What The Past Teaches Us About the FutureMaking predictions is hard, especially about the future. But we still have to try, because our best projections, even if they are flawed, are still better than whistling in total darkness. And the best way to make informed projections about the future is to look at the past and see what happened over time when different things happened.
Global warming is one such thing we can learn about by studying the past. There are differences, of course, since in the past most instances of warming took place over much longer periods and were always from natural causes, while now the warming is much faster and is anthropogenic. But there's still a lot to be learned.
A recent study published in Nature Geoscience looked at Antarctica's past climate:
By examining plant leaf wax remnants in sediment core samples taken from beneath the Ross Ice Shelf, the research team found summer temperatures along the Antarctic coast 15 to 20 million years ago were 20 degrees Fahrenheit (11 degrees Celsius) warmer than today, with temperatures reaching as high as 45 degrees Fahrenheit (7 degrees Celsius). Precipitation levels also were found to be several times higher than today. [...]
The peak of this Antarctic greening occurred during the middle Miocene period, between 16.4 and 15.7 million years ago. This was well after the age of the dinosaurs, which became extinct 64 million years ago. During the Miocene epoch, mostly modern-looking animals roamed Earth, such as three-toed horses, deer, camel and various species of apes. Modern humans did not appear until 200,000 years ago.
Warm conditions during the middle Miocene are thought to be associated with carbon dioxide levels of around 400 to 600 parts per million (ppm). In 2012, carbon dioxide levels have climbed to 393 ppm, the highest they've been in the past several million years. At the current rate of increase, atmospheric carbon dioxide levels are on track to reach middle Miocene levels by the end of this century.
That last part is important. This huge warming in Antarctica was believe to have been caused by CO2 levels around 400 to 600 PPM, while we're currently at 393 PPM. We're getting close... Of course, there are other factors, but the CO2 composition of the atmosphere certainly is one of the most important ones.
Via Science Daily