Arctic Storms, Warming Mean More Methane Released

• Published: November 24th, 2013

Underneath the Arctic Ocean sits a large reserve of methane, a potent greenhouse gas. Understanding how much of that is making it to the atmosphere is an important but relatively new area of research. The latest findings published on Sunday in Nature indicate that more could be escaping than previously thought, thanks in part to stormy weather.

The East Siberian Arctic Shelf is a swath of land underneath the shallows of the East Siberian Sea, which is part of the Arctic Ocean. It stretches for 2 million square miles and contains large deposits of methane hydrates, which are frozen deposits of highly concentrated methane.

Canadian and American Coast Guard ships on a survey of the Arctic.
Credit: DVIDSHUB/Flickr

When the hydrates melt, they turn into methane gas, a greenhouse gas that is 25 times more potent than carbon dioxide. Methane hydrates are found throughout the world’s oceans but generally under hundreds of feet of water. That means as they melt, there’s more time for the gas to disperse and mix with the surrounding ocean water. But because the East Siberian Arctic Shelf is much shallower, with an average depth of 150 feet, there’s more of a chance for that methane gas to reach the surface. That’s why understanding how much methane is stored in the shelf and if those stores are stable is so important to climate researchers.

Some scientists suggested earlier this year that a massive release of methane from the shelf, referred to as a “methane bomb,” could cause abrupt climate change and cost the global economy $60 trillion. That claim has been met with much skepticism, in part because the amount of methane the shelf is currently releasing and the conditions it’s stored under aren’t fully understood. The remoteness, logistics and inclement weather have impeded scientists’ research access to the region until fairly recently and data has been sparse.

That, however, is beginning to change.

“In 2003, we started from zero observational data on methane available for this area,” Natalia Shakhova, an Arctic researcher at the University of Alaska and lead author of the new study, said. Her previous work built a body of evidence for how methane leaked from the seabed while her new study refines the numbers a bit more and finds that strong storms can help stir methane up the water column quickly and release it into the atmosphere.

Shakhova has spent the past decade compiling data on the East Siberia Arctic Shelf through research cruises and flyovers of the region. She published initial results in 2010, which showed that methane has been escaping at hot spots where vents have formed from a combination of geothermal heat as well as warmer river water flowing into the region. Those results showed that 7 teragrams of methane is bubbling to the surface annually. That’s roughly the equivalent of 10 percent of the methane emissions from U.S. oil and natural gas production and transmission in 2012.

The new research refined those results, showing the amount of methane reaching the surface is more than double those previous estimates. In all, Shakhova and her colleagues estimate that 17 teragrams are escaping each year, though the new study says the estimates are likely on the conservative end. Shakhova said those totals are on par with emissions from the Arctic tundra.

One of the reasons for the revised estimates was more rigorous measurements using an unmanned underwater vehicle with advanced sonar technology. It provided a clearer image of the seafloor and the amount of methane escaping from vents.

Shakhova’s research also shows that annual bottom water temperatures have increased 0.9°F over the past 14 years while summer temperatures have increased 1.8°F over the same period. That’s due in large part to increased runoff from rivers, which generally have warmer water than the Siberian Sea. Other research has pegged that increase at 7 percent from 1936 to 1999.

A sonar image showing the location of methane vents in a portion of the East Siberian Arctic Shelf.
Click image to enlarge. Credit: Shakhova et al., 2013

Another method Shakhova and her colleagues used to update their estimates involved taking methane measurements before and after storms passed over the shelf. The Siberian Sea has up to 70 stormy days annually when winds can help churn deeper water toward the surface.

Shakhova measured the amount of methane before and after storms in both the water column and atmosphere. After storms, methane was greatly reduced in the water column, indicating storms were helping ventilate methane into the atmosphere more rapidly.

“We should have much more concerns regarding subsea permafrost than we previously had,” Shakhova said about her results.

At the same time, she downplayed tying the research to the methane bomb theory espoused earlier this year, saying there’s not enough evidence to make that connection.

David Archer, a carbon cycle expert at the University of Chicago agreed. “In order to ignite an Arctic methane bomb you would have to ramp up (emissions) by a factor of 10 or 100 very quickly, and there’s no evidence or any proposed mechanism that could make it blow up that quickly,” he said in an email. Archer also said that while the new research shows more methane is being emitted from the area than previously thought, it still represents only about 3 percent of global methane emissions from natural and human sources.

