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Ice-free
Arctic in two years heralds methane catastrophe – scientist
Professor
Peter Wadhams, co-author of new Nature paper on costs of Arctic
warming, explains the danger of inaction
Nafeez
Mossadeq Ahmed
24
July, 2013
A new
paper in
the journal Nature argues that the release of a 50 Gigatonne (Gt)
methane pulse from thawing Arctic permafrost
could destabilise the climate system and trigger costs as high as the
value of the entire world's GDP. The East Siberian Arctic Shelf's
(ESAS) reservoir of methane gas hydrates could be released slowly
over 50 years or "catastrophically fast" in a matter of
decades – if not even one decade – the researchers said.
Not
everyone agrees that the paper's scenario of a catastrophic and
imminent methane release is plausible. Nasa's Gavin Schmidt has
previously argued that the danger of such a methane release is
low,
whereas scientists like Prof Tim Lenton from Exeter University who
specialises in climate tipping points, says the process would
takethousands
if not tens of thousands of years,
let alone a decade.
But
do most models underestimate the problem? A new
paper in Proceedings of the National Academy of Sciences (PNAS)
projects that the Arctic will be ice free in September by around
2054-58. This, however, departs
significantly from empirical observations of
the rapid
loss of Arctic summer sea ice which
is heading for disappearance within
two or three years according
to Nature co-author and renowned Arctic expert Prof Peter Wadhams,
head of the Polar ocean physics group at Cambridge University.
If
Prof Wadhams is correct in his forecast that the summer sea ice could
be gone by 2015, then we might be closer to the tipping point than we
realise. To get to the bottom of the scientific basis for the Nature
paper's scenarios, I interviewed Prof Wadhams. Here's what he had to
say:
How long do we have before the Arctic summer sea ice disappears?
Given
present trends in extent and thickness, the ice in September will be
gone in a very short while, perhaps by 2015. In subsequent years, the
ice-free window will widen, to 2-3 months, then 4-5 months etc, and
the trends suggest that within 20 years time we may have six ice-free
months per year.
Why do the climate models not match empirical observations - and why is your estimate of the Arctic sea ice disappearance so different from most model projections?
The
modellers did not pay sufficient regard to observations, especially
of ice thickness. They considered certain physical processes in the
model, then when the rate of retreat greatly outstripped the
predictions of the model, they ignored the observations and stuck
with the model. A very great physicist, Richard Feynmann, said that
when a model comes up against measurements that contradict it, it is
the measurements that must be preferred and the model must be
abandoned or changed. Scientists who have a lot of their credibility
bound up in a model are reluctant to do this. Then there are a number
of key processes that can only be represented if the model has a very
fine grid scale, such effects as the break-up of ice due to waves
generated in the large areas of open water that we now have in
summer; or the additional weakening of the ice by meltwater pools
that melt their way right through the ice sheet. A modeller who
represents all these fine scale processes is Wiselaw Maslowsky
(Monterey) and his models agree with my empirical predictions.
Our global emissions trajectory is already on track to breach 2C in coming decades. What does a 2C world imply for the Arctic melt and the potential for methane release?
We
are already in a 2C world in terms of the heating potential of carbon
dioxide that we have already put into the atmosphere. The heating
will reach 2C before 2050 and will then go on to 3-4C globally by the
end of the century. Even a 2C world involves the probable loss of
Arctic sea ice for much of the year (and 4C for most of it), which
will ensure maximum methane release from the exposed shallow seas of
the continental shelves.
What does the loss of the Arctic summer sea ice mean for the climate? How will this impact on society and the economy?
Our
own model shows that the methane release from the ice retreat will
add about 0.6C to global warming by 2040. Adding on the faster sea
level rise, and trend towards greater extremes in weather (due to jet
stream displacement) means increased risk of catastrophic floods in
less developed countries and a decrease in food production at a time
when world population is rapidly increasing.
What is the link between permafrost melt, methane release and the loss of the Arctic sea ice? After 2015, if the Arctic becomes ice free in the summer, is there a heightened danger of methane release?
The
loss of sea ice leads to seabed warming, which leads to offshore
permafrost melt , which leads to methane release, which leads to
enhanced warming, which leads to even more rapid uncovering of
seabed. If a large release has not occurred by 2016 the danger will
be continuously increasing. It is thought that at 2-3C of global
warming, which means 6-8C of Arctic warming, methane release from
permafrost on land will be greatly increased.
Some people say that a catastrophic methane release over 10 years - your worst-case scenario - is a very low probability event and we don't really need to worry about it. What's your response to that?
Those
who understand Arctic seabed geology and the oceanography of water
column warming from ice retreat do not say that this is a low
probability event. I think one should trust those who know about a
subject rather than those who don't. As far as I'm concerned, the
experts in this area are the people who have been actively working on
the seabed conditions in the East Siberian Sea in summer during the
past few summers where the ice cover has disappeared and the water
has warmed. The rapid disappearance of offshore permafrost through
water heating is a unique phenomenon, so clearly no "expert"
would have found a mechanism elsewhere to compare with this.
Would Arctic experts agree with you?
I
think that most Arctic specialists would agree that this scenario is
plausible.
What about scientists like Prof Tim Lenton, a climate tipping point expert, who argues that a methane release is a long-term problem, not an immediate danger?
His
earlier conclusions are out of date. His oft-cited paper on tipping
points is two years old now and was based on literature surveys
rather than direct research. An ice-free summer (September) Arctic is
clearly nearly upon us, and will be achieved within three years or
less - this is plain from the observational data on ice extent
(satellites) and thickness (submarines and altimeter satellites). I
am sure that he is about to revise his views if he hasn't already
done so.
Dr
Nafeez Ahmed is
executive director of the Institute
for Policy Research & Development and
author of A
User's Guide to the Crisis of Civilisation: And How to Save It among
other books. Follow him on Twitter @nafeezahmed
See also -
(Common Dreams)
(BBC)
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