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Paleocene eocene thermal maximum petm for global warming

Gas, Probably Methane, Is Seeping From 570 Sites off the East Coast One of the best ways to explore how human-induced global warming will affect Earth in future is to study the way our planet responded to climate change in the past.

Many researchers think the Paleocene—Eocene Thermal Maximum PETM 55 million years ago is particularly relevant to our current situation, because it also involved a massive injection of carbon into the atmosphere that led to spiraling global temperatures. Not all researchers have been convinced we have much to learn from the PETM, though.

Paleocene-Eocene Thermal Maximum

Some studies suggested the climate back then changed far more slowly than it is changing now, with atmospheric carbon building up gradually over about 20,000 years, perhaps because of the slow release of volcanic gases. Still other studies concluded that the PETM changes occurred far too rapidly for comparisons with our present situation.

Ancient Climate Events: Paleocene Eocene Thermal Maximum

A study last year suggested that atmospheric carbon soared within just a few yearsmaybe due to a massive influx of carbon from a comet impact. Researchers led by Gabe Bowen at the University of Utah drilled an 820-foot core out of the ground near Powell, Wyoming. Their sample cuts through ancient soils—now turned to stone—that formed before, during and after the PETM.

The soil layers contain thousands of carbonate nodules, each of which holds varieties of carbon that reflect the composition of the atmosphere at the time the nodule formed.

Paleocene-Eocene Thermal Maximum (PETM)

By measuring these varieties, or isotopes, within each nodule, the researchers could build a picture of how carbon was added to the ancient atmosphere. Gray, roundish nodules of carbonate dot these sediment cores drilled from northern Wyoming. But perhaps the most interesting finding was that the PETM seems to have involved two separate carbon pulses. A few thousand years before the PETM got into full swing, there was a short-lived period of global warming.

Atmospheric carbon levels shot up over the course of perhaps 1500 years, stayed high for a millennium or so then rapidly returned to normal. After another couple of millennia, carbon levels shot up again—but this time they stayed high for tens of thousands of years, causing the true PETM event.

And because there were two distinct pulses of warming, the comet scenario looks weak too.

Ancient Earth Warmed Dramatically After a One-Two Carbon Punch

William Clyde, University of New Hampshire Instead, the authors argue that a release of methane from deposits below the seafloor would explain both the rate of change and the curious double pulses. This methane is normally safely locked away in a solid form called methane clathratebut even an undersea landslide might have been enough to destabilize an area of the seafloor and unlock a vast clathrate deposit.

That kind of event could have triggered the short-lived pulse of global warming before the main PETM event. Warmer oceans can themselves destabilize clathrate deposits, which might explain where the second carbon pulse came from, says Wing.

When global warming made our world super-hot

If this scenario is correct, it makes the PETM even more relevant to today—the oceans are warming up once more, and clathrate deposits below the seafloor are again beginning to destabilize.

Methane clathrates released from sediments in Russia's Lake Baikal seem to bubble through the ice. Other researchers say they have seen hints of the two pulses in their earlier studies.

Even so, not everyone is convinced that the latest evidence sounds the death knell for previous warming scenarios. The world was a very different place 55 million years ago. For instance, even before the PETM, the planet was already so warm that there were no ice caps.