In just two hundred years, humans have reversed a long-term cooling trend, pushing the climate clock back by at least 50 million years, an accelerated rate of change that appears to be faster than anything life on the planet has experienced before, say researchers.
The study, published in the Proceedings of the National Academy of Sciences, warned that by 2030, the Earth's climate is expected to resemble that of the mid-Pliocene, going back more than three million years in geologic time.
Without reductions in our greenhouse gas emissions, our climate by 2150 could compare to the warm and mostly ice-free Eocene, an epoch that characterized the globe 50 million years ago.
While our ancestors survived the Eocene and the Pliocene, whether all of humans and the flora and fauna living on Earth currently can adapt to these rapid changes remains to be seen.
"If we think about the future in terms of the past, where we are going is uncharted territory for human society," said lead author Kevin Burke, from the University of Wisconsin-Madison.
"We are moving towards very dramatic changes over an extremely rapid time frame, reversing a planetary cooling trend in a matter of centuries," he added.
During the Eocene, the Earth's continents were packed more closely together and global temperatures averaged 23.4 degrees Fahrenheit (13 degrees Celsius) warmer than they are today. Dinosaurs had recently gone extinct and the first mammals, like ancestral whales and horses, were spreading across the globe.
In the Pliocene, North and South America joined tectonically, the climate was arid, land bridges allowed animals to spread across continents and the Himalayas formed.
Temperatures were between 3.2 and 6.5 degrees Fahrenheit (1.8 to 3.6 degrees Celsius) warmer than they are today.
The study relies on extensive data about climate conditions to probe much deeper into Earth's geologic past and expand those comparisons.
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