/environment

  • Melting glaciers force Switzerland and Italy to redraw part of Alpine border

    Two countries agree to modifications beneath Matterhorn peak, one of Europe’s highest summits

    Switzerland and Italy have redrawn a border that traverses an Alpine peak as melting glaciers shift the historically defined frontier.

    The two countries agreed to the modifications beneath the Matterhorn, one of the highest mountains in Europe, which straddles Switzerland’s Zermatt region and Italy’s Aosta valley.

    Glaciers in Europe, the world’s fastest-warming continent, are retreating at an accelerated pace because of human-caused climate breakdown.

    “Significant sections of the border are defined by the watershed or ridge lines of glaciers, firn or perpetual snow,” the Swiss government said in a statement cited by Bloomberg. “These formations are changing due to the melting of glaciers.”

    The famed Zermatt ski resort is affected by the change, with the two countries agreeing to modify the border around the landmarks of Testa Grigia, Plateau Rosa, Rifugio Carrel and Gobba di Rollin based on their economic interests, Bloomberg reported.

    A joint Italian-Swiss commission agreed to the changes in May 2023. Switzerland officially approved the treaty on Friday, but Italy still needs to sign.

    The changes come after a disagreement between the two countries over the peak’s territory that lasted for years.

    Swiss glaciers lost 4% of their volume in 2023, the second-biggest annual decline on record, according to the Swiss Academy of Sciences. The largest decline was 6% in 2022.

    Experts have stopped measuring the ice on some Swiss glaciers because there is none left.

    The remains of a German mountain climber who disappeared while crossing a glacier near the Matterhorn nearly 40 years ago were discovered in melting ice in July last year.

    Experts in Italy said this month that the Marmolada glacier, which is the largest and most symbolic of the Dolomites, could melt completely by 2040 as a result of rising average temperatures.

    The collapse of part of the Marmolada killed 11 people in 2022.

    The glacier has been measured every year since 1902 and is considered a “natural thermometer” of climate change.

    https://www.theguardian.com/environment/2024/sep/29/melting-glaciers-switzerland-italy-alpine-border-matterhorn
    #frontières #frontière_mobile #Suisse #Italie #Alpes #Matterhorn #Cervin #visualisation #fonte_des_glaciers #glaciers #Zermatt #traité

    ping @reka

    • Switzerland and Italy redraw border due to melting glaciers

      Switzerland and Italy have redrawn part of their border in the Alps due to melting glaciers, caused by climate change.

      Part of the area affected will be beneath the Matterhorn, one of Europe’s tallest mountains, and close to a number of popular ski resorts.

      Large sections of the Swiss-Italian border are determined by glacier ridgelines or areas of perpetual snow, but melting glaciers have caused these natural boundaries to shift, leading to both countries seeking to rectify the border.

      Switzerland officially approved the agreement on the change on Friday, but Italy is yet to do the same. This follows a draft agreement by a joint Swiss-Italian commission back in May 2023.

      Statistics published last September showed that Switzerland’s glaciers lost 4% of their volume in 2023, the second biggest loss ever after 2022’s record melt of 6%.

      An annual report is issued each year by the Swiss Glacier Monitoring Network (Glamos), which attributed the record losses to consecutive very warm summers, and 2022 winter’s very low snowfall. Researchers say that if these weather patterns continue, the thaw will only accelerate.

      On Friday, Switzerland said that the redefined borders had been drawn up in accordance with the economic interests of both parties.

      It is thought that clarifying the borders will help both countries determine which is responsible for the upkeep of specific natural areas.

      Swiss-Italian boundaries will be changed in the region of Plateau Rosa, the Carrel refuge and Gobba di Rollin - all are near the Matterhorn and popular ski resorts including Zermatt.

      The exact border changes will be implemented and the agreement published once both countries have signed it.

      Switzerland says that the approval process for signing the agreement is under way in Italy.

      Last year, Glamos warned that some Swiss glaciers are shrinking so fast that it is unlikely they can be saved, even if global temperatures are kept within the Paris climate agreement’s 1.5C target rise.

      Experts say that without a reduction in greenhouse gases linked to global warning, bigger glaciers like the Aletsch - which is not on the border - could disappear within a generation.

