Yale University’s recently opened Kroon Hall is a state-of-the-art model of where the green building movement is headed. Yet even this showcase for renewable energy highlights the difficulties of creating a building that is 100 percent carbon neutral.

The clearing of Indonesia’s rain forest for palm oil plantations is having profound effects threatening endangered species, upending the lives of indigenous people, and releasing massive amounts of carbon dioxide into the atmosphere.

Scientists have long believed that thawing permafrost in Arctic soils could release huge amounts of methane, a potent greenhouse gas. Now they are watching with increasing concern as methane begins to bubble up from the bottom of the fast-melting Arctic Ocean.