Posted on 12/13/2001

Christmas Not What It Used To Be
By Cat Lazaroff

WASHINGTON, DC, December 12, 2001 (ENS) - 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 National Research
Council. The study suggests 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." Most climate change research
has focused on gradual changes, such as the processes by which emissions of
greenhouse gases lead to warming of the planet.

But 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,
the National Research Council (NRC) says. "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."

The committee that wrote the report said there is no need for undue alarm
about the possibility of sudden climate change, because societies have
learned to adapt to these changes over the course of human history. The
collapse of some ancient civilizations has been associated with abrupt
climate changes, especially severe droughts, but humans have also shown
great resilience. The committee said that research into the causes,
patterns and likelihood of abrupt climate change is the best way to reduce
its impact.

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 planet's past climate record also needs to be understood better,
according to the report. Scientists have a variety of means to study what
the climate was like thousands of years ago. For example, researchers look
at tree rings to examine the frequency of droughts and analyze gas bubbles
trapped in ice cores to measure past atmospheric conditions. With such
techniques, scientists have discovered repeated instances of particularly
large and abrupt climate changes over the last 100,000 years during the
slide into and climb out of the most recent ice age.

For 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.

Many factors may contribute to suggen changes in regional or global
climate. Earlier this year, Pennsylvania State University associate
professor Richard Alley, chair of the NRC committee that wrote the current
study, cited greenhouse gases and ocean circulation as particularly
important in rapid climate changes. "The secret of why the whole world
rides a roller coaster in the ice age and freezes and thaws is probably
greenhouse gases, especially carbon dioxide," Alley told attendees of the
annual meeting of the American Association for the Advancement of Science.
"The seesaw effect of rapid climate change is probably caused by ocean
circulation and the keys to this change are locked in the polar ice."

Simulating abrupt climate changes using computer models is difficult
because most climate models assume a linear relationship between the
factors which are forcing change - greenhouse gas emissions, for example -
and the response of the global climate. Such a relationship would mean that
as greenhouse gas emissions double, the rate of climate change doubles. But
abrupt climate changes show 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.

If the ocean currents slow or halt, the result could be a deep freeze in
northern regions, and far warmer temperatures in equatorial regions. "We
don't know how this cycle begins, nor do we know geographically where the
salty water begins to sinks to return circulation. However, this pattern of
cold north with warm far south has occurred repeatedly," said Penn State's
Alley.

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. Some steps that the committee says
deserve a look include reducing emissions to slow global warming, improving
climate forecasting, slowing biodiversity loss, and improving water, land
and air quality. "We need to get our politicians to take the issue of
global climate change seriously," said Jonathan Overpeck, director of the
Institute for the Study of Planet Earth at the University of Arizona, and a
coauthor of the NRC study. "The economic and quality of life costs of not
acting could far outweigh the costs of fixing the problem now."

The report was sponsored by the U.S. Global Change Research