New Evidence of Climate Change in Western Canada

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 University of Toronto 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 IGBP-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 a glacier near the peak 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.

The result is consistent with much other research around the world. “There is a large and growing body of evidence, including changes in the cryosphere, changes in the timing and pattern of biological activity, and direct measurements of temperature, that shows that the Earth is warming,” says Dr Will Steffen, Executive Director of the International Geosphere-Biosphere Programme (IGBP). PAGES is one of the core projects of IGBP.

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 co-author Dr Keith Alverson, Executive Director of the PAGES International Project Office. “There is little doubt in the bulk of the scientific community that global warming is occurring. The current debate is about what its consequences may be. What our results show is that global warming can manifest itself, in part, with a strong regional amplification as an amplification of a naturally occurring climatic mode. Thus, study of how the climate has varied in the past can provide key evidence as to its likely consequences in the future.”

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.