Tag Archives: coastlines

New Study Reveals U.S. Coastlines Facing Accelerated Marine Disaster Risk

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A significant ocean current system that plays a crucial role in regulating the climate across the Northern Hemisphere is projected to weaken more dramatically by the end of this century than previously anticipated, according to a new study published in Scientific Progress.

The Atlantic Meridional Overturning Circulation (AMOC) is an extensive ocean current system transporting warm water north from the tropics, releasing heat into the atmosphere before descending and returning south.

“This system essentially forms a loop that transports heat from the equator to the North Atlantic,” stated Dr. Valentin Portman, the lead author of the study from France’s Bordeaux Southwest Research Center, during an interview with BBC Science Focus.

“Warm, salty water flows north, releasing heat, thickening, sinking, and then traveling south through deep ocean currents.”

Research indicates a projected 51% slowdown by 2100, a figure approximately 60% higher than average projections derived from conventional climate models, with significantly lower uncertainty.

The weakening of AMOC could lead to severe consequences. Sea levels along the northeastern U.S. coast are already rising faster than the global average, partially due to a weakening AMOC.

Globally, the tropical rain belt is expected to weaken and shift southward, jeopardizing the monsoons on which millions in West Africa and South Asia depend for agriculture.

In Europe, these changes could result in harsher, colder winters as the conveyor belt of warm water to the continent decelerates.

Worryingly, each additional weakening increases the system’s proximity to a tipping point where complete collapse becomes more probable, posing potentially catastrophic risks.

The AMOC extends across the Atlantic Ocean, forming a part of a vast network of ocean currents – Photo credit: Getty

Understanding a Complex System

Predicting the future of AMOC as the Earth warms is notoriously challenging due to the system’s vast complexity and influence from both local and global factors.

Previous forecasts about AMOC’s future varied significantly based on the employed climate prediction models. While most agree the system is weakening, the degree of potential collapse ranges from minimal to complete failure.

The new study identified two systematic errors prevalent in much of the prevailing modeling: underestimating salinity in the South Atlantic and overestimating coldness in the North Atlantic.

These biases cause models to underestimate how dense, saline water sinks and maintains current flow across the system.

By correcting these variables using a statistical approach called ridge-normalized linear regression, seldom applied in climate research, the expected weakening escalated to 51%, significantly lowering uncertainty surrounding the results.

“Typically, only one variable is used in studies, such as a singular observation of AMOC’s strength in the past,” Portman explained.

“This study aimed to incorporate more information by leveraging multiple variables simultaneously, which is vital due to AMOC’s complexity and dependence on various processes.”

The current strength of AMOC is already notably weak. Recent observations suggest a decline of 10% to 20% since the mid-2000s, equating to hundreds of millions of gallons of water no longer flowing north each second.

A 2025 study disclosed that the recent weakening of currents has contributed to nearly 50% of flooding along the northeastern U.S. coast since 2005.

However, attributing this decline to human-induced climate change rather than natural fluctuations remains a challenge. Experts state that it may take until 2033 (with 29 years of data) to confidently distinguish between the two.

Not a Complete Collapse—But It’s Worrisome

Results from this recent study are concerning, but researchers emphasize clarity regarding what they do and do not illustrate. In the 6th assessment report, the Intergovernmental Panel on Climate Change (IPCC) expressed confidence that AMOC would diminish throughout this century, albeit with “moderate confidence” that it would not collapse by 2100.

Yet, such assurances may offer little comfort given the extensive changes that collapse could entail, whether prior to or following this century’s conclusion.

For instance, a 2025 study in Geophysical Research Letters predicted that under such circumstances, temperatures in London could plummet to -20°C (-4°F) and -48°C (-54°F) in Oslo, despite global warming driven by greenhouse gases.

As human-driven climate change causes polar ice melting, ocean salinity decreases, disrupting AMOC processes.

Moreover, a weakening AMOC risks crossing an unknown tipping point threshold. A study suggests that the AMOC may hold two stable “on” or “off” states, with reversals potentially taking thousands of years to rectify.

