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  • — News and information about meteor showers, solar flares, auroras, and near-Earth asteroids

    3 MILLON YEARS AGO, AN INTERSTELLAR CLOUD HIT EARTH: Today, Earth is in a safe space. Like all the other planets in the Solar System, it is cocooned within the sun’s magnetic field—a giant bubble called “the heliosphere.” The heliosphere protects us from dangerous things in the Galaxy like interstellar clouds and cosmic rays.

    3 million years ago, the heliosphere may have collapsed. A new paper just published in Nature Astronomy argues that a dense cloud of gas hit the Solar System, compressing the heliosphere to a fraction of its usual size.

    “Earth suddenly was outside the protective bubble,” says the paper’s lead author Merav Opher, a fellow at Harvard Radcliffe Institute and professor at Boston University. “Earth and all the planets were exposed to massive amounts of hydrogen, increased radiation, and interstellar dust.”

    Researchers have long wondered if something happened to Earth 2 to 3 million years ago. Deep-sea sediments, Antarctic snow, and lunar samples from that time period all contain extraterrestrial radioactive isotopes (iron-60 and plutonium-244). The peak is quite striking.

    A nearby supernova might have peppered Earth with these substances, but Opher and colleagues had a different idea. In the constellation Lynx there is a ribbon-shaped cluster of dense interstellar clouds. Using a velocity model for the clouds, they found that the sun and at least one of the clouds may have crossed paths 2 to 3 million years ago

    “We show that during the cloud’s passage, the heliosphere shrinks to a scale of 0.22 AU, smaller than the Earth’s orbit around the sun,” says Opher. According to their simulation, the helioshere was compressed and stretched into a tadpole-like structure with Earth’s orbit (red circle) on the outside:
    There is some evidence that Earth cooled while it was outside the heliosphere. Deep in our oceans, fossils of tiny marine organisms known as foraminifera preserve ancient climate data. Oxygen isotopes in those fossils suggest the temperature dropped 2–3 million years ago. Could this be a result of interstellar gas and cosmic rays altering our atmosphere?

    “This idea should be revisited with modern atmospheric modelling,” the authors urge.

    Eventually, the cloud passed and the heliosphere bounced back. “Earth was inside its protective bubble again,” says Opher. It’s a good place to be.

    L’étude complète :

  • #2023 recorded as hottest in 2000 years

    When you look at the long sweep of history, you can see just how dramatic recent global warming is, says Prof Ulf Büntgen

    Researchers have found that 2023 was the hottest summer in the Northern Hemisphere in the past two thousand years, almost four degrees warmer than the coldest summer during the same period.

    Although 2023 has been reported as the hottest year on record, the instrumental evidence only reaches back as far as 1850 at best, and most records are limited to certain regions. Now, by using past climate information from annually resolved tree rings over two millennia, scientists from the University of Cambridge and the Johannes Gutenberg University Mainz have shown how exceptional the summer of 2023 was.

    Even allowing for natural climate variations over hundreds of years, 2023 was still the hottest summer since the height of the Roman Empire, exceeding the extremes of natural climate variability by half a degree Celsius.

    “When you look at the long sweep of history, you can see just how dramatic recent global warming is,” said co-author Professor Ulf Büntgen, from Cambridge’s Department of Geography. “2023 was an exceptionally hot year, and this trend will continue unless we reduce greenhouse gas emissions dramatically.”
    1.5°C already breached

    The results, reported in the journal Nature, also demonstrate that in the Northern Hemisphere, the 2015 Paris Agreement to limit warming to 1.5°C above pre-industrial levels has already been breached.

    Early instrumental temperature records, from 1850-1900, are sparse and inconsistent. The researchers compared early instrumental data with a large-scale tree ring dataset and found the 19th century temperature baseline used to contextualise global warming is several tenths of a degree Celsius colder than previously thought. By re-calibrating this baseline, the researchers calculated that summer 2023 conditions in the Northern Hemisphere were 2.07°C warmer than mean summer temperatures between 1850 and 1900.

    “Many of the conversations we have around global warming are tied to a baseline temperature from the mid-19th century, but why is this the baseline? What is normal, in the context of a constantly-changing climate, when we’ve only got 150 years of meteorological measurements?” said Büntgen. “Only when we look at climate reconstructions can we better account for natural variability and put recent anthropogenic climate change into context.”
    Tree rings reveal two millennia of climate data

    Tree rings can provide that context, since they contain annually-resolved and absolutely-dated information about past summer temperatures. Using tree-ring chronologies allows researchers to look much further back in time without the uncertainty associated with some early instrumental measurements.

    The available tree-ring data reveals that most of the cooler periods over the past 2000 years, such as the Little Antique Ice Age in the 6th century and the Little Ice Age in the early 19th century, followed large-sulphur-rich volcanic eruptions. These eruptions spew huge amounts of aerosols into the stratosphere, triggering rapid surface cooling. The coldest summer of the past two thousand years, in 536 CE, followed one such eruption, and was 3.93C colder than the summer of 2023.
    The amplifying effect of El Niño on recent heat waves

    Most of the warmer periods covered by the tree ring data can be attributed to the El Niño climate pattern, or El Niño-Southern Oscillation (ENSO). El Niño affects weather worldwide due to weakened trade winds in the Pacific Ocean and often results in warmer summers in the Northern Hemisphere. While El Niño events were first noted by fisherman in the 17th century, they can be observed in the tree ring data much further back in time.

    However, over the past 60 years, global warming caused by greenhouse gas emissions are causing El Niño events to become stronger, resulting in hotter summers. The current El Niño event is expected to continue into early summer 2024, making it likely that this summer will break temperature records once again.

    “It’s true that the climate is always changing, but the warming in 2023, caused by greenhouse gases, is additionally amplified by El Niño conditions, so we end up with longer and more severe heat waves and extended periods of drought,” said Professor Jan Esper, the lead author of the study from the Johannes Gutenberg University Mainz in Germany. “When you look at the big picture, it shows just how urgent it is that we reduce greenhouse gas emissions immediately.”

    The researchers note that while their results are robust for the Northern Hemisphere, it is difficult to obtain global averages for the same period since data is sparse for the Southern Hemisphere. The Southern Hemisphere also responds differently to climate change, since it is far more ocean-covered than the Northern Hemisphere.
    #climat #record #changement_climatique #statistiques #chiffres #chaleur

    • 2023 was the warmest year in the modern temperature record

      The year 2023 was the warmest year since global

      records began in 1850 at 1.18°C (2.12°F) above the 20th-century average of 13.9°C (57.0°F). This value is 0.15°C (0.27°F) more than the previous record set in 2016. The 10 warmest years in the 174-year record have all occurred during the last decade (2014–2023). Of note, the year 2005, which was the first year to set a new global temperature record in the 21st century, is now the 12th-warmest year on record. The year 2010, which had surpassed 2005 at the time, now ranks as the 11th-warmest year on record.

