Snow shows western Canada's warming

Mount Logan's icy summit hides a centuries-old story

By Alex Kirby BBC News Online environment correspondent

Scientists in Canada say they have found evidence that the west of the country has warmed significantly over the last 150 years.

They say the evidence comes from a study of snow accumulation on Canada's highest mountain.

The build-up of snow they have detected there has been most marked over the last decade.

There is a large and growing body of evidence... that shows that the Earth is warming

Dr Will Steffen

The scientists say their findings are consistent with other research suggesting the Earth is warming.

Their study, published in the journal Nature, examines climate change in the region over the last 300 years.

The team was led by Professor Kent Moore, a physicist at the University of Toronto, and included members from the University of Calgary and the IGBP-Pages (International Geosphere-Biosphere Programme - Past Global Changes) office in Switzerland.

Recent acceleration

The researchers studied the accumulation of snow on Mount Logan in the Yukon territory, drilling out of a glacier near the peak 5,300 metres (17,400 feet) above sea level a 100-m ice core.

Chemical analysis of the core showed that the average annual snow accumulation had remained roughly constant from about 1700 to 1850.

Stored ice cores in a US laboratory

But from then on there was a marked increase in accumulation, with the greatest changes happening in the last 10 years.

Professor Moore said he believed the increase was associated with a warming of the atmosphere over western Canada, because warmer air held more moisture than could be released in winter as snow.

Dr Will Steffen is executive director of the IGBP. He said the findings were consistent with much other research around the world.

Dr Steffen said: "There is a large and growing body of evidence, including changes in the cryosphere [the Earth's frozen regions], changes in the timing and pattern of biological activity, and direct measurements of temperature that shows that the Earth is warming."

But some scientists still argue that the evidence for climate change is too tenuous to allow any firm conclusions to be drawn.

Influential patterns

They point, for example, to the discrepancy often found between rising temperatures at the Earth's surface and unchanging atmospheric temperatures.

Snowfall has increased this decade

Professor Moore says his team's findings provide the evidence for warming both at the surface and in the atmosphere.

He points to two specific patterns of regional climate variability as possible causes of the warming he has identified.

One is the Pacific-North America Pattern, which associates high pressure and warming over the north-western part of the North American continent with low pressure and cooling over the Pacific.

More to come

The other is the Pacific Decadal Oscillation, a long-lived El Nino-like pattern of Pacific climate variability which during the 20th Century typically persisted for periods of 20 to 30 years.

Professor Moore said: "We're seeing evidence that both of these climate modes have been intensifying.

"This is evidence that the atmosphere in the region has warmed up, and that it's doing it through an intensification of some natural modes of climate variability."

The study says that if the trend continues western Canada could see warmer winters and changes in weather patterns.