Mail on Sunday, 6 July 2014
The levels of Antarctic sea-ice last week hit an all-time high – confounding climate change computer models which say it should be in decline.
America’s National Snow And Ice Data Center, which is funded by Nasa, revealed that ice around the southern continent covers about 16million sq km, more than 2.1 million more than is usual for the time of year.
It is by far the highest level since satellite observations on which the figures depend began in 1979.
In statistical terms, the extent of the ice cover is hugely significant.
It represents the latest stage in a trend that started ten years ago, and means that an area the size of Greenland, which would normally be open water, is now frozen.
The Antarctic surge is so big that overall, although Arctic ice has decreased, the frozen area around both poles is one million square kilometres more than the long-term average.
In its authoritative Fifth Assessment Report released last year, the UN Intergovernmental Panel on Climate Change admitted that the computer models on which scientists base their projections say Antarctic ice should be in decline, not increasing.
The report said: ‘There is low confidence in the scientific understanding of the observed increase in Antarctic sea ice extent since 1979, due to… incomplete and competing scientific explanations for the causes of change.’
Some scientists have suggested the Antarctic ice increase may itself be caused by global warming. But Professor Judith Curry, head of climate science at the Georgia Institute of Technology in Atlanta, said the arguments were not convincing.
She added: ‘We do not have a quantitative, predictive understanding of the rise in Antarctic sea ice extent.’
She said it was becoming increasingly apparent that long-term cycles in ocean temperatures were responsible for a significant proportion of the ice decline in the Arctic – a process that may be starting to reverse.
I found an interesting paper: Antarctic precipitation and climate-change predictions: horizontal resolution and margin vs plateau issues, by C. GENTHON, G. KRINNER, H. CASTEBRUNET (Annals of Glaciology 50 2009)ReplyDelete
The paper suggests that the INCREASE in snow and ice on the margins of Antarctica may cause the rate of rise in global sea level to be 1 mm per year LESS than the rate of rise otherwise expected..
The increase in sea ice can be linked to increase in precipitation on the margins of Antarctica. This is what one would expect intuitively, since the melting of the grounded coastal ice in accompanied by an endothermic process that causes refreezing as sea ice.
A buildup of snow on top of the glacier adds weight and causes strain within the ice (shear) and thus increases the amount of ice moving down slope and calving from the seaward margin of the grounded ice.
What needs to be explained is the increase in precipitation over the margins of Antarctica.
Since the interior of the continent is a desert, snowfall on the plateau can be ignored.
Thanks Frank, I'll take a look at that when I return from the ICCC meetingDelete