      This map shows 2023 temperatures compared to the 1991-2020 average. Most of the globe was warmer-than-average (red). Only a few areas were colder than average (blue). The animated bar graph shows yearly average temperature since 1976 compared to the 20th-century average. It’s been 47 years—nearly half a century—since Earth’s temperature was colder than average. 2023 set a new warmest-year record by a wide margin.

      Unlike the previous two years (2021 and 2022), which were squarely entrenched in a cold phase El Niño Southern Oscillation (ENSO) episode, also known as La Niña, 2023 quickly moved into ENSO neutral territory, transitioning to a warm phase episode, El Niño, by June. ENSO not only affects global weather patterns, but it also affects global temperatures. As seen in the image below, during the warm phase of ENSO (El Niño), global temperatures tend to be warmer than ENSO-neutral or La Niña years, while global temperatures tend to be slightly cooler during cold phase ENSO episodes (La Niña). Despite 2021 and 2022 not ranking among the five warmest years on record, the global annual temperature increased at an average rate of 0.06°C (0.11°F) per decade since 1850 and more than three times that rate (0.20°C / 0.36°F) since 1982.,decade%20(2.

    • 2023 summer warmth unparalleled over the past 2,000 years

      Including an exceptionally warm Northern Hemisphere (NH) summer1,2, 2023 has been reported as the hottest year on record3-5. Contextualizing recent anthropogenic warming against past natural variability is nontrivial, however, because the sparse 19th century meteorological records tend to be too warm6. Here, we combine observed and reconstructed June-August (JJA) surface air temperatures to show that 2023 was the warmest NH extra-tropical summer over the past 2000 years exceeding the 95% confidence range of natural climate variability by more than half a degree Celsius. Comparison of the 2023 JJA warming against the coldest reconstructed summer in 536 CE reveals a maximum range of pre-Anthropocene-to-2023 temperatures of 3.93°C. Although 2023 is consistent with a greenhouse gases-induced warming trend7 that is amplified by an unfolding El Niño event8, this extreme emphasizes the urgency to implement international agreements for carbon emission reduction.

  • Les ados sentent la chèvre mais « nous ne le percevons pas » | Le Télégramme

    Les adolescents sentent la chèvre en raison de certains acides présents dans leur transpiration, affirme une étude scientifique. Âge, bactéries, hormones, émotions… À quels facteurs et procédés chimiques nos odeurs corporelles sont-elles dues ?

    Les bébés sentent-ils la rose et les adolescents la chèvre ? C’est, vite résumé, ce qui ressort d’une étude menée par des chercheurs des universités allemandes d’Erlangen-Nuremberg et Dresde, à partir d’échantillons de transpiration comparés de 18 enfants en bas âge et de 18 ados. Selon ses résultats, publiés dans Communications Chemistry et relayés par le New York Times, la sueur, au moment de la puberté, contient des acides carboxyliques caractéristiques du sébum, notamment responsable des points noirs et des cheveux gras de nos grands rejetons. Ces substances qui, rapporte le New York Times, ont un « parfum de moisi, de fromage et de chèvre ». Et qui, au même âge, se combinent aux stéroïdes, porteurs d’une touche « de musc » et « d’urine » !

    La présence de ces composants dans la sueur des adolescents en fait-elle pour autant des êtres puants ?

    Laurent Misery, chef du service dermatologie du CHRU de Brest, nous rassure : « Pour qu’entre humains nous les percevions, il faudrait qu’ils soient présents en quantité ».

    Les animaux, en revanche, les détectent fort bien. Chiens et chats reconnaissent, par exemple, l’odeur de leur maître passé par une pièce, de la même manière qu’ils sentent à distance les phéromones que produit une femelle en chaleur de leur espèce.

    Chacun a une odeur unique
    Notre odorat n’est pas aussi développé que celui de nos amis à quatre pattes. Pour autant, chaque individu possède une signature olfactive unique, tout comme son ADN ou ses empreintes digitales qui lui sont propres. À une différence près : « Cette odeur n’est pas constante mais varie en fonction de l’évolution de notre microbiote cutané », poursuit le Dr Misery. En clair, tout dépend des bactéries hébergées par notre corps, et dont la présence « par milliards » évolue « en fonction de l’âge, des toilettes que l’on fait ou encore des zones de la peau ». Car la sueur elle-même est inodore. « Ce sont les bactéries qui la transforment en composés organiques odorants », illustre le spécialiste brestois. Comme nous n’avons pas tous les mêmes bactéries, la chimie opère différemment. Cela explique que certaines personnes sentent davantage des pieds que d’autres, ou attirent les moustiques quand leur voisin de chambrée, lui, dort peinard.

    Un domaine encore peu exploré
    Et les hormones, dans tout ça ? « Elles donnent le message aux cellules. » Un oral d’examen ou un entretien d’embauche à passer ? Vous êtes bon pour une décharge de cortisol, d’adrénaline et autres hormones de stress qui vous font transpirer illico. Et pof, voilà que vos bactéries s’en mêlent, transformant l’auréole sous vos aisselles en effluve malodorante. Un mécanisme naturel lorsqu’il répond à un pic d’activité ou à une émotion intense (anxiété, peur…), et non à un défaut d’hygiène.

    Selon le médecin brestois, l’alimentation n’a que « peu d’effets » sur l’odeur corporelle. « La perception qu’une odeur est désagréable est, par ailleurs, très subjective », suggère-t-il, certain que l’étude allemande ouvre un champ encore peu exploré, celui « du mécanisme qui régule la composition de la sueur et des odeurs chez l’être humain ». Un sujet captivant, quand on voit la faculté qu’ont des chiens entraînés à détecter la covid-19 ou la présence d’un cancer.

    • bizarrement (!), le mot chèvre ne fait pas partie du résumé (abstract) de l’article d’origine…

      Body odor samples from infants and post-pubertal children differ in their volatile profiles | Communications Chemistry

      Target compounds were quantified in the distillates of pooled body odor (BO) and room samples of infants (0–3 years) and post-pubertal children (14–18 years). In total, per age group three pools were analyzed including samples of six children each. Concentrations of (a) 6MHO, (b) GA, and (c) SQ in the BO and room samples of infants and post-pubertal children (see also Supplementary Note 2 Table S3 online); concentration ratios 6MHO/SQ and GA/SQ in BO samples are depicted in d and e. Note that SQ was out of calibration range in the room samples, due to considerably lower abundance than in the BO samples. For results of statistical comparison, see main text.

