National Geographic : 2011 Oct
• ions to make more calcium carbonate. e pro- cess, called weathering, happens all the time, but it happened faster during the PETM, because the climate was hotter and the rain more acidic. Gradually the rain scrubbed the added CO from the atmosphere, and eventually it wound up in limestone at the bottom of the sea. e climate slowly returned to its previous state. "It's just like with fossil fuels today," Zachos says. "We're tak- ing what took millions of years to accumulate and releasing it in a geologic instant. Eventually the system will stick it back into rock, but that will take hundreds of thousands of years." 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 o 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 three centuries' worth of human-caused emis- sions at the current rate. ough the data aren't conclusive, most scientists assume the PETM release was slower, taking thousands of years. However fast the carbon was released, it would have taken far longer for geologic processes to remove it. As the carbonates on the sea oor dis- solved, counteracting the acidi cation, the ocean was able to absorb more CO , and within a few centuries or millennia of the sudden release, the atmospheric CO peak had passed. Meanwhile CO was also dissolving into rain droplets, which leached calcium from rocks on land and washed it to the sea, where it combined with carbonate Using a technology that might forestall a warmer epoch, test tanks at an American Electric Power plant in West Virginia cap- tured a fraction of the plant's CO . But until the government sets limits on emissions, the company has shelved the costly project.