The exact location of this threshold remains uncertain. Extending existing models beyond the typical 2100 cutoff, a 2025 study in Environmental Research Letters indicated AMOC shutdowns could occur in 67% of high-emission scenarios and 30% under moderate conditions.

“We don’t definitively know where the threshold lies or if this situation truly applies,” Portman noted. “We can speculate that this decline, even more significant than predicted, may be approaching a tipping point.”

Critical Action Window

Portman’s team tested four distinct emissions scenarios. Three (ranging from moderate to very high) consistently yielded results of approximately 50% weakening, suggesting that many impacts of human-induced climate change could become irreversible beyond a certain threshold.

“We are introducing considerable heat into the ocean, which will persist for centuries,” Portman stated.

However, the most optimistic scenario, marked by robust and sustained emissions reductions, resulted in only about a 20% decline.

“There are two perspectives here. One is that it may be a bit too late, given significant CO2 emissions leading to long-term effects,” Portman explained.

“Conversely, if we dramatically lower CO2 emissions prior to hitting the tipping point, we can avert a serious decline.”

While Portman expresses confidence in his research’s projections for this important ocean system, he acknowledges that other significant processes may still need to be considered.

“This necessitates prudence regarding the findings,” he emphasized. “Substantial uncertainty remains in climate models concerning AMOC’s future. Addressing this issue is vital.”

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Source: www.sciencefocus.com

New Study: U.S. Coastlines Facing Accelerated Marine Disaster Risks

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A major ocean current system, crucial for regulating the climate across the Northern Hemisphere, is expected to weaken far more severely by the end of this century than previously estimated, according to a new study published in Scientific Progress.

The Atlantic Meridional Overturning Circulation (AMOC) is a vast ocean current system that transports warm water north from the tropics, releasing heat into the atmosphere, then sinking and returning south.

Dr. Valentin Portman, lead author from Bordeaux Southwest Research Center in France, explains, “This loop transports heat from the equator to the North Atlantic Ocean,” as reported by BBC Science Focus.

The warm, salty water moves north, releases heat, thickens, sinks, and subsequently flows south through deep ocean currents.

Research predicts a 51% slowdown of AMOC by 2100, approximately 60% higher than average projections from standard climate models and with considerably lower uncertainty.

The implications of a weakened AMOC could be dire. Sea levels along the Northeast Coast of the United States are already rising faster than the global average, partly due to AMOC’s decline.










Globally, the tropical rain belt is anticipated to weaken and shift south, endangering the monsoon systems vital for agriculture in West Africa and South Asia.

In Europe, these changes could result in colder, harsher winters as the warm water conveyor belt slows down.

Every further weakening brings the AMOC closer to a tipping point, increasing the chances of complete collapse with potentially catastrophic outcomes.

The AMOC stretches the length of the Atlantic Ocean, forming part of a vast network of ocean currents – Photo credit: Getty

The Importance of AMOC

Predicting the future of AMOC as global temperatures rise is notoriously challenging. Its vast, complex nature is influenced by both local and global factors.

Previous assessments of AMOC’s future varied widely between climate models. While most agree on its weakening, estimates of its collapse range from minimal to catastrophic.

The latest study identified systematic errors in some of the best existing models: underestimating salinity in the South Atlantic and overestimating temperature in the North Atlantic.

These biases lead to an underestimation of the critical process that allows dense, saline water to sink, maintaining current flow within the system.

After correcting these discrepancies using ridge-normalized linear regression — a rarely applied technique in climate science — researchers found the expected weakening of AMOC increased to 51%, considerably lowering result uncertainty.

“Typically, models use one variable as input, like past AMOC strength,” Portman noted.

“Our goal was to utilize more comprehensive data by analyzing multiple variables concurrently, considering the complexity of AMOC.”

The current AMOC is already showing signs of weakness, as evidenced by observational data revealing a 10% to 20% intensity decline since the mid-2000s — equivalent to significant volumes of water no longer flowing north each second.

