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http://www.salon.com/env/feature/2008/12/12/deep_carbon/

Global boiling

Some geologists say rising temperatures will uncork vast deposits of 
undersea methane. If they're right, we're cooked.

By Kirsten Weir

Dec. 12, 2008 |

By now we all know what's in store for us if we continue on our 
emissions-happy path: increasingly hotter days, horrific droughts and 
floods, angrier storms, acidic ocean waters that will dissolve coral 
reefs, and a surging sea level that will swallow our coastal cities. 
Still, that scenario is a virtual sunny day by the pool compared to 
the cataclysmic climate picture being drawn by some scientists. Never 
mind carbon dioxide emissions. Let's talk about the vast stores of 
carbon hidden deep beneath our feet.

During the last year, geoscientists have held several workshops and 
conferences to discuss what is known -- and the great deal that isn't 
-- about the "deep carbon" cycle. Next week, at the annual meeting of 
the American Geophysical Union, scientists plan to hold a special 
session devoted to one potentially frightening aspect of that cycle: 
a strange little substance known as methane hydrate.

Methane hydrates, or clathrates, are icelike gas deposits buried 
under permafrost and deep below the seafloor. Some researchers fear 
that the hydrates are on the verge of melting en masse and belching 
out a cloud of methane gas that will send global temperatures 
skyrocketing.

The doomsday scenario goes something like this: If global 
temperatures keep rising, some methane hydrates will melt, sending 
methane gas bubbling up through the ocean and into the atmosphere. 
Like any good greenhouse gas, the methane will trap heat close to 
Earth's surface, causing temperatures to climb even higher. Hotter 
temperatures will melt more hydrates, and on and on. In other words, 
methane hydrates could trigger the mother of all feedback loops. The 
story, says David Archer, a geophysicist at the University of 
Chicago, "has a great apocalyptic side to it."

Methane is the same natural gas that we burn for fuel. Under the 
right combination of intense pressures and chilly temperatures, the 
gas becomes trapped inside icy cages of hydrogen bonds. These methane 
hydrates look like chunks of ice, with the nifty difference that they 
eagerly burst into flame when sparked. Methane hydrates are also a 
lot less stable than your average ice cube. If the temperature rises 
or pressure eases, the hydrates essentially melt to form methane gas.

Methane hydrates aren't unusual, astronomically speaking. They exist 
on Mars, inside comets, and on at least a couple of Saturn's frosty 
moons. Here on Earth, they form deep below permafrost and under 
seafloor sediments, where temperature and pressure conspire to keep 
the structures stable. It's not certain how much methane is locked up 
in hydrates, but some estimates put the total as high as 10,000 
gigatons, says Gerald Dickens, a professor of earth sciences at Rice 
University. To put it in perspective, he says, "the estimates for all 
of the oil, gas, and coal [on Earth] is about 5,000 gigatons."

As a greenhouse gas, methane is in the big leagues, some 20 times as 
potent as carbon dioxide. If all the methane trapped underground were 
to wind up in the atmosphere, you could kiss your winter boots 
goodbye. "There is so much [methane hydrate] in the ocean that if you 
gave the planet a big shake and it came out all at once, it would be 
a climate disaster far worse than anything we have with carbon 
dioxide," Archer says.

Are we giving the planet that kind of shake? To predict the future, 
climate scientists begin by peering into the past. Human-induced 
global warming may be a new trend, but Earth has certainly 
experienced rapid and dramatic climate changes in its ancient 
history. Methane hydrates may have played a role in a period of 
abrupt warming 635 million years ago, according to a paper published 
in Nature last spring. The researchers, from UC-Riverside and 
Flinders University in Australia, point to high levels of methane 
present in the atmosphere at that time.

Around 55 million years ago, Earth again shifted abruptly from snowy 
to steamy. Many researchers have fingered hydrates in that warming 
spell, too. "Methane hydrates may not be the only explanation, but 
very likely played a large role," says Carolyn Ruppel, a research 
geophysicist with the U.S. Geological Survey, who will co-chair with 
Dickens the upcoming American Geophysical Union panel on hydrates.

James Kennett, a professor of earth sciences at UC-Santa Barbara, is 
a vocal proponent of the idea that methane hydrates have played a 
role in past climate changes. He also fears they are poised do so 
again. "The gas hydrates are inherently unstable with warming of the 
oceans. I can't see why [melting hydrates] would not be inevitable," 
he says. "The question is just how sensitive the system is."

Kennett argues that much of the geological research community has 
turned a blind eye to the evidence of methane hydrate's role in 
climate change. "It's a paradigm problem. The community is not 
prepared at this time to make a paradigm shift," he says. "[Climate 
change] is the biggest issue of our time. I think we need to look at 
this."

He suggests we start by taking a cold, hard look at the Arctic, where 
a great deal of methane hydrate exists in permafrost and under the 
continental shelf. Because of the extreme cold, hydrates are stable 
at shallower depths in the Arctic than anywhere else on Earth. Warm 
up the Arctic a bit, and these shallow hydrates will be the first to 
come apart, Kennett warns. "Is this already happening? Are we living 
in it now?"

