Abrupt climate change more common than believed
Date: Friday, March 30, 2007 @ 23:51:07 EDT
It came on quickly and then lasted nearly two decades, eventually
killing more than one million people and affecting 50 million more. All
of this makes the Sahel drought, which first struck West Africa in the
late 1960s, the most notorious example of an abrupt climatic shift
during the last century.
Dramatic as this single event was, University of Wisconsin-Madison
researchers have now uncovered 29 other regions worldwide that endured
similarly precipitous climatic changes during the 20th century - far
more than scientists previously thought. Their study publishes today
(March 30) in the online edition of Geophysical Research Letters.
The work represents the first systematic survey of abrupt climate
changes that have occurred in recent history, says postdoctoral
researcher Gemma Narisma, who led the study with professor Jonathan
Foley, director of the UW-Madison Center for Sustainability and the
Global Environment in the Nelson Institute for Environmental Studies.
The National Academies' National Research Council has called for more
research on abrupt climate change, warning that it's more likely to
happen as global temperatures rise and humans continue to alter the
"This study is important, because previous work largely focused on
ancient climates or theoretical changes in future climates," says
Foley. "But our work here is showing that abrupt climatic changes are
real, are with us today, and that they have major impacts on human
By identifying diverse regions around the globe where rapid
climatic shifts have taken place, the study opens up new opportunities
for understanding why these changes happen and what makes areas
susceptible to them, says Narisma. A range of factors is likely
involved, including human activities, such as deforestation and land
degradation, and natural phenomena, like sea surface temperatures.
The work might also lead to interventions that would make systems less vulnerable to sudden climate change, Narisma adds.
Unlike other research studies, which have focused on sudden shifts
in ancient climates or possible future changes, Narisma's survey of
abrupt climate change during the past 100 years offers something else:
a chance to learn how people coped.
"We're interested in the human side mainly," says Narisma. "In the
more recent history, you really get to see what the impacts were on the
current society, and that gives you an idea of the potential impacts in
the future, as well."
Abrupt climate change is generally known as a quick and drastic shift
in climate that makes it difficult for society and the environment to
adapt. In the study, Narisma and her colleagues defined it as a drop in
rainfall to levels at least five percent below the normal average,
which took much less time to settle in than the drought's total length.
They also stipulated that drought conditions had to last at least five
"Since these changes are a switch to a new state - the drought
state - the tendency is for them to persist for awhile," says Narisma.
"It's the combination of abruptness and persistence that gives these
events the potential to have serious consequences."
The scientists pored over precipitation records from 1901 to 2000
and then used wavelet analysis and statistical techniques to pinpoint
climate shifts matching their criteria. In addition to familiar events,
such as the Sahel drought and the Dust Bowl in the Midwestern United
States, they detected lesser-known droughts in virtually all corners of
the globe, including Europe, North America, Australia, China, the
former Soviet Union, the Middle East, Africa, India and Bangladesh.
Although diverse geographically, the 30 affected regions were
mostly arid or semi-arid, says Narisma, a result consistent with other
modeling studies. Most saw rainfall decrease by 10 percent or more
below normal levels, and in all cases drought lasted for at least 10
Why is abrupt climate change of such concern today? Narisma thinks
much of it traces back to the tragedy in the Sahel, whose causes - and
terrible consequences - have been well documented.
"The Sahel and the Dust Bowl had huge impacts," she says. "But we
thought that before we can even begin to analyze the mechanisms behind
these abrupt changes or their potential impacts, we had to ask
ourselves, 'Are there other regions where abrupt changes have
occurred?' We think this study is a major first step in answering these
The paper's other authors are Rachel Licker of the Nelson Institute
and Navin Ramankutty of McGill University in Montreal, Canada.
Source: University of Wisconsin-Madison