According to a 2025 study, recent AMOC weakening has contributed up to 50% of flooding along the U.S. Northeast coast since 2005.

However, researchers caution that linking this decline directly to anthropogenic climate change, rather than natural fluctuations, remains uncertain until at least 2033, when sufficient data will be available.

Understanding the Risks

While the findings of this study are concerning, researchers clarify what they do and don’t imply.

The 6th Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) expressed confidence that AMOC will weaken throughout this century but reported “moderate confidence” that it would avoid total collapse by the year 2100.

However, these reassurances may offer little comfort given the impact of such a collapse, whether it occurs before or after 2100.

Moreover, a 2025 study published in Geophysical Research Letters indicated that under serious collapse scenarios, severe cold temperatures could drop to -20°C (-4°F) in London and -48°C (-54°F) in Oslo, despite global warming trends.

As human-induced climate change melts polar ice, ocean salinity decreases, hindering processes driving the AMOC.

A weakening AMOC also raises the risk of breaching an unknown tipping point. According to a study, AMOC may exist in two stable states, and once reversed, it could take thousands of years to revert.

The exact location of this threshold is uncertain. A 2025 study in Environmental Research Letters revealed that under high emissions, AMOC shutdowns could occur in 67% of operations, and 30% under moderate emissions.

“The threshold remains elusive,” Portman stated, “but this accelerated decline we observe may be approaching a tipping point.”

Future Projections

Portman’s team assessed four different emissions scenarios, three of which (from moderate to very high) indicate similar 50% weakening results, suggesting that beyond a certain emissions level, many consequences of climate change become inevitable.

“We’ve introduced significant heat into the ocean, and its chilling effects will last for centuries,” Portman warned.

The most optimistic scenario, emphasizing strong and sustained emissions reductions, resulted in only a 20% weakening of AMOC.

“We can frame it two ways: it’s late, given our high CO2 emissions and their long-term impacts,” Portman said, “but we can also assert that significant reductions before reaching a tipping point can avert a serious decline.”

Currently, Portman believes his research offers a clearer view of the AMOC’s future, though he acknowledges ongoing uncertainties and the potential for additional undiscovered processes.

“That’s why it’s critical to approach these findings cautiously,” he emphasized. “Addressing uncertainty in climate models is essential for understanding AMOC’s fate.”

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Source: www.sciencefocus.com

Study shows wave activity causing erosion along the coastlines of Titan’s largest lakes and oceans

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Titan, Saturn’s largest moon, is the only known planet other than Earth that still retains liquid water. Liquid hydrocarbons fed by rain from Titan’s thick atmosphere form rivers, lakes, and oceans, most of which are found in the polar regions. In a new study, a team of MIT geologists surveyed Titan’s coastline and found that the moon’s large lakes and oceans were likely formed by waves.

Artist’s rendering of the surface of Saturn’s largest moon, Titan. Image by Benjamin de Bivort, debivort.org / CC BY-SA 3.0.

The existence of waves on Titan has been a somewhat controversial topic ever since NASA’s Cassini spacecraft discovered liquid puddles on Titan’s surface.

“Some people who have looked for evidence of waves haven’t seen any waves at all and have said, ‘The ocean is as smooth as a mirror,'” said Dr. Rose Palermo, a geologist with the U.S. Geological Survey. “Others have said they saw some roughness in the water but didn’t know if it was caused by waves.”

“Knowing whether there is wave activity in Titan’s oceans can provide scientists with information about the moon’s climate, including the strength of the winds that generate such waves.”

“Wave information could also help scientists predict how the shape of Titan’s ocean will change over time.”

“Rather than looking for direct signs of wave-like features in Titan images, we wanted to take a different approach and see if just looking at the shape of the coastline could tell us what it is that is eroding the coast.”

Titan’s oceans are thought to have formed when rising waters flooded a landscape crisscrossed by river valleys.

