We owe the mild climate in Europe to the Atlantic circulation flow (AMOC), which also includes the Gulf Stream. However, the global warming makes this sea flow, which transport warm water from the tropics north, and weaker. Some model calculations even assumed that she collapsed completely in a few decades. Using extensive modeling, a new study now confirms the assessment of the IPCC world climate that the AMOC will weaken considerably, but will not be abandoned. Winds above the southern ocean apparently have a stabilizing effect.
The Gulf Stream transports warm water from Gulf from Mexico to the North Atlantic. As part of the meridional Atlantic revolution (Atlantic Meridional Overturning Circulation, AMOC), he makes a decisive contribution to global heat distribution and ensures that we have milder temperatures in Europe than can be expected without the AMOC based on the geographical location. On the way to the north, the warm water gradually cools down and becomes more salt -containing due to evaporation. This increases its density so that it sinks down in the area of Greenland and flows back to the equator as deep water.
No complete collapse
This “engine” of the huge natural circulation pump is in danger due to climate change. Because of the global warming, the temperature gradient in the water changes and the melting Glacier Greenland’s rinsing large amounts of fresh water into the sea that reduce the salinity. The AMOC has therefore become significantly weaker in recent years. Some studies even assumed that she could collapse completely this century.
According to a new study, the prospects are not that bleak. A team led by Jonathan Baker from the British Met Office in Exeter has used 34 of the best available climate models of the IPCC to model how the AMOC would behave under extreme scenarios, including a four-time increase in the CO2 concentration in the atmosphere and a large entry of sweet water in the North Atlantic. In accordance with previous studies, Baker and his team found that the AMOC drive, which is dependent on the salt content, came to a standstill under these conditions. However, according to the modeling, another, previously less noticeable effect, keeps the circulation flow going – albeit significantly weaker.
Winds as a drive
“Our modeling study indicates that the AMOC will resist the pressure due to rising global temperatures and the supply of fresh water to the North Atlantic, whereby the weakened system is largely powered by winds above the southern ocean,” explains Baker. Above the southern ocean, strong winds promote cold water from the depths to the surface. To compensate, surface water must flow down elsewhere. In the calculated extreme scenarios, this is partly due to a newly occurring circulation circulation in the Pacific. “However, this is not strong enough to compensate for the entire wind -driven buoyancy in the southern ocean,” said Baker. “Therefore, a certain degree of drops in the North Atlantic must be maintained.”
The results confirm the most recent assessment of the IPCC, after which the AMOC does not come to a standstill in this century. However, according to the researchers, this does not mean the all -clear: “Although our study shows that a collapse is unlikely in the next 75 years, the AMOC will most likely weaken what will bring with it for Europe and beyond,” says Baker. This assessment also shares Niklas Boers from the Potsdam Institute for Climate Impact Research (PIK). “It is important to emphasize that even when preventing a collapse, the AMOC could weaken up to over 80 percent, which would have globally devastating consequences and to cool down in Europe, to change tropical precipitation patterns and especially to shift the monsoon systems in South America, Africa, and Asia,” he explains.
Hope for climate protection measures
But even if a strong weakening of the AMOC can result in similarly serious consequences as the complete collapse, the result from Boer’s point of view gives reason to hope. “A difference is that an actual collapse would be much more difficult to reverse,” he explains. “This means that the global temperatures may have to be reduced much further to bring the AMOC back to its original strength than is the case with a mere weakening.” As long as the Atlantic upheaval flow is going, climate protection measures can help to reverse the worst consequences.
Source: Jonathan Baker (Met Office, Exeter, UK) et al., Nature, DOI: 10.1038/S41586-024-08544-0