The scientific consensus on global warming is sobering: It's real, it's happening now and carbon-dioxide emissions caused by the burning of fossil fuels are almost certainly responsible. Predicting what the exact effects will be on humanity and the planet's living resources is trickier, but a growing body of evidence suggests they will be profound. The international community generally -- and the European Union in particular -- take the threat very seriously, and most wealthy industrial nations have adopted mandatory limits on carbon emissions under the 2005 Kyoto Protocol. The United States -- the world's largest carbon emitter -- has refused to sign the protocol or adopt mandatory limits, and is seen by other nations as obstructing progress on the issue. Kyoto expires in 2012, and world governments are working on a successor agreement. Many experts say the effort will fail without active U.S. leadership and the participation of major developing-world polluters such as China and India, with potentially dire consequences.

Colin Woodard has reported from more than 40 foreign countries on six continents and lived in Eastern Europe for more than four years. He is the author of Ocean's End: Travels Through Endangered Seas, a narrative, nonfiction account of the deterioration of the world's oceans. He also writes for The Christian Science Monitor and The Chronicle of Higher Education.