Scientists studying ancient Antarctic ice are uncovering new details about how Earth's climate has changed over the past 3 million years. By analyzing both the ice and the tiny pockets of air trapped inside it, researchers are building a longer and more complete record of past climate conditions. Two new studies published in the journal Nature reveal a surprising pattern. While the planet gradually cooled over this time, levels of heat-trapping greenhouse gases in the atmosphere declined only slightly. A Long-Standing Climate Mystery For more than a century, scientists have known that Earth was significantly warmer about 3 million years ago. Evidence includes fossils of temperate and subtropical forests found in places like Alaska and Greenland, as well as ancient shorelines along the U.S. East Coast from Georgia to Virginia, showing that sea levels were much higher. However, the reason behind this warm period and the cooling that followed has remained unclear.…