This summer a Russian research ship found hundreds of plumes of methane, “of a fantastic scale”, bubbling up from the sea floor off the East Siberian coast:
• Steve Connor, Shock as retreat of Arctic sea ice releases deadly greenhouse gas, 13 December 2011.
Here are the quotes with actual new information:
In late summer, the Russian research vessel Academician Lavrentiev conducted an extensive survey of about 10,000 square miles of sea off the East Siberian coast. Scientists deployed four highly sensitive instruments, both seismic and acoustic, to monitor the “fountains” or plumes of methane bubbles rising to the sea surface from beneath the seabed.
“In a very small area, less than 10,000 square miles, we have counted more than 100 fountains, or torch-like structures, bubbling through the water column and injected directly into the atmosphere from the seabed,” Dr Semiletov said. “We carried out checks at about 115 stationary points and discovered methane fields of a fantastic scale – I think on a scale not seen before. Some plumes were a kilometre or more wide and the emissions went directly into the atmosphere – the concentration was a hundred times higher than normal.”
“This is the first time that we’ve found continuous, powerful and impressive seeping structures, more than 1,000 metres in diameter. It’s amazing,” Dr Semiletov said. “I was most impressed by the sheer scale and high density of the plumes. Over a relatively small area we found more than 100, but over a wider area there should be thousands of them.”
Scientists estimate that there are hundreds of millions of tonnes of methane gas locked away beneath the Arctic permafrost, which extends from the mainland into the seabed of the relatively shallow sea of the East Siberian Arctic Shelf. One of the greatest fears is that with the disappearance of the Arctic sea-ice in summer, and rapidly rising temperatures across the entire region, which are already melting the Siberian permafrost, the trapped methane could be suddenly released into the atmosphere leading to rapid and severe climate change.
Dr Semiletov’s team published a study in 2010 estimating that the methane emissions from this region were about eight million tonnes a year, but the latest expedition suggests this is a significant underestimate of the phenomenon.
I’d like to know more about Igor Semiletov’s work and what he’s just found. He was mentioned in this earlier very good article:
• Amanda Leigh Mascarelli, A sleeping giant?, Nature Reports Climate Change, 5 March 2009.
The Siberian Shelf alone harbours an estimated 1,400 billion tonnes of methane in gas hydrates, about twice as much carbon as is contained in all the trees, grasses and flowers on the planet. If just one per cent of this escaped into the atmosphere within a few decades, it would be enough to cause abrupt climate change, says Shakhova. “When hydrates are destabilized, gas is released under very high pressure,” she says. “So emissions could be massive and non-gradual.” Shakhova and her colleague Igor Semiletov of the University of Alaska, Fairbanks, believe the plumes they’ve observed confirm previous reports that the permafrost cap is beginning to destabilize, allowing methane to escape from the frozen hydrates below. “Subsea permafrost is like a rock,” explains Semiletov. “It works like a lid to prevent escape of any gas. We believe that the subsea permafrost is failing to seal the ancient carbon pool.”
But Carolyn Ruppel, a geophysicist with the US Geological Survey in Woods Hole, Massachusetts, isn’t yet ready to attribute the methane plumes to a breakdown in methane hydrates in the subsea permafrost. “We have proof from studies that have been carried out in the past few years that there’s a lot of methane in certain shallow marine environments offshore in the Arctic,” says Ruppel. “But can we prove that the methane comes from methane hydrates? That is a critical question.”
Why is it critical? Because people are worried about global warming melting permafrost and gas hydrates on the ocean floor. Suppose these release large amounts of methane, a greenhouse gas vastly more potent than carbon dioxide. This will then makes the Earth even warmer, and so on: we have a feedback loop. In a real nightmare scenario, we could imagine that this feedback actually leads to a ‘tipping point’, where the climate flips over to a much warmer state. And in the worst nightmare of all, we can imagine something like Paleocene-Eocene Thermal Maximum, a spike of heat that lasted about 20,000 years, causing significant extinctions.
Are any of these nightmares really possible? I wrote about this question before, assembling what facts I could easily find:
How much new light does Semiletov’s work shed on this question?
