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Accelerated Melting in Antarctica May Support Key Ocean Currents

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Impact of Melting Antarctic Ice on Ocean Currents

Juan Barretto/AFP via Getty Images

The melting of Greenland’s ice sheet is predicted to hinder or disrupt the Atlantic current that helps keep Europe warm; however, meltwater from West Antarctica might help maintain this essential flow.

That said, it won’t be sufficient to prevent significant climate changes. The Atlantic Meridional Overturning Circulation (AMOC) is already down by 60% and could take up to 3,000 years to recover fully.

“I suggest caution in predicting an AMOC collapse,” states Sasha Sinnett from Utrecht University in the Netherlands. “However, my findings don’t alter what is forecasted for the next century. We may never see if West Antarctica successfully stabilizes the AMOC.”

The AMOC is a system of ocean currents that transports warm surface water from the tropics to northern Europe. Here, the water cools and sinks, then flows back south to Antarctica. This current carries an enormous amount of heat—1.2 petawatts—equivalent to the output of one million power plants, keeping Europe notably warmer than regions like Labrador or Siberia at similar latitudes. Lighter, fresher meltwater from Greenland is expected to obstruct the sinking of the denser, saltier AMOC water, thereby slowing its flow.

If the AMOC were to collapse, winter temperatures in Northern Europe could drop to almost -50℃ (-58°F). Recently, Iceland declared the closure of the AMOC as an “existing” security threat. Additionally, rising sea levels are threatening the U.S. East Coast, while Africa may face even more severe drought conditions.

A recent study indicates that even if we achieve net zero emissions by 2075 and begin reducing CO2 from the atmosphere, there is still a 25% risk of AMOC collapse. One study forecasts its closure in the coming decades, while another suggests that it will remain weakened due to Antarctic winds.

Currently, the melting of the West Antarctic ice sheet has accelerated, with some research indicating a probable complete collapse. However, the impact on AMOC remains uncertain.

The timing of the melting is crucial, according to simulations by Sinet and his team. If pulses of ancient Antarctic meltwater coincide with substantial meltwater from Greenland, the AMOC’s closure will be expedited.

Conversely, if the Antarctic water arrives about 1,000 years prior to the peak melting of Greenland, the AMOC may weaken for a few centuries but then recover over the next 3,000 years. While AMOC shows eventual recovery in all scenarios, early Antarctic melting prevents total collapse and accelerates its resurgence.

This phenomenon could be due to the relocation of the sinking, salty AMOC water moving south as lighter, fresher meltwater accumulates around Greenland, with the flow regaining strength as Antarctic melting decreases.

Though it’s improbable that West Antarctica melts at such a rapid pace while Greenland melts more slowly, these results illuminate a significant connection between AMOC and Antarctic ice melt, notes Louise Sim from the British Antarctic Survey.

“Prior to this study, the extent to which Antarctic changes could significantly influence the effects of Greenland’s ice sheet melting on the AMOC was largely unknown,” she remarks.

However, the study does not address potential feedback effects, such as shifts in wind patterns that might increase Antarctic sea ice, so this relationship needs to be explored in more complex models moving forward, she adds.

Even if rapid melting in West Antarctica prevents the AMOC from collapsing, it could still lead to sea-level rises of up to 3 meters, inundating coastal cities.

“Unfortunately, while one potential disaster may lessen the danger of another, this is little consolation,” concludes Stefan Rahmstorf from the University of Potsdam, Germany.

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Source: www.newscientist.com

AMOC: An Ambitious Strategy to Preserve Vital Ocean Currents Using Giant Parachutes

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Strategies to uphold the current involve oversized versions of parachute-like ocean anchors

Ed Darnen (2.0 by CC)

As part of an ambitious initiative to avert severe climate change, large parachutes could be deployed into Atlantic waters using transport tankers, drones, and fishing vessels.

The Atlantic Meridional Overturning Circulation (AMOC) moves warm water from the tropics northward and helps stabilize temperatures in Northern Europe.