      A number of discoveries have been made on Swiss glaciers in recent years due to their melting and rapid shrinking.

      Last July, human remains found close to Matterhorn were confirmed to be those of a German climber missing since 1986.

      Climbers crossing the Theodul glacier above Zermatt noticed a hiking boot and crampons emerging from the ice.

      In 2022, the wreckage of a plane that crashed in 1968 emerged from the Aletsch glacier.

      And the body of missing British climber Jonathan Conville was discovered in 2014 by a helicopter pilot who spotted something unusual while delivering supplies to a mountain refuge on the Matterhorn.

      https://www.bbc.com/news/articles/cgk7r0rrdnmo

  • Europe saved its predators from the brink of extinction. So why is it killing thousands of bears, wolves and lynx? | Hunting | The Guardian

    https://www.theguardian.com/environment/2024/sep/12/europe-saved-its-predators-from-brink-of-extinction-so-why-killing-thou

    Europe saved its predators from the brink of #extinction. So why is it killing thousands of #bears, #wolves and #lynx?

    Nelly Didelot
    @nellydidelot

    A 2022 study founds #wolf_attacks were associated with #far-right gains in #German #municipal_elections of 1-2%

    via #Nelly_didelot, twitter https://x.com/nellydidelot

  • ‘We should have better answers by now’: #climate scientists baffled by unexpected pace of heating | Climate crisis | The Guardian
    https://www.theguardian.com/environment/article/2024/aug/15/we-should-have-better-answers-by-now-climate-scientists-baffled-by-unex
    https://i.guim.co.uk/img/media/f300cc8293799af3c9d158742d5e1e338d6eebc7/0_0_5000_3000/master/5000.jpg?width=1200&height=630&quality=85&auto=format&fit=crop&overlay-ali

    In a remarkably candid essay in the journal Nature this March, one of the world’s top climate scientists posited the alarming possibility that global heating may be moving beyond the ability of experts to predict what happens next.

    “The 2023 temperature anomaly has come out of the blue, revealing an unprecedented knowledge gap perhaps for the first time since about 40 years ago, when satellite data began offering modellers an unparalleled, real-time view of Earth’s climate system,” wrote Gavin Schmidt, a British scientist and the director of the Nasa Goddard Institute for Space Studies in New York.

    If this anomaly does not stabilise by August, he said, it could imply “that a warming planet is already fundamentally altering how the climate system operates, much sooner than scientists had anticipated”.

    Many in the science and environment community read these words with alarm. Was the leap in temperatures over the past 13 months, which has exceeded the global heating forecasts of experts, a sign of a systemic shift, or just a temporary anomaly? If the world was warming even faster than scientists thought it would, seemingly jumping years ahead of predictions, would that mean even more crucial decades of action had been lost?

    No shit ?

  • Ocean spray emits more PFAS than industrial polluters, study finds
    https://www.theguardian.com/environment/2024/apr/19/ocean-spray-pfas-study
    Quand tu respires à pleins poumons en regardant la mer, il y a des chances que tu absorbes une bonne dose de PFAS.

    The study measured levels of #PFAS released from the bubbles that burst when waves crash, spraying #aerosols into the #air. It found sea spray levels were hundreds of thousands times higher than levels in the water.

    The contaminated spray likely affects groundwater, surface water, vegetation, and agricultural products near coastlines that are far from industrial sources of PFAS, said Ian Cousins, a Stockholm University researcher and the study’s lead author.

    There is evidence that the ocean can be an important source [of PFAS air emissions],” Cousins said. “It is definitely impacting the coastline.

    [...] It is unclear what the findings mean for human exposure. Inhalation of PFAS is an issue, but how much of the chemicals are breathed in, and air concentrations further from the waves, is still unknown.

    [...] He said that the results showed how the chemicals are powerful surfactants that concentrate on the surface of water, which helps explain why they move from the ocean to the air and atmosphere.

    We thought PFAS were going to go into the ocean and would disappear, but they cycle around and come back to land, and this could continue for a long time into the future,” he said.

