The Canadian flag flies over the Athabasca Glacier, part of the Columbia Icefields, in Jasper National Park. Photo: THE CANADIAN PRESS/Jeff McIntosh The world’s glaciers have been shrinking since the end of the Little Ice Age but scientists say they now have “unambiguous evidence” that human activities are making them melt faster.
Over the last 20 years, human influences on the global climate have become the strongest driver of melting glaciers, a team of Austrian and Canadian glaciologists reported Thursday in the journal Science.
As co-author Graham Cogley at Trent University puts it: “The glaciers are shrinking faster and it’s mainly our fault.”
Glaciers are in retreat from the Alps to the Himalayas — the famed Columbia Icefield in the Canadian Rockies is losing more than five metres of ice every year.
But they have been shrinking since the Little Ice Age ended in about 1850 and Cogley says it’s been difficult for scientists to tease out how much of the loss is due to natural causes and how much is attributable to human activities, like the burning of fossil fuels that has pumped vast amounts of heat-trapping greenhouse gases into the atmosphere.
Glaciers tend to be remote and inhospitable and he and his colleagues just this year managed to finish mapping the world’s glaciers — a task glaciologists started in 1956. The global inventory includes almost 200,000 glaciers, which together would blanket an area larger than Alberta in ice.
For the study released Thursday, Cogley and a team led by Ben Marzeion at the University of Innsbruck assessed how the glaciers have changed in the last 160 years using 12 different global climate models.
The models enable researchers to look at “two virtual worlds, one with us and one without,” Cogley said in an interview.
“We can assess how the world might have changed if we hadn’t been screwing it up,” he said.
To gauge the forces melting the glaciers, the researchers reconstructed the area and volume of each of the glaciers in 1851 as the Little Ice Age ended. Then using the sophisticated climate models they assessed how the glaciers would have retreated over the years under only natural climate factors, such as solar variability and volcanic eruptions, and compared that to the results when they included anthropogenic, or human, factors such as changes in land use and greenhouse gas emissions.
The team says the results point to a clear and growing human impact.
The analysis found that only about one quarter of the global glacier mass loss during the period of 1851 to 2010 is attributable to human causes. But over the two decades between 1991 and 2010 it shows the fraction increased to about two thirds. “In the 19th and first half of 20th century we observed that glacier mass loss attributable to human activity is hardly noticeable but since then has steadily increased,” Marzeion said in a statement released with the study.
While shrinking glaciers are widely seen as an iconic symbol of climate change, skeptics argue natural changes are responsible.
Cogley says the new study is important, as it is “another nail in the coffin” for such arguments.
“What it means is that the people who don’t believe that human activity is responsible for most of the climatic change are running out of places to hide,” he says, pointing to evidence tying human activities to the rise of global temperatures, sea level and more extreme weather.
“The whole kit and caboodle adds up to a coherent picture,” says Cogley.
The world’s glaciers contain less than one per cent of the ice on the planet but are important global players as they are more vulnerable to melting than the massive Antarctic and Greenland ice sheets.
The glaciers are a major contributor to sea level rise and are also important sources of fresh water.
A U.S. climate assessment report earlier this year pointed to melting glaciers in British Columbia and Alaska as a major climate change issue with implications for hydro power production, ocean circulation patterns, fisheries and global rise in sea levels.
Cogley says glaciers are crucial in Peru and Asian countries where meltwater from huge glaciers is a major source of water. Not only do melting glaciers impact water supplies, but they can destabilize mountain slopes and create meltwater lakes, “increasing the risk of rock slides and catastrophic outburst floods,” he and his colleagues say.
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