Nevertheless, the swift melting of Arctic ice and rising sea temperatures have hampered these currents, prompting some scientists to warn that they could falter entirely within this century. Such an event would disrupt marine ecosystems and exacerbate the cooling of the European climate.

Experts emphasize the urgent need to cut greenhouse gas emissions to mitigate the risk of AMOC collapse and other catastrophic climate “tipping points.” However, some are exploring alternative, more fundamental methods to preserve the current.

Stuart Haszeldine from the University of Edinburgh, along with David Sevier, introduced a concept from the British water treatment firm Strengite during a recent meeting in Cambridge, UK. They propose utilizing just 35 ocean tugs, each capable of pulling underwater parachutes roughly half the size of a soccer pitch, which could effectively move enough water to maintain the current. “A modest amount of energy and equipment can yield a significant impact,” Haszeldine remarks.

These parachutes, designed similarly to existing ocean anchors, stabilize containers in rough weather while also aiding in water movement across the sea surface. Each parachute features a central hole 12 meters wide to allow marine creatures to escape.

The operation would run 365 days a year in a rotating schedule, using drones, transport tankers, tugs, or wind kits. “It’s a small but consistent intervention,” notes Haszeldine.

Sevier refers to this proposal as “any Mary,” indicating a solution to stave off the severe consequences of AMOC collapse. “This is about buying time,” he asserts, emphasizing the need for the world to reduce emissions sufficiently to stabilize global temperatures at safe levels.

However, leading AMOC researchers express skepticism about the idea. Rene van Westen from the University of Utrecht, Netherlands, highlights that the density differences between cold, salty water and warm, fresh water play a crucial role in the descent and upwelling movements that sustain AMOC.

“If this idea is to work,” Van Westen argues, “you can only use surface wind to influence the top layer of water.

Stephen Rahmstoef from the Potsdam Institute for Climate Impact Research concurs. “The challenge lies not in moving surface water horizontally but in sinking it to depths of 2,000 to 3,000 meters and returning it south as a cold, deep current,” he states.

Meric Srokosz of the UK National Oceanography Centre believes the proposal is “unlikely to succeed,” given the variable weather conditions that complicate equipment deployment in the oceans.

Haszeldine welcomes feedback from fellow scientists regarding the proposal and hopes it will inspire ocean and climate modelers to assess the ecological and environmental ramifications of the plan. “I believe this warrants further investigation,” he asserts.

More generally, Haszeldine argues for increased research focused on climate intervention strategies to sustain ocean circulation: “I don’t see anyone else working on ocean currents.”

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Source: www.newscientist.com

As Key Atlantic Currents Decelerate, US East Coast Confronts Rising Sea Levels

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AMOC is a system of ocean currents that circulates water in the Atlantic Ocean.

NASA/Goddard Space Flight Center Scientific Visualization Studio

The decline in significant Atlantic currents is contributing to flooding linked to rising sea levels in the northeastern United States, which are already affected by climate change. As global temperatures increase, a total collapse of the Atlantic Meridional Overturning Circulation (AMOC) could exacerbate sea level rise.

“If AMOC collapses, this will greatly increase flood frequency along the US coastline, independent of major storms,” states Liping Chan from the Geophysical Fluid Dynamics Laboratory at the US National Oceanic and Atmospheric Administration (NOAA) in New Jersey. “Even a partial reduction in current strength can have significant consequences.”

The warm waters melting ice sheets and rising sea levels are influenced by climate change, which leads to uneven rates of sea level rise across different regions. For instance, some coastal areas have subsided, increasing the relative rate of sea level rise there. Local sea levels are also affected by the circulation of heat, water, and salt in the ocean, with warm, fresh water occupying more volume than cold, salty water.

Over the past few decades, sea levels along the northeastern US coast have risen 3-4 times faster than the global average. The slowing of AMOC—responsible for transporting warm water from lower latitudes to the North Atlantic, where it cools and sinks—has long been considered a potential cause of this phenomenon. As this circulation weakens, warm deep water expands, pushing more water onto the shallow continental shelf.

