Scientists have announced that a river in northern Canada has been dramatically re-routed due to the effects of global warming. Meltwater from the Yukon territory’s Kaskawulsh glacier, formerly flowing north into the Yukon River via the Slims River, now flows south into the Alsek River, emptying into the Pacific Ocean. The event underscores how rapidly potential changes can happen when systems that are affected by climate change reach their tipping points.

The Slim River’s sudden change in course, dubbed "rapid river piracy" by the research team, was caused by the triggering of a tipping point in the retreat of the Kaskawulsh glacier, when meltwater broke through an ice channel that caused a glacial lake that ordinarily fed the Slims to drain instead into the Alsek. The Slims was a large river, up to 150 meters (500 feet) wide in places, but now has been reduced to a mere trickle.

“The river wasn’t what we had seen a few years ago. It was a faded version of its former self,” explains Daniel Shugar of the University of Washington at Tacoma. “It was barely flowing at all. Literally, every day, we could see the water level dropping, we could see sandbars popping out in the river.” Conversely, the flow in the Alsek River, previously on par with the Slims, increased dramatically, and is now 60 to 70 times greater than its northward brother.

Although this sort of phenomenon has been evident throughout Earth’s geological history, the researchers involved say that, to their knowledge, this hasn’t happened as a modern-day event, and definitely not with the suddenness that it occurred: transitions such as this tend to take place over longer periods of time, but this event occurred over a matter of four days during the summer of 2016, with the researchers calling it "geologically instantaneous."

The sudden draining of the Slims River has also resulted in record-level low levels of the Yukon’s largest lake, Kluane Lake, last August. If the low water levels prove to be permanent, it may force the two small communities that rely on the lake to adapt to the change.

"The Kluane lake level dropped last year and is likely to continue dropping," continues Shugar. "If it drops enough that the lake level is below its other outlet, at the north end, it becomes what is called a closed basin. That will have changes to the chemistry, the structure of the lake, the biology."

Shugar and his team also looked at the possibility that the water flow could return to its previous state, but their estimates indicate that the new southward flow is permanent.

"We did some preliminary estimates of what it would take for the Slims River to be reestablished, and it seems unlikely to occur in the current climate."