Scientific American: Abrupt climate change is not only imminent, it's already here. The rapid dwindling of summer Arctic sea ice has outpaced all scientific projections, which will have impacts on everything from atmospheric circulation to global shipping. And plants, animals and other species are already struggling to keep up with rapid climate shifts, increasing the risk of mass extinction that would rival the end of the dinosaurs. So warns a new report from the U.S. National Research Council. That's exactly why longtime...