AMOC strength varies naturally over different timescales, and climate change has contributed to its slowdown as the North Atlantic and its waters have become warmer and clearer in recent decades. However, it remained uncertain whether this decrease significantly affected sea levels.

Chang and her team utilized tidal gauge measurements from the New England coast to reconstruct local sea levels dating back over a century. Alongside a steady rise due to climate change, they identified significant fluctuations between low and high sea levels every few decades. Low sea levels correlated with periods of weak AMOC, while high sea levels were also aligned with these intervals, which brought more frequent coastal flooding.

The researchers then employed two distinct ocean models to quantify the impact of AMOC intensity variations on local sea levels. While the primary driver of change was the steady rise due to climate change, they discovered that weakened AMOCs significantly increased sea-level-related flooding. In multiple coastal regions, they noted that the slowdown in AMOC has contributed to delaying flooding by 20-50% since 2005.

Given that the natural cycle of AMOC strength is largely predictable, Zhang asserts that these findings enable researchers to forecast potential flooding events up to three years in advance. This foresight can guide long-term infrastructure planning and emergency preparedness.

“This highlights the critical role of AMOC in [sea level rise],” remarks Chris Hughes, who was not involved in the research, from the University of Liverpool in the UK. “It’s not merely theoretical; it’s evident in the real world.”

It remains unclear how much of the recent AMOC weakening is attributable to climate change versus natural variability. Nevertheless, the findings bolster predictions that if AMOC were to completely collapse due to climate change, significant portions of the US East Coast could experience a surge in sea levels.

Hughes warns that if AMOC nearly collapses, sea levels could rise by around 24 centimeters. “While it may not seem dramatic, even a small increase can have a substantial effect.”

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Source: www.newscientist.com

Researchers find that melting ice sheets are causing a reduction in the speed of the world’s strongest ocean currents

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Antarctic Circulating Current (ACC), which is more than four times as strong as the Gulf Stream, is the world’s strongest ocean current and plays an unbalanced role in the climate system due to its role as a major basin conduit. Scientists at the University of Melbourne and the Research Centre in Nordic Norway have shown that ACC will slow by about 20% by 2050 in high carbon emission scenarios. This influx of freshwater into the southern ocean is expected to alter the properties such as the density (salinity) of the ocean and its circulation patterns.

Sohail et al. High-resolution ocean and sea ice simulations of ocean currents, heat transport, and other factors were analyzed to diagnose the effects of temperature changes, saltiness, and wind conditions. Image credit: Sohail et al. , doi: 10.1088/1748-9326/adb31c.

“The oceans are extremely complex, finely balanced,” says Dr. Bishakhdatta Gayen, liquid mechanic at the University of Melbourne.

“If this current ‘engine’ collapses, serious consequences, including more climate change, including extreme extreme climate variability in certain regions, will accelerate global warming due to a decline in the ability of the ocean to function as a carbon sink. “

The ACC acts as a barrier to invasive species, like the southern burkelp and marine vectors such as shrimp and mollusks, which travel in the current from other continents reaching Antarctica.

If this current slows and weakens, it is more likely that such species will head towards the fragile Antarctica, potentially serious effects on food webs, which could change the available diet of Antarctic penguins, for example.

The ACC is an important part of the marine conveyor belt around the world, moving water around the world and linking the Atlantic, Pacific and Indian seas. These are the main mechanisms of exchange of heat, carbon dioxide, chemicals and biology throughout these basins.

In their study, the authors used Gadi, the fastest supercomputer in Australia located on the Access National Research Infrastructure.

They discovered that transport of seawater from the surface to the deepest could also be slower in the future.

“If ice melting accelerates as predicted by other studies, slowdowns are predicted to be similar in low emission scenarios,” Dr. Sohail said.

“The 2015 Paris Agreement aims to limit global warming to 1.5 degrees Celsius above pre-industrial levels.”

