"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."