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• Posted in Causes, Greenhouse Gases, Trends, Projections, Climate, Snow & Ice, Landscapes, Arctic & Greenland

Sea Level Experts Concerned About ‘High-End’ Scenarios

• Published: November 22nd, 2013 , Last Updated: November 22nd, 2013

A survey of nearly 100 experts on sea level rise reveals that scientists think there is a good chance the global average sea level rise can be limited to less than 3.3 feet by 2100 if stringent reductions in planet-warming greenhouse gases are rapidly instituted. However, the survey, which is the largest such study of the views of the most active sea level researchers ever conducted, found that if manmade global warming were to be on the high end of the scale — 8°F by 2100 — the global average sea level is likely to jump by between 2.3 and 3.9 feet by the end of this century.

Worse yet, such a temperature increase could boost sea levels by up to 9.9 feet by 2300, the study found. Such a drastic increase in sea level would not just put heavily populated coastal cities at risk of flooding, but could also jeopardize the existence of low-lying island nations, the study found.

Projections of global mean sea level rise over the 21st century relative to 1986–2005 from the combination of the computer models with process-based models, for greenhouse gas concentration scenarios. The assessed likely range is shown as a shaded band.
Click image to enlarge. Credit: IPCC Working Group I.

The study, led by Ben Horton of Rutgers University and published in Quaternary Science Reviews, solicited sea level rise projections from the most active researchers in the field, scientists who had published at least six papers on the subject during the previous 5 years. Since computer modeling approaches and other methods have yielded a wide range of projections, a poll of expert opinions provided Horton and his colleagues a different way of estimating the odds of particular sea level rise scenarios.

The study’s projections overlap, but are generally higher than, the most recent report from the U.N. Intergovernmental Panel on Climate Change (IPCC), which raised its sea level rise projections by about 60 percent between its 2007 report and the assessment released in September.

Horton said there is broad agreement among sea level rise experts that if emissions are significantly curtailed beginning in the next few years, the amount of sea level rise could be limited. “If we can have mitigation measures to reduce GHG emissions we can keep sea level below a meter which is a rate that the vast majority of our coastlines can withstand,” Horton said in an interview.

However, the study found that scientists are especially concerned about the consequences of high-end warming scenarios.

“You get a group of scientists together and you find that they’re projecting a lot higher level of sea level rise,” Horton said in an interview. ”… The ranges now overlap with the IPCC, but they’re higher.”

For example, 13 experts who responded to the survey estimated a 17 percent chance that sea level rise would exceed 6.6 feet by 2100, which would have potentially catastrophic consequences for coastal cities like Manila in the Philippines, and U.S. cities such as Miami, New York, and New Orleans.

“While the results for the scenario with climate mitigation suggest a good chance of limiting future sea-level rise to one meter, the high emissions scenario would threaten the future survival of some coastal cities and low-lying islands”, said co-author Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research.

This type of study peels back the curtain on sea level specialists, allowing the public to get a better idea of their views and giving policy makers the chance to assess various risk management approaches, the study said.

Sea level rise exacerbates storm surge-related flooding.
Credit: NOAA.

The IPCC projected that global mean sea level rise for 2081-2100 will likely be in the range of 10.2 to 32 inches, depending on greenhouse gas emissions. However, the report notes, as other studies have found, that local amounts of sea level rise could be much higher in some coastal areas. The scenario with the highest amounts of greenhouse gases in the atmosphere shows a mean sea level rise range between 21 and 38.2 inches, which would be devastating for many highly populated coastal cities at or near current sea levels.

During the 1901-2010 period, the report said, global averaged sea level rise was 0.07 inches per year, which accelerated to .13 inches per year between 1993 and 2010.

The IPCC’s four scenarios of the amount of greenhouse gases in the atmosphere through 2100 all show faster rates of sea level rise compared to that observed during 1971-2010, the report said.

The sea level rise scenarios in the recent report were considerably higher than those in the 2007 report, when the IPCC projected a global mean sea level rise of just 7.1 to 23.2 inches by 2100, and did not take into account the probable influence of the melting Greenland ice sheet and parts of Antarctica.

Because long-lived greenhouse gases like carbon dioxide (CO2) remains in the atmosphere at least for several hundred years, and because the oceans and ice sheets respond relatively slowly to global warming, multiple studies have pointed out that sea level rise will continue long after the amount of greenhouse gases in the air have stabilized.

This study also showed that some sea level rise experts are concerned about the possibility of extremely high long-term increases in sea level, on the order of up to 46 feet by the year 2300. Such massive fluxes in global mean sea level have been documented in Earth’s history, but never when so many people were living along the shoreline. For example, the last time that the Earth had as much CO2 in the air as it does now was before humans existed, when global sea level was up to 100 feet higher than they are today.

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• Posted in Causes, Greenhouse Gases, Impacts, Projections, Oceans & Coasts, Sea Level, Policy, Global