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
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
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
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
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?
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,"
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,"
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
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