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Question: Why should we believe in the PIOMAS model trend curve?
Answer: Although the sea ice extent has held up since its dramatic decline in September
2007, it has been steadily thinning and hence its volume has been on the decline. At
some point it won’t be able to get any thinner without a collapse in extent.
Question: What is driving the sea ice retreat so rapidly?
Answer: The original Arctic warming came, directly or indirectly, from global warming.
But as soon as the sea ice started to retreat, the albedo effect took over: where the sea ice
gives way to sea, the sea is warmed and there’s more melting of sea ice, etc. in a vicious
cycle known as “positive feedback”. Similarly where there was snow on land, the land
will absorb more heat. Thus the Arctic Ocean will warm faster and faster as the sea ice
retreats, and the rivers flowing into the ocean will also warm faster and faster.
Question: What is “ESAS”?
Answer: It is the East Siberian Arctic Shelf, of over 2 million square kilometres in area,
the largest continental shelf in the world. 75% of the sea over the shelf is less than 50
metres deep. But when we refer to ESAS, we sometimes mean the sea rather than the
shelf under the sea.
Question: How did permafrost and methane hydrate get into the shelf?
Answer: At the last glacial maximum (LGM), at the height of the ice age about 20
thousand years ago, the sea level was approximately 120 metres lower than it is today.
The ESAS shelf was well above sea level and the cold air temperature would have
cooled the land surface to considerable depth, freezing water around organic matter into
permafrost. Then the sea level rose, and the land and permafrost were inundated. Some
of the organic matter would have decomposed producing methane which could, at certain
pressures and temperatures, combine with groundwater to form methane hydrate. Thus
below the permafrost is now a mixture of hydrate and free methane gas.
Question: Which could produce more methane – the terrestrial permafrost or the marine
methane store (permafrost and below)?
Answer: There are similar estimates for both quantities, at around 1700 Gt (gigatonnes).
Question: Which is more dangerous and why?
Answer: Both are dangerous in that they will inevitably discharge their methane if the
Arctic is allowed to continue warming unchecked. However we consider that the ESAS
area has the most immediate potential to produce abrupt climate change, because of its
vast area, the shallowness of the sea (so methane reaches the surface) and the fact that the
permafrost is being extensively perforated as it is heated by geothermal heat from below
and warming seawater above. This is certainly the opinion of the leader of the team who
have researched ESAS over a number of years, Dr Igor Semiletov. They have discovered
gigantic plumes of bubbles rising to the surface.
Question: If the ESAS methane is being emitted in ever larger quantities, why hasn’t the
methane been detected in the atmosphere?
Answer: It is not possible to characterise the methane in the atmosphere, esp. by isotope
analysis or geographic location, such as to determine its source and whether it originates
from the Arctic or not, or from anthropogenic sources or not. For example some of
the atmospheric methane may come from leakage of natural gas where it is mined; but
some could come from the similar gas leaking from the seabed. However, recently
some spikes of methane have been observed in the atmospheric level at the Svalbard and
Barrow monitoring stations. These spikes are almost certainly due to an oceanic source
of methane, and there is concern that a methane feedback could be starting.
Question: What is the lifetime of methane?
Answer: Estimates vary from 8 to 12 years. There is a general flow of methane from
high latitudes to low latitudes, where 90% of methane is destroyed by OH radicals. But
there is a limited amount of OH produced, so if the methane burden in the atmosphere
increases significantly, its lifetime will be longer.
Question: How does methane compare with CO2 as a greenhouse gas?
Answer: Methane is more powerful than CO2 at reflecting thermal radiation back to the
planet’s surface, which is how a greenhouse gas acts as a blanket. If there is a sudden
injection of methane into the atmosphere, the effect over the first few years is over
100 times as powerful as if an equal weight of CO2 were injected. After 20 years the
methane has decayed such that its average global warming effect is down to 72 times
CO2 (IPCC’s figure). And after 100 years, it is down to between 20 and 25 times CO2.