February 15, 2013

56 Million Years Ago, the Earth Was Warmer Than It Is Today. ~ Julie Freydlin

Photo: Phil Plait

Sandy, Irene, Katrina…hurricanes are fast becoming household names and have many people worried over the connection between extreme weather and the amount of greenhouse gases people are pumping into the atmosphere.

No one can predict for sure what will happen decades or centuries from now as such gas concentrations increase. But scientists have a pretty good picture of what did happen in the past; greenhouses gases were released into the atmosphere in massive amounts at least once before—around 56 million years ago.

Sixty million years ago the earth was already at least a few degrees warmer than it is today.

At that point, there was little or no ice at the poles, and alligators were probably swimming in areas where polar bears roam today. But four million years later (56 million years ago) the world was about to undergo major change—in an event called the Paleocene-Eocene Thermal Maximum (PETM). During the PETM, massive amounts of greenhouse gases, probably in the form of methane that later oxidized to carbon dioxide, were spewed into the atmosphere.

Scientists are still uncertain what caused the release, but they do know that it happened in a short time period—probably a few thousand years. This CO2 explosion is similar to the one being produced by people now, which is why it is of such interest to scientists.

“The amount of carbon released in the PETM is thought to be similar to if we burn all of our fossil fuel reserves,” says Phillip Jardine, who is studying the effects of PETM on plants as part of the Bighorn Basin Coring Project (BBCP) in Wyoming.

Together with the massive carbon release, the PETM is marked by another distinct feature—a rise of five to eight degrees Celsius in global temperatures, a rise scientists say would be catastrophic for human civilization today.

“The PETM is especially valuable to climate scientists to understand better how the climate system actually works, and especially how releasing carbon impacts on temperatures,” says Dr. Jardine. “The PETM studies have shown the link between the two very nicely, with rapid shifts in both the carbon cycle and global temperatures.”

So, instead of trying to predict what happens when massive amounts of CO2 are released into the atmosphere, scientists can look at the past and see what actually did happen.

View of Bighorn Basin in Wyoming, showing the sediments which scientists drill through. Photo courtesy of Phillip Jardine.

The BBCP is a collaboration of 30 scientists around the world and aims to find new evidence about changes in the carbon cycle, climate, and plant life during the PETM. In August of 2011, scientists completed drilling for the project and extracted cores—columns of earth. Like the cross section of a layered cake, these 250-meter columns have colored bands of earth, which reveal Earth’s history spanning hundreds of thousands of years. About 50 meters of the cores’ sediment was formed during the PETM.

Scientists are still analyzing data from the project. However, they do know that many plant types shifted their geographic ranges, sometimes by thousands of kilometers, in response to the massive climate changes of the period.

“Many of the plant types that were present during the late Paleocene (birches, walnuts, elms, bald cypress) either moved out or became rare during the PETM,” says Dr. Jardine. Seeking cooler temperatures, these plants probably migrated to higher latitudes. “We see movements to higher latitudes and that is consistent with an interval of global warming.”

Previous studies show that ocean temperatures also rose during this time—by as much as eight degrees in some areas. Ocean waters also became more acidic and Bighorn Basin was frequently flooded by overflowing rivers.

The effects of massive carbon release are not limited to the past.

If people continue to produce carbon dioxide at the current rate, in less than 300 years, the levels of CO2 could reach levels last present on Earth 50 million years ago.

It took over 150,000 years for all that carbon dioxide to be reabsorbed and for Earth to return to pre-PETM conditions, a time scale which would be catastrophic for people.

“The PETM does show that the aftereffects can last far longer than the period of carbon release, and on a human time scale this could result in very different climatic conditions for many, many generations to come,” says Jardine.

Written by Julie Freydlin, from our friends at mongabay.com.


Mongabay.com provides news, information and analysis on environmental issues, with a special focus on tropical rainforests. The web site features more than 70,000 photos and has a section about forests for children available in nearly 40 languages.


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Assistant Ed.: Jayleigh Lewis

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