Tag Archives: AMOC

How Reducing Air Pollution May Impact Key AMOC Currents

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Smog particles reflecting sunlight

Smog Contains Particles That Reflect Sunlight and Cool Earth’s Surface

Credit: Dennis McDonald/Alamy

Addressing air pollution in Europe and North America could inadvertently weaken the Atlantic Meridional Circulation (AMOC), a crucial ocean current influencing Europe’s climate.

Air pollution, including smog and soot, claims approximately 7 million lives annually and contributes to widespread health issues. Interestingly, aerosols, which are tiny particulate pollutants like sulfur dioxide, can reflect sunlight, making clouds brighter and reducing surface heat absorption.

Recent research indicates that reducing air pollution from maritime sources and other sectors could accelerate global temperature increases. “If we cut back on aerosols, we will start to see the extent of warming,” says Michael Diamond from Florida State University.

Historically, scientists’ insights into aerosols’ climatic impact have relied on global simulations akin to those used for examining the greenhouse effect. These models suggest that “higher aerosol levels cool the North Atlantic surface and strengthen the AMOC,” according to Robert Allen from the University of California, Riverside. Conversely, if global aerosol emissions are reduced, the Earth’s surface may warm, weakening the AMOC.

Nonetheless, these simulations often overlook the regional characteristics of air pollution. Unlike greenhouse gases, which linger in the atmosphere for years, most aerosols dissipate within a week, meaning their climatic effects typically manifest close to their source, revealing the complex consequences of pollution reductions.

To gain deeper insights into the impacts of clean air initiatives, Allen and his team employed eight distinct climate models to assess how changes in regional aerosol emissions impact both local and global climates. The models evaluated AMOC strength under high-emission scenarios established by the Intergovernmental Panel on Climate Change and reformulated these scenarios with enhanced air quality regulations.

The findings indicate that if greenhouse gas emissions continue to rise but aerosol pollutants decrease, the AMOC could weaken by a third by mid-century compared to scenarios where aerosol levels remain elevated.

While Allen’s research does not delve into the regional weather implications of AMOC weakening, previous studies suggest that such a decline could lead to adverse outcomes, including increased droughts across Europe, exacerbated sea level rise in northeastern North America, and disruption of global monsoons and rising temperatures in Northern Europe.

Allen’s analysis revealed that the most significant impact on AMOC would stem from reduced aerosol levels in Europe and North America. However, he noted that air quality improvement initiatives in East Asia are also proving impactful. Cleaner air in East Asia is affecting global temperatures—despite their short lifespan, aerosols can travel long distances and mask warming effects wherever they reach, potentially leading to further weakening of the AMOC.

“To improve air quality, we must acknowledge that there will be associated climate changes,” Allen states. “To achieve clean air while minimizing our climate impact, we must simultaneously reduce other greenhouse gases like CO2 and methane.”

Diamond echoes this sentiment, stating, “When considering clean air policies, it’s vital to concurrently address decarbonization strategies.”

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Source: www.newscientist.com

How a Massive Bering Strait Dam Could Prevent AMOC Collapse

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The Bering Strait

The Bering Strait separates Alaska and Russia

Ocean Color/OB.DAAC/OBPG/NASA

An ambitious engineering project looms on the horizon: constructing a dam between Alaska and eastern Russia. This innovative proposal aims to combat the dire consequences of a weakening ocean current, and is under serious consideration at a prominent conference this week.

The seeds of this groundbreaking idea were sown by Jere Soon and his collaborator Henk Dijkstra, a researcher focused on the Atlantic Meridional Overturning Circulation (AMOC) at Utrecht University, Netherlands. This current system, including the Gulf Stream, is crucial for keeping northern Europe warmer than its geographical latitude would suggest.

Current data indicates that the AMOC is weakening. The potential effects of its collapse are uncertain, but many models hint at a possible significant drop in temperatures across Northern Europe.

The concept was inspired by the Pliocene era, when sea levels were considerably lower and a land bridge existed where the Bering Strait now lies. During this time, simulations revealed a stronger AMOC due to the presence of this land bridge. “I thought: can we replicate this?” says Soon.

To explore the implications of such dam construction, Soon and Dijkstra simulated various AMOC scenarios, adjusting the construction date and freshwater levels.

Freshwater plays a crucial role in this dynamic, currently flowing from the Pacific Ocean into the North Atlantic through the Bering Strait, which in turn disrupts the AMOC. Constructing a dam could either halt or considerably slow this freshwater flow.

In a recent study, Soons and Dijkstra obtained mixed results: in certain scenarios, dams seemed to enhance the AMOC, while in others, they produced the opposite effect. It’s important to note that these findings were derived from relatively basic, low-resolution models.

On May 5, Dr. Soons presented significant research results at the European Geosciences Union General Assembly in Vienna, Austria. Simulations were re-evaluated using a supercomputer that employed advanced climate models. The results indicate that closing the strait could reinforce the AMOC, particularly if dams are constructed by 2050. “I was surprised at how robust the recovery was,” Soon remarked.

The Bering Strait, at its deepest point, measures only 59 meters and features two small islands in the middle, suggesting the viability of constructing a barrier. Ed McCann, former president of the Japan Society of Civil Engineers and current head of expedition engineering, suggests that rather than concrete, using flotation machinery to build barriers with rock and dredged sand would be most efficient. “This type of construction is straightforward, albeit large-scale and costly,” he commented via email.

Jonathan Rosser, a researcher at the London School of Economics, finds the study intriguing. However, he emphasizes that due to the AMOC’s complexities, we cannot fully predict the outcomes of such interventions. “These drastic measures come with significant uncertainty.”

Suhn concurs, cautioning that while dam construction may benefit Northern Europe, it could lead to adverse effects elsewhere, such as altered rainfall patterns. “Are we ready to take this seriously? I don’t think we’re there yet,” he concluded.

This isn’t the first consideration of constructing gigantic ocean dams to address climate change. In 2020, Sjoerd Groeskamp from the Royal Netherlands Marine Institute proposed the “Northern European Enclosure Dam,” designed to create barriers around the sea between the UK and mainland Europe, protecting low-lying areas from rising seas.

Such dams would undoubtedly impact not only the climate but also marine mammal migration, tidal patterns, and transport access to isolated regions. Mr. Soons noted that he has explored ideas like constructing partial barriers or lowering them to a depth of approximately 10 meters. These concepts are “interesting,” he said, though he has yet to thoroughly analyze their feasibility.

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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

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

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