A massive release of methane from the Arctic seafloor would have catastrophic impacts on the world's economy, possibly costing $60 trillion or more because of associated problems such as sea-level rise and drought, according to a comment published yesterday in Nature.
The $60 trillion -- roughly the size of the entire global economy last year -- considers a 50-gigaton belch of the greenhouse gas over a decadelong period from the East Siberian Sea, where scientists in recent years discovered perforations in permafrost and seeping methane plumes offshore. In addition to economic costs, the release would speed up by 15 to 35 years the date by which the world experience a 2-degree-Celsius temperature rise above preindustrial levels, according to the analysis.
Even a much smaller leak of methane, spread out over three decades, could speed up warming and lead to economic costs in the trillions by the end of the century, the scientists said.
"This is an economic time bomb," said Gail Whiteman, co-author of the commentary and a professor of sustainability, management and climate change at Erasmus University Rotterdam.
The study is unique for assessing costs of a very specific Arctic response. The alarming dollar figures also add to an ongoing debate about the climate implications of methane; some scientists believe a massive spurt of the greenhouse gas in a short period of time is unlikely and called the new paper "alarmist."
"It's over the edge. ... There's no rationale why that amount of methane should come out at once," said David Archer, a chemical oceanographer at the University of Chicago.
Others say that degree of leakage is possible. A paper in 2008 stated that a 50-gigaton spurt is "highly possible for abrupt release at any time." One of the authors of that paper, scientist Natalia Shakhova, said yesterday that the topic requires much more investigation to "decrease uncertainties."
Price tag could drop to $37T with climate action
Regardless, the authors say they published their data as a commentary to change the debate about the Arctic, so it is not just about scientific study of sea ice loss and the possible benefits of commercial activity in newly open waters. Many current climate models do not consider this type of methane pulse, they added.
"We wanted to have a dialogue, and we wanted to increase awareness that the Arctic is not just important for the polar bear," said Whiteman.
A possible rapid methane release of 50 gigatons, or 50 billion tons, could occur because of melting permafrost offshore in the East Siberian Sea, where methane is stored in the form of hydrates, said Peter Wadhams, a professor of ocean physics at the University of Cambridge and study co-author. The shelf is very shallow, as well, providing a faster route for sunlight to warm water and for long-stored methane to reach the air than some other places in the Arctic, he said.
The scientists then assessed what would happen in an economic model known as PAGE09 if the 50 gigatons were released between 2015 and 2025. The economic model has been used by the federal government and the 2006 "Stern Review on the Economics of Climate Change" to estimate the costs of warming temperatures.
Under a business-as-usual scenario of emissions, the team found the methane release would add $60 trillion in economic damage to the world's economy and would speed up the time by which the world experiences the 2-degree threshold by 15 years, to 2035.
Sixty trillion dollars was the mean of the model, meaning some of the results produced much higher climate costs, more than $200 trillion.
Under a slightly different scenario, in which emissions elsewhere were curbed, the methane cost would hit $37 trillion and temperatures would cross the 2-degree benchmark by 2040, they said. The economic model ran through 2200, but most of the costs would occur this century, said Chris Hope, a business school analyst at the University of Cambridge and the third author.
Most costs felt in the poorest countries
A slower release of methane -- over 20 or 30 years rather than a decade -- also would cause the mean costs to be close to $60 trillion, the team found. A later release would allow the methane to be present later in the century, when some of the biggest impacts of climate change will be occurring, said Hope.
The results were roughly linear, meaning a smaller percentage amount of methane release would lead to a similar cut in cost estimates, said Wadhams.
Possible economic benefits from Arctic ice melt, such as new oil drilling and shipping revenues, were not considered in the modeling. Investments in the Arctic could reach $100 billion within a decade, according to some projections, but the benefits are tiny in comparison to the costs, said Wadhams.
Eighty percent of the costs would be felt in developing countries in Africa, Asia and South America because of extreme weather, flooding and public health problems, the analysis says. For this reason, it is important that policymaking in the Arctic move beyond the Arctic Council -- a body made of Arctic nations -- into forums such as the World Economic Forum, so there can be discussions about equity, said Whiteman.
But Archer and some other scientists said it is important to consider that Arctic methane is still a smaller source of the greenhouse gas than natural processes generating it from tropical swamps. Current measurements of methane typically are listed in teragrams. A teragram is the equivalent of about a million tons, much smaller than the 50-billion-tons figure in the paper, he noted.
A study in Science in 2010, for instance, reported that the East Siberian Sea Arctic shelf was releasing around 7 million tons (7 teragrams) of methane annually. Carbon dioxide is by far a bigger villain in the Arctic and the rest of the world, according to Archer.
'Terrifyingly large' costs must be considered
"The Arctic issue that is going to clobber us is the melting of sea ice and how that affects weather patterns. That is happening right now. That we will notice," he said. It's not that 50 gigatons of methane won't be released, but it might take centuries, he said.
The Arctic is warming twice as fast as the global average, according to scientists.
Similarly, Ted Schuur, a scientist at the University of Florida, said the idea of a 50-gigaton release is a "worst-case scenario or bad scenario."
"It's important to consider 'worst case scenarios' because we haven't ruled these out, but at the same time a large methane emission in a short time (decade) does not seem to be the 'most likely' or 'average' scenario that Earth system scientists are converging upon," he said.
It is known that methane is more potent than carbon dioxide and shorter-lived in the atmosphere, but there is much uncertainty surrounding the molecule. The total amount of methane hydrate and submerged permafrost in the Arctic is uncertain, for example.
Furthermore, atmospheric levels of methane flattened for about a decade before rising again in 2007, prompting scientists to grapple with the reasons for the methane stagnation (ClimateWire, Aug. 24, 2012).
One of the most comprehensive assessments of massive methane release came five years ago, when the former U.S. Climate Change Science Program concluded that "catastrophic release of methane to the atmosphere in the next century appears very unlikely" but also emphasized uncertainty, saying very large increases could not be discounted.
Economic modeling of climate change also is fraught with uncertainty, said Frank Ackerman, a senior economist at Synapse Energy Economics. The PAGE09 model is "one of the better ones" but still produces wide number ranges, he said.
What is important, he said, is that climate change will have significant costs, even if it may not be possible to exactly pinpoint a cost for a specific amount of methane.
"We can't rule out terrifyingly large numbers," he said.