2011/01/01

Running Hot and Cold

The recent extreme cold events in Europe have understandably given some folk cause to mutter about the supposed direction of climate change and global temperatures.
But we can be assured that we are on track to our ultimate destination; plus more degrees C than normal civilised life can sustain.
Hansen sums it up thus:
"...Sea ice insulates the atmosphere from ocean water warmth, allowing surface air to achieve temperatures much lower than that of the ocean. It is for this reason that some of the largest positive temperature anomalies on the planet occur in the Arctic Ocean as sea ice area has decreased in recent years. 
The cold anomaly in Northern Europe in November has continued and strengthened in the first half of December. Combined with the unusual cold winter of 2009-2010 in Northern Hemisphere mid-latitudes, this regional cold spell has caused widespread commentary that global warming has ended. That is hardly the case. On the contrary, globally November 2010 is the warmest November in the GISS record...."  (Hansen et al 20101211)
http://www.columbia.edu/~jeh1/mailings/2010/20101211_TemperatureAndEurope.pdf
Other recent research has attributed the same sea ice effect on the location of the jet streams, and this is found to be a primary cause of the European winter chills.
"It is nevertheless no contradiction between a global warming and cold winters in regions like Europe. Rather, recent analysis suggest that the global mean temperature is marching towards higher values (see figure below), and Petoukhov and Semenov argue that the cold winter should be an expected consequence of a global warming..." (Rasmus Benestad 20101214)

http://www.realclimate.org/index.php/archives/2010/12/cold-winter-in-a-world-of-warming/

Both commentaries note the potential importance of Arctic sea ice cover.
Running totals of sea ice cover are found at:
http://arctic.atmos.uiuc.edu/cryosphere/
in particular  the long term record:
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/sea.ice.anomaly.timeseries.jpg


From the time series there is evidence of a steady (and increasingly rapid) decline in seasonal ice cover.   The Cryosphere charts show that the minimum ice area has fallen from typical historic lows of about 5 million square kilometres to around three million.   


But that is only part of the story.  The surface of your glass of freshly made lemonade can be covered in ice if that ice is only a thin veneer or if it extends all the way to be bottom to be mashed and swizzled with your straw.


The volume of the sea ice is the key indicator of how things are going.   The volume of Arctic sea ice  figure is calculated every few weeks by the University of Washington's Polar Science Centre.
http://psc.apl.washington.edu/ArcticSeaiceVolume/IceVolume.php
But while this shows the anomaly (the variance from a running trend) it does not give us a real clue about how much ice volume remains.
The site comments:
"Monthly average Arctic Ice Volume for Sept 2010 was 4,000 km^3, the lowest over the 1979-2010 period, 78% below the 1979 maximum and 9,400 km^3 or 70% below its mean for the 1979-2009 period. "


From the text and chart on the Washington U Ice Volume site I have extracted a few salient points which as far as I can tell give a true indication of how much ice is left in the Arctic glass.
From this we can see that the summer minimum ice volume has diminished from the 1979 September minimum of 19,000 cubic kilometres to the 2010 September minimum of 4000 cubic kilometres.


I have not joined the dots with a curve, as its non-linear, and the site does not give me enough data to confidently make those interpolations.  But the points for 1979, 2009 and 2010 provide sufficient evidence for us to see that, while sea ice cover is still remaining fairly high, the actual volume of ice beneath that cover is declining drastically.  The ice on your glass is getting very thin indeed.  A layman could be forgiven for drawing the conclusion that an ice-free arctic is not many seasons away.


With that ice goes an enormous heat sink and stabilising influence on the rate of global temperature rise, which will further hasten the rate of loss of grounded ice, and the consequent rate of sea level rise.


If we think back now to the present anomalous state of Europe's recent summer and winter weather with a very modest loss of Arctic sea ice cover, we can only begin to appreciate what may be in store when that last fragile 4000 cubic kilometres of Arctic ice turns to mush not many summers from now, and the lid comes off the Arctic Ocean Weather Machine.


Keep thinking.  Keep acting.  
Kind regards
Nigel

No comments:

Post a Comment