    #pollution #plastique #océan

    • « (...) il n’est plus possible de traiter les profondeurs comme étant d’une manière ou d’une autre séparée de l’activité humaine. Il n’est pas non plus possible de le considérer simplement comme une nouvelle frontière à exploiter, comme le prévoient les projets d’exploitation minière en haute mer . Au lieu de cela, tout comme la découverte du temps profond a modifié la façon dont la culture occidentale comprenait la place de l’humanité dans l’histoire plus vaste de l’histoire de la Terre, reconnaître que les profondeurs sont intimement liées au reste de la planète exige un changement dans notre compréhension de l’échelle et de la complexité réelles. de la biosphère de notre planète et, par extension, le fait que l’avenir non seulement de la vie humaine, mais de toute vie sur Terre, est inextricablement lié aux profondeurs. » James Bradley, romancier et critique australien.

  • Cancer-causing PCB chemicals still being produced despite 40-year-old ban
    https://www.theguardian.com/environment/2024/mar/08/cancer-causing-pcb-chemicals-still-produced-despite-40-year-old-ban

    Research seen by the Guardian and Watershed Investigations shows that PCBs are being produced as byproducts in chemical reactions, which means small proportions of them are present in many chemicals used today.

    This is staggering given that production of PCBs was banned over 40 years ago and we are supposed to be eliminating them under the Stockholm convention,” said the environmental forensic scientist Dr Dave Megson from Manchester Metropolitan University, who conducted the study.

    When we take into account the volumes of these chemicals and the small levels of PCBs within them then this adds up to a massive number – around 45,000 tonnes per year in the US alone.” During peak commercial production in the 1970s about 39,000 tonnes were made each year, states the study.

    Most people associate this accidental production of PCBs with paints and pigments, but our research shows it’s much broader than that,” said Megson. Chlorinated solvents, which are used in chemical manufacturing, are a major source according to the research.

    PCBs are currently going undetected in many studies as the specific PCBs produced accidentally are different from the PCBs that were produced intentionally in the commercial mixtures of 50-plus years ago.”

    The study says these kinds of by-product PCBs are not measured in many existing monitoring programmes and may pose a “growing, unmonitored environmental and human health risk”. It suggests they should be classified as “a pollutant of emerging concern” and that they need to be addressed urgently as all PCBs are considered toxic, not just legacy PCBs from commercial mixtures.

    Lee Bell from the international chemicals NGO network who is also a member of the Stockholm convention PCB expert group said: “Not a lot of effort has been made in regulating unintentional production of PCB from chemical manufacture. In the case of intentional PCB production, the parties to the convention have a deadline to eliminate all stockpiles of old PCB by 2028. They are woefully behind on this task and about 80% of PCB stockpiles have yet to be destroyed."

    [...]

    “_It is disappointing that hundreds of millions of dollars are being spent to destroy legacy PCBs while regulators allow unintentional PCB contamination to spread virtually unabated.

    [...]

    PCB production was banned in the US in 1979 and in 1981 in the UK, and work to restrict their use in electrical equipment in the UK is continuing. Sources of legacy pollution from commercially made PCBs include landfills and materials in buildings.

    #PCB #pollution #Monsanto #biodiversité

  • Microplastics found in every human #placenta tested in study | Plastics | The Guardian
    https://www.theguardian.com/environment/2024/feb/27/microplastics-found-every-human-placenta-tested-study-health-impact

    Microplastics have been found in every human placenta tested in a study, leaving the researchers worried about the potential health impacts on developing foetuses.

    The scientists analysed 62 placental tissue samples and found the most common plastic detected was polyethylene, which is used to make plastic bags and bottles. A second study revealed microplastics in all 17 human arteries tested and suggested the particles may be linked to clogging of the blood vessels.

    #plastique

  • Move to sustainable food systems could bring $10tn benefits a year, study finds

    Existing production destroys more value than it creates due to medical and environmental costs, researchers say

    A shift towards a more sustainable global food system could create up to $10tn (£7.9tn) of benefits a year, improve human health and ease the climate crisis, according to the most comprehensive economic study of its type.

    It found that existing food systems destroyed more value than they created due to hidden environmental and medical costs, in effect, borrowing from the future to take profits today.

    Food systems drive a third of global greenhouse gas emissions, putting the world on course for 2.7C of warming by the end of the century. This creates a vicious cycle, as higher temperatures bring more extreme weather and greater damage to harvests.