      Body odors change during development, and this change influences the interpersonal communication between parents and their children. The molecular basis for this chemical communication has not been elucidated yet. Here, we show by combining instrumental and sensory analyses that the qualitative odorant composition of body odor samples is similar in infants (0-3 years) and post-pubertal children (14-18 years). The post-pubertal samples are characterized by higher odor dilution factors for carboxylic acids and by the presence of 5α-androst-16-en-3-one and 5α-androst-16-en-3α-ol. In addition to the olfaction-guided approach, the compounds 6-methylhept-5-en-2-one (6MHO), geranyl acetone (GA) and squalene (SQ) were quantified. Both age groups have similar concentrations of 6MHO and GA, whereas post-pubertal children tend to have higher concentration of SQ. In conclusion, sexual maturation coincides with changes to body odor chemical composition. Whether those changes explain differences in parental olfactory perception needs to be determined in future studies with model odors.

    • la liste des composés odorants détectés…
      et leur description olfactive

      | Identified compound                    | Odor attributef                              |
      | -------------------------------------- | -------------------------------------------- |
      | Octanal a, b, c, d                     | Soapy, citrus-like                           |
      | Oct-1-en-3-one a, c                    | Mushroom-like                                |
      | Nonanal a, b, c                        | Soapy, citrus-like                           |
      | Unknown c, d, e                        | Flowery, soapy                               |
      | Decanal a, b, c, d                     | Soapy                                        |
      | (E)-Non-2-enal a, b, c, d, e           | Fatty, cardboard-like                        |
      | Linalool a, b                          | Flowery                                      |
      | Undecanal a, b, c, d, e                | Soapy, citrus-like, coriander-like           |
      | 3-Methylbutanoic acid a                | Cheesy                                       |
      | (2E,4E)-Nona-2,4-dienal a, d           | Fatty, nutty                                 |
      | Dodecanal a, b, c, d, e                | Soapy, coriander-like                        |
      | (2E,4E)-Deca-2,4-dienal a, c           | Fatty, deep-fried                            |
      | α-Isomethylionone a, b, c, d, e        | Violet-like                                  |
      | Geranyl acetone a, b                   | Soapy                                        |
      | Unknown d, e                           | Soapy, coriander-like                        |
      | Polysantol a                           | Sandalwood-like                              |
      | Unknown                                | Fatty, fruity, coconut-like                  |
      | β-Ionone a, b                          | Flowery, violet-like                         |
      | 2-Methylheptanoic acid a               | Fruity, dried plum-like                      |
      | Unknown e                              | Soapy, coriander-like                        |
      | (E)-4,5-Epoxy-(E)-2-decenal a, c, d, e | Metallic                                     |
      | Octanoic acid a, b                     | Musty, coriander-like, fatty                 |
      | p\-Cresol a, c                         | Fecal, horse stable-like                     |
      | Unknown c, d, e                        | Sandalwood-like, perfume-like                |
      | Sandranol a, b, c, d, e                | Sandalwood-like                              |
      | Patchouli alcohol a, c                 | Earthy                                       |
      | Sotolon a, d, e                        | Savory, celery-like                          |
      | Unknown                                | Fecal, earthy                                |
      | 4-Ethyloctanoic acid a                 | Goat-like                                    |
      | Unknown                                | Soap-like, perfume-like                      |
      | γ-Undecalactone a, c, d                | Peach-like, soapy                            |
      | Unknown                                | Fecal, musty                                 |
      | Unknown                                | Soapy, coriander-like                        |
      | γ -Dodecalactone a, c, d, e            | Peach-like, flowery                          |
      | Dodecanoic acid a, b                   | Wax-like, soapy                              |
      | Unknown c, d                           | Vanilla-like                                 |
      | Unknown                                | Vanilla-like                                 |
      | Vanillin a, b, c, d, e                 | Vanilla-like                                 |
      | Myristoleic acid a, b                  | Earthy, green/grassy, green bell pepper-like |
      | Raspberry ketone a, c, d, e            | Raspberry-like                               |
      | 5α-Androst-16-en-3-one a               | Sweaty, urinal, musk-like                    |
      | 5α-Androst-16-en-3α-ol a               | Sandalwood-like, musk-like                   |

      a Compound was tentatively identified by GC-O by comparison of odor quality and retention indices on DB-FFAP and DB-5 of reference compound.
      b Mass spectrum was compared with reference compound/in-house library.
      c Detected in blank unworn cotton pads.
      d Detected in perfume-free shower gel.
      e Detected in perfume-free detergent.
    • Selon le médecin brestois, l’alimentation n’a que « peu d’effets » sur l’odeur corporelle.

      Il a jamais mangé d’ail ou d’oignon ou bien ? :-)

  • The atlas of unburnable oil for supply-side climate policies | Nature Communications

    To limit the increase in global mean temperature to 1.5 °C, #CO2 emissions must be drastically reduced. Accordingly, approximately 97%, 81%, and 71% of existing coal and conventional gas and oil resources, respectively, need to remain unburned.

    #climats #énergies_fossiles

  • Frequency, kinetics and determinants of viable SARS-CoV-2 in bioaerosols from ambulatory COVID-19 patients infected with the Beta, Delta or Omicron variants | Nature Communications

    To our knowledge, there has been no systematic large scale study of culturability of virus in #aerosols and whether this is consistent across variants or whether this is affected by proximity to symptom onset and with differing patterns of host immunity. Thus, critically, the final proof that human-generated aerosols <10 μm can harbour replicating virus remains largely unclarified.


    The frequency of aerosol virus culturability was high at ~60%…. About a third of patients were probably non-infectious, 50% probably highly infectious, and ~20% moderately infectious by our definitions. These data may be in line with the ‘super-spreader’ hypothesis… Here we show for the first time that asymptomatic persons may also produce infectious aerosol <10 μm which is potentially suspensible for several hours and may be deeply inoculated by inhalation into the small airways and alveoli of the lung.


    These data support the need for prevention of airborne transmission risk using better ventilation in public transports, and indoor environments, especially hospitals, workplaces and schools, and the use of other airborne infection controls in health care facilities caring for COVID-19 patients.


  • Generative AI’s environmental costs are soaring — and mostly secret

    Most experts agree that nuclear fusion won’t contribute significantly to the crucial goal of decarbonizing by mid-century to combat the climate crisis. Helion’s most optimistic estimate is that by 2029 it will produce enough energy to power 40,000 average US households; one assessment suggests that ChatGPT, the chatbot created by OpenAI in San Francisco, California, is already consuming the energy of 33,000 homes. It’s estimated that a search driven by generative AI uses four to five times the energy of a conventional web search. Within years, large AI systems are likely to need as much energy as entire nations.

