Science

Study finds early warning signals of global ocean conveyor belt collapse

Study finds early warning sign...
The collapse of the Atlantic Meridional Overturning Circulation would trigger cooling and sea level rises in the North Atlantic region and encourage drought in central Africa (Photo: Shutterstock)
The collapse of the Atlantic Meridional Overturning Circulation would trigger cooling and sea level rises in the North Atlantic region and encourage drought in central Africa (Photo: Shutterstock)
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The collapse of the Atlantic Meridional Overturning Circulation would trigger cooling and sea level rises in the North Atlantic region and encourage drought in central Africa (Photo: Shutterstock)
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The collapse of the Atlantic Meridional Overturning Circulation would trigger cooling and sea level rises in the North Atlantic region and encourage drought in central Africa (Photo: Shutterstock)

We could see early warning signs of the collapse of a key component of the global climate up to 250 years in advance, a new study has shown – ample time to either prevent or prepare for the consequences of abrupt climate change. The University of Exeter study analyzed the Atlantic Meridional Overturning Circulation (AMOC), sometimes referred to as the global ocean conveyor belt, in a highly-complex and realistic simulation model, and identified the likely mechanisms that would drive such a collapse.

The AMOC is crucial to Earth's climate. It transports heat from the tropics to the cooler North Atlantic and then up into the atmosphere, driven by differences in density in ocean layers that are caused by salinity and temperature variations. Without it, the surface air temperature of the North Atlantic region would cool by around 1-3 degrees Celsius, with isolated pockets cooling by up to 8°C.

It would drive the intertropical convergence zone southward, encouraging drought in the Sahel region (south of the Sahara desert). And it would result in dynamic sea level changes on the coasts of Europe and North America of up to 80 cm (31 in). (Dynamic sea level relates to the sea level deviation from the geoid, which is the level the ocean would be at if affected only by Earth's rotation and gravitation – not wind, tides, and other circulatory forces.)

As freshwater glacial ice melts or surface temperature increases, the density of surface waters in the North Atlantic shrinks. This appears to be happening now, and it's triggering a positive feedback loop that accelerates the process, though there's little evidence as yet of any impending collapse.

In the long run, though, the system could cross a threshold known as "critical slowing down," which would make it unstable and likely lead to relatively sudden collapse – on the scale of months. The researchers sought to identify the early warning signals that precede this phenomenon.

They ran simulations with the FAMOUS climate model, which predicts AMOC collapse in around 800 years under a scenario that has the rate of freshwater flows into the system in line with recent history. Their analysis found that telltale signs of critical slowing down appeared around 250 years before the collapse: the natural fluctuations in the circulation got longer and longer, and the warning signals were latitude dependent.

Moreover, notes co-author Tim Lenton, "The best early warning signals in the model world are in places where major efforts are going into monitoring the circulation in the real world – so these efforts could have unexpected added value."

So is forecasting AMOC collapse as simple as monitoring the real-world circulation and comparing the data to simulations? Not quite. The study may have used a more realistic simulation of the climate system to search for early warning signals than any that came before, but it still relied on assumptions that may not pan out. Freshwater forcing of the system, for instance, could increase at a greater rate than the simulations considered, and the scientists are unsure if the early warning signals would still appear if that happened.

Regardless, the researchers advocate caution and increased monitoring. "We don’t know how close we are to a collapse of the circulation, but a real-world early warning could help us prevent it, or at least prepare for the consequences," says Lenton.

A paper describing the research was published in the journal Nature Communications.

Source: University of Exeter

26 comments
Diane Wendt
This situation was addressed, among several others, in a great series of three books by Kim Stanley Robinson -- Forty Signs of Rain, Fifty Degrees Below, Sixty Days and Counting. These are a story of the impact of global weather change, based on hard science, wrapped in the lives of some very interesting characters. Must reads for anyone interested in the impact of climate change, as well as near-future scifi fans.
b@man
HAHAHA... groping for disaster:)
Guy Beebe
Very nice propaganda piece. Mislead, misdirect and imply. Using fact to mislead, is a classic propaganda strategy.
In this case, the sensational claim, "the system could cross a threshold known as "critical slowing down," which would make it unstable and likely lead to relatively sudden collapse – on the scale of months."
Should be completely ignored. Since they also said, " predicts AMOC collapse in around 800 years." Eight. Hundred. Years. Just to be clear, these same idiots aren't able to say we are definitely in an El Nino event now, while it is happening.
Stephen Thomas
let's hope the modeling for this is a bit better than the CDC's "1.4 million ebola cases by January" ridiculous alarm blast. Also this conveyor belt business is serious. Is that [disastrous breakdown in this mechanism] what we need for "leaders" to finally start being responsible? WE CAN'T WAIT FOR RESPONSIBLE LEADERS. We have to start being responsible citizens.
Earl Decker
So they used the FAMOUS climate model to come up with their assumptions that may or may not be correct. Some science!!! All the other hundreds of climate models , graphs and charts have been wrong in their predictions and what makes these researchers think this "FAMOUS" model is any different? Bottom line is the last 2 paragraphs sums it up that the study from the model tells them absolutely nothing concerning the real world. No model built by man can ever duplicate what occurs in the real natural world.
piperTom
We expect this disaster in 800 years, with confirmation in just over 500 years? Is it too soon to start drinking?
YukonJack
My money will be invested in learning how the Eskimo survives. Anybody foolish enough to believe we humans will be able to turn up the Earth's thermostat may be in for a very rude surprise from Mother Nature. Just like Mom at home you never mess with her thermostat!
Wolf0579
I really love it when the science deniers use the web to bash science... oh, the delicious irony!
Steve Fisher
The US as a conveyor belt stopped functioning around the time Kennedy was killed.
Such a lovely planet, or it was. Bye. Bye.
Rann Xeroxx
I really love it when reality deniers keep saying calling people who are skeptical about one facet of climate science, namely AWG, "deniers" as if they are ignorant or creationalist or something.
The fact is it takes more faith to believe in the "science" of AGW than not. There is absolutely no "science" that has proven that the doubling of a trace that is still only a percentage of a percentage of the make up of the Earth's air is driving recent warming when the Earth has been warming and cooling during this interglacial period for thousands of years. Fact is we maybe heading for an extended cooling period soon.
But just keep screaming "deniers" from your AGW temple. The believers will chant your proclamations.