Scientists Now Fear ‘Abrupt’ Global Warming Changes
Just six months after informing the White House that global warming is indeed real, largely the result of human activity and likely to cause adverse effects, the National Academy of Sciences issued an even more disturbing alert Tuesday.
Global warming, the academy reported, could trigger “large, abrupt and unwelcome” climatic changes that could severely affect ecosystems and human society.
Until recently, most discussion of global warming has assumed that change would occur gradually, with average temperatures slowly increasing over the next century.
The idea that large changes in climate could instead occur abruptly and with little warning has been percolating through the climate research community but had remained controversial. The consensus report from the academy indicates that the idea has reached the scientific mainstream.
“We’re reflecting the thinking,” said Richard Alley, a Penn State University climate expert and the report’s lead author. “We’re not driving it.
“We need to deal with this because we are likely to be surprised,” Alley added.
A prime example of what scientists mean when they talk about the possibility of abrupt change involves the Gulf Stream. It is a current of warm water that runs from the Caribbean Sea across the Atlantic Ocean, keeping the climate of northern Europe temperate.
Scientists know that in the past, melting of arctic ice caused a flow of fresh water into the North Atlantic that reversed the Gulf Stream.
Many scientists believe the current could reverse again--over a period of a decade or two, rather than a century--leaving much of Europe far colder than it now is.
“It’s as if climate change were a light switch instead of a dimmer dial,” Alley said.
The possibility of such abrupt changes complicates the task of policymakers in two ways. It could mean that the amount of time available to adjust to climate change is much shorter than government officials have thought. It also increases the uncertainty of predictions, indicating that future climate cannot simply be projected forward in a straight line from the present.
Prolonged Droughts, Extensive Flooding
Scientists cannot yet be certain of any predictions about the Earth’s shifting climate, but many scenarios show climate change could lead to the sudden onset of prolonged droughts, extensive flooding and sudden temperature shifts. Predicting exactly where such changes might occur is even trickier.
New research on abrupt changes in climate is being presented here at the annual meeting of the American Geophysical Union, a gathering of nearly 9,000 Earth and space scientists. There is much talk of crossing crucial climate thresholds, or “kicking the system.”
Part of the reason that climate change until recently has been seen as gradual is that the warming of recent decades has been subtle, with little effect on people’s lives.
“We’re a little spoiled by the last 30 years,” said John M. Wallace, an atmospheric scientist at the University of Washington and the report’s co-author. “Many years, we’re just barely breaking the previous record.”
Scientists who have looked to the past, however, have found repeated instances of sudden and severe change, including the abrupt onset of cooling that drove the Vikings from Greenland in the 14th century and the Dust Bowl drought that devastated the Great Plains during the 1930s. In some areas, temperatures have risen 16 degrees within one decade.
Abrupt climate changes in the past may have decimated forests, speeded the extinction of mastodons and mammoths, promoted the spread of tropical diseases and vastly altered the ocean currents that modify and warm many coastal regions, new research indicates.
Alley and others have used gases within ice cores drilled from the Earth’s remaining ice sheets to produce a detailed record of the Earth’s climate for the last 110,000 years. It reads like a seesaw.
“We’ve gotten better and better records, and we’ve been able to say the changes were really big and really fast and affected a lot of the world at the same time.”
The report, which was commissioned by the U.S. Global Change Research Program, includes a plea for more research on the links between the land, oceans and ice that may trigger abrupt change. The report also suggests that many of today’s models of climate change are too simple because they do not include such changes.
The scientific report does not include policy directives but does suggest that nations begin to take “no regrets” strategies to protect themselves from possible change. These include conserving water to buffer against drought or planting trees to offset the climate-induced loss of vegetation.
“It’s ‘no regrets’ because even if nothing goes wrong, you still like the trees,” Alley said. His report also suggests that poorer nations, with less scientific and economic resources, receive help in planning for change.
Industry Group Issues Warning
But officials of the Global Climate Change Coalition, an industry group, warned against making policy decisions on climate with science so uncertain.
“This really highlights the uncertainties and complexities that remain,” Frank Maisano, a spokesman for the coalition, said of the report.
Other scientists said the possibility of abrupt climate change made it even more important that the federal government establish a reliable climate monitoring system. Federal agencies have been unwilling to spend the estimated $10 million to $15 million needed for the system, said Bruce A. Wielicki, a climate researcher at NASA’s Langley Research Center in Hampton, Va., who was not involved with the new report.
