Washington Post: Activists around the globe are staging thousands of demonstrations Saturday aimed at prodding policymakers to cut carbon concentrations to below their current levels, at a time when many U.S. officials and experts are trying to dampen expectations for international climate talks that culminate in Copenhagen in December. The more than 4,500 events in 173 countries include such activities as children racing through the main square in Addis Ababa, Ethiopia, to Chinese university students …