As the Intergovernmental Panel on Climate Change has shown, carbon dioxide levels in the atmosphere are higher than at any time in human history. The last time that atmospheric CO2 concentrations reached today’s level – about 412 parts per million – was 3 million years ago, during the Pliocene Epoch.
Because the oceans were warmer and there were no large ice sheets in the Northern Hemisphere, sea levels were 30 to 50 feet (9 to 15 meters) higher around the globe than they are today. Coastlines were far inland from their current locations. The areas that are now California’s Central Valley, the Florida Peninsula and the Gulf Coast all were underwater. So was the land where major coastal cities like New York, Miami, Los Angeles, Houston and Seattle stand.
Warmer winters across what is now the western U.S. reduced snowpack, which these days supplies much of the region’s water. Today’s Midwest and Great Plains were so much warmer and dryer that it would have been impossible to grow corn or wheat there.Yahoo The Arctic hasn’t been this warm for 3 million years – and that foreshadows big changes for the rest of the planet