“Many scientists agree that we have already reached this 1.5 degree target, which could have an impact on the melting of Antarctic ice, making it even hotter.”

“Cooperative efforts to limit global warming (by reducing carbon emissions) will limit the melting of Antarctic ice and avoid the expected slowdown in ACC.”

This study reveals that the effects of ice melting and ocean warming on ACC are more complicated than previously thought.

“The melted ice sheets throw a large amount of fresh water from salt water into the salty sea.”

“This sudden change in ocean salinity has a series of results, including weakening of subsidence to the depths of surface seawater (called Antarctic bottom water), and based on this study, it includes weakening of the powerful marine jets surrounding Antarctica,” Dr. Gayen said.

study Published in the journal Environmental Survey Letter.

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Taimoor Sohail et al. 2025. Decreasing the polar current in the Antarctic due to polarization. environment. res. Rent 20, 034046; doi:10.1088/1748-9326/adb31c

Source: www.sci.news

AMOC: Crucial ocean currents are unlikely to shut down completely by the end of the century

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AMOC brings warm water north from the tropical region near the surface and takes cold water in opposite directions of the deep sea

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Important ocean currents will rarely close by the end of this century, according to new findings that undermine the end of the impending catastrophic collapse.

The Atlantic Meridian Surrounding Circulation (AMOC) transports warm water from the tropical north and helps maintain temperatures in Northern Europe. The temperature and the influx of cold water from the Arctic ice weakens the current temperature, and scientists fear it can stop it completely. This will disrupt marine ecosystems and cool the European climate a few degrees faster.

Some researchers say that the irreversible closure of AMOC could be in the century. But I say this worst-case scenario is unlikely Jonathan Baker At the Met Office in the UK.

To investigate whether a complete AMOC collapse of this century is possible, Baker and his colleagues used 34 climate models to simulate changes in AMOC under extreme climate change, and greenhouse gas levels trained overnight from today's levels. The team also modeled a large amount of freshwater entering the North Atlantic at many times the rate of ice melting now.

They found that although AMOC is significantly weakened in these two scenarios, ocean currents continue in their weakened state, supported by deep-sea upwellings in the North Atlantic, driven by southern sea winds. “The Southern Ocean winds continue to blow, and this brings deep waters up to the surface. This works like a powerful pump,” Baker says. “This keeps AMOC running on models of this century.”

This finding helps explain why climate models generally simulate more stable AMOCs in the warming world compared to studies that rely on statistical methods. This tends to suggest that AMOC is more vulnerable.

Niklas Bore The Potsdam Climate Impact Institute in Germany said the findings are “good news” for those worried about the imminent collapse of the AMOC. “I agree that all cutting-edge climate models will not show a complete AMOC collapse within the 21st century.

However, the model does not predict a complete collapse of AMOC, but shows that quaternary reddish CO2 concentrations lead to a 20-81% reduction in the current intensity.

With AMOC weaker by about 50%, the impact on climate will become important, Baker says it will be important due to marine ecosystem disruption, sea level rise on the North Atlantic coastline, and changes in global rainfall patterns that affect crop harvests around the world. However, this type of weakening does not bring rapid cooling to Europe, he says.

In comparison, Bohr emphasizes that AMOC, which is 80% less than today, will have a devastating effect. “Of course, it's a nearly blocked AMOC,” he says. “It has all the impact on Europe's cooling and changing patterns of tropical monsoon, and all the things we are concerned about.”

Stephen RahmstoefHe is also at the Potsdam Institute for Climate Impact in Germany, and agrees that under the extreme warming of this century, there may be a weak and shallow AMOC trend left in the world. Some studies even define AMOC disintegration as this type of substantial weakening, he says. “A new study is investigating the remaining wind-driven covers [current] In more detail, this is a valuable contribution to the scientific literature,” he says. “However, in response to human-induced global warming, we will not change our assessment of the risks and impacts of future AMOC changes.”

