Arctic's big melt challenged

New data suggest the North Pole got a little thicker in the 90s

By BBC News Online's Jonathan Amos

If ever you needed convincing that climate science was complex stuff, just look at the Arctic. We are told the sea ice in the northern polar region is disappearing fast; some computer models even suggest there could be completely open water there during the summers at the end of this century.

I believe we have been a little bit overly stampeded into the idea that there is a terribly alarming melting taking place

Dr Greg Holloway

If this really is the case, the implications could be immense - and not just for the polar bears which rely on the ice to go hunting for seals. The cryosphere plays a crucial role it helping to regulate the climate on planet Earth. An ice-free Arctic would likely accelerate any global warming process that was taking place.

But a new, and as yet unpublished, piece of research is challenging the idea that a big melt is underway. Dr Greg Holloway, of the Institute of Ocean Sciences in Sidney, Canada, has got tongues wagging with his suggestion that the missing ice is still there, piled up in locations where researchers have not been looking for it.

The evidence for major thinning is supported by submarine data. Upward-looking sonar readings, studied by both US and British scientists, have produced broadly similar results: about a 40% reduction in draught between the 1960s and 1990s - by draught, researchers mean the difference between the surface of the ocean and the bottom of the ice pack.

But the submarine data are not exactly comprehensive: the cruises were not continuous and the data sets only cover certain areas in the Arctic. And this is partly what got Dr Holloway into thinking the ice may simply have been "mislaid".

Satellite methods

He wondered if multi-decadal wind patterns known to operate in the Arctic could have shifted the ice into areas not surveyed by the submarines, giving the illusion that the ice was losing volume over a period of time. And when he matched the timing of the submarine visits with what he knew about wind cycles, his suspicions were confirmed.

Satellites show a 3%-per-decade reduction in area - but assessing thickness is more difficult

"It's a circumstance where the ice tends to leave the central Arctic and then mostly pile up against the Canadian side, before moving back into the central Arctic again," he told BBC News Online. "Because of territorial waters and where US submarines weren't allowed to go in the 1990s - the submarines couldn't enter Canadian waters and that's where the ice was."

Dr Holloway believes the fact that the British research tallied with the American studies was purely coincidental - a "fluke".

"Trying to get a picture of the volume of Arctic ice is pretty sketchy," he said. "It's a question of what other information we can bring to bear so that we get a fuller picture. The great hope for the future is that satellite methods may be able to observe the thickness of the ice as well as the extent."

But Dr Peter Wadhams, of the Scott Polar Research Institute in Cambridge, UK, and one of the world's leading experts on Arctic ice, is not yet prepared to accept the Canadian's analysis.

Stability returns

"It needs testing obviously, but I think on the whole the evidence is against it," he told BBC News Online. "There are some submarine data sets from these regions that are not yet published and they show no thickening, and data from radar altimetry suggest thinning over the entire Arctic, not just over the regions where the submarine data exist."

Polar bears use the ice to hunt for seals

Dr Wadhams said he also thought some of the theoretical basis underpinning Holloway's ideas was not supported by what science had learnt about ice dynamics.

"Modellers suspect it is not as simple as Dr Holloway suggests - the ice will not simply pile up in some other place. There will be a change in the distribution of ice thickness around the Arctic but it won't involve any massive build-ups to compensate for overall thinning."

If the submarines have got it right then at least some stability appears to have returned to the Arctic. The latest and most comprehensive analysis yet of the sonar data collected in the 1990s shows little if any thinning - at least towards the end of that decade. Indeed, at the North Pole, there are indications in the data that the ice even got a little thicker.

For Dr Holloway, there is a recognition that he needs to put his research through peer review and get it published. "There are certainly regional changes taking place," he said. "And if you take the western Hudson Bay, it may well be that the Polar bears are being stressed there because of declining ice coverage. But I believe we have been a little bit overly stampeded into the idea that there is a terribly alarming melting taking place."