Geologists and paleo-climatologists know that in the past the Earth's temperature has been substantially warmer than it is today, and that this warming has occurred under purely natural circumstances. Until we can say precisely how much of the current global… — Greg Benson Copy Share Image
Several times in Earth's history, rapid global warming occurred, apparently spurred by amplifying feedbacks. In each case, more than half of plant and animal species became extinct. New species came into being over tens and hundreds of thousands of years.… — James Hansen Copy Share Image