    Food insecurity also puts a burden on medical systems. The study predicted a business-as-usual approach would leave 640 million people underweight by 2050, while obesity would increase by 70%.

    Redirecting the food system would be politically challenging but bring huge economic and welfare benefits, said the international team of authors behind the study, which aims to be the food equivalent of the Stern review, the 2006 examination of the costs of climate change.

    Johan Rockström, of the Potsdam Institute for Climate Impact Research and one of the study’s authors, said: “The global food system holds the future of humanity on Earth in its hand.”

    The study proposes a shift of subsidies and tax incentives away from destructive large-scale monocultures that rely on fertilisers, pesticides and forest clearance. Instead, financial incentives should be directed towards smallholders who could turn farms into carbon sinks with more space for wildlife.

    A change of diet is another key element, along with investment in technologies to enhance efficiency and cut emissions.

    With less food insecurity, the report says, undernutrition could be eradicated by 2050, with 174 million fewer premature deaths, and 400 million farm workers able to earn a sufficient income. The proposed transition would help to limit global heating to 1.5C above pre-industrial levels and halve nitrogen run-offs from agriculture.

    Overall, they estimate the costs of the transformation at between 0.2% and 0.4% of global GDP per year.

    In early research, Rockström and his colleagues found food was the largest sector of the economy breaching planetary boundaries. As well at the climate impact, it is a major driver of land-use change and biodiversity decline, and is responsible for 70% of freshwater drawdown.

    The report was produced by the Food System Economics Commission, which has been formed by the Potsdam Institute, the Food and Land Use Coalition, and EAT, a holistic food-system coalition of the Stockholm Resilience Centre, the Wellcome Trust and the Strawberry Foundation. Academic partners include the University of Oxford and the London School of Economics.

    It estimated the hidden costs of food, including climate change, human health, nutrition and natural resources, at $15tn, and created a new model to project how these hidden costs could develop over time, depending on humanity’s ability to change. Their calculations were in line with a report last year by the United Nations Food and Agriculture Organization, which estimated off-books agrifood costs at more than $10trillion globally in 2020.

    Dr Steven Lord, of the University of Oxford’s Environmental Change Institute, said in a statement: “This analysis puts a first figure on the regional and global economic opportunity in transforming food systems. While not easy, the transformation is affordable on a global scale and the accumulating costs into the future of doing nothing pose a considerable economic risk.”

    Numerous other studies have demonstrated the health and climate benefits of a shift towards a plant-based diet. A report last year by the Climate Observatory notes that Brazil’s beef industry – and its related deforestation – now has a bigger carbon footprint than all the cars, factories, air conditioners, electric gadgets and other sources of emissions in Japan.

    The new study is not prescriptive about vegetarianism, but Rockström said demand for beef and most other meat would fall if hidden health and environmental costs were included in the price.

    Nicholas Stern, the chair of the Grantham Research Institute on Climate Change and the Environment at the London School of Economics, welcomed the study: “The economics of today’s food system are, sadly, broken beyond repair. Its so-called ‘hidden costs’ are harming our health and degrading our planet, while also worsening global inequalities. Changing the ways we produce and consume food will be critical to tackling climate change, protecting biodiversity, and building a better future. It is time for radical change.”

    The main challenge of the proposed food transition is that costs of food would rise. Rockström said this would have to be handled with political dexterity and support for poor sections of society otherwise the result could be protests, such as the gilets jaunes (yellow vests) demonstrations held in France over petrol price hikes.

    Christiana Figueres, the former executive secretary of the UN Framework Convention on Climate Change, emphasised the forward-looking nature of the report: “This research … proves that a different reality is possible, and shows us what it would take to turn the food system into a net carbon sink by 2040. This opportunity should capture the attention of any policymaker who wants to secure a healthier future for the planet and for people.”

    https://www.theguardian.com/environment/2024/jan/29/sustainable-food-production-economic-benefits-study?CMP=share_btn_tw

    #système_alimentaire #alimentation #agriculture #coût #bénéfices #économie #agriculture_biologique #

    • The Economics of the Food System Transformation

      The text emphasizes the urgent need for a transformation of food systems, highlighting the economic, environmental, and social benefits of such a transformation. It outlines the negative impacts of current food systems on health, the environment, and climate change, identifying unaccounted costs estimated at 15 trillion USD a year. The report also discusses the unsustainable trajectory of the global food system and the potential economic benefits of a transformation, estimating them to be worth 5 to 10 trillion USD a year.

