Signs show we're dangerously near some climate tipping points
CBC
England and France could suddenly get a new, colder climate, as the ocean current that gives them their normally mild winters is close to collapse, a new study suggests.
The current known as the Atlantic Meridional Overturning Circulation (AMOC), crucial for warming Western Europe, could disappear as soon as 2025, according to research published this week in Nature Communications. And that would literally cast a sudden chill over the region.
The authors, Peter Ditlevsen and his sister, statistics professor Susanne Ditlevsen at the University of Copenhagen, found signs that we're close to the "tipping point" that will trigger the current's demise.
It's just one climate signal suggesting we may now be getting dangerously close to some irreversible climate "tipping points" that scientists have warned about. Here's what that means.
When it comes to climate change, a tipping point is a major, irreversible change that happens suddenly when a certain threshold is reached, such as a certain temperature.
We understand most changes as being gradual and linear (such as more heat waves as the average global temperature increases). In theory, those can be gradually reduced and even reversed if we cut and remove harmful emissions from the atmosphere.
But tipping points are different. They can happen suddenly, like an on-off switch, pushing climate systems into a completely new state. And they're generally irreversible or difficult to reverse.
"The irreversibility is the really scary part," said Vasilis Dakos, a researcher who has studied early warning signs of approaching transition or tipping points at the Centre national de la recherche scientifique in Montpellier, France.
The new study gives a stark climate example: England and France have milder winters than most of southern Canada despite being at a similar latitude. That's thanks to the Atlantic Meridional Overturning Circulation (AMOC), combined with the Gulf Stream. The AMOC is part of a global conveyor belt that circulates warm water from the tropics to colder regions and vice versa.
Models predict an important climate tipping point will come when the AMOC shuts down or collapses, and stops circulating heat through the Atlantic. That's because it's powered by the sinking of dense salt water in the North Atlantic, and that process is getting swamped by the influx of lighter, freshwater from rapidly melting ice in Greenland.
"Then the conveyor stops," explained Peter Ditlevsen.
The study says the collapse will happen as early as 2025 and no later than 2095.
The last time that current collapsed and was restored, during the last ice age period, it caused temperature fluctuations of 10 to 15 C in just a decade, and signs of its impact could be seen all over the world, Peter Ditlevsen said.
This time, the researchers predict the AMOC's collapse will, among other things:
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