    And it’s not just energy. Generative AI systems need enormous amounts of fresh water to cool their processors and generate electricity. In West Des Moines, Iowa, a giant data-centre cluster serves OpenAI’s most advanced model, GPT-4. A lawsuit by local residents revealed that in July 2022, the month before OpenAI finished training the model, the cluster used about 6% of the district’s water. As Google and Microsoft prepared their Bard and Bing large language models, both had major spikes in water use — increases of 20% and 34%, respectively, in one year, according to the companies’ environmental reports. One preprint1 suggests that, globally, the demand for water for AI could be half that of the United Kingdom by 2027 . In another2, Facebook AI researchers called the environmental effects of the industry’s pursuit of scale the “elephant in the room”.

  • Why flying insects gather at artificial light | Nature Communications

    Fig. 1: Insects flying around a light source in the field display 3 common behavioural motifs not seen in normal flight.
    The unusual flight motifs were: a Orbiting, b Stalling, and c Inverting. (Above) Diagrammatic representations of the three behavioural motifs. (Below)_ Overlaid flight trajectories of insects performing these characteristic patterns around UV light sources. Overlaid frames are separated by aesthetically chosen fixed intervals of 52 ms (left), 20 ms (middle), and 24 ms (right) for visualization.

    Explanations of why nocturnal insects fly erratically around fires and lamps have included theories of “lunar navigation” and “escape to the light”. However, without three-dimensional flight data to test them rigorously, the cause for this odd behaviour has remained unsolved. We employed high-resolution motion capture in the laboratory and stereo-videography in the field to reconstruct the 3D kinematics of insect flights around artificial lights. Contrary to the expectation of attraction, insects do not steer directly toward the light. Instead, insects turn their dorsum toward the light, generating flight bouts perpendicular to the source. Under natural sky light, tilting the dorsum towards the brightest visual hemisphere helps maintain proper flight attitude and control. Near artificial sources, however, this highly conserved dorsal-light-response can produce continuous steering around the light and trap an insect. Our guidance model demonstrates that this dorsal tilting is sufficient to create the seemingly erratic flight paths of insects near lights and is the most plausible model for why flying insects gather at artificial lights.

    Fig. 3: Motion capture of the flying insects demonstrated that the animals maintain a consistent tilt of their dorsum towards the direction of the light.
    a (Left) The insect’s dorsal axis is projected onto the ground plane to compare with the light source direction. The reference axis is a global orientation reference. (Right) The direction of dorsal tilt is plotted against the direction to light. Dashed line shows a gradient of 1. Insects flying around a point source of light maintained extreme bank and pitch attitudes, as compared to animals flying under control conditions. b The relative body pitch and bank angle are plotted on a 2D distribution map. For each species, in-flight bank-pitch distribution under control conditions and near a point light source are presented on the left and right respectively.

  • L’extraction minière, dévastatrice, est nécessaire au maintien de CETTE société

    Toujours plus de mines, et donc d’énergies, de pollutions, de déforestation et de dépossessions. Toujours plus de minerais pour alimenter la soif insatiable d’argent du capitalisme. Toujour plus d’extractivisme pour assurer le besoin de puissance des Etats. Deux articles explorent l’arnaque de la (pseudo) transition « verte », qui sert de justification à la continuation de la civilisation industrielle et des désastres écocidaires associés. Des mines il en faut pour développer la 5G et le (...) #Les_Articles

    / #Catastrophes_climatiques_et_destructions_écologiques, #Le_monde_de_L'Economie

  • The decimal point is 150 years older than historians thought

    The decimal point was invented around 150 years earlier than previously thought, according to an analysis of astronomical tables compiled by the Italian merchant and mathematician Giovanni Bianchini in the 1440s. Historians say that this discovery rewrites the origins of one of the most fundamental mathematical conventions, and suggests that Bianchini — whose economic training contrasted starkly with those of his astronomer peers — might have played a more notable part in the history of maths than previously realized. The results are published in Historia Mathematica1.

    “It’s a very nice discovery,” says José Chabás, a historian of astronomy at the Pompeu Fabra University in Barcelona, Spain. The decimal point was “a step forward for humanity”, he says, enabling the ease and efficiency of calculations that underpin modern science and technology. Previously, its earliest-known appearance was generally said to be in an astronomical table written by the German mathematician Christopher Clavius in 1593. But now it’s clear that “the inspiration was taken from Bianchini”, Chabás says.

    Bianchini worked as a Venetian merchant before becoming an administrator of the estate of the powerful d’Este family, who ruled the Duchy of Ferrara at the time. As well as managing assets and guiding investments, Bianchini was responsible for casting horoscopes, which meant that he had to master astronomy. He published several works on topics ranging from planetary motions to predicting eclipses.

    Glen Van Brummelen, a historian of mathematics at Trinity Western University in Langley, Canada, had hoped that Bianchini’s work might help to reveal how and when Islamic astronomical knowledge reached Europe. As a merchant, “Bianchini would have travelled all over the place, so it seems natural that he might have found something in Islamic science in his journeys and used that as an inspiration”, says Van Brummelen. But instead, “it seems a lot of things he did were simply out of his own incredibly creative mind”.
    Tricky divisions

    At the time of Bianchini, European astronomers were exclusively using the sexagesimal (base 60) system inherited from the Babylonians. The sexagesimal system is still in use today for writing latitudes and longitudes, both celestial and terrestrial. It divides a full circle into 360 degrees, each degree into 60 minutes, and each minute into 60 seconds. But it’s difficult to carry out operations such as multiplication with sexagesimal numbers. Astronomers would have to convert a value into the smallest unit to do the calculation, for example, and then convert back afterwards.

    Traders and accountants, on the other hand, were taught to calculate using real-world weights and measures, in which units could be divided in a variety of ways: there are 12 inches in a foot, for example, and 3 feet in a yard. To enable simpler calculations, Bianchini invented his own decimal scheme, describing a system for measuring distances in which a foot (30 centimetres) was divided into ten equal parts called untie, each of which was divided into ten minuta, and then into ten secunda. This didn’t catch on, and his penchant for base 10 wasn’t previously thought to have influenced his astronomy.

    But, in poring over a treatise that Bianchini wrote in the 1440s, called Tabulae primi mobilis B, Van Brummelen realized that in places he was using not only a decimal number system, but also a decimal point like the one we use today.

