Wallace S. Broecker of Columbia University's Lamont-Doherty Earth Observatory speaks on the "greenhouse future" in the David L. Call Alumni Auditorium of Kennedy Hall July 22. Frank DiMeo/University Photography
In what may be geochemist Wallace S. Broecker's favorite metaphor, Earth's climate system is a fearsome, untamed animal that mankind had better be careful about messing with.
"We're poking the climate system by adding greenhouse gases" like carbon dioxide, the Columbia University scientist said in a July 22 Summer Sessions lecture. "Will poking this angry beast cause it to lash out?" he asked the large Call Auditorium audience in Kennedy Hall, displaying a homemade drawing of the metaphorical "beast" incarnate.
Broecker doesn't know the answer to his question, he admitted, nor does anyone else. But he doesn't want the world to find out the answer by continuing to release tremendous amounts of greenhouse gases into the atmosphere. These gases, emitted when fossil fuels are burned, could alter the behavior of the "beast," unleashing radical changes in temperature and rainfall, he said.
The conviction that greenhouse gases potentially promise climate damage has led Broecker to offer some unorthodox technical solutions (pumping carbon dioxide to the bottom of the ocean) and unpalatable policy suggestions (increasing gasoline taxes "dramatically").
But the conviction is based on a patchwork of evocative evidence that Broecker pieced together last year in the Geological Society of America's "GSA Today" newsletter, the science editor of which is Suzanne M. Kay, Cornell associate professor of geological sciences. Broecker's lecture was a live, though harder-to-follow, version of the article he published, "Will Our Ride Into the Greenhouse Future Be a Smooth One?"
The question is directed at those who have argued lately that global warming will proceed gradually and be of minor consequence; to date, the effect of greenhouse gases on temperature has been smaller than predicted.
Broecker's evidence, however, compels one to see some rough terrain ahead. That's because geological data indicate past climate changes have been anything but gradual, he said.
Studies of Greenland ice and California sediments point to rapid shifts in temperature and rainfall that happened in a matter of decades or less. So it is best to conceptualize the climate system as having several "modes of operation," Broecker said. Rather than changing slowly, as some would have it, Broecker said that climate can switch from one state to another abruptly.
"Whatever this phenomenon is, it's global and it's big," he said. In Broecker's view, likely causes of climate shifts are changes in patterns of ocean currents, which carry heat to and from continents, and the amount of atmospheric water vapor, which increases with the level of carbon dioxide and raises temperature.
Fiddling with these factors is not something Broecker recommends. The ever-present danger is that a different climate state than what exists now might be far less amenable to humanity. Since no one understands exactly how the climate system works, why take the chance that adding such large quantities of greenhouse gases to the atmosphere might trip some unknown threshold level and provoke a climate shift?
"We get 300 pounds of carbon dioxide from one gas tank. What kind of risk are we running by continuing this way of life?" Broecker asked.
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