The inception of the "Keeling Curve," a history of atmospheric carbon dioxide levels, marked a key moment in American science history. The record began in March, 1958 at a small observatory on the top of Hawaii's Mauna Loa.

Emperor penguins can flourish in locales where few other animals roam. But scientists now wonder if they can adapt to a new threat: climate change.

An ancient global warming episode drastically changed the planet. Life on Earth needed 200,000 years to recover. What we're headed for in the next century could be even bigger.