In the Arctic, the summer ice is melting, making it hard for polar bears and their cubs to survive. Why is the world getting warmer? The heat of the sun is trapped by the "greenhouse" gases that surround Earth-carbon dioxide, methane, nitrous oxide, and water vapor. If there is just the right amount of these trapped gases, the air is warm enough for plants, animals, and people to thrive. But, now there is too much greenhouse gas, especially carbon...

The Arctic has reacted more quickly and dramatically to global warming than many had anticipated. Scientists are urgently trying to predict just how the Arctic will change and how those changes will in turn affect the rest of the planet. But plenty of other people, driven by profit rather than data, are interested as well. The riches of the world's last virgin territory have spurred the reawakening of old geopolitical rivalries. The United States,...