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Source: www.newscientist.com

Vital Atlantic currents at risk of collapse, warn scientists

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Overview

A recent report has highlighted the concerning state of Earth’s snow and ice, indicating that various key climate tipping points are more likely to be reached than previously thought. These include significant ice melt leading to severe sea level rise and disruptions to crucial ocean currents controlling the Atlantic heat cycle.

The report reveals alarming statistics such as Venezuela losing its last glacier this year, Greenland’s ice sheet losing an average of 30 million tons of ice per hour, and the impending collapse of Thwaites Glacier, also known as the “terminal glacier.” This collapse could potentially result in the rapid disappearance of Antarctic ice.

Compiled by over 50 leading snow and ice scientists as part of the International Cryosphere Climate Initiative, the report summarizes the conditions for 2024, highlighting the disastrous impact of global warming on the planet’s frozen regions.

Of particular concern is the potential collapse of the Atlantic Meridional Overturning Circulation (AMOC), which could lead to drastic changes in weather patterns, such as rapid cooling in the North Atlantic and warming in the Southern Hemisphere.

Additionally, the report underscores the rising consensus among scientists that these climate tipping points are now more likely to be surpassed, with the window for mitigating actions rapidly narrowing.

The report’s release coincided with the United Nations’ COP29 climate change conference in Azerbaijan, where global leaders gathered to address pressing environmental concerns. Despite some progress, particularly in carbon credit trading, the report emphasizes that current climate policies are inadequate to meet global climate goals.

While the scientific community continues to sound the alarm about the escalating climate crisis, there are growing fears that world leaders are failing to grasp the gravity of the situation. Urgent action is needed to address the imminent threats posed by melting ice, collapsing glaciers, and disruptions in vital ocean currents.

In conclusion, the report serves as a stark reminder of the urgent need for decisive action to combat climate change before irreversible consequences unfold.

Source: www.nbcnews.com

The Impending Collapse of Atlantic Currents: The Impact on our Planet

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The frozen River Thames is being hit by cold winds, the Mersey docks are blocked by ice floes, and crops are failing in the UK. Meanwhile, rising sea levels are flooding the east coast of the United States, and the Amazon ecosystem is experiencing disruptions due to changing seasons. The world has undergone significant changes. What has caused this?

These events may seem like scenes from a disaster movie, but a recent scientific study focusing on the Atlantic Meridional Overturning Circulation (AMOC) warns that these scenarios could become a reality as early as 2050. Learn more.

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What is AMOC, why is it vital, and what changes can we expect? Will disruptions lead to catastrophic events, and how can we address the situation?

The Importance of AMOC and Expected Changes

The AMOC, also known as the “Great Ocean Conveyor,” is a vast ocean current system that includes the Gulf Stream. It transports warm, salty water from the tropics northward into the North Atlantic Ocean. As this water cools and becomes denser, it sinks, flows back southward at depth, and eventually rises to the surface, creating a continuous circulation loop.

This circulation system moves significant amounts of heat around the Atlantic Ocean, equivalent to boiling approximately 100 billion kettles. The AMOC plays a crucial role in distributing heat input to the Northern Hemisphere and affects climate zones worldwide. Any weakening of the AMOC could lead to shifts in global climate patterns, impacting various regions.

Changes in wind patterns can also influence AMOC. Stronger winds during ice ages bolstered parts of the Gulf Stream, while in a warmer future world, wind effects might weaken the AMOC.

Evidences of AMOC Changes

Direct measurements of AMOC strength started in 2004 using the RAPID array across the Atlantic Ocean. Observations indicate a 10% decline in intensity over nearly two decades, but year-to-year variations pose challenges in determining a clear long-term trend.

Past indirect measures, such as cooling trends in southern Greenland, suggest a weakening AMOC. Salt accumulation in the South Atlantic further supports the notion of reduced heat and salt transport due to system weakening.

By studying marine sediment cores and ancient shells, paleoclimatologists have discovered that the current AMOC weakening is unparalleled in the last 1,600 years, indicating a potential 15% decline in the system’s strength.