    Van Brummelen made the discovery while teaching at a maths camp for middle schoolers. One evening, he was discussing the Tabulae with a colleague over Zoom, trying to translate Bianchini’s dense medieval Latin. They came across a passage in which Bianchini introduces a number “with a dot in the middle” — 10.4 — and shows how to multiply it by 8. “I realized that he’s using this just as we do, and he knows how to do calculations with it,” says Van Brummelen. “I remember running up and down the hallways of the dorm with my computer trying to find anybody who was awake, shouting ‘look at this, this guy is doing decimal points in the 1440s!’”
    The second page of Bianchini’s decimal tangent table, showing decimal points in the interpolation columns.

    A trigonometric table showing decimal points, from Bianchini’s Tabulae primi mobilis B.Credit: Van Brummelen, G./Historia Mathematica

    The key part of the manuscript is a series of trigonometric tables, including a sine table. Astronomers at the time used spherical trigonometry to calculate the positions of celestial bodies on the surface of a sphere. Bianchini still divides angles into minutes and seconds, but gives the sines — which astronomers interpreted as distances — as decimals, with tenths, hundredths and thousandths. He introduces his decimal point when stating the amount that the user should add or subtract to calculate values that fall between one entry and the next. Tellingly, this is exactly how Clavius uses his decimal point in 1593. Historians have always wondered why Clavius never mentions the innovation again. “Why would you invent something that’s clearly so powerful and then just drop it?” asks Van Brummelen. But the advance fits perfectly with Bianchini’s broader work. Van Brummelen concludes that Clavius must have appropriated the decimal point from his predecessor. “It’s impossible that he didn’t know about Bianchini,” agrees Chabás.
    Pointing forward

    The beauty of the decimal system, says Sarah Hart, a historian of maths at Birkbeck, University of London, is that it makes non-whole numbers as easy to calculate with as whole ones. There’s no need for “all this malarkey that you have to do with fractions”, she says. “With a decimal point you can use the same process on numbers of any size.”

    Van Brummelen suggests that Bianchini’s schooling in economics might have been key to his invention, because he wasn’t embedded in sexagesimal numbers from early in his career, as other astronomers were. But his approach was perhaps too revolutionary to catch on at first. “In order to understand what Bianchini was doing, you had to learn a completely new system of arithmetic,” he says.

    A century and a half later, however, “decimal notation was in the air”. Astronomers working with smaller and smaller subdivisions were inventing different systems, desperate for ways to simplify complex calculations. Clavius’s work influenced later popularizers of decimal fractions, such as Flemish mathematician Simon Stevin, as well as Scottish astronomer and inventor of logarithms John Napier, who adopted the decimal point. Chabás argues that historians should reassess Bianchini’s importance. Although he has been “eclipsed” by other figures, there’s clearly “a path of ideas”, he says, leading back to Bianchini.

    The implications of the invention have spread far beyond astronomy. Decimal fractions have enabled and inspired scientists to pin down nature with much greater precision, says Hart, and raise ideas that weren’t even possible before, such as that “of a number that goes on forever and never stops”. She notes that the power of the decimal point relied on other developments, including the arrival of Hindu–Arabic numerals in Europe a few centuries earlier — largely through the work of Leonardo Pisano, known as Fibonacci — and the gradual introduction of a symbol for zero. Bianchini’s story illustrates the “constant cross-fertilization” between practical needs, number systems and theoretical ideas, she says, and his well-placed dot has changed how we see the world.


    Van Brummelen, G. Hist. Math. (2024).

  • Widespread contamination of soils and vegetation with current use pesticide residues along altitudinal gradients in a European Alpine valley

    Pesticides are transferred outside of cropland and can affect animals and plants. Here we investigated the distribution of 97 current use pesticides in soil and vegetation as central exposure matrices of insects. Sampling was conducted on 53 sites along eleven altitudinal transects in the Vinschgau valley (South Tyrol, Italy), in Europe’s largest apple growing area. A total of 27 pesticides (10 insecticides, 11 fungicides and 6 herbicides) were detected, originating mostly from apple orchards. Residue numbers and concentrations decreased with altitude and distance to orchards, but were even detected at the highest sites. Predictive, detection-based mapping indicates that pesticide mixtures can occur anywhere from the valley floor to mountain peaks. This study demonstrates widespread pesticide contamination of Alpine environments, creating contaminated landscapes. As residue mixtures have been detected in remote alpine ecosystems and conservation areas, we call for a reduction of pesticide use to prevent further contamination and loss of biodiversity.
    #montagne #Alpes #Tyrol_du_sud #contamination_du_sol #sols #sol #pollution #agriculture #pollution_du_sol #pommes #pesticides #Sud-Tyrol #Italie #cartographie #visualisation

  • Stocker l’#eau en #sous-sol, mieux que les #mégabassines

    Les #eaux_souterraines s’épuisent partout dans le monde. Une catastrophe qui ne cesse de s’accélérer d’après une étude publiée dans la revue Nature, qui déconseille la création de #réserves_d’eau en surface telles que les mégabassines. Des chercheurs de l’université de Santa Barbara (Californie) y présentent la plus grande évaluation de niveaux des eaux souterraines dans le monde, s’étendant sur près de 1 700 #aquifères, ces sols ou roches #réservoirs contenant des #nappes_d’eau_souterraine.

    L’étude tire la sonnette d’alarme quant à l’épuisement des ressources en eau : le niveau diminue dans 71 % des réserves mesurées. Surtout, le #déclin perçu dans les années 1980 puis 1990 s’est largement accéléré depuis les années 2000. Scott Jasechko, co-auteur de l’étude et professeur agrégé à la Bren School of Environmental Science & Management, présente toutefois des motifs d’espoir par l’action humaine. Le chercheur prend l’exemple de la ville de #Tucson, en Arizona, où l’eau provenant du fleuve Colorado est utilisée pour reconstituer l’aquifère dans la vallée voisine d’#Avra.

    « Moins cher, moins perturbateur et moins dangereux »

    D’après lui, les #stockages_souterrains réalisés dans ces réserves déjà existantes sont bien plus efficaces et moins onéreux que les stockages d’eau en surface. « Le remplissage intentionnel des aquifères nous permet de stocker ces réserves jusqu’au moment où nous en avons besoin, indique Scott Jasechko. On peut dépenser beaucoup d’argent pour construire des infrastructures pour retenir l’eau à la surface. Mais si on a la bonne géologie, stocker de grandes quantités d’eau sous terre est moins cher, moins perturbateur et moins dangereux. »

    Ce type d’intervention a toutefois participé à diminuer le débit du #Colorado. Épuisé par les activités humaines, le fleuve n’a la plupart du temps plus assez d’eau pour atteindre son embouchure dans le golfe de Californie. D’après l’étude, la seule autre solution pour contenir l’épuisement des réserves d’eau souterraines est une réglementation institutionnelle (délivrance de permis, frais d’utilisation) pour en restreindre l’accès.

