Methane from Tundra, Ocean Floor Didn't Spike During Previous Natural Warming Period

The last ice age transition to a warmer climate some 11,500 years ago did not include massive methane flux from marine sediments or the tundra, new research suggests. Instead, the likely source of rising levels of atmospheric methane was from tropical wetlands, authors of the new study say.

Scientists concerned that global warming may release huge stores of methane from reservoirs beneath Arctic tundra and deposits of marine hydrates -- a theory known as the "clathrate gun" hypothesis -- have turned to geologic history to search for evidence of significant methane release during past warming events.

A new study published this week in the journal Nature suggests, however, that the last ice age transition to a warmer climate some 11,500 years ago did not include massive methane flux from marine sediments or the tundra.  Instead, the likely source of rising levels of atmospheric methane was from tropical wetlands, authors of the new study say.

While this certainly is good news, the study also points at a larger role of humans in the recent methane rise, noted Edward Brook, an Oregon State University paleoclimatologist and co-author on the study

"Our findings show that natural geologic emissions of methane -- for example, leakage from oil seeps or gas deposits in the ground -- are much smaller than previously thought," Brook said. "That means that a greater percentage of the methane in the atmosphere today is due to human activities, including oil drilling, and the extraction and transport of natural gas."

The study suggests that human emissions of geologic methane may be as much as 25 percent higher than previous estimates.  Although not as abundant as carbon dioxide, methane is a much more powerful greenhouse gas and therefore the rising levels are an important contributor to global warming.

"This means we have even more potential to fight global warming by curbing methane emissions from our fossil fuel use," said Vasilii Petrenko, an associate professor of earth and environmental sciences at the University of Rochester, and lead author on the study.

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