#science_et_politique

  • The Climate Expert Who Delivered News No One Wanted to Hear | The New Yorker
    https://www.newyorker.com/magazine/2009/06/29/the-catastrophist

    Hansen, who is sixty-eight, has greenish eyes, sparse brown hair, and the distracted manner of a man who’s just lost his wallet. (In fact, he frequently misplaces things, including, on occasion, his car.) Thirty years ago, he created one of the world’s first climate models, nicknamed Model Zero, which he used to predict most of what has happened to the climate since. Sometimes he is referred to as the “father of global warming,” and sometimes as the grandfather.

    Hansen has now concluded, partly on the basis of his latest modelling efforts and partly on the basis of observations made by other scientists, that the threat of global warming is far greater than even he had suspected. Carbon dioxide isn’t just approaching dangerous levels; it is already there. Unless immediate action is taken—including the shutdown of all the world’s coal plants within the next two decades—the planet will be committed to change on a scale society won’t be able to cope with. “This particular problem has become an emergency,” Hansen said.

    Hansen’s revised calculations have prompted him to engage in activities—like marching on Washington—that aging government scientists don’t usually go in for. Last September, he travelled to England to testify on behalf of anti-coal activists who were arrested while climbing the smokestack of a power station to spray-paint a message to the Prime Minister. (They were acquitted.) Speaking before a congressional special committee last year, Hansen asserted that fossil-fuel companies were knowingly spreading misinformation about global warming and that their chairmen “should be tried for high crimes against humanity and nature.” He has compared freight trains carrying coal to “death trains,” and wrote to the head of the National Mining Association, who sent him a letter of complaint, that if the comparison “makes you uncomfortable, well, perhaps it should.”

    Hansen insists that his intent is not to be provocative but conservative: his only aim is to preserve the world as we know it. “The science is clear,” he said, when it was his turn to address the protesters blocking the entrance to the Capitol Power Plant. “This is our one chance.”

    When Hansen began his modelling work, there were good theoretical reasons for believing that increasing CO2 levels would cause the world to warm, but little empirical evidence. Average global temperatures had risen in the nineteen-thirties and forties; then they had declined, in some regions, in the nineteen-fifties and sixties. A few years into his project, Hansen concluded that a new pattern was about to emerge. In 1981, he became the director of GISS. In a paper published that year in Science, he forecast that the following decade would be unusually warm. (That turned out to be the case.) In the same paper, he predicted that the nineteen-nineties would be warmer still. (That also turned out to be true.) Finally, he forecast that by the end of the twentieth century a global-warming signal would emerge from the “noise” of natural climate variability. (This, too, proved to be correct.)

    Throughout the nineteen-eighties and nineties, the evidence of climate change—and its potential hazards—continued to grow. Hansen kept expecting the political system to respond. This, after all, was what had happened with the ozone problem. Proof that chlorofluorocarbons were destroying the ozone layer came in 1985, when British scientists discovered that an ozone “hole” had opened up over Antarctica. The crisis was resolved—or, at least, prevented from growing worse—by an international treaty phasing out chlorofluorocarbons which was ratified in 1987.

    “At first, Jim’s work didn’t take an activist bent at all,” the writer Bill McKibben, who has followed Hansen’s career for more than twenty years and helped organize the anti-coal protest in D.C., told me. “I think he thought, as did I, If we get this set of facts out in front of everybody, they’re so powerful—overwhelming—that people will do what needs to be done. Of course, that was naïve on both our parts.”

    What is now happening, Hansen explained to the group in New Hampshire, is that climate history is being run in reverse and at high speed, like a cassette tape on rewind. Carbon dioxide is being pumped into the air some ten thousand times faster than natural weathering processes can remove it.

    “So humans now are in charge of atmospheric composition,” Hansen said. Then he corrected himself: “Well, we’re determining it, whether we’re in charge or not.”

    Among the many risks of running the system backward is that the ice sheets formed on the way forward will start to disintegrate. Once it begins, this process is likely to be self-reinforcing. “If we burn all the fossil fuels and put all that CO2 into the atmosphere, we will be sending the planet back to the ice-free state,” Hansen said. “It will take a while to get there—ice sheets don’t melt instantaneously—but that’s what we will be doing. And if you melt all the ice, sea levels will go up two hundred and fifty feet. So you can’t do that without producing a different planet.”

    Once you accept that CO2 levels are already too high, it’s obvious, Hansen argues, what needs to be done. He displayed a chart of known fossil-fuel reserves represented in terms of their carbon content. There was a short bar for oil, a shorter bar for natural gas, and a tall bar for coal.