      Proposed Solutions for Food System Transformation:

      1. Shifting consumption patterns towards healthy diets: The report suggests regulating the marketing of unhealthy foods to children, providing front-of-pack nutritional guidance, targeting public food procurement on healthy options, taxing sugar-sweetened beverages and unhealthy foods, and reformulating packaged food to encourage healthier dietary choices.

      2. Resetting incentives by repurposing government support for agriculture: It is recommended to repurpose subsidies to improve access to healthy diets and make them more affordable. This involves reforming agricultural support to incentivize choices in line with the goals of the food system transformation, with a focus on lowering the hidden costs of food systems.

      3. Targeting revenue from new taxes to support food system transformation: The report recommends taxing carbon and nitrogen pollution to help achieve positive outcomes and align with expert recommendations from bodies such as the IPCC and OECD. Designing new taxes to suit the local context and targeting resulting revenues towards direct and progressive benefits for poorer households is essential to ensure inclusive outcomes and garner political support for a food system transformation.

      4. Innovating to increase labor productivity and workers’ livelihood opportunities: Public institutions can accelerate the development and diffusion of innovations that meet the needs of poorer producers and remove barriers to their adoption. Priority areas for public research and innovation include improving plant breeding, supporting environmentally sustainable, biodiversity-friendly, and low-emission farming systems, and developing digital technologies useful to small farmers.

      5. Scaling-up safety nets to keep food affordable for the poorest: Developing and strengthening safety nets is crucial to making food system transformations inclusive and politically feasible. Countries should prioritize targeting limited transfer resources on children’s nutritional needs and mobilizing more resources to put in place comprehensive safety nets.

      Additionally, the report addresses various tensions and obstacles in transforming food systems, highlighting the need to manage concerns such as fears of food price rises, job losses, policy siloes, global inequalities, and entrenched vested interests. It emphasizes the importance of addressing these concerns to facilitate change and ensure that the benefits of food system transformation can be realized. The report also highlights the rising visibility of transforming food systems as a policy priority, as well as the new ambition to seize the opportunities offered by such transformation, as evidenced by the COP28 UAE declaration on Sustainable Agriculture, Resilient Food Systems, and Climate Action signed by over 150 countries.

      https://knowledge4policy.ec.europa.eu/publication/economics-food-system-transformation_en
      https://foodsystemeconomics.org/wp-content/uploads/FSEC-Global_Policy_Report.pdf
      #rapport #coûts_cachés #pauvreté

  • Cop28 president says there is ‘no science’ behind demands for phase-out of fossil fuels
    https://www.theguardian.com/environment/2023/dec/03/back-into-caves-cop28-president-dismisses-phase-out-of-fossil-fuels

    The president of Cop28, Sultan Al Jaber, has claimed there is “no science” indicating that a phase-out of fossil fuels is needed to restrict global heating to 1.5C, the Guardian and the Centre for Climate Reporting can reveal.

    Al Jaber also said a phase-out of fossil fuels would not allow sustainable development “unless you want to take the world back into caves”.

    #climat

  • Microplastic-eating plankton may be worsening crisis in oceans, say scientists | Marine life | The Guardian
    https://www.theguardian.com/environment/2023/nov/09/microplastic-eating-plankton-worsening-crisis-oceans-plastic-pollution

    Phytoplankton found in marine and fresh water can ingest and break down microplastics, scientists have discovered. But rather than providing a solution to the threat plastics pose to aquatic life, the tiny creatures known as rotifers could be accelerating the risk by splitting the particles into thousands of smaller and potentially more dangerous nanoplastics.

    #plancton #rotifères #plastiques #nano

  • Allegations of extensive sexual abuse at Kenyan offsetting project used by Shell and Netflix
    https://www.theguardian.com/environment/2023/nov/07/accusations-of-widespread-sexual-abuse-at-offsetting-project-used-by-ne

    Male staff at a leading Kenyan carbon-offsetting project used by Netflix, Shell and other large companies have been accused of extensive sexual abuse and harassment over more than a decade, following an investigation by two NGOs.

