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 waterClimate change is expected to exacerbate current stresses on water resources from population growth and economic and land-use change, including urbanisation. On a regional scale, mountain snow pack, glaciers and small ice caps play a crucial role in freshwater availability. Widespread mass ... 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 agricultureCultivation of the ground and harvesting of crops and handling of livestock, the primary function is the provision of food and feed., industry and drinking waterDrinking water quality has a micro-biological and a physico-chemical dimension. There are thousands of parameters of water quality. In public water supply systems water should, at a minimum, be disinfected—most commonly through the use of chlorination or the use of ultra violet ... and add even more urgency to the need for reducing fossil-fuel emissionsEmissions of greenhouse gases, greenhouse gas precursors, and aerosols associated with human activities, including the burning of fossil fuels, deforestation, land-use changes, livestock, fertilisation, etc. (IPCC) that cause climate changeClimate change is a lasting change in weather patterns over long periods of time. It can be a natural phenomena and and has occurred on Earth even before people inhabited it. Quite different is a current situation that is also referred to as climate change, anthropogenic climate change, or ....

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 floodsThe overflowing of the normal confines of a stream or other body of water, or the accumulation of water over areas that are not normally submerged. Floods include river (fluvial) floods, flash floods, urban floods, pluvial floods, sewer floods, coastal floods, and glacial lake outburst floods ..., droughtsA period of abnormally dry weather long enough to cause a serious hydrological imbalance. Drought is a relative term, therefore any discussion in terms of precipitation deficit must refer to the particular precipitation-related activity that is under discussion. For example, shortage of ... and shrinking water supplies. They are also causing sea levels to rise, putting coastal areas around the world at risk of floodingThe overflowing of the normal confines of a stream or other body of water, or the accumulation of water over areas that are not normally submerged. Floods include river (fluvial) floods, flash floods, urban floods, pluvial floods, sewer floods, coastal floods, and glacial lake outburst floods ... and erosion.

And now we know, as the researchers put it, “Radical reorganizations of drainageDrainage is the natural or artificial removal of surface and sub-surface water from an area. Many agricultural soils need drainage to improve production or to manage water supplies. 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.

Correction: April 21, 2017

An earlier version of this article included an incorrect credit line with the attached photo. The photographer, Dan Shugar, took the photo for University of Washington-Tacoma, not Agence France-Presse — Getty Images.