The main circulation system of the Atlantic Ocean, and an important regulator of the world’s climate, It has lost almost all stability over the past century and may be on the verge of reaching a critical point and not reversing.
By analyzing sea surface temperature and salinity patterns in the Atlantic, the study indicates that the weakening over the past century is likely related to the loss of stability.
“The results support the assessment that the AMOC decline is not just an oscillation or linear response to warming, but likely means a critical limit approach beyond which the circulation system may collapse.”acknowledged lead author of the study.
AMOC operates like the Northern Hemisphere Climate Engine, being a large system of ocean currents that transport hot water from the tropics north to the ocean surface and cold water south to the ocean floor, more relevant to the relatively mild temperatures of Europe. Moreover, it affects weather systems all over the world.
With global warming, as the atmosphere warms due to increased greenhouse gas emissions, the surface of the ocean retains more heat. Thus, if this system collapses, there could be dire consequences for the world’s climate systems.
“The collapse from the current strong state to the weak state would have severe effects on the global climate system and the other multiple stable components of the Earth system.”, reads the report.
The authors caution, among other effects, This phenomenon could “cool Europe considerably”, and have severe consequences for tropical monsoon systems., for example.
If this system reaches a critical limit, it can Changing basic rainfall regimes to feed millions of people in India, South America and West Africa. can also It leads to increased storms and lower temperatures in Europe, as well as sea level rise in eastern North America. The Amazon and Antarctic forests will also be severely affected.
It is necessary to reduce emissions
The complexity of the AMOC system and the uncertainty about future global warming make it impossible to predict, at present, when that system might collapse. The study authors stressed that the effect of this would have underlined the need to prevent this from happening.
“The already visible signs of destabilization are unexpected and frightening.”Niclas Boers of the Potsdam Institute for Climate Impact Research in Germany, lead author of the investigation, which was cited by The Guardian, said. “It’s something we cannot allow to happen.”
Furthermore, it is not known how much carbon dioxide can lead to AMOC breakdown.
“So the only thing to do is to keep emissions as low as possible. The likelihood of this very high-impact event increases with every gram of carbon dioxide we put into the atmosphere.”.
But in addition to global warming, the influx of fresh water is also a factor linked to climate change. In May, Bowers and his team revealed that a large portion of Greenland’s ice sheet was about to melt, threatening to raise sea levels.
It is possible that several factors are important in explaining this phenomenon – factors that contribute to the direct influence of the warming of the Atlantic Ocean on its circulation. This includes freshwater inflow from melting Greenland’s ice sheet, melting sea ice, increased precipitation, and river run-off. Fresh water is lighter than salt water and reduces the tendency of water to sink from the surface to greater depths, and is one of the engines of circulation.
“I did not expect that the extra amounts of fresh water that have been added over the last century would have such an effect on circulation.”Boer said. “We urgently need to review our models and monitoring data to assess how close or how close the AMOC is in reality”.
Ice cores and other data from the last 100,000 years show that the AMOC has two states: a fast and strong one, as we’ve seen for the past few millennia, and a slow and weak state. Several investigations have shown that rising temperatures can cause the AMOC to shift abruptly between states over the course of one to five decades.
Therefore, AMOC is driven by the sinking of thick, salty seawater into the Arctic Ocean, but freshwater thawing from the Greenland ice sheet impedes this process sooner than climate models predict.
In 2018, two studies were also published in nature He warned of the weakening of the Atlantic Current system due to melting sea ice and ice shelves releasing fresh water into the North Atlantic Ocean. According to David Thornali, a researcher at University College London and co-author of one of the studies, “Fresh water weakens AMOC because it prevents the water from being thick enough to sink in.”
Recently, four months ago, an investigation published in Nature Geosciences and based on computer simulations with data from Earth’s past, the so-called “paleoclimatic proxy records”, showed that the current was at its weakest in the last 1,600 years.
