New perils of global warming described Wild fluctuations in climate feared

July 15, 1993|By Los Angeles Times

Evidence frozen in a core of ice from Greenland suggests that global warming, rather than a slow, steady phenomenon, could trigger wild climate fluctuations in the next 100 years.

Global weather patterns have been remarkably consistent since the last ice age 10,000 years ago, so scientists came to believe that a stable climate was the norm for interglacial periods.

But evidence from a slender ice core pulled out of the Greenland ice sheet last summer indicates this was not always be the case -- and, scientists fear, it may not be in the future, if pollution changes the atmosphere enough.

"Previously we just assumed the last warm period was very similar to the present period and just stable like it is now," Eric Wolff of the British Antarctic Survey told Reuters. "Finding that it wasn't raises fears about what could happen if it gets warmer."

Dust and gas trapped in the ice suggest that the last interglacial period more likely was a chaotic jumble of climatic swings apparently caused by radical changes in atmospheric gases and Atlantic Ocean circulation patterns.

The 40 scientists on the Greenland Ice Core Project, whose report appears in today's issue of the journal Nature, said they were troubled by the news because that last interglacial period, about 120,000 years ago, is often considered much like what today's world would be if it were slightly warmer.

If the global-warming theory proves true and air pollution causes Earth to gain several degrees in average temperature, they speculated that the planet could experience a similar period of wild climatic swings between today's temperate weather and near-ice age conditions. Each period could last from a few decades to a few millenniums.

Mr. Wolff and his colleagues retrieved the ice sample on which they based their conclusions by drilling nearly 10,000 feet into the ice sheet covering the island. Confirmation of this hypothesis could come from a second ice core now being drilled near the first, the team of European and U.S. scientists said.

Concern about a modern warming trend grows out of evidence from the ice core indicating that when temperatures in the interglacial period rose an average of 3.8 degrees Fahrenheit above current levels, they started fluctuating by as much as 18 degrees in as little as one to two decades.

In the past, scientists had predicted that the release of carbon dioxide and other pollutants -- most often from the burning of gasoline and other fossil fuels -- could raise global temperatures by 3 degrees to 9 degrees Fahrenheit over the next 100 years. But some scientists have challenged that figure as too high, and a small minority even question whether pollution is having a measurable effect on the climate at all.

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