Earth's hot past could be prologue to future climate

[caption] A pair of chinstrap penguins in Antarctica. New research suggests that, if carbon dioxide emissions continue on their current trajectory, Earth may return to a climate of tens of millions of years ago when the Antarctic ice sheet did not exist.
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[A new study] warns that, if carbon dioxide emissions continue at their current rate through the end of this century, atmospheric concentrations of the greenhouse gas will reach levels that existed about 30 million to 100 million years ago, when global temperatures averaged about 29 degrees Fahrenheit (16 degrees Celsius) above pre-industrial levels.