Idag gen-besøger vi et emne vi i sin tid havde Jesper Theilgaard inde og tale om. Verdenshavene og strømmene. Der sker lidt!
Her er Karina’s noter.
AMOC:
The Atlantic Meridional Overturning Circulation (AMOC) is a major system of ocean currents, including the Gulf Stream, that transports warm water to the North Atlantic and colder water south. It acts as a vital heat conveyor, ensuring mild temperatures in Europe. Due to climate change—specifically freshwater influx from melting glaciers—the AMOC is weakening, threatening a potential collapse that could drastically alter global weather patterns.
Function: It acts like a conveyor belt, transporting warm, salty water from the tropics to the North Atlantic and cold, deep water back south.
Significance: It keeps Europe warmer than other regions at similar latitudes and influences global climate patterns, including the monsoon in Asia.
Weakening Trend: Studies suggest the AMOC is at its weakest in over 1,000 years.
Risks: A collapse could cause severe consequences, including much colder European winters, accelerated sea-level rise, and shifts in tropical rainfall.
Potential Collapse: Research indicates the system is approaching a critical tipping point, with some studies suggesting a potential collapse this century.
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Klimaforsker: 5 ting, jeg ville ønske, alle vidste om AMOC-havstrømme:
Den globale opvarmning gør havvandet lettere, og øget tilførsel af ferskvand fra blandt andet Grønland reducerer saltholdigheden.
Det betyder, at mindre af det tungere kolde vand i Nordatlanten synker mod bunden og dermed giver plads til lunere vand i overfladen.
Det bremser cirkulationen af det varme og kolde vand og svækker det samlede system.
For 12800 år siden - den yngre Dryas periode - dengang Istidens store iskapper var på retræte, mener man at der var en svækkelse af AMOC pga store intense tilførsler af ferskvand fra smeltende iskapper i Nordamerika til Nordatlanten.
Under Yngre Dryas opstod en næsten istidslignende periode i Nord- og Vesteuropa, hvor temperaturerne faldt voldsomt inden for få årtier og forblev lave i 1.000 år.
Gletsjere rykkede frem igen, og vegetationen ændrede sig hurtigt i retning af mere kuldetolerante arter.
Dette kan muligvis været triggeret af et vulkanudbrud: Undervurderet joker kan før have udløst voldsomme klimaforandringer
Vulkanudbrud puffede dengang til et klimasystem, der i forvejen var ude af balance. Ubalancen skyldtes blandt andet, at enorme mængder fersk smeltevand fossede ud i det nordatlantiske hav fra de flere kilometer tykke iskapper, der dækkede store dele af den nordlige halvkugle.
Ferskvandet forstyrrede havets saltbalance og dermed de vigtige nordatlantiske strømme, der fordeler varme fra Jordens sydlige halvkugle til den nordlige.
»I istiden var klimaet tæt på et 'tipping point'. Når noget er lige ved at vælte, skal der ikke meget til at skubbe det ud over kanten,« siger en anden af forskerne bag studiet, Peter Ditlevsen, der er professor i klimamodellering på Niels Bohr Institutet i København.
Udsigterne:
AMOC kollaps allerede 2065. Man ved ikke om det er en langsom svækkelse eller et pludseligt skift.
Det er IKKE en kommende istid. Det er ændringer i havcirkulationen, som kan gøre vores klima køligere og mere ustabilt.
CO2 niveauer som for 2-3 millioner år siden.
Regional temperature changes would be even more pronounced than global mean temperature change. In one scenario at CO₂ concentrations of 450ppm – last experienced by the Earth several million years ago, when polar ice was significantly reduced – Antarctic temperatures rise by 6°C while Arctic temperatures drop by 7°C due to AMOC collapse.(fra PIK)
Et kollaps af AMOC can frigive CO2 i de sydlige have, hvilket vil tilføre yderligere 0.2°C til global opvarming.
Antartika
https://www.asoc.org/learn/antarctic-ice-and-rising-sea-levels/
Forskere har kortlagt, hvor Antarktis' afsmeltning vil få de største konsekvenser
Højere saltindhold:
Rising surface salinity and declining sea ice: A new Southern Ocean state revealed by satellites
Antarctica has lost a Greenland’s worth of sea ice (på 10 år) – and the effects are troubling.
A dramatic transformation is unfolding in the waters around Antarctica. Since 2015, the continent has lost as much sea ice as the entire size of Greenland, but that’s not even the scariest part.
Scientists have discovered that the Southern Ocean, which once freshened and helped preserve the ice, is now becoming saltier. This saltier surface allows deep ocean heat to rise, melting the ice from below. It’s a reversal of decades-long trends – and it’s doing damage fast.
One striking consequence: the return of the Maud Rise polynya, a massive hole in the sea ice nearly four times the size of Wales, unseen since the 1970s. It’s a symptom of a dangerous feedback loop – less ice leads to more ocean heat, which leads to even less ice – potentially destabilizing one of Earth’s key climate regulators.
And the impacts extend far beyond the poles. Sea ice acts as a mirror, reflecting sunlight. Without it, oceans absorb more heat, amplifying global warming, fueling more extreme storms, and collapsing ecosystems that depend on stable ice – from penguins to krill and beyond.
Now, with real-time satellite and robotic monitoring in place, scientists warn we may be witnessing a fundamental shift in the planet’s climate engine – one that’s unfolding faster than expected, and with global consequences.
Pingvin lort
Pingvinlort danner skyer over Antarktis: En overset beskyttelse mod klimaforandringer?
Pungent Penguin Poop Produces Polar Cloud Particles - Eos
Regn på Antarktis
Regn på vej til Antarktis, og det vil forandre det isdækkede kontinent
Mærkeligt liv fundet under Antarktis:
Gamle ting vi har snakket om tidligere:
1) Fra episode nov/dec 2022:
Under iskappen på Antarkis løber der en 460 kilometer lang flod.
The researchers behind the discovery used a combination of airborne radar surveys that can peer through the ice, plus water flow modeling. The large area under examination includes ice from both the east and west ice sheets in the Antarctic, with water running off into the Weddell Sea.
"The region where this study is based holds enough ice to raise the sea level globally by 4.3 meters," says glaciologist Martin Siegert from Imperial College London in the UK.
"How much of this ice melts, and how quickly, is linked to how slippery the base of the ice is. The newly discovered river system could strongly influence this process."
"When we first discovered lakes beneath the Antarctic ice a couple of decades ago, we thought they were isolated from each other," says Siegert.
"Now we are starting to understand there are whole systems down there, interconnected by vast river networks, just as they might be if there weren't thousands of meters of ice on top of them."
https://www.sciencealert.com/scientists-just-discovered-a-huge-river-hidden-under-antarctica
2) I 2018, nævnte vi at man havde fundet en varmekilde under isen i Antarktis:
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