Future Outlook for AMOC

Climate models predict a 30-50% weakening of AMOC by the end of the century if greenhouse gas emissions continue. This could result in altered weather patterns, increased extreme events, and sea level rise along certain coastlines.

A small increase in global temperatures might trigger a swift shutdown of the AMOC, leading to severe climate impacts. Understanding the potential collapse mechanisms, such as “salt feedback,” highlights the need for immediate climate action to prevent such scenarios.

Managing AMOC Risk

To mitigate the risks associated with AMOC collapse, we must urgently reduce greenhouse gas emissions, enhance climate resilience, and prepare for potential disruptions in food and water supplies. Addressing the root cause of global warming and implementing sustainable practices are crucial in safeguarding the stability of the Earth’s climate system.

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Source: www.sciencefocus.com

The impact of the melting Greenland Ice Sheet on ocean currents

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Climate change affects our planet and our lives in many ways. Dry the atmosphere To Increase in home runs Climate change accelerates glacial melt with each Major League Baseball season. Greenland Ice Sheet The land ice mass that covers about 80% of Greenland. When glaciers melt, icebergs form, a process called “iceberg formation.” Glacier collapse Recent climate change has increased the rate at which icebergs are flowing from the Greenland Ice Sheet into the North Atlantic.

Scientists have found that in the past, large increases in the rate of glacial collapse have disrupted important ocean current systems in the Atlantic Ocean. Atlantic Meridional Gyre Or as the AMOC, it carries warm water north and cold water south, affecting global temperatures and moving nutrients across the Atlantic Ocean, meaning that disrupting the AMOC could change the climate and destabilize marine ecosystems. Recently, scientists conducted a study to determine whether the current increase in glacier collapse could disrupt the AMOC.

For this study, the researchers developed a method to quantify glacial runoff during past periods of increased glacial collapse in the North Atlantic that disrupted the AMOC. Heinrich Event They began by looking at present-day glaciers in the North Atlantic and the Arctic. As icebergs break up, they deposit sediment. This sediment includes sand and rocks from the land below the ice sheet, as well as the remains of organisms that lived on the ice sheet. When the icebergs melt at sea, the sediment is released and sinks to the ocean floor.

Scientists observed modern glaciers melting and measured the average amount of sediment, by volume, that they released. Using this average, the researchers estimated how much ice was released during past Heinrich events, based on the amount of sediment that was deposited on the floor of the North Atlantic Ocean.

Scientists used this method to estimate the total amount of ice lost during 10 Heinrich events (the last of which) that occurred over the past 140,000 years. Glacial Cycle Previous scientists had determined the duration of Heinrich events, which allowed the researchers to estimate the ice runoff rate during each event. The researchers compared their estimated runoff rates to current ice runoff rates and found that current ice runoff rates are similar to those of previous mid-sized Heinrich events that disrupted the AMOC. However, the scientists who conducted the study also noted that the AMOC is currently stable.

The researchers suggested two factors that could help explain why the current increase in glacial collapse is not disrupting the AMOC as much as it has in the past. First, the researchers think that the AMOC was stronger when the current glacial runoff rate began to increase than it was at the start of past Heinrich events, which may make the current AMOC more resistant to disruptions. Second, each of the 10 Heinrich events the scientists used in their study lasted about 250 years, while the faster glacial collapse seen today may have been due to a slowdown in the early Heinrich events. It began in recent decades They suggested that AMOC collapse could only occur after a longer period of increased glacier calving than has happened previously.

If the rate of glacial calving continues to increase by the time the AMOC collapses, the size of the Greenland Ice Sheet may limit its influence on the AMOC. The researchers noted that if the Greenland Ice Sheet continues to melt at its current rate, the rate of calving will slow before 250 years have passed. The icebergs that caused the Heinrich events in the last glacial cycle broke off from a much larger ice sheet. Laurentide Ice Sheet It no longer exists.

