What started out as a moderate global warm-up about 55 million years ago triggered a massive injection of greenhouse gases into the atmosphere that sent temperatures skyrocketing, a new study says.
The finding suggests that today's temperature rise may just be priming the planet for a carbon belch of epic proportions.
"You've got these feedbacks, these chain reactions of events in the atmosphere-ocean system," said Appy Sluijs, a paleoecologist at Utrecht University in the Netherlands.
Sluijs and his colleagues found evidence for the chain reaction in two sections of sediment that accumulated on an ocean floor in what is now New Jersey.
The abundance and distribution of marine algae indicate the environment started to change and the ocean surface began to warm several thousand years before the large temperature spike.
The finding implies that the earlier warming triggered the injection of greenhouse gases visible in the geological record around 55 million years ago.
"That's actually the first time we can see that in such a clear fashion," Sluijs said.
The study appears in tomorrow's issue of the journal Nature.
"Swampy" Arctic
Scientists have long studied the ancient temperature spike, called the Paleocene-Eocene thermal maximum or PETM, for clues to what could happen as a result of today's global warming.
Research shows that during the PETM, global temperature shot up at least 9 degrees Fahrenheit (5 degrees Celsius), and swamp forests with redwoods and broad-leaved trees filled the Arctic.
A key unanswered question is what—if anything—triggered the substantial warming, noted Scott Wing, a paleobiologist at the Smithsonian Institution in Washington, D.C., who was not involved in the new research.
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