Small Shift Big Change Climate*

Scientists suggest small shifts affect global climate

Usha Lee McFarling

Los Angeles Times

Saturday, July 14, 2001

As climate scientists gathered this week in Amsterdam, Netherlands, to discuss new research on global warming, a disquieting idea has been gaining currency the possibility that small shifts in global temperature could lead to sudden and abrupt climate changes.

What makes such projections important is not their likelihood, which is uncertain, although a growing number of scientists believe sudden changes in climate are a possibility. Instead, the chief significance for policymakers and the public lies in what the new research suggests about scientific uncertainty and risk.

Until recently, much of the climate debate has centered on whether global warming is occurring at all. Most climate models had assumed a slow, steady increase in temperature and forecast gradual changes that would have gradual effects.

But newer, more sophisticated models suggest that the Earth's climate system is "nonlinear" -- in other words, small changes can have large effects on everything from ocean and land temperatures to drought and monsoon patterns, ice caps and tropical rain forests.

An increasing number of experts publicly are beginning to discuss -- and personally fear -- changes that are far more dramatic, and potentially faster, than previously discussed.

For example, one projection that has attracted considerable attention from climate scientists is that melting Arctic ice could cause a flow of fresh water into the North Atlantic that would shut down the Gulf Stream this century. That warm current moderates Europe's climate, and turning it off would make a swath of land from London to Stockholm miserable, if not uninhabitable.

"Sometimes very small, innocent changes can trigger huge changes," said Will Steffen, executive director of the Sweden-based International Geosphere-Biosphere Program (IGBP), which is coordinating the conference in Amsterdam. "Sometimes you hit it with a hammer and nothing happens."

In the global warming debate, a chief argument advanced by industry representatives, joined by Bush administration officials and some scientists, is that the United States and its allies should not rush into potentially costly measures to head off possible climate change because our knowledge of the subject is limited.

Scientific uncertainty

Many scientists, however, say that argument is backward. The possibility of sudden, dramatic climate shifts means that, although there is a risk that current models are too pessimistic, there is also a substantial risk that they are too optimistic.

"Scientific uncertainty goes both ways," said Robert Watson, chief scientist at the World Bank and chairman of the United Nations' Intergovernmental Panel on Climate Change.

A prominent advocate of the go-slow school of thought is Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics, an expert on how the sun and its heat output have varied through time.

Baliunas' research is funded by federal agencies, such as NASA, but she accepts industry funding to "travel around and speak." She argues that computer models are unreliable, exaggerate warming trends, fail to adequately take into account natural fluctuations in the Earth's temperature and do not explain why no warming has been seen in the upper atmosphere.

"The best evidence says [climate change] is slow to work, so we have a window of opportunity," she said.

As advocates of that school of thought note, many climate scientists a decade ago feared that global warming could cause a catastrophic melting of the massive West Antarctic ice sheet. Such an event would release huge amounts of water into the seas, devastating many of the world's highly populated, low-lying coastal areas.

Recent studies, though, suggest that the Antarctic ice cap is stable -- and actually growing as more precipitation falls over the frozen continent.

Tiny shifts, big results

Other scientists, including Watson, argue that because knowledge is uncertain, it is crucial to begin cutting emissions of carbon dioxide and other so-called greenhouse gases to slow the rate of climate change.

Paul Crutzen, an atmospheric chemist working in Germany who won the Nobel Prize for explaining the hole in the atmosphere's ozone layer, makes a similar point. There is simply not enough room to take chances with the climate, he says.

What climate watchers fear most are shifts that could "kick the climate system" into an entirely new state, said Berrien Moore III, chairman of the IGBP. That could cause "unpredictable consequences with cascading effects."

Such shifts have occurred in the past. A tiny change in the Earth's orbit, for example, altered precipitation and temperature patterns enough to convert what was once a large chunk of fertile African savanna into today's Sahara Desert.

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