University of Toronto study reveals climate change in western Canada

November 27, 2002

A new study of snow accumulation on Canada's highest mountain provides strong evidence that significant climate change has occurred in Western Canada over the past 150 years.

The study, which will appear in the Nov. 28th issue of Nature, examines climate change over the past 300 years and provides evidence that both surface and atmospheric temperatures have risen in Western Canada since the middle of the 19th century. Led by U of T physicist, Professor Kent Moore, the international team of researchers warns that if the trend continues, the region could see warmer winters and changes in weather patterns.

Along with researchers from the University of Calgary and the PAGES International Project Office in Bern, Switzerland, Moore studied snow accumulation on Mount Logan in the Yukon Territory. The snow accumulation record was found in an approximately 100-metre-long ice core drilled out of the mountain at over 5,300 metres above sea level.

Chemical analysis of the ice core showed that between roughly 1700 and 1850 AD, the average annual snow accumulation at the site remained constant. But starting around 1850, there has been a marked increase in snow accumulation, with the largest changes taking place in the past decade. "We argue that this increase in snow accumulation is associated with a warming of the atmosphere over Western Canada," says Moore. This seemingly paradoxical effect is due to the fact that warmer air holds more moisture that - in winter - can be released as snow.

Although the last century has seen an increase in surface temperatures in the region, the short length of atmospheric data sets, typically 50 years or less, has made it difficult to identify a similar trend in the atmosphere. Current theories and models demand that both higher surface temperatures and atmospheric warming must exist for there to be evidence of climate change due to an increase in greenhouse gases, and Moore says his team's study provides this evidence.

The paper points to two specific climate "modes" - patterns of regional climate variability - as possible causes of warming in Western Canada. These modes are called the Pacific North America pattern and the Pacific Decadal Oscillation. "We're seeing evidence that both of these climate modes have been intensifying," says Moore. "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."

If this is a manifestation of regional climate change, Moore warns that these intensified modes may affect regional winter weather patterns. "Western Canada will continue to warm," he says.

The finding promises to intensify the debate over whether humans are responsible for such climate change, says Moore. Previous research has shown that levels of atmospheric carbon dioxide - a major greenhouse gas linked to climate change - also began to rise in Western Canada around 1850, due partly to the Industrial Revolution and land clearing for farming.

In the present day, Moore says, the atmospheric warming findings refute the argument that climate change is not related to human activities and highlight the critical need to take action to reduce global warming. "We have to be serious about this. Kyoto is a start - I don't know if it's all we have to do. But, for our children and our children's children's sake, we need to deal with this because we've caused it."
The study was funded by the International Arctic Research Center in Fairbanks, Alaska, the Geological Survey of Canada, the National Institute of Polar Research in Tokyo and the Natural Sciences and Engineering Research Council of Canada.


G. W. Kent Moore
Department of Physics

Sue Toye
U of T Public Affairs

Nicolle Wahl
U of T Public Affairs

University of Toronto

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