    • Rapid groundwater decline and some cases of recovery in aquifers globally

      Groundwater resources are vital to ecosystems and livelihoods. Excessive groundwater withdrawals can cause groundwater levels to decline1,2,3,4,5,6,7,8,9,10, resulting in seawater intrusion11, land subsidence12,13, streamflow depletion14,15,16 and wells running dry17. However, the global pace and prevalence of local groundwater declines are poorly constrained, because in situ groundwater levels have not been synthesized at the global scale. Here we analyse in situ groundwater-level trends for 170,000 monitoring wells and 1,693 aquifer systems in countries that encompass approximately 75% of global groundwater withdrawals18. We show that rapid groundwater-level declines (>0.5 m year−1) are widespread in the twenty-first century, especially in dry regions with extensive croplands. Critically, we also show that groundwater-level declines have accelerated over the past four decades in 30% of the world’s regional aquifers. This widespread acceleration in groundwater-level deepening highlights an urgent need for more effective measures to address groundwater depletion. Our analysis also reveals specific cases in which depletion trends have reversed following policy changes, managed aquifer recharge and surface-water diversions, demonstrating the potential for depleted aquifer systems to recover.

      via @freakonometrics

  • Who Are Western Europeans? New Study Reveals True Origins - Archaeology -

    Mesolithic tomb at Téviec, with two women between 25 and 35 with head injuries and arrow wounds.
    Credit: Didier Descouens

    Three great migrations
    The ancestry of today’s western Europeans was determined largely by three great migrations, the paper sums up. The first was the exit from Africa around 45,000 years ago.

    Indeed, representatives of Homo sapiens had been leaving Africa for at least 200,000 years, going by (somewhat controversial) fossil finds in Israel and Greece. But those lineages apparently died out, meaning they have no descendants alive today insofar as is known.

    Finally, modern humans who reached Eurasia didn’t die, though it was so cold 45,000 years ago they may have wished they had. But while the chill apparently didn’t deter our ancestors, who plausibly had invented footwear by then, plants can be more persnickety.

    The last Ice Age peaked perhaps 26,000 years ago, and some people around the Mediterranean began to abandon the cave. In southeast Turkey, archaeologists have uncovered the stunning prehistoric monumental architecture of the “Gobekli culture” starting about 12,000 years ago, which had been built by hunter-gatherers. There is no sign that agriculture had begun to emerge yet, archaeologists there told Haaretz.

    "Urfa Man," a statue found at Gobekli. Now at the Sanliurfa Museum.
    Credit: Valence Levi Schuster

    But by 11,000 to 10,000 years ago, agriculture and animal husbandry had begun to emerge there and in the Fertile Crescent. That spurred the second great migration that would shape today’s western Europeans: early farmers spreading out of Anatolia.

    The Neolithic clime in Anatolia was apparently so gorgeous that some think this is where the legendary Garden of Eden was. Be that as it may, shortly after their newfound knack emerged, early farmers began to disperse. We don’t know why. Possibly the lifestyle based on taming plants and animals combined with settlement could support larger populations and created density that needed alleviating.

    These early farmers brought not only knowhow but also their plants and animals with them: cereals, legumes, and cows, sheep and goats. As they spread, they mixed with local hunter-gatherers, begetting early European farmers – but only to the west of that invisible Black Sea-Baltic line.

    Simplified diagram of the spread of agriculture between 11,600 and 5,800 years ago (approximated dates and routes of diffusion)
    Credit: Detlef Gronenborn, Barbara Horejs, Börner, Ober

    To its east, hunting and gathering as a subsistence lifestyle persisted for another 3,000 years. This is even though the distances from Anatolia were about the same, the team elaborates.

    Why would early farmers penetrate western Eurasia but not the east? Maybe because the entire transition to farming was based on crops and animals of Middle Eastern origin.

    Consider the chickpea, a staple in the Middle East that actually has a very small natural stamping ground. The nutritious legume is native only to part of Turkey. Today it grows around the world, including in Israel because we force it to.

    Not every crop and animal can thrive wherever we so wish, leaving technology out of it. Plausibly the conditions east of that boundary were unsuitable to farming practices developed in the paradisiacal conditions of the Neolithic Near East and therefore, hunter-gatherer societies persisted there for 3,000 years more than in the West, the team postulates.

    And then came the third great migration, which eradicated that invisible boundary once and for all: nomads of the Yamnaya culture riding out of the Pontic steppe 5,000 years ago, on the newly domesticated horse. And they brought a little something with them.

    The clue of the multiple sclerosis
    The Pontic steppe sprawls from Europe to central Asia. As the Yamnaya nomads raced over the grasslands into western Eurasia, they brought not only their enslaved steeds (who exactly domesticated the horse and climbed on its back is controversial).

    The Yamnaya also carried elevated genetic risk for multiple sclerosis, according to a separate paper published in Nature on Thursday by William Barrie of the University of Cambridge, UK. Age spread of Yamnaya steppe pastoralist ancestry into Europe and South Asia from about 5,000 years ago
    Credit: פטליפוטרה_

    Today, the highest incidences of this incurable neurodegenerative disease are in northern Europe. There is a clear north-south gradient. Now, the genetic information from the Mesolithic onward, compared with information on 410,000 white Europeans, may have solved the enigma of why that is, Barrie and the team posit. Their results indicate that the genetic risk for multiple sclerosis emerged among the Yamnaya.

    • Population genomics of post-glacial western Eurasia | Nature
      10/01/2024 (article librement accessible, 161 co-auteurs…)

      a,b, Geographical (a) and temporal (b) distribution of the 317 ancient genomes sequenced and reported in this study. Insert shows dense sampling in Denmark34. The age and the geographical region of ancient individuals are indicated by the colour and the shape of the symbols, respectively. Colour scale for age is capped at 15,000 years; older individuals are indicated with black. Random jitter was added to geographical coordinates to avoid overplotting. c,d, PCA of 3,316 modern and ancient individuals from Eurasia, Oceania and the Americas (c), and restricted to 2,126 individuals from western Eurasia (west of the Urals) (d). Principal components were defined using both modern and imputed ancient (n = 1,492) genomes passing all filters, with the remaining low-coverage ancient genomes projected. Ancient genomes sequenced in this study are indicated with black circles (imputed genomes passing all filters, n = 213) or grey diamonds (pseudo-haploid projected genomes; n = 104). Genomes of modern individuals are shown in grey, with population labels corresponding to their median coordinates. BA, Bronze Age.

