Paleontologists and geologists are looking to the ancient past for clues about whether global warming will result in mass extinctions. What they're finding is not encouraging.

The world's greatest lake, holding 20 percent of the planet's surface fresh water, has long remained one of the most pristine places on earth. Now, as Russia's economy booms and its climate warms, the Siberian lake faces new threats.

In the discussion of the global food emergency, one underlying factor is barely mentioned: The world is running out of water. A British science writer, who authored a major book on water resources, here explores the nexus between water overconsumption and current food shortages.

The burgeoning amount of carbon dioxide in oceans is affecting a lot more than coral reefs. It is also damaging marine life and, most ominously, threatening the future survival of marine populations.

Quietly and somewhat surprisingly, green groups are cropping up throughout China and are starting to have an impact. In the first in a series on Chinese environmentalists, journalist Christina Larson visits with Zhao Zhong, who is leading the fight to save the Yellow River.