By ANDREW C. REVKIN
Campaigners against global warming have drawn on an arsenal of visually startling tactics over the years, from posing nude on a Swiss glacier to scaling smokestacks at coal-fired power plants.
On Saturday, they tried something new with the goal of prodding countries to get serious about reaching an international climate accord: a synchronized burst of more than 4,300 demonstrations, from the Himalayas to the Great Barrier Reef, all centered on the number 350.
For some prominent climate scientists, that is the upper limit for heat-trapping carbon dioxide in the atmosphere, measured in parts per million. If the gas concentration exceeds that for long, they warn, the world can expect decades of disrupted climate patterns, rising sea levels, drought and famine. The current concentration is 387 parts per million.
Organizers said their goal, in the prelude to global climate talks in Copenhagen in December, was to illustrate the urgent need to cut emissions by pointing out that the world passed the 350 mark two decades ago. Yet while agreeing that unabated emissions pose serious risks, some prominent scientists and economists focusing on climate policy said the 350 target was so unrealistic that the campaign risked not being taken seriously — or could convey the wrong message.
“Three-fifty is so impossible to achieve that to make it the goal risks the reaction that if we are already over the cliff, then let’s just enjoy the ride until it’s over,” said John M. Reilly, an economist at M.I.T.
“The message needs to be that there are risks at the current level, and those risks increase the further we push the system,” he said.
In a prominent recent study, scientists concluded that carbon dioxide levels were almost certainly headed beyond any levels experienced on the planet in the last 15 million years.
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