Talks

New discovery creates good news on methane

 By RP Siegel

One of the major concerns that climate scientists have had regarding climate change is positive feedback loops. These are phenomena in which the warming creates secondary effects that in themselves, can lead to more warming. One classic example is snow cover…

When snow cover, which is very reflective, melts, it allows the earth to absorb more heat than it did when the snow was there, which causes further warming. Some of these feedback loops have been observed, while others have merely been hypothesized.
One particularly frightening scenario involves methane, a greenhouse gas that is 30 times more potent than carbon dioxide. It is known that enormous quantities of methane are stored beneath the ocean floor and underneath a deep layer of permafrost in tundra regions. This is estimated to be as high as 5 trillion metric tons. If the warming should reach a level where that permafrost should melt, or the deep ocean water temperatures rise, vast amounts of methane could be released, which could dramatically accelerate the rate of warming, potentially overwhelming all scenarios that have been put forth to date. This phenomenon is sometimes known as the “clathrate gun.” Methane clathrate is another term used for methane hydrate, the form in which the gas is found in these deep repositories.

Recent research, however, has provided evidence that this scenario is less likely than had previously been thought. Vasilii Petrenko, Associate Professor of Environmental Science at the University of Rochester and his team went to Antarctica and spent two months extracting ice samples, looking for tiny trace amounts of Carbon-14 that could unlock the secret of where a large increase in atmospheric methane that emerged at a time of last major warming, 11,500 years ago, came from.
That warming, which occurred at a moment in geologic time called the Younger Dryas – Preboreal Transition, saw an increase of 20° F in Central Greenland over a period of just twenty years. This was superimposed over a background global warming rate of 7.2° F over roughly 7,000 years.
The researchers wanted to see if such an abrupt climate shock on top of a prolonged warming period would have been precipitated a massive release of methane from what Petrenko calls “fossil sources.” If it had, that would add support to the idea that it will likely happen again.
In fact, the data showed the opposite. Based on the amount of Carbon-14 present in the six samples weighing over 1,000 kg each, the researchers could see that the methane released at that time was of recent origin, most likely emitted from wetlands, as opposed to being released from deep “fossil” stores buried beneath the sea as hydrates or under permafrost.

We probably shouldn't be too worried about a giant methane burp from ocean hydrates that would increase the greenhouse effect dramatically

The way they could tell was because of their use of Carbon-14 as a tracer. It has a half-life of 5,700 years. If the methane had been stored for thousands of years before becoming trapped in the ice, most or all of it would have decayed away. What they found instead was no appreciable drop in the Carbon-14 level.
Citing this result, Petrenko told Eniday, “We probably shouldn’t be too worried about a giant methane burp from ocean hydrates that would increase the greenhouse effect dramatically.”
This observation is supported by other research that has investigated the possibility of major releases of methane hydrates from beneath the sea floor. While they found that the possibly of the methane clathrates becoming destabilized entirely plausible, they also found that the microbes found within the ocean sediments and the water column would tend to oxidize any methane passing through it, thereby diminishing its impact.
The other thing that the researchers discovered was that overall, in the past atmosphere, the amount of methane coming from old carbon sources was extremely low. This would include any methane escaping from seeps, or other types of natural releases.

There is no reason to believe that this would have changed between that time on now. “So,” says Petrenko, “that means that the amount of methane coming from these types of sources are really, really tiny.” Until now, it was believed that as much as a quarter to a third of all the fossil methane in today’s atmosphere was from these natural methane seeps. These results suggest that this contribution is closer to 5%. This also means that nearly all the fossil methane in the atmosphere today is from human activity.

Petrenko says his team will follow this research with a more detailed study looking at the last 200 years to see how much fossil methane was in the atmosphere in the pre-industrial period.

READ MORE: Are methane hydrates the new shale gas? by Mike Scott

about the author
RP Siegel
Skilled writer. Technology, sustainability, engineering, energy, renewables, solar, wind, poverty, water, food. Studied both English Lit.and Engineering at university level. Inventor.