Day 89: Good news for Earth out of Boulder, CO. Sorta.

The Pakitsoq ice margin, where the ice study took place. Image courtesy of Vasilii Petrenko.

The good news — as it’s being couched out of the University of Colorado in Boulder — is that global warming is not likely to engender a great belch of methane from the permafrost that will kickstart a deadly methane cycle leading to further warming.

But I don’t suppose it’s any more comfortable to realize warming is likely to cause an outpouring of methane from the world’s wetlands.

Vasilii Petrenko, a CU-Boulder postdoctoral fellow, led a research team that investigated the cause of a burst of methane that took place immediately after an abrupt transition between climatic periods known as the Younger Dryas and Preboreal, about 11,600 years ago.

During this event, temperatures in Greenland rose 18° F (10° C) in 20 years. Methane levels in the air, over 150 years, rose about 50 percent, from 500 parts per billion to 750 parts per billion.

The researchers mined 1.1-ton (1,000-kg) samples from the west Greenland ice margin and analyzed changes in the trapped methane over time. Their findings were released today by the journal Science.

Methane is the third most powerful greenhouse gas behind water vapor and C02 and accounts for roughly 20 percent of human greenhouse gas-induced warming. Petrenko said rice cultivation, livestock, the burning of grasslands, forests and wood fuels, gas leaks from fossil fuel production and landfills have nearly tripled methane concentrations in Earth’s atmosphere in the past 250 years.

Wetlands in the tropics and emerging from under receding Northern Hemisphere glaciers have been considered the most likely source of rising atmospheric methane in a warming world. But scientists have been worried about another, unquantified potential source for the gas: methane clathrate, which is bound up in ocean sediments and permafrost.

Methane clathrate has been worrisome for scientists because of its huge volume, greenhouse gas potency and potential for release during periods of warming, Petrenko said. 

The amount of carbon held in methane clathrate deposits on Earth may equal the amount of carbon in all oil, coal and gas reserves on the planet, he said: “If we found that clathrates release a lot of methane to the atmosphere during abrupt episodes of warming, that could signal big trouble for the planet.” 

The research team extracted several tons of ancient ice from the western margin of the Greenland ice sheet, the largest ice samples ever recovered for a climate change study. The researchers cut the ice into blocks with electric chain saws, dumped 17 cubic feet at a time into a vacuum melting tank heated by powerful propane torches, and transferred ancient air released from bubbles in the ice into cylinders for subsequent laboratory analysis.

The five-year effort was “an undertaking of epic proportions,” said Petrenko. “This was the first measurement of its kind, and we really pushed the envelope. It represents a major advance in analytical methods for studying ancient ice.”

Using carbon 14 as a marker to date and distinguish methane from wetlands and clathrates, Petrenko and his team determined the methane jump 11,600 years ago likely came primarily from Earth’s wetlands.

I’m still not certain why the CU Boulder press release touted the discovery as ‘good news’ for the planet, and apparently, neither is Euan G. Nisbet, an Earth scientist from the University of London, who wrote an accompanying Perspectives piece in Science. 

“As a warming event is sustained, decomposing northern methane hydrates (clathrates) may inject fossil methane into the air with wetland, thawing permafrost, and clathrate emissions reinforcing each other in a feedback loop,” he said. “Petrenko et al.’s data leave such a scenario unconstrained but imply that wetlands were the main driver.”

Still, he writes, “If a shift on the scale and rapidity of past changes were to happen tomorrow— including intensified methane emissions from wetlands, decaying permafrost, and hydrate breakdown on Arctic continental margins and slopes— then the consequences for humanity could be very severe. Far from the Arctic, crops could fail and nations crumble. It is thus essential to decipher what took place in the past.”

Besides CU Boulder, researchers for the study hailed from the Scripps Institution of Oceanography, the Australian Nuclear Science and Technology Organisation (ANSTO), Oregon State University, the National Institute of Water and Atmospheric Research in New Zealand, the Technical University of Denmark and the Commonwealth Scientific and Industrial Research Organisation in Australia. 

Source: CU Boulder press release (first spotted on Eurekalert). The paper and accompanying editorial will appear tomorrow in Science.