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Gulfstream before the crash? If the flow motor fails, it will have dire consequences for the climate

Dangerous triggers: Climate researchers warn that the North Atlantic capsize current may be on the cusp of a tipping point – and therefore more unstable than expected. Because the ocean currents engine is already showing the first signs of tipping over to a weakened state.

The consequences of such a collapse of the circulation pump will be as great for the Earth’s climate and especially for Europe, as its climate The study appears in the journal Nature Climate Change..

The Atlantic Overturning Current (AMOC) is a driver of ocean circulation – and a major player in the climate system. Sinking large amounts of water off Greenland pushes up the Gulf Stream and ensures Europe’s temperate climate. But the circulation pump is weak. It is currently as weak as it was a thousand years ago. Models also suggest that the combined effects of warming, retreating sea ice, and increased meltwater influx could push the AMOC to the tipping point.

Normal volatility or imminent coup?

“From computer simulations and paleoclimate data, we know that the fluctuating current can adopt two different modes – the currently dominant strong mode and a second, significantly weaker mode,” explains Niclas Bowers of the Potsdam Institute for Climate Impact Research (PIK) and the University of Exeter. . “This binary stability suggests that abrupt changes between these two types of flow are in principle possible.”

This makes the current North Atlantic core a component of the shift in the climate system. If it changes its status, this could have serious and possibly irreversible consequences for the global climate. Europe will be particularly affected, because then district heating on our continent could be eliminated. However, it is not yet clear whether the current changes in AMOC portend an inversion or are simply linear and essentially stable fluctuations.

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Search for omens

The Boers have now studied these questions more closely. For his study, he analyzed eight different indicators of temperature and salinity of the Atlantic Ocean and looked in chronology for signs of instability. These include increased volatility and increased autocorrelation of the measured values. This means that deviations from the mean increasingly lead to similar fluctuations. It was only recently that researchers noticed these warning signs on the Greenland ice sheet.

As a measure of this sign, the Boers identified the factor λ (lambda). The researcher explains that “the values ​​of λ are negative for the steady states of the system.” “The point at which the characteristic value λ reaches zero indicates the tipping point. This is where the control parameters reach the critical value at which the abrupt change occurs.” So the question was where would the characteristic value λ of AMOC be.

Amok before the critical threshold

Analyzes showed: “Over the past century, the λ factor has increased almost linearly from values ​​close to minus 1 to nearly zero,” according to Boyers’ report. This is reflected in the increased variability and increased autocorrelation between temperature and salinity in the North Atlantic. The researcher was able to observe this pattern of increased instability in all eight factors examined.

“This indicates that the cyclic flow impairment is not just a natural oscillation or a linear response to rising temperatures,” says Bowers. “Instead, it means that the system is approaching a critical threshold above which the flow system can collapse.” Therefore, AMOC is more sensitive to warming and meltwater influx than previously thought and could be on the verge of tipping point.

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Surprising and disturbing

According to Boyer, this discovery is as surprising as it is alarming. Many previous climate models did not anticipate such an early reaction to climate change. They assumed that the current AMOC situation is too stable to enter an inversion at the current level of warming. “This may be due to an underestimation of the meltwater influx from the North Atlantic,” Bowers says. It is now necessary to adapt the models to the monitoring data.

This is also worrisome because some simulations in Boyer’s study indicate that the circulating flow can collapse before a critical threshold value λ = 0 is reached. Another research team recently discovered something similar: according to their models, particularly rapid warming can cause AMOC inversion prematurely – and the current climate change is relatively rapid.

This article was written by Nadja Podbregar