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Is the AMOC Current Slowdown Gradual and Reversible? Insights and Implications

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Visualization of Atlantic Ocean Flows from Satellite Images

Carsten Schneider/Science Photo Library

The Atlantic Meridional Overturning Circulation (AMOC) may face weakening due to freshwater influx from Greenland’s snowmelt. However, cutting-edge climate models indicate this slowdown is likely to be gradual and reversible if global warming is curbed.

AMOC is a critical ocean current system that conveys warm, salty water from the tropics to the North Atlantic. There, it cools, sinks, and circulates back southward along the ocean floor. The influx of fresh meltwater from Greenland’s ice sheet appears to be mixing with denser seawater, slowing its downward flow.

<p>Recent estimates indicate Greenland is losing approximately <a href="https://www.nature.com/articles/s41586-023-06863-2">30 million tons of ice</a>. Some experts express concerns that AMOC could undergo a sudden and irreversible collapse, potentially plunging Europe into near-Arctic conditions. One <a href="https://iopscience.iop.org/article/10.1088/1748-9326/adfa3b">study</a> suggests that AMOC might cross a crucial tipping point within decades.</p>
<p>However, modeling by <a href="https://research-portal.uu.nl/en/persons/oliver-mehling/">Oliver Mehring</a> and colleagues at Utrecht University revealed that while AMOC may weaken steadily under ongoing global warming, it is unlikely to reach a point of no return solely due to Greenland’s snowmelt.</p>
<p>“The prevailing notion that melting from the Greenland ice sheet could trigger an irreversible AMOC collapse is a significant oversimplification,” stated Mehring. “The snowmelt from Greenland alone is insufficient to push AMOC past its tipping point.”</p>

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<p>It is believed that atmospheric warming not only accelerates Greenland's melting but also directly undermines the AMOC by preventing brine in the North Atlantic from cooling adequately. This warming allows the ocean to hold more freshwater, which ultimately leads to increased rainfall, diluting saltwater, and reducing ocean mixing. This combination of warming and freshwater influx diminishes the sinking action crucial to AMOC.</p>

<p>While most predictive models of future climate change concentrate on atmospheric warming's impact on AMOC, <a href="https://research-portal.uu.nl/en/persons/oliver-mehling/">Mehring</a> and his team found that atmospheric warming could weaken AMOC by a staggering 60% by 2300. If the volume of Greenlandic snowmelt were to increase, the AMOC's strength could diminish by an additional 20%.</p>

<p>Nonetheless, their research indicates that if atmospheric CO2 levels were to decrease by 1% annually starting in 2250, AMOC could fully recover by around 2400. Although these models are not designed to predict the exact timeline or extent of AMOC changes, they imply that increased freshwater input from Greenland won't lead the AMOC over the tipping point.</p>

<p>A reduction of 80% in AMOC could still lead to crop failures in Western Europe, ice formation in the North Sea, and disruption of tropical monsoon patterns. Fortunately, the study indicates that such declines would be gradual, predictable, and reversible if humanity ceases fossil fuel combustion. As <a href="https://www.bas.ac.uk/profile/lsim/">Louise Sim</a> from the British Antarctic Survey commented, "While scenarios of AMOC crashing are conceivable, they are unlikely to occur. Instead, AMOC shows a strong linear relationship with cumulative CO2 emissions."</p>

<p>Despite these findings, the possibility of a tipping point cannot be completely dismissed. Previous research conducted by <a href="https://www.uu.nl/staff/RMvanWesten">René van Westen</a> and colleagues at Utrecht University, using a different model, suggested that significant melting from Greenland could lead to AMOC's irreversible collapse. However, this model applied meltwater at a constant rate rather than simulating the gradual increases observed in reality.</p>

<p>“Other climate models have predicted crossings of the tipping point under 21st-century climate change, illustrating that results can be model-dependent,” van Westen remarked.</p>

<p>In addition to Greenland’s melting, several other climate changes pose risks to the AMOC. For instance, freshwater from Antarctic snowmelt could disrupt global circulation dynamics, of which AMOC is a vital component. However, the impacts remain uncertain; depending on the timing of Antarctic melt, it could also help sustain the AMOC.</p>

<p>This new study does not eliminate the risk of an AMOC tipping point but contributes valuable insights to the ongoing climate discussion, highlighted <a href="https://scholar.google.com/citations?user=Cn7wuysAAAAJ&amp;hl=en">Jonathan Baker</a> from the UK’s Met Office.</p>

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Source: www.newscientist.com

Falling Asleep: A Sudden Shift, Not a Gradual Process.

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We never just drift off; we abruptly enter slumber.

Dead Mitiei/Shutterstock

The brain doesn’t transition into sleep gradually. Instead, we hit a critical moment where we swiftly shift from being awake to asleep within just minutes. This finding could enhance the understanding and treatment of sleep-related issues like insomnia.

“Sleep is crucial to our existence, yet the mechanisms behind how our brain falls asleep have remained elusive,” states Nil Grossman from Imperial College London. It’s commonly thought that this change occurs gradually, with the brain smoothly moving from wakefulness to sleep; however, evidence for this phenomenon is sparse.