    The Kasigau Corridor conservation project in southern Kenya, operated by the California-based firm Wildlife Works, generates carbon credits by protecting dryland forests at risk of being destroyed in key elephant, lion and wildlife habitats west of Mombasa. The scheme was the first ever forest protection scheme approved by Verra, the world’s leading certifier of carbon offsets, and has also been accredited for its biodiversity and community benefits, probably generating millions of dollars in revenue in carbon-credit sales.

    #crédits_carbone #violence_sexuelle

  • Revealed: the industry figures behind ‘declaration of scientists’ backing meat eating
    https://www.theguardian.com/environment/2023/oct/27/revealed-industry-figures-declaration-scientists-backing-meat-eating

    A public statement signed by more than 1,000 scientists in support of meat production and consumption has numerous links to the livestock industry, the Guardian can reveal. The statement has been used to target top EU officials against environmental and health policies and has been endorsed by the EU agriculture commissioner.

    #lobbying

  • EU abandons promise to ban toxic chemicals in consumer products | PFAS | The Guardian
    https://www.theguardian.com/environment/2023/oct/16/eu-abandons-promise-ban-toxic-chemicals-consumer-products

    Exclusive: Plan to outlaw all but the most vital of harmful chemicals is not included in leaked policy proposals

    Exclusif, l’Europe abandonne toute idée de progrès. Nous sommes en Guerre contre le reste du monde, et en premier lieu, donc, contre notre population.

  • Experts fear US carbon capture plan is ‘fig leaf’ to protect fossil fuel industry | Fossil fuels | The Guardian
    https://www.theguardian.com/environment/2023/aug/11/us-government-biden-carbon-capture

    The Biden administration delivered a historic climate bill last August though the president’s record on the climate has been undercut by his aggressive giveaway of oil and gas drilling leases on public land, including the controversial Willow oil project in Alaska.

    #climat #états-unis #foutage_de_gueule

    • The US energy department has announced it is awarding up to $1.2bn to two projects to directly remove carbon dioxide from the air, a fledgling technology that some climate experts worry will distract and undermine efforts to phase out fossil fuels.

      #DAC (direct air capture)

    • The chief executive of Occidental Petroleum, one of the largest U.S. oil companies, touted its $1 billion-plus project in West Texas to remove carbon dioxide directly from the air [...]

      We believe that our direct capture technology is going to be the technology that helps to preserve our industry over time,” [Occidental CEO Vicki] Hollub told the audience. “This gives our industry a license to continue to operate for the 60, 70, 80 years that I think it’s going to be very much needed.”

      https://www.politico.com/news/2023/03/08/oil-industry-shift-climate-tech-00085853

  • Gulf stream could collapse as early as 2025, study suggests | Climate crisis | The Guardian
    https://www.theguardian.com/environment/2023/jul/25/gulf-stream-could-collapse-as-early-as-2025-study-suggests
    https://i.guim.co.uk/img/media/c48440be715898be21be5636ac64d179db67ec45/0_0_3500_2102/master/3500.jpg?width=1200&height=630&quality=85&auto=format&fit=crop&overlay-ali

    Prof Niklas Boers, from the Potsdam Institute for Climate Impact Research in Germany, revealed the early warning signs of Amoc collapse in 2021. “The results of the new study sound alarming but if the uncertainties in the heavily oversimplified model [of the tipping point] and in the underlying [sea temperature] data are included, then it becomes clear that these uncertainties are too large to make any reliable estimate of the time of tipping.”

    Prof David Thornalley, at University College London, UK, agreed the study had large caveats and unknowns and said further research was essential: “But if the statistics are robust and a relevant way to describe how the actual Amoc behaves, then this is a very concerning result.”

    Dr Levke Caesar, at the University of Bremen, Germany, said using sea surface temperatures as proxy data for the strength of the Amoc currents was a key source of uncertainty: “We only have direct observational data of the Amoc since 2004.”

