Approaching a Dangerous Tipping Point in the Atlantic Ocean
Clarifying recent reporting on the Atlantic Ocean Overturning Circulation (AMOC)
The oceans are the beating heart of our home. They gave birth to life and provided the climatic conditions that enable humanity to thrive by distributing heat around our blue planet.
There’s been a lot of media recently about the deep-ocean current system known as the Atlantic Meridional Overturning Circulation (AMOC). The AMOC moves warm water from the tropical Atlantic to the northern Atlantic region. This moderates temperatures in the UK and western Europe as well as eastern North America. It also prevents a build-up of heat in the tropics.
For example, Stockholm is further north than the Canadian town of Churchill, Manitoba on the edge of the Arctic tundra, where polar bears roam the streets.
Need-to-Know: Any substantial change in the AMOC is a BFD
My first clarification is that the Gulf Stream is not the same as the AMOC. It is a small part of the overall AMOC system. I’ve written about the importance of the AMOC a few times over the years. Sadly much of the recent media coverage has been misleading. So here’s some facts you should know:
The AMOC shut down or collapsed at the end of the last ice age 14,500 years ago. That pushed the Northern Hemisphere back into near-ice-age conditions for another 3000 years.
The AMOC is now weaker than at any time in the past 1000 years.
Recent evidence shows the AMOC has a tipping point, a critical threshold where the inflow of freshwater from melting ice in the Arctic and Greenland slows the current enough to allow more freshwater to accumulate further slowing it down even more.
A new analysis of the evidence shows we are past the tipping point and that an AMOC collapse is imminent, according to a study published in Nature Communications. Many scientists I spoke with disagree. They don’t think the AMOC is past its tipping point but they do agree it’s not far off.
Need-to-Know: An AMOC collapse is decades away
Now here’s what some media got wrong. “Imminent” in that Nature study means a very remote chance a collapse could start to happen as soon as 2025. The far more likely timeline for a substantial slowdown or partial collapse to be underway is between 2040 and 2060. However, this is only one study. This is an active area of research and more studies are coming.
Need-to-Know: Avoiding an AMOC collapse requires a 50% cut in emissions by 2030
Secondly, it would take decades for this massive current to stop completely.
The only way to prevent this is to slash carbon emissions fast enough, such as a 50% reduction by 2030. However, once it begins in earnest there’s nothing we can do but try to slow it down and prevent a complete collapse. (We may already be too late to do anything else now.)
Even an AMOC slowdown or partial collapse is a place we don’t want to go. Without the transfer of enormous amounts of heat from the tropics much of the Northern Hemisphere will become much cooler. Meanwhile, heat will build up in the Southern Hemisphere. Imagine how much this would mess up weather systems around the planet.
Need-to-Know: An AMOC collapse would be catastrophic
Some studies estimate a complete AMOC collapse would mean average annual temperatures in Western Europe and eastern North America would plunge 15 degrees Celsius, and could be up to 30 degrees C colder in winter over a decade or two. That would be the end of farming in northern Europe and eastern Canada. (Scandinavia had record-cold temperatures this winter, hopefully, that is just an anomaly and not a confirmation of anything.)
This would not stop global warming. A collapse would just trap all the heat in the Southern Hemisphere. Large areas would become too hot to survive.
Sea level would rise as much as a meter along the U.S. east coast because the Gulf Stream would no longer flow north and water would pile up along the coast.
Those are just a couple of the nightmare impacts.
The scientific evidence now is that we can't even rule out crossing a tipping point already in the next decade or two. Given the impacts, the risk of an AMOC collapse is something to be avoided at all cost.
— Stefan Rahmstorf, an oceanographer and Head of Earth System Analysis at Germany’s Potsdam Institute for Climate Impact Research
Need-to-Know: Climate policies are not designed to prevent AMOC collapse or any of a dozen climate tipping points.
Perhaps the biggest current nightmare is that there are no global policies specifically intended to prevent the enormous risks of triggering climatic tipping points like an AMOC collapse.
Given the potentially catastrophic impacts, the additional costs of far more aggressive emission-reduction efforts are worth paying.
Hardly anyone is fully aware of the risks we face. Nor are they aware that the enormous costs to reduce those risks are well worth the investment, so please share this information.
Until next time. Be well.
Stephen