    “We’ve already used about half of the oil,” he observed. “And we’re going to use all of the oil and natural gas that’s easily available. It’s owned by Russia and Saudi Arabia, and we can’t tell them not to sell it. So, if you look at the size of these fossil-fuel reservoirs, it becomes very clear. The only way we can constrain the amount of carbon dioxide in the atmosphere is to cut off the coal source, by saying either we will leave the coal in the ground or we will burn it only at power plants that actually capture the CO2.” Such power plants are often referred to as “clean coal plants.” Although there has been a great deal of talk about them lately, at this point there are no clean-coal plants in commercial operation, and, for a combination of technological and economic reasons, it’s not clear that there ever will be.

    Hansen continued, “If we had a moratorium on any new coal plants and phased out existing ones over the next twenty years, we could get back to three hundred and fifty parts per million within several decades.” Reforestation, for example, if practiced on a massive scale, could begin to draw global CO2 levels down, Hansen says, “so it’s technically feasible.” But “it requires us to take action promptly.”

    “In nearly all areas, the developments are occurring more quickly than had been assumed,” Hans Joachim Schellnhuber, the head of Germany’s Potsdam Institute for Climate Impact Research, recently observed. “We are on our way to a destabilization of the world climate that has advanced much further than most people or their governments realize.”

    Scientifiques et responsablité : une véritable question à dépasser. Si on se limite à ce qui est « acceptable politiquement », est-on encore un scientifique quand la réalité de l’évolution de la planète est en jeu ? C’est à ce moment là qu’on devient un sciento-politique conservateur. La « communauté scientifique » a peur de son ombre, et pas seulement dans ce domaine. Hansen a raison de dire les conséquences politiques de ce que son travail scientifique lui a permis de découvrir.

    But if Hansen’s anxieties about D.A.I. and coal are broadly shared, he is still, among climate scientists, an outlier. “Almost everyone in the scientific community is prepared to say that if we don’t do something now to reverse the direction we’re going in we either already are or will very, very soon be in the danger zone,” Naomi Oreskes, a historian of science and a provost at the University of California at San Diego, told me. “But Hansen talks in stronger terms. He’s using adjectives. He has started to speak in moral terms, and that always makes scientists uncomfortable.”

    Hansen is also increasingly isolated among climate activists. “I view Jim Hansen as heroic as a scientist,” Eileen Claussen, the president of the Pew Center on Global Climate Change, said. “He was there at the beginning, he’s faced all kinds of pressures politically, and he’s done a terrific job, I think, of keeping focussed. But I wish he would stick to what he really knows. Because I don’t think he has a realistic view of what is politically possible, or what the best policies would be to deal with this problem.”

    #Climat #Jim_Hansen #Science_et_politique

  • Les politiques d’#austérité : à cause d’une erreur Excel ?

    Comment un article économique ayant eu une influence majeure sur les politiques d’austérité s’est finalement révélé faux, à cause d’une erreur de calcul sous #Excel.

    https://www.youtube.com/watch?v=yeX_Zs7zztY&feature=youtu.be


    #science #politique #science_et_politique #croissance #dette #vidéo #économie #erreur #dette_publique #90_pourcent #politique_économique #Thomas_Herndon

    Le seuil de 90% de dette, cité dans l’article de #Reinhart - #Rogoff comme étant le seuil qui ne permet plus de croissance, et utilisé par les politiciens depuis...

    • The #Reinhart - #Rogoff error – or how not to Excel at economics

      Last week we learned a famous 2010 academic paper, relied on by political big-hitters to bolster arguments for austerity cuts, contained significant errors; and that those errors came down to misuse of an Excel spreadsheet.

      Sadly, these are not the first mistakes of this size and nature when handling data. So what on Earth went wrong, and can we fix it?

      Harvard’s Carmen Reinhart and Kenneth Rogoff are two of the most respected and influential academic economists active today.

      Or at least, they were. On April 16, doctoral student Thomas Herndon and professors Michael Ash and Robert Pollin, at the Political Economy Research Institute at the University of Massachusetts Amherst, released the results of their analysis of two 2010 papers by Reinhard and Rogoff, papers that also provided much of the grist for the 2011 bestseller Next Time Is Different.

      Reinhart and Rogoff’s work showed average real economic growth slows (a 0.1% decline) when a country’s debt rises to more than 90% of gross domestic product (GDP) – and this 90% figure was employed repeatedly in political arguments over high-profile austerity measures.

      During their analysis, Herndon, Ash and Pollin obtained the actual spreadsheet that Reinhart and Rogoff used for their calculations; and after analysing this data, they identified three errors.

      The most serious was that, in their Excel spreadsheet, Reinhart and Rogoff had not selected the entire row when averaging growth figures: they omitted data from Australia, Austria, Belgium, Canada and Denmark.

      In other words, they had accidentally only included 15 of the 20 countries under analysis in their key calculation.