The scientists who conducted the study said that freshwater runoff from the melting Greenland Ice Sheet could also disrupt the AMOC, but its impact would be less severe than ice runoff. However, they noted that freshwater runoff is likely to increase as glacial collapse slows in the coming decades, which could have unpredictable consequences. The researchers suggested that the scientific community should continue their work to model the impacts of a melting Greenland Ice Sheet as accurately as possible, because, in their words, “the fate of the AMOC remains uncertain.”


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Source: sciworthy.com

The Possible Collapse of AMOC: Simulations Highlight Real Danger of Stopping Atlantic Currents

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Ocean currents flowing from the tropics to the North Atlantic have a major influence on Europe's climate.

jens carsten roseman

As the planet warms, is there a serious risk that the Atlantic Current that warms Europe will slow down and stop? Yes, according to the most detailed computer simulation ever performed. The likelihood of this scenario remains highly uncertain.

“We have demonstrated that it is indeed possible with our current setup,” he says. René van Westen At Utrecht University in the Netherlands.

Now, warm water, made more salty by evaporation, flows north from the tropics along the surface of the Atlantic Ocean, keeping Europe much warmer than it would otherwise be. When this water cools, it sinks because it becomes more salty and denser. It then returns to the tropics and flows along the ocean floor into the southern hemisphere.

This is known as the Atlantic Meridional Overturning Circulation (AMOC). Studies of past climate suggest that the dramatic cooling episodes that have occurred around Europe over the past 100,000 years or so have been associated with so-called tipping points, when reverse currents slow down or stop completely, and small changes in may convert one system to another. state.

The cause is thought to be melting ice sheets. The influx of large amounts of fresh water into the North Atlantic reduces salinity, which in turn reduces surface water density and reduces the amount of water that sinks.

However, this has proven difficult to model. Most shutdown simulations require adding unrealistically large amounts of fresh water at once. Some also question whether this is a potential tipping point, since recent simulations using more advanced models have not shown any shutdowns.

Now, van Westen's team has run the most sophisticated simulation to date, which took a total of six months to run on the Dutch state-run supercomputer Sunellius. It was very expensive, he says.

Unlike previous simulations, the team added fresh water gradually rather than all at once. This created a positive feedback that amplified the effect. The decrease in salinity reduced the amount of water sinking, which reduced the amount of brine flowing north, further reducing salinity.

This eventually broke the overturning circulation, causing temperatures to rise in the Southern Hemisphere but plummet in Europe. For example, in this model, London would be 10°C (18°F) cooler on average, and Bergen, Norway would be 15°C (27°F) cooler on average. Other impacts include localized sea level rise in areas such as the East Coast of the United States.

Additionally, some of the changes seen in the model before the collapse are consistent with changes seen in the real Atlantic Ocean in recent decades.

But to cause this collapse, the researchers had to run the model for 2,500 years. And they needed to add huge amounts of fresh water. Although less than previous simulations, it is still about 80 times the amount that is currently flowing into the ocean from the melting Greenland ice sheet. “So it's absurd and not very realistic,” Van Westen said.

Furthermore, this simulation did not include global warming. The team now plans to rerun the simulation with that in mind.

“This is the most cutting-edge model in which such experiments have been performed,” he says. Peter Ditlefsen He is a co-author of a 2023 study predicting that the Atlantic overturning current could break up between 2025 and 2095, based on changes in sea surface temperatures.

The model suggests it will take large amounts of fresh water and centuries to stop the circulation from reversing, but why do we think climate models are underestimating the risk of nonlinear changes like the Atlantic tipping point? There are several, Ditlefsen said.

Climate models need to divide the world into large cubes to make their calculations workable, he says, and this has a smoothing effect. Additionally, the model has been calibrated based on how well it simulates the 20th century climate, although there was a linear relationship between greenhouse gas emissions and the resulting changes. may not be applicable in the future.

“We should expect the model to be less sensitive than the real world,” Ditlevsen says.

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Source: www.newscientist.com