evidence: That, at least, is the story told by a new paper published in Nature on April 5 that reconstructs the end of the last ice age. Researchers examined sediment cores collected from deep beneath the sea and from lakes as well as the tiny bubbles of ancient air trapped inside ice cores taken from Antarctica, Greenland and elsewhere. (Scientific American is part of Nature Publishing Group.) The research suggests that—contrary to some prior findings—CO2 led the prior round of global warming rather than vice versa, just as it continues to do today thanks to rising emissions of CO2 and other greenhouse gases. [...] Of course, modern global warming stems from a clear cause—rising levels of CO2 (and other greenhouse gases) from fossil fuel burning, cutting down forests and other human activities. And, in the past rising CO2 levels at the very least magnified global warming, ushering in the relatively balmy, stable climate sometimes called the "long summer" that has allowed human civilization to flourish. Humanity has now raised global CO2 levels by more than the rise from roughly 180 to 260 ppm at the end of the last ice age, albeit in a few hundred years rather than over more than a few thousand years. "The end of an ice age, you have a sense in your bones what that means: a big, significant change for the planet," Shakun says. "It's a tangible example of what rising CO2 can mean for the planet over the long-term."