Bloomberg: A warm period 3 million years ago, when forests dotted the Arctic region and sea levels were 80 feet (24 meters) higher, is providing clues about how heat-trapping greenhouse gases can boost global temperatures, scientists said. Fossils from the mid-Pliocene epoch reveal a far warmer planet with a concentration of carbon dioxide in the atmosphere of only about 5 percent more than exists today, said Harry Dowsett, a U.S. Geological Survey scientist. A reconstruction of the climate 3 …