CLIMATE: by Peter WestmoreNews Weekly
Don't get steamed up over Arctic melting
, October 22, 2005
Global warming has been blamed for a dramatic reduction in the Arctic ice cap. Peter Westmore looks at the evidence and asks if this is true.Global warming has been blamed for a dramatic reduction in the Arctic ice cap. The 2005 northern summer melting of the ice cap has been the largest measured over 21 years, according to an American study.
Britain's Channel 4 claimed: "By the end of the century, and possibly much earlier, the region is likely to be ice-free through the summer months - pushing temperatures not seen there for around a million years." (Channel 4 News UK
, September 29, 2005). Similar reports appeared in the Australian media.What does it mean?
What are the facts, and what does all this mean?
America's National Snow and Ice Data Center (NSIDC) released a report late in September which said: "For the fourth consecutive year, NSIDC and NASA scientists using satellite data have tracked a stunning reduction in Arctic sea ice at the end of the northern summer."
It added: "If current rates of decline in sea ice continue, the summertime Arctic could be completely ice-free well before the end of this century."
However, a careful examination of the report and accompanying information, gives a considerably more complex picture. There have, indeed, been four years of significantly warmer temperatures in the Arctic than previously; but if these are discounted, the previous 20 years show no clearly discernible trend.
Further, history records that there have been many periods of warming and cooling of the polar regions. A prolonged cooling phase in the late 1840s, which saw no melting of the Arctic ice in summer, is now believed to be the cause of the failure of Franklin's expedition to find the Northwest passage from Europe to Asia, which resulted in the death of every man in the expedition.
The Arctic is subject to complex ocean currents, which influence both sea and atmospheric temperatures. Among the most important of these are the global thermohaline currents, which push warmer waters towards the Arctic in both the Pacific and Atlantic oceans.
If the Arctic Ocean is warming up, eventually the atmosphere above it will become warmer and wetter, leading to heavy snow falls which will increase the size of the ice cap.
This feedback mechanism will counter the effect of solar radiation which the report suggests will cause further warming of the Arctic atmosphere.
The NSIDC web site reports that, since satellite data has been available in 1972, "Arctic ice has been decreasing at an average rate of about 3 percent per decade, while Antarctic ice has increased by about 0.8 percent per decade".
If global warming has caused the decline in the Arctic ice cap, it would be expected to have caused the same effects in Antarctica. In fact, the opposite is happening.
More significantly, the total ice area of Antarctica is far greater than that of the Arctic. The land mass of Antarctica is 13 million square km, and the band of sea ice surrounding it is a further 20 million square km in winter. In contrast, the Arctic ice cap area typically is less than half this, 14-16 million square km.
According to the Australian Antarctic Division, the Antarctic ice sheet "holds 90 percent of the world's ice".
In the Antarctic, the increase in the ice cap points to increasing rain/snow fall.
A study, published some years ago in the Journal of Climate
, suggested that during the next century, the Antarctic's ice volume could grow a little, on account of global warming It suggested that increased snow falls would occur because warmer air, when saturated, carries more water vapour.
In any event, in relation to global warming, there is no scientific consensus. Critics argue that short-term climate variations are sufficiently large to mask long-term trends.
Further, while computer models forecast rapidly rising global temperatures, owing largely to increased carbon dioxide in the atmosphere, data from weather satellites and balloon instruments over the past 25 years show no warming trend.
All this indicates that melting of the arctic ice cap is an extremely complex phenomenon, which cannot be attributed to one factor.
William Kininmonth, former head of the National Climate Centre in Canberra, wrote recently that the temperatures of the polar regions are mainly regulated by energy carried from the tropics towards the poles by ocean currents and wind. Without this, the poles would be much colder.Seven years
He said: "A one-percent increase in the annual average transport in the Northern Hemisphere, if sustained, would transport additional energy sufficient to melt the Arctic Ocean sea ice in about seven years (and computer models cannot simulate the poleward transport of energy with such accuracy!)."
After observing that climatic trends oscillate over periods ranging from decades to centuries, he concluded: "We should not be too concerned about recent rises in temperatures over the Arctic. There will not be a runaway warming because the region is reliant upon transport of energy from the tropics to maintain its 'warmth'."