It happened 55 million years ago for natural reasons, and it may happen today because of human pollution.
"It" is a chain-reaction that leads rapidly from modest global warming to catastrophic global warming via a series of "positive feedback loops." The concept isn't new, but a study published today in Nature shows for the first time how it happened in the past, its authors say.
Last time, it happened during the Paleocene-Eocene thermal maximum, a period of warming that the authors say is the prehistoric period during which the Earth experienced warming most similar to what we're seeing today.
Then, it started most likely with a volcano, the authors think, which pumped enough greenhouse gases into the atmosphere to trigger a modest amount of warming, similar perhaps to the amount we've seen over the last several decades.
What happened next is the important part. The earth became warm enough that icelike structures in the ocean melted, releasing massive amounts of methane that bubbled up, fueling rapid warming of the atmosphere. While carbon is more long-lived, methane is more than 20 times more potent as a greenhouse gas.
Some scientists have been nervously watching greenhouse gas sinks on Earth today, like the methane trapped in tundra, fearing that enough warming might force these sinks to release massive amounts of greenhouse gases suddenly, feeding additional warming that causes the release of more gases...and so on.
"The study for the first time shows such a chain-reaction during rapid warming in a greenhouse world," according to the information about the study on the Website of the lead author, Appy Sluijs, a paleoecologist from Utrecht University, the Netherlands.
Here's the rest of his description:
Analogous to the modern situation, the phase of greenhouse warming 55 million years ago was caused by a relatively rapid increase of CO2 concentrations in the atmosphere. This phase, known as the Paleocene-Eocene thermal maximum, was studied using sediments that accumulated 55 million years ago on the ocean floor in what is now New Jersey. The new study shows that a large part of the greenhouse gases was injected as a result of a chain-reaction of events. Likely through intense volcanism, CO2 concentrations in the atmosphere became higher and the ensuing greenhouse warmed the Earth. As a result, marine methane hydrates, ice-like structure in which massive amounts of methane are stored, melted and released large amounts of methane into the atmosphere. This 'positive feedback' amplified the magnitude of global warming, which comprised about 6° C in total.
The new research confirms that climate warming can enforce mechanisms that inject massive amounts of stored carbon into the atmosphere. Current and future warming will likely see similar feedbacks, such as methane hydrate dissociation, adding additional greenhouse gases to those resulting from fossil fuel burning.
Last year, the same group of researchers showed in Nature that 55 million years ago tropical algae migrated into the Arctic Ocean, when temperatures rose to 24° C. Current climate models are not capable of simulating the high temperatures at that time, which has repercussions for the predictions of future climate change. In addition to Al Gores presentation, this type of research shows what a greenhouse world looks like, including palm trees and crocodiles in the Arctic.
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