      Western Eurasia witnessed several large-scale human migrations during the Holocene. Here, to investigate the cross-continental effects of these migrations, we shotgun-sequenced 317 genomes—mainly from the Mesolithic and Neolithic periods—from across northern and western Eurasia. These were imputed alongside published data to obtain diploid genotypes from more than 1,600 ancient humans. Our analyses revealed a ‘great divide’ genomic boundary extending from the Black Sea to the Baltic. Mesolithic hunter-gatherers were highly genetically differentiated east and west of this zone, and the effect of the neolithization was equally disparate. Large-scale ancestry shifts occurred in the west as farming was introduced, including near-total replacement of hunter-gatherers in many areas, whereas no substantial ancestry shifts happened east of the zone during the same period. Similarly, relatedness decreased in the west from the Neolithic transition onwards, whereas, east of the Urals, relatedness remained high until around 4,000 BP, consistent with the persistence of localized groups of hunter-gatherers. The boundary dissolved when Yamnaya-related ancestry spread across western Eurasia around 5,000 BP, resulting in a second major turnover that reached most parts of Europe within a 1,000-year span. The genetic origin and fate of the Yamnaya have remained elusive, but we show that hunter-gatherers from the Middle Don region contributed ancestry to them. Yamnaya groups later admixed with individuals associated with the Globular Amphora culture before expanding into Europe. Similar turnovers occurred in western Siberia, where we report new genomic data from a ‘Neolithic steppe’ cline spanning the Siberian forest steppe to Lake Baikal. These prehistoric migrations had profound and lasting effects on the genetic diversity of Eurasian populations.

  • Mucosal boosting enhances vaccine protection against #SARS-CoV-2 in macaques | Nature

    Here we show that intratracheal boosting with a bivalent Ad26 based SARS-CoV-2 vaccine results in substantial induction of mucosal humoral and cellular immunity and near complete protection against SARS-CoV-2 BQ.1.1 challenge. 40 previously immunized rhesus macaques were boosted with a bivalent Ad26 vaccine by the intramuscular, intranasal, and intratracheal routes or with a bivalent mRNA vaccine by the intranasal route. Ad26 boosting by the intratracheal route led to substantial expansion of mucosal neutralizing antibodies, IgG and IgA binding antibodies, and CD8+ and CD4+ T cell responses, which exceeded those induced by Ad26 boosting by the intramuscular and intranasal routes. Intratracheal Ad26 boosting also led to robust upregulation of cytokine, NK, T and B cell pathways in the lung. Following high-dose SARS-CoV-2 BQ.1.1 challenge, intratracheal Ad26 boosting provided near complete protection, whereas the other boosting strategies proved less effective. Protective efficacy correlated best with mucosal humoral and cellular immune responses. These data demonstrate that novel immunization strategies induce robust mucosal immunity, suggesting the feasibility of developing vaccines that block respiratory viral infections.


  • Inhaled #SARS-CoV-2 vaccine for single-dose dry powder aerosol immunization | Nature

    (Chez les animaux)

    […] findings support the use of this inhaled vaccine as a promising multivalent platform for fighting #COVID-19 and other respiratory infectious diseases.


  • The most important issue about water is not supply, but how it is used

    The world faces a series of deep and worsening crises that demand radical changes in how we understand, manage and use fresh water.

    Floods, droughts, pollution, water scarcity and conflict — humanity’s relationship with water is deteriorating, and it is threatening our health and well-being, as well as that of the environment that sustains us. The good news is that a transition from the water policies and technologies of past centuries to more effective and equitable ways of using and preserving this vital resource is not only possible, but under way. The challenge is to accelerate and broaden the transition.

    Water policies have typically fostered a reliance on centralized, often massive infrastructure, such as big dams for flood and drought protection, and aqueducts and pipelines to move water long distances. Governments have also created narrow institutions focused on water, to the detriment of the interconnected issues of food security, climate, energy and ecosystem health. The key assumption of these ‘hard path’ strategies is that society must find more and more supply to meet what was assumed to be never-ending increases in demand.

    That focus on supply has brought great benefits to many people, but it has also had unintended and increasingly negative consequences. Among these are the failure to provide safe water and sanitation to all; unsustainable overdraft of ground water to produce the food and fibre that the world’s 8 billion people need; inadequate regulation of water pollutants; massive ecological disruption of aquatic ecosystems; political and violent conflict over water resources; and now, accelerating climate disruption to water systems1.

    A shift away from the supply-oriented hard path is possible — and necessary. Central to this change will be a transition to a focus on demand, efficiency and reuse, and on protecting and restoring ecosystems harmed by centuries of abuse. Society must move away from thinking about how to take more water from already over-tapped rivers, lakes and aquifers, and instead find ways to do the things we want with less water. These include, water technologies to transform industries and allow people to grow more food; appliances to reduce the amount of water used to flush toilets, and wash clothes and dishes; finding and plugging leaks in water-distribution systems and homes; and collecting, treating and reusing waste water.

    Remarkably, and unbeknown to most people, the transition to a more efficient and sustainable future is already under way.

    Singapore and Israel, two highly water-stressed regions, use much less water per person than do other high-income countries, and they recycle, treat and reuse more than 80% of their waste water2. New technologies, including precision irrigation, real-time soil-moisture monitoring and highly localized weather-forecasting models, allow farmers to boost yields and crop quality while cutting water use. Damaging, costly and dangerous dams are being removed, helping to restore rivers and fisheries.

    In the United States, total water use is decreasing even though the population and the economy are expanding. Water withdrawals are much less today than they were 50 years ago (see ‘A dip in use’) — evidence that an efficiency revolution is under way. And the United States is indeed doing more with less, because during this time, there has been a marked increase in the economic productivity of water use, measured as units of gross domestic product per unit of water used (see ‘Doing more with less’). Similar trends are evident in many other countries.

    Overcoming barriers

    The challenge is how to accelerate this transition and overcome barriers to more sustainable and equitable water systems. One important obstacle is the lack of adequate financing and investment in expanding, upgrading and maintaining water systems. Others are institutional resistance in the form of weak or misdirected regulations, antiquated water-rights laws, and inadequate training of water managers with outdated ideas and tools. Another is blind adherence by authorities to old-fashioned ideas or simple ignorance about both the risks of the hard path and the potential of alternatives.

    Funding for the modernization of water systems must be increased. In the United States, President Biden’s Infrastructure Investment and Jobs Act provides US$82.5 billion for water-related programmes, including removing toxic lead pipes and providing water services to long-neglected front-line communities. These communities include those dependent on unregulated rural water systems, farm-worker communities in California’s Central Valley, Indigenous populations and those in low-income urban centres with deteriorating infrastructure. That’s a good start. But more public- and private-investments are needed, especially to provide modern water and sanitation systems globally for those who still lack them, and to improve efficiency and reuse.

