Purdue Climate Change Research Center

Hothouse Earth: World without Ice

Inuit Johnny Issaluk holds a recent photo of a South Carolina swamp. That’s what his home, near the Arctic Circle on Baffin Island, would have looked like 56 million years ago, when summer water temperatures at the North Pole hit 74°F.otograph by Ira Block

Central to understanding, predicting and mitigating the impact of climate change is understanding how the Earth’s climate changed in the past. The Paleocene-Eocene  Thermal Maximum (PETM) was a period in Earth’s history (around 56 million years ago) that is characterized by an exceptionally large release of carbon into the atmosphere and the highest global temperatures of the Cenozoic Era; it was a “world without ice.” How much carbon was transferred to the atmosphere? Scientists estimate that it would be roughly the amount released if we burned through the Earth’s entire reserve of conventional fossil fuels (oil, coal, natural gas). The PETM lasted more than 150,000 years, until the excess carbon was reabsorbed. A recent (October 2011) National Geographic article, “Hothouse Earth,” by Robert Kunzig explores this time in Earth’s history and considers how it relates to current climate warming. An excerpt highlighting the research of PCCRC associate director and professor, Matthew Huber, is given below:

Matt Huber, a climate modeler at Purdue University who has spent most of his career trying to understand the PETM, has also tried to forecast what might happen if humans choose to burn off all the fossil fuel deposits. Huber uses a climate model, developed by the National Center for Atmospheric Research in Colorado that is one of the least sensitive to carbon dioxide.  The results he gets are still infernal. In what he calls his "reasonable best guess at a bad scenario" (his worst case is the "global-burn scenario"), regions where half the human population now lives become almost unbearable. In much of China, India, southern Europe, and the United States, summer temperatures would average well over 100 degrees Fahrenheit, night and day, year after year.

Climate scientists don't often talk about such grim long-term forecasts, Huber says, in part because skeptics, exaggerating scientific uncertainties, are always accusing them of alarmism. "We've basically been trying to edit ourselves," Huber says. "Whenever we see something really bad, we tend to hold off. The middle ground is actually much worse than people think.

"If we continue down this road, there really is no uncertainty. We're headed for the Eocene. And we know what that's like."

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