Taking a dip in the Arctic Ocean (Image: Morgan Scheweitzer)
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Pack your cozzie, we’re going to the Arctic. It’s going to be hot and steamy. There will be palm trees and crocodiles.
This is the Paleocene-Eocene thermal maximum, or PETM, of 55 million years ago. For the past few million years, Earth has gradually been getting hotter and hotter and is now on the verge of a planetary heatwave the likes of which have rarely been seen.
Even before the mercury peaks, it’s pretty toasty. The poles are essentially ice-free, the deepest reaches of the oceans are 8 °C warmer than today, sea levels are roughly 70 metres higher and there are crocodile-like champsosaurs in the Arctic Ocean. The fact that they thrived so close to the North Pole means water temperatures must have been no less than 5 °C even in the permanent darkness of winter. Today’s average winter temperatures at the North Pole hover around -34 °C. You may also catch a glimpse of the hippopotamus-like Coryphodon in the warm swampy forests along the ocean shores.
Fast-forward a few million years and you will see freshwater turtles, which seems bizarre until you consider that the Arctic basin is almost entirely enclosed by land. River water streaming off the land is floating on top of the heavier saltwater, forming what may have been one of the biggest lakes the planet has ever seen. Great for swimming, too, as the water is a pleasant 23 °C.
The other end of the world would also have been experiencing swimsuit weather. “At the peak of the PETM you get ferns on Antarctica, so that’s seriously toasty,” says Kate Littler of the University of Exeter in the UK.
All this warmth is the result of a big rise in greenhouse gases in the atmosphere, though no one knows what caused it. One possibility is intense volcanic activity, another that deposits of solid methane sitting at the bottom of the sea melted, releasing their load in one great gassy belch. Or maybe Antarctica’s permafrost thawed, releasing a big puff of CO2.
Either way, after millions of years of gradual warming, temperatures suddenly jumped by at least 5 °C in just 20,000 years. It is a tough time for life on the sea floor, where an extinction was going on, but life on land seems to be flourishing. If you drop down in the lush forests of South-East Asia, you might be lucky enough to spot a new class of mammal that has only just evolved: the primates. They look a bit like tarsiers or bush babies, eat insects, and in the very, very distant future will give rise to the only animal to have occupied all four corners of the planet: us.
Our species is also the only one with the power to trigger something even greater than the PETM: a similar amount of warming but 100 times faster. The PETM is firmly in Earth’s past – temperatures returned to normal after about 200,000 years – but some say it is a window onto the future.
Read more: “A time traveller’s guide to Earth”
This article appeared in print under the headline “Super-greenhouse”
