Update 20 September:
EXTENT: Satellite data shows Arctic melt sea-ice extent probably reached the minimum for the year at around 3.4 million square kilometres on Monday 17 September, 18 per cent less than the previous record in 2007 of 4.2 m.sq.kms. The JAXA daily raw data is
here and the NSIDC date is
here. This extent is now well
less than half of the average extent of the 1980s.
VOLUME: The sea-ice volume is now down to just
one-fifth of what it was in 1979. Latest
PIOMAS volume from September 3, 2012 is 3407 cubic kilometers of
ice remaining in the Arctic. Contrasted with the 16,855 of 1979, that is
just about 20 per cent. Extent has dropped further since 3 September, so minimum volume this melt season will be about 5–10 per cent less than the early-September figure.
ICE-FREE ARCTIC: Debate rages within the scientific community. Previously we covered
Big call: Cambridge prof. predicts Arctic summer sea ice “all gone by 2015”. On Monday the Guardian reported
"Arctic expert predicts final collapse of sea ice within four years", in which Prof. Peter Wadhams of Cambridge said: "I have been predicting [the collapse of sea ice in summer months]
for many years. The main cause is simply global warming: as the climate
has warmed there has been less ice growth during the winter and more ice
melt during the summer… in the end the summer melt
overtook the winter growth such that the entire ice sheet melts or
breaks up during the summer months. This collapse, I predicted
would occur in 2015-16 at which time the summer Arctic (August to
September) would become ice-free.
The final collapse towards that state
is now happening and will probably be complete by those dates. As the sea ice retreats in summer the ocean
warms up (to 7C in 2011) and this warms the seabed too. The continental
shelves of the Arctic are composed of offshore permafrost, frozen
sediment left over from the last ice age. As the water warms the
permafrost melts and releases huge quantities of trapped methane, a very
powerful greenhouse gas so this will give a big boost to global
warming." Unforntunately, the eviednce is on his side.
 |
Northern Polar Institute Research Director Kim Holmen, left,
with
UN Foundation Board Chairman Ted Turner and
President Timothy Wirth in the Arctic
|
Post of 13 September:
By
David Spratt,
published in
ReNewEconomy on 12 September 2012
and in
Climate Progress on 13 September 2012
The Arctic sea-ice
big melt of 2012 “has taken us by surprise and we must adjust our understanding of the system and
we must adjust our science and we must adjust our feelings for the nature around us”, according to Kim Holmen, Norwegian Polar Institute (NPI) international director.
From Svalbard (halfway between mainland Norway and Greenland), the BBC’s David Shukman
reported on 7 September that Holmen had described the current melt rate “a greater change than we could even imagine 20 years ago, even 10 years ago”.
As
detailed last week, the thin crust of sea-ice which floats on the north polar sea is now only half of the average minimum summer extent of the 1980, and just one-quarter of the volume twenty years ago.