The researchers zeroed in on three scenarios for what happened next: no coastal erosion, wave-driven erosion, and uniform erosion caused by either dissolution, where liquids passively dissolve coastal material, or a mechanism where the coast gradually peels away under its own weight.

They simulated how different coastline shapes would change under each of the three scenarios.

To simulate wave erosion, the researchers took into account a variable called “fetch,” which describes the physical distance from one point on the shoreline to the other side of a lake or ocean.

“Wave erosion depends on the height and angle of the waves,” Dr Palermo said.

“We used the fetch to estimate wave height because the bigger the fetch, the further away the wind will blow and the bigger the waves will be.”

Cassini observed Titan’s surface with microwaves and found several grooves that are deep canyons filled with liquid hydrocarbons, including Vid Fulmina, a branching network of thin lines in the upper left quadrant of the image. Image credit: NASA / JPL-Caltech / ASI.

To test how coastline shape would differ between the three scenarios, the scientists started with a simulated ocean area with a flooded river valley all around it.

For wave erosion, we calculated the fetch distance from every point along the coastline to every other point and converted that distance to wave height.

They then ran simulations to see how waves would erode the original shoreline over time.

They compared this to how the same coastline would change due to erosion caused by uniform erosion.

The authors repeated this comparative modelling for hundreds of different initial shoreline configurations.

They found that the shape of the termini varies greatly depending on the underlying mechanism.

Most notably, uniform erosion produced a bulging shoreline that was evenly distributed all around, even in flooded river valleys, whereas wave erosion smoothed out portions of the shoreline exposed primarily to long downstream distances, leaving the flooded valleys narrow and rough.

“Although the initial coastline was the same, we found that uniform erosion and wave erosion resulted in very different final shapes,” Dr Perron said.

“Although it looks like a flying spaghetti monster because of the flooded river valley, the endpoints created by the two types of erosion are very different.”

This image is a composite of images taken during two flybys of Titan in 2006. A large circular feature near the center of Titan’s disk may be the remnant of a very old impact basin. The mountain range southeast of the circular feature and the long, dark linear feature northwest of the old impact site may be the result of deformation of Titan’s crust caused by energy released when the impact occurred. Image credit: NASA/JPL/University of Arizona.

Dr. Perron and his colleagues verified their results by comparing their simulation results with actual lakes on Earth.

They found the same shape differences between Earth’s lakes known to have been eroded by waves and those affected by homogeneous erosion, such as dissolved limestone.

Their modelling revealed distinct and distinctive shapes depending on the mechanism by which the shoreline evolved.

So they wondered: Where does Titan’s coastline fit into these distinctive shapes?

In particular, they focused on four of Titan’s largest and best-mapped oceans: Kraken Mare, which is comparable in size to the Caspian Sea; Ligeia Mare, which is larger than Lake Superior; Punga Mare, which is longer than Lake Victoria; and Lake Ontario, which is about 20% the size of the land-based lake of the same name.

The researchers used Cassini’s radar images to map the coastlines of each of Titan’s oceans, and then applied their model to the coastlines of each ocean to see which erosion mechanisms best explain their shape.

They found that all four oceans fit closely to the wave-induced erosion model, meaning that waves created the closest coastlines to Titan’s four oceans.

“We found that when the shoreline is eroding, its shape is more consistent with wave-driven erosion than uniform erosion or no erosion,” Dr Perron said.

Scientists are trying to figure out how strong Titan’s winds would need to be to churn up waves strong enough to repeatedly scrape away the shoreline.

They also hope to learn from the shape of Titan’s coastline which direction the winds primarily blow from.

“Titan shows us that this case is completely pristine,” Dr. Palermo said.

“It may help us learn more fundamental things about how coasts erode without human influence, which in turn may help us better manage coastlines around the world in the future.”

of Investigation result Published in today’s journal Scientific advances.

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Rose V. Palermo others2024. Evidence of wave erosion on Titan’s coast. Scientific advances 10(25); Source: 10.1126/sciadv.adn4192

Source: www.sci.news