Climate Central: Climate scientists don't just rely on computer models and contemporary observations to understand the intimate relationship between CO2 in the atmosphere and environmental conditions on Earth. They also look to the ancient past and two reports in recent days have made it clear how intimate that relationship is. One chronicles an episode 2.4 billion years in the past, when the entire planet was covered in a layer of ice hundreds of feet thick, oceans and all, while global average temperatures hovered...