    The extrapolation in the new analysis was reasonable, according to Prof Tim Lenton, at the University of Exeter, UK. He said the tipping point could lead to a partial Amoc collapse, for example only in the Labrador Sea, but that this would still cause major impacts. Divlitsen said he hoped the debate would drive new research: “It’s always fruitful when you do not exactly agree.”

    Prof Stefan Rahmstorf, at the University of Potsdam, Germany, said: “There is still large uncertainty where the Amoc tipping point is, but the new study adds to the evidence that it is much closer than we thought. A single study provides limited evidence, but when multiple approaches have led to similar conclusions this must be taken very seriously, especially when we’re talking about a risk that we really want to rule out with 99.9% certainty. Now we can’t even rule out crossing the tipping point in the next decade or two.”

    • le titre de l’article est trompeur (Gulf stream en lieu et place d’AMOC)

      Le Gulf Stream va-t-il sauver l’Europe du changement climatique ?
      https://bonpote.com/le-gulf-stream-va-t-il-sauver-leurope-du-changement-climatique

      Après avoir quitté la côte américaine, une partie de l’eau transportée par le #Gulf_Stream (de l’ordre de 20 %) circule, en surface, vers le nord, puis traverse le bassin d’ouest en est vers 50°N. Ensuite elle rejoint soit les mers d’Irminger et du Labrador qui entourent la pointe Sud du Groenland, soit encore plus au nord les côtes norvégiennes.

      La chaleur transportée est transférée dans l’atmosphère, surtout en hiver, ce qui rend l’eau en surface plus lourde. C’est pourquoi dans ce parcours, elle a tendance à “couler” en profondeur où elle alimente les courants profonds qui s’orientent en moyenne vers le sud.

      Dans l’ensemble, cette circulation occupe tout l’#océan_Atlantique, et s’oriente vers le nord proche de la surface et vers le sud en profondeur, ce qui décrit une boucle de retournement, d’où la dénomination française de circulation de retournement (et en anglais #AMOC pour Atlantic Meridional Overturning Circulation).

      Ce qu’il faut surtout retenir, c’est que cette circulation n’est pas un seul courant, mais une moyenne, une construction mathématique qui regroupe, fusionne plusieurs courants différents dans tout l’Atlantique Nord, dont le Gulf Stream. Sa définition ne s’arrête pas à l’équateur : on la calcule aussi dans l’hémisphère sud et dans tous les autres bassins.

      Comment connaît-on ces phénomènes et comment les étudie-t-on ?
      Comment observe-t-on le Gulf Stream ?

      Le Gulf Stream, courant océanique bien connu des marins depuis le XVIème siècle et dont la température chaude est mesurée dès le XVIIIème par Benjamin Franklin, est observé régulièrement par des navires océanographiques depuis bientôt un siècle. On mesure son intensité en continu grâce à un câble sous-marin entre la Floride et les Bahamas depuis les années 1980. On l’observe par satellite depuis les années 1990. La situation n’a rien de comparable pour la circulation de retournement…

      Comment observe-t-on la circulation de retournement ?
      Depuis 2004, un ensemble d’instruments océanographiques sont disposés le long d’une ligne imaginaire qui relie la côte Est des États-Unis à l’Afrique à la latitude 26°N, de la surface jusqu’au fond de l’océan. Cette section océanographique permet de mesurer en continu l’intensité de la circulation de retournement.

      Parce que ces observations directes restent peu nombreuses, les océanographes ont beaucoup recours aux modèles numériques pour étudier la circulation de retournement et ses impacts. Ces outils, basés sur la mécanique des fluides, les mathématiques et les sciences du calcul intensif, permettent de réaliser des expériences virtuelles pour tester des hypothèses (quel serait l’impact sur le climat en Europe d’un arrêt de la circulation de retournement ?) et tenter de reproduire les océans actuels, passés et futurs.

      Enfin, les paléo-océanographes essaient de reconstruire les fluctuations de la circulation de retournement en utilisant des mesures indirectes de son intensité, estimées à partir de divers prélèvements sédimentaires terrestres et marins.

      Historiquement, on pensait que la circulation de retournement était entraînée presque exclusivement par les contrastes, liés à la température et la salinité (d’où la dénomination de circulation “thermohaline”). On sait maintenant que d’autres processus physiques l’influencent, comme le vent et le mélange océanique.