Luckily, a team of scientists is gearing up to answer it:
Here’s a paper by this team:
To get the ball rolling, they surveyed themselves. That may seem like a lazy way to write a paper, but I don’t mind it as a quick way to get a sense of the conventional wisdom… and they probably wanted to do it just to find out what they all thought! Here are the results—emphasis mine:
Our survey asks what percentage of the surface permafrost is likely to thaw, how much carbon will be released, and how much of that carbon will be CH4, for three time periods and under four warming scenarios that will be part of the Intergovernmental Panel on Climate Change Fifth Assessment Report. The lowest warming scenario projects 1.5 °C Arctic warming over the 1985–2004 average by the year 2040, ramping up to 2 °C by 2100; the highest warming scenario considers 2.5 °C by 2040, and 7.5 °C by 2100. In all cases, we posited that the temperature would remain steady from 2100 to 2300 so that we could assess opinions about the time lag in the response of permafrost carbon to temperature change.
The survey was filled out this year by 41 international scientists, listed as authors here, who publish on various aspects of permafrost. The results are striking. Collectively, we hypothesize that the high warming scenario will degrade 9–15% of the top 3 metres of permafrost by 2040, increasing to 47–61% by 2100 and 67–79% by 2300 (these ranges are the 95% confidence intervals around the group’s mean estimate). The estimated carbon release from this degradation is 30 billion to 63 billion tonnes of carbon by 2040, reaching 232 billion to 380 billion tonnes by 2100 and 549 billion to 865 billion tonnes by 2300. These values, expressed in CO2 equivalents, combine the effect of carbon released as both CO2 and as CH4.
Our estimate for the amount of carbon released by 2100 is 1.7–5.2 times larger than those reported in several recent modelling studies, all of which used a similar warming scenario. This reflects, in part, our perceived importance of the abrupt thaw processes, as well as our heightened awareness of deep carbon pools. Active research is aimed at incorporating these main issues, along with others, into models.
Are our projected rapid changes to the permafrost soil carbon pool plausible? The survey predicts a 7–11% drop in the size of the permafrost carbon pool by 2100 under the high-warming scenario. That scale of carbon loss has happened before: a 7–14% decrease has been measured in soil carbon inventories across thousands of sites in the temperate-zone United Kingdom as a result of climate change. Also, data scaled up from a single permafrost field site point to a potential 5% loss over a century as a result of widespread permafrost thaw. These field results generally agree with the collective carbon-loss projection made by this survey, so it should indeed be plausible.
Across all the warming scenarios, we project that most of the released carbon will be in the form of CO2 with only about 2.7% in the form of CH4. However, because CH4 has a higher global-warming potential, almost half the effect of future permafrost-zone carbon emissions on climate forcing is likely to be from CH4. That is roughly consistent with the tens of billions of tonnes of CH4 thought to have come from oxygen-limited environments in northern ecosystems after the end of the last glacial period.
All this points towards significant carbon releases from permafrost-zone soils over policy-relevant timescales. It also highlights important lags whereby permafrost degradation and carbon emissions are expected to continue for decades or centuries after global temperatures stabilize at new, higher levels. Of course, temperatures might not reach such high levels. Our group’s estimate for carbon release under the lowest warming scenario, although still quite sizeable, is about one-third of that predicted under the strongest warming scenario.
I found this sentence is a bit confusing:
These values, expressed in CO2 equivalents, combine the effect of carbon released as both CO2 and as CH4.
But I guess that combined with a guess like “30 billion to 63 billion tonnes of carbon by 2040”, it means that they’re expecting a release of carbon dioxide and methane that’s equal, in its global warming potential, to what you’d get from burning 30 to 63 billion tonnes of carbon, turning it all into carbon dioxide, and releasing it into the atmosphere.
For comparison, in 2010 humanity burnt 8.3 billion tonnes of carbon. So, at least up to 2040, I guess they’re expecting the effect of melting permafrost to be roughly 1/8 to 1/4 of the direct effect of burning carbon.