Methane deposits in Antarctica and more emitted from Arctic permafrost. What does this mean for the climate?
- 30 Aug 2012, 15:05
- Verity Payne
Jim Elliott/British Antarctic Survey/AP
Two new research papers published today improve our
understanding of the planet's methane emissions, and might raise
worries about the role of the gas in warming the planet. The first
suggests that there may be extensive methane deposits under the
Antarctic ice sheets. Meanwhile, the second concludes that
emissions of the gas from Arctic permafrost have been
Methane is a potent greenhouse gas - accounting for around
14 per cent of the warming effect of current man made
greenhouse gas emissions. Recent research has focused on measuring
emissions from methane sources, both natural and manmade.
Antarctic methane reservoirs
Scientists have been particularly interested in methane emitted
from the Arctic. This is because the region is warming particularly
rapidly. In addition, methane released from melting
permafrost and escaping
methane hydrate deposits could exacerbate climate change. But
research published today in the journal Nature suggests for the
first time that there might also be large stores of methane at the
other end of the planet, under the Antarctic ice sheet.
Plants thrived on Antarctica before the continent was covered by
ice some 35 million years ago. Lab experiments show that microbes
living beneath the ice are able to convert plant remains into
methane, and scientists calculate that half of the West Antarctic
Ice Sheet (1 million square kilometers) and a quarter of the East
Antarctic Ice Sheet (2.5 million square kilometers) could cover
carbon-rich sediments containing up to 4 billion metric tons of
methane in the form of methane hydrates. These are an ice-like
substance formed when methane and water combine.
The researchers suggest methane could be released if ice sheets
retreat as global warming continues.
According to study co-author Slawek Tulaczyk, professor of
Earth and planetary sciences at UC Santa Cruz, the findings
underline "the need for continued scientific exploration of remote
sub-ice environments in Antarctica, because they may have far
greater impact on Earth's climate system than we have appreciated
in the past."
Media outlets have reported the findings widely, with most
headlines focusing on potential impacts of escaping methane. For
example, Reuters headlines the story '
Antarctic methane could worsen global warming - scientists',
while the UK Press Agency goes for '
Methane fear beneath Antarctic ice'.
So how realistic is the prospect of enough of the Antarctic
melting to release methane that might be beneath the ice?
The study's authors highlight that "significant uncertainty
exists" in their estimates of methane reservoirs beneath Antarctic
ice. But they calculate that Antarctic ice sheet retreat at the
rate of 1,000 square kilometres per year - comparable to previous
episodes of ice sheet collapse - could result in enough methane
release to affect atmospheric methane levels.
At the moment, this isn't happening. The West Antarctic ice
sheet is losing
ice mass, but slower than an ice sheet which is collapsing. And
with most of the potential methane under the East Antarctic ice
sheet, it looks unlikely that there will be significant methane
release from Antarctica soon.
Arctic methane underestimated
What about Arctic methane sources? Another
new Nature paper finds ten times more carbon than previously
thought is escaping from coastal permafrost in the East Siberian
Arctic Shelf - an amount that dwarfs emissions from land and
submarine permafrost in the region.
The escaping carbon has been trapped for tens of thousands of
years, but with summer sea ice declining, Arctic coastlines are
vulnerable to erosion from waves and storms. With roughly
three-quarters of the Arctic coastline made of permafrost, it is
perhaps not surprising that the crumbling coastline is releasing
more methane and carbon dioxide than previously estimated.
The scientists warn
that erosion of permafrost coasts might worsen as the Arctic
warms, and that this will have "consequences for the temperatures
all over the world."
research also suggests that methane emissions from the Arctic
have been previously underestimated. Such stories have tended in
the past to lead to claims of a "
methane time bomb" or "Arctic
apocalypse", since enough methane escape could lead to further
warming, which would lead to more methane escape, and so-on, in a
self-reinforcing warming cycle. This time, though, the coverage has
been more restrained, with less dramatic
headlines and an informative segment about the research on the
BBC Radio 4's Today
Wetlands dominate in the near future?
Despite recent research suggesting that we've underestimated
Arctic methane sources, there isn't yet evidence to suggest that
these sources are having a significant effect on atmospheric
methane. For example, weekly air
samples from Arctic sites show that there is as yet no direct
atmospheric evidence that emissions of methane or carbon dioxide
from the Arctic are changing.
studying the composition of methane in the air over Siberia
find that during the summer most methane emissions come from
wetlands, and in winter most methane comes from leaking gasfields.
Even though there are plumes of methane in the seawater nearby,
suggesting methane escaping from seabed
methane hydrate deposits, only a negligible amount appears to
be making it into the atmosphere.
In fact the
majority of methane emissions into the atmosphere are currently
from wetlands - such as marshes, bogs, peatland and paddy fields.
climate model projections of increasing methane emissions over
the coming century are largely controlled by wetland methane
As Dr Vincent Gauci, a researcher at the Open University and
director of the website
MethaneNet.org told us last
"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."
Important warming feedbacks from methane emissions in the polar
regions - particularly to the Arctic - have the potential to occur.
But different feedbacks are likely to act over different
timescales, and the possibility of sudden and catastrophic methane
may be overstated. In a
recent review of the subject, methane experts write:
"We speculate that, in the short term
(few decades), melting permafrost will result in larger wetland
areas; when combined with warmer temperatures, this will result in
increased [methane] emissions. The impact of a warming Arctic will
probably only slowly increase emissions from hydrates".
So although polar methane hydrate sources will probably become
important over the long term, particularly if Arctic warming
continues, in the nearer future it looks like wetlands will remain
the major determining factor in global methane emissions.