An ABC report at the weekend on the Wilkins Ice Shelf being in danger of breaking off from Antarctica sent me scurrying back to look at the data for myself because I had risked being called a climate change sceptic back in June by writing in Crikey that “when you look at the sea ice in the southern hemisphere the evidence for damage from global warming is certainly much harder to see” than you get from looking at pictures of polar bears stranded without ice in the Arctic.
The mistake I was making, several correspondents informed me, was that the evidence I quoted for the ice coverage in the southern hemisphere actually being greater than at any time in the last 30 years did not take account of the fact that while the area might be greater the thickness was left. The evidence produced by the European Space Agency that “a large plate of floating ice shelf attached to Antarctica is breaking up, in a troubling sign of global warming” on which the ABC story was based suggested that I should prepare a mea culpa.
The National Snow and Ice Data Center (NSIDC), part of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder, collates information on ice coverage around both poles gained from satellites and it told me the following story: it’s true that one large section of the Antarctic has a substantially lower concentration of ice than the average over the reference period of 1979-2000. It is shown in blue on the map where the land mass (shown in grey) points towards the tip of South America on the left.
Get Crikey FREE to your inbox every weekday morning with the Crikey Worm.
What you will also see are substantial coloured red areas where the ice concentration is higher than normal. The total anomaly is a million more square kilometres covered by ice than the average. If the ice breaking off is caused by global warming, what causes the increased concentration elsewhere?
The NSIDC figures for the extent of ice coverage in June for the last 30 years show the following pattern:
The trend is certainly towards increasing ice coverage. In a probably futile attempt to avoid being dismissed as a sceptical climate change troglodyte, I include the date for the Arctic where the pattern is not only the reverse of down south but the rate of decrease in ice coverage is far greater than the southern increase.
In an attempt to understand the seemingly different behaviour at the two poles, I turned to the NASA’s Goddard Institute for Space Studies (GISS) which uses its satellites to analyse the world’s surface temperatures. Over the last 20 years, it seems, the further north you go, the greater the increase in temperature.
The mean temperature at the South Pole actually has been marginally colder during the years from 1998 to 2007 than in the GISS reference period of 1951-1980 while at latitude 90 degrees North temperatures have got some 1.5 degrees centigrade hotter.
This year has shown a similar pattern in the southern hemisphere to the last 20 years with June being an especially cold month with temperatures at 90 degrees south being four degrees colder than normal.
Don’t ask me what it all means but it does make me think that decisions on climate change are being made on some very uncertain hypotheses.