Rising air pollution in the wake of the Industrial Revolution seems to be the explanation for a long-standing enigma in glaciology. The emission of soot from Europe’s proliferating factory smokestacks and steam locomotives explains why glaciers in the Alps began their retreat long before the climate warming caused by human activities kicked in, a study suggests.
The 4,000 or so large and small Alpine glaciers — which today are acutely threatened by rising air temperatures — did well throughout the relatively cool 500-year period known as the Little Ice Age, which began around the end of the thirteenth century. At its maximum in the middle of the nineteenth century, the extent and volume of Alpine glaciers was at least twice what it is now.
But then these glaciers suddenly began to retreat. Other regions of the world may also have been affected — the decline was only well documented in the Alps — and, conventionally, climate scientists consider the Little Ice Age to have ended soon after 1850.
However, despite the glaciers' shrinking, average global temperatures did not rise significantly until the end of the century. In fact, Alpine climate records — among the most abundant and reliable in the world — suggest that glaciers should have continued to grow for more than a half century, until around 1910.
“Something gnawed on the glaciers that climate records don’t capture,” says Georg Kaser, a glaciologist at the University of Innsbruck in Austria and a member of the team that built the case against black carbon, or soot, this week in Proceedings of the National Academy of Sciences1. “A strong decline in winter snowfall was often assumed to be the culprit,” he says. “But from all that we know, no such decline occurred.”
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