    Regulations have been helpful in setting standards to cut waste and improve water quality, but further standards — and stronger enforcement — are needed to protect against new pollutants. Providing information on how to cut food waste on farms and in food processing, and how to shift diets to less water-intensive food choices can help producers and consumers to reduce their water footprints3. Corporations must expand water stewardship efforts in their operations and supply chains. Water institutions must be reformed and integrated with those that deal with energy and climate challenges. And we must return water to the environment to restore ecological systems that, in turn, protect human health and well-being.

    In short, the status quo is not acceptable. Efforts must be made at all levels to accelerate the shift from simply supplying more water to meeting human and ecological water needs as carefully and efficiently as possible. No new technologies need to be invented for this to happen, and the economic costs of the transition are much less than the costs of failing to do so. Individuals, communities, corporations and governments all have a part to play. A sustainable water future is possible if we choose the right path.
    #eau #disponibilité #efficacité #transition #infrastructure #sécheresse #inondations #barrages #acqueduc #réusage #technologie #pertes #Israël #Singapour #recyclage #agriculture

  • Infectivity of exhaled SARS-CoV-2 aerosols is sufficient to transmit covid-19 within minutes | Scientific Reports

    Exhaled SARS-CoV-2-containing aerosols contributed significantly to the rapid and vast spread of covid-19. However, quantitative experimental data on the infectivity of such aerosols is missing. Here, we quantified emission rates of infectious viruses in exhaled aerosol from individuals within their first days after symptom onset from covid-19. Six aerosol samples from three individuals were culturable, of which five were successfully quantified using TCID50. The source strength of the three individuals was highest during singing, when they exhaled 4, 36, or 127 TCID50/s, respectively. Calculations with an indoor air transmission model showed that if an infected individual with this emission rate entered a room, a susceptible person would inhale an infectious dose within 6 to 37 min in a room with normal ventilation. Thus, our data show that exhaled aerosols from a single person can transmit covid-19 to others within minutes at normal indoor conditions.

    • Introduction

      The transmission routes that enabled the efficient spread of covid-19 have been debated, but it has become evident that short-range aerosol transmission has contributed significantly[1,2]. However, as the infectivity peaks at or even before symptom onset it has been challenging to collect experimental data on the quantified infectivity of exhaled SARS-CoV-2 aerosols.

      Three previous studies have reported attempts to cultivate exhaled aerosol samples from patients with covid-19. In one of these, no aerosol samples were positive when cultured[3], but the other two studies reported qualitative results of culture-positive virus in exhaled air[4,5]. Two additional studies successfully quantified SARS-CoV-2 infectivity of aerosol samples[6,7]. However, these were from room or car air, and collected over hours which made it difficult to derive emission rates. Moreover, Kitagawa et al. recently measured the 50% tissue culture infectious dose (TCID50) in air samples from a hospital patient room, but did not calculate individual emission rates[8]. To our knowledge, no quantification has been done on virus isolated from exhaled aerosols of infected individuals. Nevertheless, this data is crucial for exposure assessments. Thus, critical information on emissions of infectious SARS-CoV-2 from exhaled air is still missing.

      Source emission rates are crucial for modelling airborne transmission, which is key to estimate the risk for infection in different settings.

      «To our knowledge, no quantification has been done on virus isolated from exhaled aerosols of infected individuals» ?!?!?

      C’est incroyable ça, en 5 ans, que zéro étude quantitative n’ait été faite. Dans le monde entier.

  • La fonte des barrières de #glace de l’#Antarctique occidental est désormais inévitable et irréversible

    La fonte qui glace. Ce processus ne peut pas être inversé et contribuera à la hausse du niveau de l’océan, même en limitant le réchauffement climatique, alerte une nouvelle étude.

    Les plateformes (ou barrières) de glace jouent un rôle stabilisateur essentiel et ralentissent la #fonte_des_glaciers dans l’#océan. Leur fonte dans l’#Antarctique_occidental va se poursuivre de manière inévitable, et ce dans tous les #scénarios de réduction des émissions de gaz à effet de serre. Autrement dit, limiter le réchauffement à +1,5°C à la fin du siècle par rapport à l’ère préindustrielle, comme le prévoit l’#Accord_de_Paris, ne suffira pas à inverser la tendance. C’est à cette glaçante conclusion que sont parvenu·es les chercheur·ses du British antarctic survey (l’opérateur britannique de recherche en Antarctique) dans cette étude parue dans Nature climate change ce lundi :

    « Nous constatons qu’un réchauffement rapide des #océans, environ trois fois plus rapide que le taux historique, est susceptible de se produire au cours du XXIème siècle », écrivent les scientifiques, qui ont modélisé la #mer_d’Amundsen, à l’ouest de l’Antarctique, pour mener l’analyse la plus complète du réchauffement dans la région à ce jour.

    La poursuite de la fonte des #barrières_de_glace dans l’Antarctique ouest pourrait entraîner la débâcle irréversible des #glaciers, de quoi élever le niveau de l’océan de cinq mètres, un processus aux conséquences potentiellement désastreuses pour la planète. « Notre étude n’est pas une bonne nouvelle : nous avons peut-être perdu le contrôle de la fonte de la #plateforme_glaciaire de l’Antarctique occidental au cours du XXIe siècle », a déclaré au Guardian Kaitlin Naughten, qui a dirigé les travaux.

    « Il s’agit d’un des effets du changement climatique auquel nous devrons probablement nous adapter, ce qui signifie très probablement que certaines communautés côtières devront soit construire [des défenses], soit être abandonnées », poursuit la chercheuse du British antarctic survey.

    Aujourd’hui, environ deux tiers de la population mondiale vit à moins de cent kilomètres d’une côte. De nombreuses mégalopoles mondiales, comme New York, Shanghai, Tokyo ou Bombay, sont situées sur le littoral et particulièrement vulnérables à la montée du niveau de la mer.
    #irréversibilité #inévitabilité #climat #changement_climatique

    • Unavoidable future increase in West Antarctic ice-shelf melting over the twenty-first century

      Ocean-driven melting of floating ice-shelves in the Amundsen Sea is currently the main process controlling Antarctica’s contribution to sea-level rise. Using a regional ocean model, we present a comprehensive suite of future projections of ice-shelf melting in the Amundsen Sea. We find that rapid ocean warming, at approximately triple the historical rate, is likely committed over the twenty-first century, with widespread increases in ice-shelf melting, including in regions crucial for ice-sheet stability. When internal climate variability is considered, there is no significant difference between mid-range emissions scenarios and the most ambitious targets of the Paris Agreement. These results suggest that mitigation of greenhouse gases now has limited power to prevent ocean warming that could lead to the collapse of the West Antarctic Ice Sheet.