      On sait aussi, notamment grâce aux modèles numériques et aux mesures directes récentes, qu’elle fluctue beaucoup d’un mois sur l’autre, d’un an sur l’autre, d’une décennie sur l’autre, d’un siècle sur l’autre… et que ces fluctuations peuvent être déclenchées par de nombreux processus différents (parmi lesquels la fonte du Groenland, mais pas que…).

      L’un des courants marins les plus complexes au monde
      Le Gulf Stream est également lui-même un des courants marins les plus complexes au monde car sous influence de multiples processus. La circulation de retournement hérite de cette complexité. Mais en tant que construction mathématique qui fusionne plusieurs courants marins dont le Gulf Stream, elle est aussi influencée par d’autres processus océaniques.

      On entend parfois que la circulation de retournement n’existe pas car les mesures RAPID à 26°N ne correspondent pas à celles prises plus au sud ou plus au nord. Ces différences, au contraire, illustrent bien que la circulation de retournement n’est pas un simple tapis roulant qui connecte l’océan Atlantique du sud au nord, comme des représentations simplifiées de l’océan ont pu le laisser à penser.

    • Scientists have long seen the Atlantic Meridional Overturning Circulation, or AMOC, as one of the planet’s most vulnerable “tipping elements” — meaning the system could undergo an abrupt and irreversible change, with dramatic consequences for the rest of the globe.
      Under Earth’s current climate, this aquatic conveyor belt transports warm, salty water from the tropics to the North Atlantic, and then sends colder water back south along the ocean floor. But as rising global temperatures melt Arctic ice, the resulting influx of cold freshwater has thrown a wrench in the system — and could shut it down entirely.

      https://www.washingtonpost.com/climate-environment/2023/07/25/atlantic-ocean-amoc-climate-change

      #AMOC : Atlantic Meridional Overturning Circulation (Circulation méridienne de retournement de l’Atlantique)

    • Les effets estimés d’un arrêt de l’AMOC :


      À gauche les températures, à droite les précipitations. À noter que ces valeurs sont une moyenne annuelle, or un des effets de l’arrêt de l’AMOC notamment dans les hautes latitudes serait un renforcement de la saisonnalité, chose qui n’est pas reflétée par les valeurs annuelles.
      L’Europe serait « sibérianisée », avec des hivers nettement plus longs (car commençant plus tôt) et plus froids (surtout en Europe du Nord), des étés plus courts (mais pas forcément plus frais), et des pluies en diminution (jusqu’à moitié moins sur la péninsule ibérique) car un Atlantique Nord plus froid évaporerait moins. On estime que la surface cultivable en blé et maïs en Europe serait réduite de plus de moitié.
      En Amérique du Nord il y aurait augmentation de la pluviométrie mais sous forme de tempêtes plus fréquentes.
      En Afrique de l’Ouest la zone très peuplée entre Sénégal et Gabon subirait une sécheresse et un réchauffement accrus (car la chaleur n’étant plus transportée vers le nord s’accumulerait dans les tropiques)
      Tout l’hémisphère Sud se réchaufferait, et la forêt amazonienne disparaîtrait encore plus vite sous l’effet de sécheresses accentuées (en relarguant son carbone au passage).
      Les courants de Humbolt (Chili Pérou) et du Benguéla (Namibie Angola) s’affaibliraient, la pêche dans ces secteurs (très importante aujourd’hui) ne donnerait plus grand chose, et l’océan global perdrait beaucoup de sa productivité et de sa capacité à absorber le CO2. Maigre consolation les déserts d’Atacama et du Namib seraient moins désertiques, le Nord-Est brésilien moins aride, mais probablement pas de quoi accueillir des centaines de millions de réfugiés climatiques.

    • d’après cette simulation la Méditerranée et l’Afrique du Nord seraient également touchées par le refroidissement de l’Atlantique Nord, la chaleur resterait piégée plus au Sud. Si on y ajoute la baisse des précipitations dans tout le pourtour méditerranéen, le Sahara s’étendrait en quelque-sorte à la fois sur le Maghreb et sur le Sahel.