Worldwide demonstrations advocate '350' carbon limit

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 to Seattle, 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 could expect decades of disrupted climate patterns, rising sea levels, drought and famine.

Current concentration

The current concentration of carbon dioxide 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.

While agreeing unabated emissions pose serious risks, some prominent scientists and economists focusing on climate policy said the 350 target was so unrealistic 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 Reilly, an economist at the Massachusetts Institute of Technology. "The message needs to be that there are risks at the current level, and those risks increase the further we push the system."

In a prominent recent study, scientists concluded carbon-dioxide levels almost certainly were headed beyond any levels experienced on the planet in the past 15 million years.

Michael Oppenheimer, a former scientist for the Environmental Defense Fund who is at Princeton University, said it would be a Herculean accomplishment to hold concentrations below 450 parts per million in decades.

But Bill McKibben, the author and activist who founded 350.org, the group coordinating the protests, defended its approach, saying that settling on a goal articulated as a number was the only way to build a "global community" for climate action.

McKibben spent Saturday morning hunkered in an office in downtown Manhattan with 20 volunteers coordinating an accelerating flow of videos and photographs from other time zones that captured demonstrations planned in 170 countries.

Seattle events

Events focusing on the number were held on every continent and from pole to pole. There were a number of events in the Seattle area. Several hundred people met at 3:50 p.m. Saturday at Seattle Center to form a human chain forming the number 350.

Other local events included an information session and rally at the Bainbridge Island farmers market, bike rides, poetry readings and art workshops.

The 350 effort was endorsed by dozens of prominent figures, including James Hansen, a NASA scientist who has been most closely associated with the 350 threshold. He has campaigned for halting emissions from coal by 2030.

Seattle Times staff reporter Nick Perry contributed to this report.