Grossman and his team have created a novel method to investigate how the brain functions during sleep by utilizing electroencephalography (EEG) data. This technique captures the brain’s electrical activity and provides insights into various sleep stages and wakefulness. The researchers analyzed 47 EEG signals using an abstract mathematical framework, treating each data point as if it were plotted on a map. This enabled them to visualize brain activity in its transition towards the designated sleep onset zone, correlating with the second phase of non-rapid eye movement (NREM) sleep.

“Now we can accurately monitor brain activity and determine how close individuals are to falling asleep each second, with a level of precision never achieved before,” explains Grossman.

The method was applied to EEG data acquired during the sleep onset phase of over 1,000 participants, measuring the proximity of brain activity to sleep onset. Generally, this proximity remained stable until about 10 minutes prior to sleep, markedly decreasing in the final moments. Researchers determined that this critical transition occurs roughly 4.5 minutes before sleep, marking the distinct switch from wakefulness to slumber, as noted by Li Junheng, also from Imperial College London. “[This is] the point of no return,” he states.

These findings indicate that the shift from wakefulness to sleep is “not a slow progression, but rather a sudden, dramatic transformation occurring in the last few minutes,” asserts Grossman. Thus, when we “fall asleep,” it closely reflects the underlying activity in our brains. “This showcases nearly the feeling of entering a different state,” he adds.

The research team subsequently gathered brainwave information from another group of 36 individuals, tracking each participant’s sleep patterns over a week. They utilized some of those nights to accurately predict when participants would fall asleep, within a minute of the actual moment.

“This indicates that while individuals differ significantly, each person seems to follow a unique sleep trajectory that recurs night after night,” remarks Laura Lewis from the Massachusetts Institute of Technology. However, she notes that it remains uncertain if these patterns alter when external conditions vary, like sleeping in a new environment.

While this framework does not explicitly identify the brain mechanisms responsible for the sleep transition, Lewis believes it could pave the way for future discoveries. “Identifying the precise moment of falling asleep has been quite challenging,” she states. “Once that is established, we can delve into the brain regions and circuits that facilitate sustained sleep.” Understanding the nuances of this transition could also aid in recognizing variations among individuals with insomnia, leading to innovative treatments.

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Source: www.newscientist.com

  • Recent Research Indicates Gradual Bottleneck Events in Neanderthal Evolution

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According to a new study led by scientists at the University of Barcelona and Alcala, the bottleneck event took place between 130,000 and 50,000 years ago.

Neanderthal. Image credit: Trustee of the Museum of Natural History in London.

“Neanderthals are the most well-written humans in the fossil record in terms of morphology, genetics, behavior and culture,” said Dr. Alessandro Urciori, a colleague of a University of Barcelona.

“Recent molecular clock-based analyses, along with Denisovan, have divergences from 765,000-550,000 years old or older human lineages based on morphological data.”

“The Neanderthal lineage was differentiated soon after, and is testified by genetic and morphological evidence from the Simah delos Hussians of the Middle Pleistocene, which was previously thought to be expressed. . HOMO HEIDELBERGENSIS And now it is considered the early population of the Neanderthal lineage. ”

“Genetic divergence times are now well established for the entire clade, but also include relationships with the medieval Pleistocene populations of Europe, the medieval and late Pleistocene Neanderthal populations, and the evolution of the complete. There is a continuing debate over the connected evolutionary processes” Classic Neanderthal “Form of the late Neanderthal.”

“This is due to the mosaic form of the intermediate Pleistocene specimen, which is claimed to have evolved by the Neanderthals.”

In this study, the researchers measured the morphological diversity of semicircular canals, the structure of the inner ear that caused sense of balance.

They focus on two exceptional collections of fossils. One is from the site of Sima de los Husos in Spain, and dates 430,000 years old, making up the largest sample of pre-production available in the fossil record. Another location 130,000 to 120,000 years ago in Krapina, Croatia.

They calculated the amount of morphological diversity (i.e., disparity) in the semicircular canals in both samples, compared them to one another, and compared them with classic Neanderthal samples of different ages and geographical origins. .

The findings show that the morphological diversity of the semicircular canals of classical Neanderthals is clearly lower than the diversity of early Neanderthal morphologies before the Nianderthals, consistent with previous palaeogenesis results. It is revealed.

“The inclusion of fossils from a wide range of geographical and temporal ranges allowed us to capture a comprehensive photograph of the evolution of Neanderthal,” said Dr. Mercedes Conde Valvade, a researcher at Alcala University. .

“The reduced diversity observed between Krapina samples and classic Neanderthals is particularly impressive and clear, providing strong evidence of bottleneck events.”

“The results, on the other hand, challenge the previously accepted idea that Neanderthal origins are associated with a significant loss of genetic diversity and encourage the need to propose a new explanation of their origins.”

“We were surprised that pre-Neanderthal people in Sima de los Husos exhibited similar morphological diversity as early Neanderthals in Krapina,” Dr. Urshuuori said.

a paper The findings were published in the journal Natural Communication.

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A. Urushiuori et al. 2025. A semicircular canal that sheds light on bottleneck events in the evolution of the Neanderthal clade. Nut commune 16, 972; doi:10.1038/s41467-025-56155-8

Source: www.sci.news