Ancient Global Warming Triggers Found

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April 26, 2007 — The rifting apart of the Earth’s crust to create the northeast Atlantic Ocean may have been triggered a mysterious past global warming episode not unlike the human-made climate crisis unfolding today. And just like the today’s climate change, the 55-million-year-ago global warming started with fossil fuels, of a sort.

The fuels weren’t necessarily coal or oil and they weren’t, of course, being burned in engines at the end of the Paleocene epoch. Instead, it was carbon-rich sediments that were baked in place in the ground by the intrusion of a lot of molten rock and an awful lot of heat into the landmass that comprised both Europe and Greenland at the time.

That baking created at least several hundred giga-tons of greenhouse gases which were exhaled from the ground and into the atmosphere, explains Michael Storey, a geochronologist at Roskilde University Center in Roskilde, Denmark.

That may have been just enough to warm the oceans and knock over the next climatic domino: vast stores of frozen methane hydrate in cold sea beds. When these thawed and bubbled up they added a few thousand more giga-tons of carbon into the atmosphere and heated up the global climate to what scientists call the Paleocene-Eocene Thermal Maximum (PETM).

At the height of the PETM, sea surface temperatures in the oceans rose 9 degrees F (5 degrees C) in the tropics and 11 degrees F (6 degrees C) in the Arctic. The oceans became more acidic and 30 to 50 percent of the sea floor life went extinct.

"The two outstanding questions about the event are what triggered it and where did all the greenhouse gases come from," said Storey, who’s paper on the matter appear in the April 27 issue of the journal Science.

To answer the first question, Storey and his colleagues Robert Duncan and Carl Swisher gathered volcanic rock specimens from the now distant edges of what was once a united Denmark and Greenland, and tested their ages to see if that matched up with the timing of the PETM.

They used a natural clock in the minerals created by different concentrations of argon-40 and argon-39 to date the rocks and found they were about the same age and fit well into the timing of the PETM, which has been identified independently from marine sediments.

"The dating allows us to link the (PETM) to what we see as a massive surge of volcanic activity," Storey told Discovery News. "It was an enormous surge." And it left behind more than 2 million cubic miles (10 cubic km) of basalt.

"This is almost perfect because you have that as a trigger," says paleo-oceanographer James Zachos of the University of California at Santa Cruz. "The (climate) system is just perched on the edge and you just need a little kicker."

After that kick, there’s plenty of methane hydrate to complete the process and keep warming things up, Zachos said.

Today there are estimates to be between 2,000 and 10,000 giga-tons of methane hydrate buried in cold ocean sediments. Humans currently release between six and seven giga-tons of carbon into the atmosphere each year.

The big unknown today is exactly how much carbon it takes to warm things up to the point that the methane hydrate breaks loose and takes the matter entirely out of human hands.