Drop the Methane Bomb
- 16 Dec 2011, 11:40
- Christian Hunt
Source: NOAA Ocean Explorer
There's a lot of methane in the Arctic deep freeze, where ice
formations called 'clathrates' trap huge amounts of the powerful
greenhouse gas in the Arctic Ocean sea bed. For the intelligent
apes currently experimenting with the Earth's atmosphere (that
would be us), that methane is in exactly the right place - kept
safely out of the atmosphere.
The question is, with the Arctic warming about twice as fast as
the rest of the planet, do we need to worry about it thawing out?
And so, every now and again, you'll see newspaper articles about a
methane time bomb' in the Arctic. The latest comes from
the Independent, who ran a story headlined '
Shock as retreat of Arctic sea ice releases deadly
Based on an interview with Igor Semiletov, a professor at the International Arctic Research
Centre in Alaska, the article details how his research has
found large 'plumes' of methane bubbling up from the sea bed of the
"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."
The Independent then gives us the background:
"...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."
This is what has been called the 'clathrate gun' hypothesis -
that by warming the Arctic ocean, we might kick-start a process
where methane clathrates melt, releasing huge amounts of the gas
into the atmosphere - a process that, like a gunshot, would be
impossible to stop.
This concern about 'catastrophic' methane release has been
fuelled by examinations of the planet's climate past. Over the past
800,000 years, temperature, carbon dioxide and methane levels have
all gone up and down, sometimes very quickly. Some of the fastest
changes saw sharp rises in temperature and methane at the same
Hence the interest in how much methane is coming out of the
Arctic sea bed.
However, scientists are usually wary of putting too much weight
on one piece of research, particularly when there's a complicated
story to tell.
I talked with Dr Vincent Gauci, a researcher at the Open
University and director of the
website MethaneNet.org. I asked him about the idea that big
shifts in temperature in the past have been driven by a 'clathrate
gun' process. Other research,
he said, suggests the methane increases associated with warming in
the past are more likely to have come from changes in the planet's
wetlands, rather than methane clathrates.
Methane contains variants of its constituent elements known as
isotopes. Scientists can use measurements of isotopes from
methane trapped in ice cores to work out where the methane has come
from, letting them build up a picture of past atmospheres:
"When we've seen big methane emissions
over the past 30-40 thousand years ... the isotopes just don't
support big hydrate emissions. They do support changes in wetland
extent and productivity having a bigger control over the amount of
methane in the atmosphere."
If it's been warmer in the past without massive Arctic methane
release from clathrates, it may be unlikely that higher
temperatures will lead to methane release from clathrates now:
"The clathrates just respond to what
conditions they get - temperature and pressure. If we know certain
conditions occurred and we didn't see a response in the isotope
record, we can tell that it's not likely to be a driver and lead to
destabilisation on a large scale in the future. The problem is
knowing how much hydrate is shallow and potentially vulnerable, and
how much is deep and relatively safe."
Another recent scientific paper (picked up by bloggers
Christopher Mims and
Andy Revkin) suggests that the methane release from the Arctic
sea-floor may be more about the planet's ongoing
and very slow response to coming out of an ice age than
man-made climate change.
Much of the methane gas currently bubbling up into the ocean is
to dissolve in the surrounding seawater, so only a tiny
fraction of the methane released this way currently reaches the
atmosphere. (It's worth noting this dissolving methane is likely to
ocean acidity, which could be
bad news for the local marine life.)
The Semiletov research is important because it's worth paying
close attention to how the planet is behaving on this one. But we
probably shouldn't conclude that 'methane plumes' equals 'methane
bomb going off' just yet.
Methane in context
In 2010 scientist and methane researcher David
Archer wrote an interesting post on the website Realclimate
about methane release from the Arctic ocean:
… so far it is at most a very small
feedback … Most of the methane in the atmosphere comes from
wetlands, natural and artificial associated with rice agriculture.
The ocean is small potatoes...
It's useful to get a sense of how Arctic methane emissions
compare with other sources. The Independent article cites another
study by Dr Semiletov's team published in 2010, which it says
estimated that methane emissions from this region were about eight
million tonnes a year - but suggests that this may not be a
significant underestimate of the phenomenon.
The most recent IPCC report sets out the best estimates of how
much methane makes it into the atmosphere each year. Overall,
methane emissions are between 500-600 million tonnes per year.
Methane from fossil fuel burning makes up around 80 million tonnes.
Waste decomposition, from landfills, is 35-69. Rice agriculture
31-112, and cows and sheep produce 76-189.
In this context, the 8 million tonnes per year that the
Semiletov study cites is significant - methane is a powerful
greenhouse gas, and any extra released because of climate change
will make it harder to stop global warming - but hardly
Don't hit the bomb shelter just yet
Meanwhile, scientists are busy measuring what's actually
happening in the atmosphere. While carbon dioxide levels continue
their steady march upwards, there don't seem to be any signs of
'catastrophic' methane release.
NASA, who maintain a record of the amount of atmospheric Methane
as recorded by their observatory in Hawaii,
"Methane was steadily increasing in the
1980's, it's growth rate slowed in the 1990's, and it has had a
near-zero growth rate for the last few years."
When it comes to methane, clathrates and the Arctic researchers
are still assembling the pieces of the scientific puzzle. New
research can help understand what's going on, but it shouldn't be
recent review of the scientific literature on the subject
"Our current estimates of gas hydrate
storage in the Arctic region are ... extremely poor. It is
still unknown whether future ocean warming could lead to
significant methane release..."
That doesn't mean clathrates should be ignored. By burning
fossil fuels we're conducting a grand experiment with the planet's
atmosphere, and it would be foolish to shrug off concerns about how
the planet might react.
But it's clear that more research is needed to fill in the
picture, and so for the moment warnings about Arctic methane
clathrates causing abrupt and severe climate change need to be