Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 294

matter that was trapped below permafrost - in some cases taking up a hydrate form within
sediments.
The future behaviour of methane sequestered beneath permafrost is a very controver-
sial topic. First, the extent and size of methane reservoirs in the Arctic is at present poorly
known. However, the estimate by Shakhova and colleagues in 2010 of 3.75×102 Gt C (car-
bon) in methane hydrates just on the East Siberian Arctic shelf gives a good idea of the
scale being discussed. What makes these Arctic methane reservoirs such a formidable wild
card in climate science is the question of whether climate warming will lead to a slow and
more or less linear release. At present, this scenario is probably supported by most scient-
ists, but there remains a low probability of the extraordinary risk associated with a possible
sudden release. IPCC AR4 estimated that if only 0.1% (1.8 Gt C) is instantaneously re-
leased to the atmosphere, CH 4 concentrations would immediately increase to about 2,900
ppb from the 2005 value of ~1,774 ppb. Imagine the impact this would suddenly have on
radiative forcing! The paper by Carolyn Ruppel explains in greater depth the physics and
uncertainties involved, while the short review by Gail Whiteman and colleagues gives a
good summary of the socioeconomic consequences. They estimate that the release of meth-
ane from the East Siberian Sea alone would cost global society about $60 trillion.
These thoughts bring our quick survey of SLCFs to an end. These are the five points
the Arctic Messenger hopes you will remember:
1. SLCFs comprise a very significant proportion of the total radiative forcing that
is ultimately driving warming of the Arctic.
2. By conspiracies between Arctic climate, seasonal solar cycle, atmospheric cir-
culation and the chemistry of SLCFs, Arctic spring is the time when the im-
pact of these substances is at its greatest strength. As a result, by accelerating
spring snow and ice melt, they decrease the snow/ice albedo effect and thus
accelerate Arctic warming.