Ancient Global Warming & What It Might Mean for the Future

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This event, the Paleocene-Eocene Thermal Maximum, is one where the global climate warmed something like 5 to 8 degrees centigrade in a period of 10,000 years. And then it remained that much warmer than it had been for the next 100,000 years, and then the temperature began to decline back towards its original state. And that warming is absolutely associated with a very large release of carbon. into the ocean atmosphere system. So we know what caused it, and what caused it was similar to what's causing global warming today. And I'm studying the plants: what happened to the plants during that period and I'm working mostly in Wyoming because it's a place where rocks of that age were being deposited very rapidly during the Paleocene-Eocene Thermal Maximum. In that part in the world, before the the Paleocene-Eocene Thermal Maximum started, the forests were composed of a mixture of plants that we think of as being sort of deciduous forest trees today, things like Birches and Walnut trees and Dogwoods but also mixed with things like Dawn Redwood as a very common kind of tree, and Palm trees, which of course grow mostly farther south. So that was kind of a typical forest type for many millions of years prior to the beginning of the Paleocene-Eocene Thermal Maximum.

Then in a very short period, in about 10,000 years, those plants are locally extirpated. We find no record of them, and they're replaced by plants that have living relatives that grow mostly in dry topical forests today, so these are plants that wouldn't be familiar to most people in the continental U.S. because they don't grow here anymore, but they are groups of plants that tolerate very warm conditions and also a pretty good dry season. More like the kinds of plants that you might find in a dry forest in Costa Rica or southern Mexico, and those plants are very abundant for the 100,000 year period of the PETM and then towards the end of that period as the climate begins to cool again, we see the return of what had been the native flora, the Walnuts and the Birch relatives and the Dogwood relatives and the Dawn Redwoods return to the area, so they must have survived some place because many of them return, though some of them don't. So we probably had some extinctions associated with that warming event, but we also had a lot of just movement of species.

They disappeared in one area, they couldn't survive there, they survived somewhere else and then they returned. The paleontological record gives us a way of studying climate change events that have already happened, where we can see what happened, we don't have to wait to see whether we're right. We can make a predication and then consult the archive of the planet's history in the rock record and in the fossil record and find out what actually did happen. It's the great advantage of working in the past. .

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