Kennett has valid reasons for wondering. Inside the Arctic Circle, 
the ocean is reportedly bubbling like a freshly uncorked magnum of 
Dom Perignon. In September, scientists aboard a Russian research 
vessel described methane gas fizzing up from the seabed in several 
areas of the Arctic. Just a few days later, British scientists 
exploring the ocean west of the Norwegian island of Svalbard reported 
hundreds of these methane plumes.

It all sounds pretty ominous, but researchers aren't ready to 
attribute the recently observed methane bubbles in the Arctic to 
melting hydrates. Scientific reports of the plumes have not yet been 
published or peer-reviewed. Although Kennett is fearful of a methane 
catastrophe, he's not yet sure this is it. "I need to be convinced," 
he says.

He's not the only one. For one thing, says Archer, "there weren't 
observations before, so it's hard to say if it's a new phenomenon." 
Perhaps methane has been sputtering up from the Arctic for decades, 
with no one around to see it. What's more, many potential sources of 
methane exist. As bacteria break down thawing organic matter, they 
release the gas as a byproduct. "There's all this juicy organic 
carbon preserved in these areas," Archer points out. "These methane 
escapes could be from decomposing peat."

Ruppel, too, is a long way from ringing any alarm bells over the 
Arctic bubbles. "Perhaps people are jumping to conclusions before the 
story is really clear in the Arctic," she says. "My suspicion is that 
almost all of that methane has nothing to do with gas hydrates."

But let's imagine, for the sake of argument, that the Arctic gas 
plumes do turn out to be from methane hydrates. Does that mean it's 
curtains for life as we know it? Not necessarily.

"Methane beneath the permafrost is probably the most sensitive to 
change, but it's a small component of the total amount [of methane 
hydrates]," Dickens says. The vast majority is buried deep below the 
seafloor, he notes, and would be considerably harder to unlock. "At 
deep water depths, temperature would have to change 10 or 15 degrees 
Celsius to remove all the methane," Dickens estimates. "It would be 
very difficult for all of it to come out."

For that matter, adds Archer, it would be very difficult for even a 
portion of it to come out. "It would be arrogant to say it's 
impossible, but nobody has come up with a mechanism to get even 10 
percent of this methane into the atmosphere," he says.

Even if methane hydrates did start melting, the gas would have to 
travel through hundreds of meters of mud and thousands of meters of 
water before it could mix with the air. "A lot of methane would 
dissolve in ocean waters," Ruppel says. "The ocean is very 
undersaturated with methane. It could accommodate a whole lot before 
the methane would get out into the atmosphere."

Furthermore, Dickens adds, it's not enough to show that methane can 
travel from the deep ocean to the atmosphere. One also has to 
consider the rate. "It is possible in the future that large amounts 
of methane can come out of these systems," he says. "Is it probable 
that significant amounts will come out in the next 100 years? 
Probably not."

Archer is also skeptical of the importance of methane hydrates in 
ancient global-warming events. "The evidence for these things being 
important for climate change in the past, I think, is kind of dodgy," 
he says. True, something released a lot of carbon into the atmosphere 
55 million years ago. But maybe, he suggests, that something was a 
volcanic event that spewed methane gas, or a bunch of carbon-rich 
sediments that were suddenly lifted above sea level and exposed to 
the air. "There's no real clear smoking gun that it was methane 
hydrates," he says.

Ruppel says there's definitely more to learn. "I think the jury is 
still out on this," she says. But she doesn't see any reason for 
panic. The story that methane hydrates are a looming catastrophe "is 
a position some of us are working hard to counteract," she says.

In fact, much of the effort put into studying methane hydrates isn't 
focused on global warming at all, but on energy. The U.S. Department 
of Energy is taking a close look at mining methane hydrates for fuel, 
and they aren't the only ones. Countries including Japan, China and 
India are also exploring ways to turn hydrates into usable energy. 
"It is getting to the point now that methane hydrates could 
definitely become a viable commercial source for natural gas within 
the next 10 years," Ruppel says.

As a fuel, methane hydrate has some advantages. It's more accessible 
than conventional natural gas resources, Ruppel points out. And it is 
cleaner to burn and emits about half as much carbon dioxide as does 
coal. "Natural gas is probably the greenest of the fossil fuels," 
adds Archer.

But it is a fossil fuel, after all, and human-induced global warming 
is still a very real phenomenon. So will methane hydrates fuel our 
future, or destroy it? That may be the ultimate question, but not an 
easy one to resolve. For those willing to try, "it is a very 
interesting time in this field," Ruppel says. "We need more good 
science. I think we're moving in that direction, but it will be a few 
years before we have the answers."

In the meantime, panic over methane hydrates is probably premature. 
"There is a tendency in some quarters to latch on to a catastrophism 
scenario," she says. "That may sell newspapers, but it may not be the 
most responsible way to portray the science."

If you're the publisher of a sensationalist newspaper, take heart. 
There's still a good deal to fear when it comes to climate change. "I 
think the trajectory we're on with CO2 is very likely to lead to 
droughts that would be destabilizing to civilization. Another thing I 
worry about is sea-level rise," Archer says. "I think we have plenty 
to worry about with CO2. We don't need methane hydrates in order to 
be very reasonably frightened about the future of our climate."

-- By Kirsten Weir