From: ANDREW C. REVKIN, The New York Times
Published March 29, 2009 10:25 AM

Among Climate Scientists, a Dispute Over Tipping Points

"The climate is nearing tipping points," the NASA climate scientist James E. Hansen wrote in The Observer newspaper of London. "If we do not change course, we’ll hand our children a situation that is out of their control."

The resulting calamities, Dr. Hansen and other like-minded scientists have warned, could be widespread and overwhelming: the loss of untold species as ocean reefs and forests are disrupted; the transformation of the Amazon into parched savanna; a dangerous rise in sea levels resulting from the melting of the mile-high ice sheets in West Antarctica and Greenland; and the thawing of the Arctic tundra, which would release torrents of the greenhouse gas methane into the atmosphere.

But the idea that the planet is nearing tipping points — thresholds at which change suddenly becomes unstoppable — has driven a wedge between scientists who otherwise share deep concerns about the implications of a human-warmed climate.

Environmentalists and some climate experts are increasingly warning of impending tipping points in their efforts to stir public concern. The term confers a sense of immediacy and menace to potential threats from a warming climate — dangers that otherwise might seem too distant for people to worry about.

But other scientists say there is little hard evidence to back up specific predictions of catastrophe. They worry that the use of the term "tipping point" can be misleading and could backfire, fueling criticism of alarmism and threatening public support for reducing greenhouse gas emissions.

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"I think a lot of this threshold and tipping point talk is dangerous," said Kenneth Caldeira, an earth scientist at Stanford University and the Carnegie Institution and an advocate of swift action to reduce carbon dioxide emissions. "If we say we passed thresholds and tipping points today, this will be an excuse for inaction tomorrow," he said. While studies of climate patterns in the distant past clearly show the potential for drastic shifts, these scientists say, there is enormous uncertainty in making specific predictions about the future.

Article continues: http://www.nytimes.com/2009/03/29/weekinreview/29revkin.html

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