Home Science Sea Level A lesson on warming, from an icy river.

A lesson on warming, from an icy river.

In the wilds of the Canadian Yukon, nature has provided fresh evidence of the destructive power of humans, and a stark warning of the dangers billions of people may face.

During last year’s unusually warm spring, meltwater from the Kaskawulsh Glacier cut a canyon through the ice that diverted water from the Slims and Yukon Rivers, which flow north into the Bering Sea, into the Alsek River, flowing south into the Pacific Ocean. Where water once coursed through the Slims River basin, dry riverbeds are now subject to frequent dust storms.

This process of “river piracy” — in which one stream captures and diverts another — appears to be the first example of river piracy observed in modern times. What has normally taken thousands of years or longer in the geological past, took just a few months in the Slims River basin.

The implications are ominous for people around the world who depend on glacier-fed rivers for agriculture, industry and drinking water and add even more urgency to the need for reducing fossil-fuel emissions that cause climate change.

The scientists who published the report of the diversion in the journal Nature Geoscience this month warned that, as glaciers melt, “we may see differences in the river networks and where rivers decide to go.”

And glaciers are melting. In just three decades, the glaciers in Montana’s Glacier National Park may no longer exist, given the rate at which they are disappearing. The glaciers in the Himalayas that feed rivers that flow into China, India, Bangladesh and Pakistan are also receding at a rapid clip, as are glaciers in Europe. Melting glaciers are already putting millions of people at risk of floods, droughts and shrinking water supplies. They are also causing sea levels to rise, putting coastal areas around the world at risk of flooding and erosion.

And now we know, as the researchers put it, “Radical reorganizations of drainage can occur in a geologic instant, although they may also be driven by longer-term climate change.”

This report should serve as an urgent call to action, not only for carbon reduction, but also to consider the onerous emergency plans that will be needed should those crucial efforts fail.