The last big ice age ended about 11,000 years ago, and not a moment too soon — it made a lot more of the world livable, at least for humans. But exactly what caused the big thaw isn\'t clear, and new research suggests that a wobble in the Earth kicked off a complicated process that changed the whole planet. Ice tells the history of the Earth\'s climate: Air bubbles in ice reveal what the atmosphere was like and what the temperature was. And scientists can read this ice, even if it\'s been buried for thousands of years. But when it comes to the last Ice Age, ice has a mixed message. The conventional wisdom is that carbon dioxide increased in the atmosphere starting about 19,000 years ago. Then the ice melted. The logical conclusion? The greenhouse effect. But the Antarctic was getting warmer even before CO2 levels went up. So which came first in the Antarctic, warming or CO2? \"The problem is, [the Antarctic is] just one spot on the map, and it\'s a dicey way to slice up global climate change by looking at one point,\" says Jeremy Shakun, a climate scientist, at Harvard University. So he went way beyond the Antarctic — he collected samples of ice, rock and other geologic records from 80 places around the world and found that CO2 levels did, in fact, precede global warming. Here\'s his scenario for what killed the ice age, which was published in the journal Nature this week...