002

Climate change may come on fast and furious, wreaking sudden and catastrophic damage on people, property, and natural ecosystems, warns a new report from the US National Research Council. The study provides further evidence that human-caused greenhouse warming may increase the possibility of abrupt and unwelcome climatic events.

Researchers do not know enough about such events to accurately predict them, so surprises are inevitable, the researchers warn in a report titled, Abrupt Climate Change: Inevitable Surprises.

New evidence shows that periods of gradual change in Earth's past were punctuated by episodes of abrupt change, including temperature changes of about 10 degrees Celsius, or 18 degrees Fahrenheit, in only a decade in some places. Severe floods and droughts also marked periods of abrupt change.

If the planet's climate is being forced to change - as most scientists believe is currently the case - it increases the number of possible mechanisms that can trigger abrupt events, the report says. The more rapid the forced change, the more likely it is that abrupt events will occur on a time scale that has immediate human and ecological consequences.

"Abrupt climate changes were especially common when the climate system was being forced to change most rapidly," the report states. "Thus, greenhouse warming and other human alterations of the earth system may increase the possibility of large, abrupt, and unwelcome regional or global climatic events."

Research should be aimed at improving modeling and statistical analysis of abrupt changes, the committee said, focusing on mechanisms that lead to sudden climate changes during warm periods, with an eye to providing realistic estimates of the likelihood of extreme events. Poor countries may need more help preparing for abrupt climate change since they lack scientific and economic resources, the committee noted.

The Greenland ice-sheet contains 11% of the world’s fresh water. Credit: NASAFor instance, the warming at the end of the last ice age triggered an abrupt cooling period, which finished with an especially abrupt warming about 12,000 years ago. Since then, less dramatic - though still rapid - climate changes have occurred, affecting precipitation, hurricanes, and the El Niño events that occasionally disrupt temperatures in the tropical Pacific.

Examples of abrupt change in the past century include a rapid warming of the North Atlantic from 1920 to 1930 and the Dust Bowl drought of the 1930s.

Experience suggests that while a small forcing may cause a small change, it may also force the climate system across a threshold, triggering huge changes.

One example of threshold crossing would be a massive discharge of fresh water from lakes previously dammed by ice sheets, which are now melting away. As that cold fresh water floods into the sea, it may alter or halt the natural circulation of ocean currents that normally bring warm water to northern climates and carry cooler water toward the equator. The result could be a deep freeze in northern regions, and far warmer temperatures in equatorial regions.

Rapid climate changes make adaptation by humans, wildlife and ecosystems more difficult. The NRC committee recommends that researchers try to identify strategies that increase the adaptability of economic and ecological systems.

The committee noted that many policies aimed at responding to catastrophic changes might provide benefits regardless of whether abrupt climate change occurs. These include reducing emissions to slow global warming, improving climate forecasting, slowing biodiversity loss, and improving water, land and air quality.

Links:
US National Research Council.
To read the report online, click here.