Timing the Apocalypse Part 2: AMOC Shutdown

The Atlantic Meridional Overturning Circulation or AMOC is the Atlantic Ocean section of this image.

The Atlantic Meridional Overturning Circulation (AMOC), is rapidly approaching a tipping point . It is a major part of the global Thermhaline Circulation current that spans the globe. The AMOC plays a vital role in the redistribution of heat and salt throughout the global oceans. It is a large system of ocean currents that, like a conveyor belt, carries warm water from the tropics northwards into the North Atlantic. This process is responsible for keeping the world’s oceans continually mixed, and that heat and energy are distributed evenly around the earth. This, in turn, contributes to the stable climate humans have thrived in for millenia. However, the AMOC is showing signs of faltering.

Scientists have been worried about this for years. In fact, it was the plot of the 2004 blockbuster The Day After Tomorrow. As most Hollywood movies do, this movie dramatizes this real scientific phenomenon to gross inaccuracies. However, it does a good job of explaining the general cause of the problem. Please watch this short clip from the movie where lead actor Dennis Quaid explains the danger of AMOC collapse to those in charge:

Over the last century, the AMOC has “moved closer to a critical threshold, where it may abruptly shift from the current, strong circulation mode to a much weaker one,” says study author Niklas Boers, a climate researcher at the Potsdam Institute for Climate Impact Research in Germany. The AMOC is the Atlantic stretch of the global conveyor belt that drives surface and deepwater currents in every ocean, and even influences the rate of sea ice formation at the poles. This ocean circulation system has exhibited two states: a strong, stable state and a slow, weak one. Warming temperatures weaken the AMOC, a new analysis suggests, ultimately pushing it toward a tipping point where it could rapidly turn off. Thus, global heating caused by human industrial activity could directly cause the AMOC to collapse. In the next video, Paul Beckwith explains what this system is, why it's important and more importantly why scientists are worried. Is the AMOC on the verge of tipping?:

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Scientists hypothesize that such a shutdown may last have occurred during the Younger Dryas around 14, 500 years ago. One theory suggests that a sudden flood of Laurentide Ice Sheet meltwater that reached the Nordic Seas leaked into the Arctic and the North Atlantic, diluting the oceans’ salinity, thus weakening the AMOC. There were other freshwater sources as well that eventually emptied into the Arctic Ocean. This influx of fresh water ultimately decreased the salinity enough to change the AMOC to its weak state.

Now, scientists are warning that the AMOC is at it's weakest in over 1000 years. From the study:

Dr Thornalley (UCL Geography) said: “Whilst climate modeling has long predicted a slowdown of the AMOC as a result of human-induced warming, this study shows the increasing evidence in support of the modern Atlantic Ocean undergoing unprecedented changes in comparison to the last millennium, and in some cases longer.

In the next video, Timothy Lenton explains the interconnectedness of climate tipping points, climate fragility and explains some of the dire consequences of a shutdown AMOC. He also goes into detail about the fate of the UK under such a scenario:

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So, how soon could this happen? In my research, some scientists believe that this will still not happen for centuries. Moreover, the slowdown would take decades to take affect. However, as you just saw in the video, Timothy Lenton believes that this event could happen much sooner. He believes that it could happen when the earth's temperature reaches 2.5°C above the preindustrial baseline. Currently, we are at close to 1.2°C in 2022. We are projected to reach 2.5°C by around mid-century. However, some people believe that there are signs that this could happen very soon! In the next video from Environmental Coffeehouse, Jennifer Hynes discusses a recent twitter thread by Kris Van Steenbergen that warns that collapse of the AMOC could be imminent:

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Here is the twitter thread that Jennifer Hynes is referring to:

Until the last few decades, the AMOC was believed to remain stable going forward for at least the next few centuries. Recent studies have put that belief into question. Will the AMOC change state around 2050 as Timothy Lenton believes or could it happen much sooner? No one really knows. The AMOC could remain stable for centuries. What we do know is that human industrial civilization is warming the earth. This warming will eventually cause the AMOC and many other tipping points to trigger. What seems apparent is that these events will not happen in isolation. Global tipping points such as the destruction of the Great Barrier Reef, the death of the Amazon rainforest, a Blue Ocean Event, just to name a few are all intimately interconnected. One tipping point falling will trigger another. At this point climate models will be meaningless. We need to act while we still can. If we still can.