      When that error was corrected, the “0.1% decline” data became a 2.2% average increase in economic growth.

      So the key conclusion of a seminal paper, which has been widely quoted in political debates in North America, Europe Australia and elsewhere, was invalid.

      The paper was cited by the 2012 Republican nominee for the US vice presidency Paul Ryan in his proposed 2013 budget The Path to Prosperity: A Blueprint for American Renewal.

      Undoubtedly, without Reinhart and Rogoff, Ryan would have found some other data to support his conservative point of view; but he must have been delighted he had heavyweight economists such as Reinhart and Rogoff apparently in his corner.

      Mind you, Reinhart and Rogoff have not tried to distance themselves from this view of their work.
      Keeping records

      As said at the outset, this is not the first time a data- and/or math-related mistake resulted in major embarrassment and expense. In a summary of such historical clangers, Bloomberg journalist Matthew Zeitlin recently pointed to:

      NASA’s Mariner 1 spacecraft, destroyed minutes after launch in 1962, thanks to “a missing hyphen in its computer code for transmitting navigation instructions”
      an Excel spreadsheet error by a first-year law firm associate, who added 179 contracts to an agreement to buy the bankrupt firm Lehman Brothers’ assets, on behalf of Barclay’s bank
      the 2010 European flight ban, following the eruption of Iceland’s Eyjafjallajokull, for which “many of the assumptions in the computer models were not backed by scientific evidence”

      While many different types of errors were involved in these calamities, the fact that the errors in the Reinhart-Rogoff paper were not identified earlier can be ascribed by the pervasive failure of scientific and other researchers to make all data and computer code publicly available at an early stage – preferably when the research paper documenting the study is submitted for review.

      We’ve discussed this topic in a previous article on Math Drudge and another in the Huffington Post – emphasising that the culture of computing has not kept pace with its rapidly ascending pre-eminence in modern scientific and social science research.

      Most certainly the issue is not just one for political economists, although the situation seems worst in the social sciences. In a private letter now making the rounds – which we have read – behavioural psychologist Daniel Kahneman (a Nobel economist) has implored social psychologists to clean up their act to avoid a “train wreck”.

      Kahneman specifically discusses the importance of replication of experiments and studies on priming effects.

      Traditionally, researchers have been taught to record every detail of their work, including experimental design, procedures, equipment, raw results, data processing, statistical methods and other tools used to analyse the results.

      In contrast, relatively few researchers who employ computing in modern science – ranging from large-scale, highly parallel climate simulations to simple processing of social science data – typically take such care in their work.

      In most cases, there is no record of workflow, hardware and software configuration, and often even the source code is no longer available (or has been revised numerous times since the study was conducted).

      We think this is a seriously lax environment in which deliberate fraud and genuine error can proliferate.
      Raising standards

      We believe, and have argued, there should be new and significantly stricter standards required of papers by journal editors and conference chairs, together with software tools to facilitate the storage of files relating to the computational workflow.

      But there’s plenty of blame to spread around. Science journalists need to do a better job of reporting such critical issues and not being blinded by seductive numbers. This is not the first time impressive-looking data, later rescinded, has been trumpeted around the media. And the stakes can be enormous.

      If Reinhart and Rogoff (a chess grandmaster) had made any attempt to allow access to their data immediately at the conclusion of their study, the Excel error would have been caught and their other arguments and conclusions could have been tightened.

      They might still be the most dangerous economists in the world, but they would not now be in the position of saving face in light of damning critiques in the Atlantic and elsewhere.

      As Matthew O’Brien put it last week in The Atlantic:

      For an economist, the five most terrifying words in the English language are: I can’t replicate your results. But for economists Carmen Reinhart and Ken Rogoff of Harvard, there are seven even more terrifying ones: I think you made an Excel error.

      Listen, mistakes happen. Especially with Excel. But hopefully they don’t happen in papers that provide the intellectual edifice for an economic experiment — austerity — that has kept millions out of work. Well, too late.

      https://theconversation.com/the-reinhart-rogoff-error-or-how-not-to-excel-at-economics-13646

  • Dès 1979, le rapport Charney annonçait le réchauffement climatique
    https://www.lemonde.fr/planete/article/2009/12/28/des-1979-le-rapport-charney-annoncait-le-rechauffement-climatique_1285427_32

    Rapport tombé dans l’oubli

    De fait, ce qu’écrivent les neuf auteurs du rapport, emmenés par Jule Charney (1917-1981), alors professeur au Massachusetts Institute of Technology (MIT), pourrait avoir été écrit hier. « Depuis plus d’un siècle, nous savons que des changements de la composition de l’atmosphère peuvent changer sa faculté à absorber l’énergie du Soleil, peut-on lire en préambule. Nous avons la preuve irréfutable que l’atmosphère change et que nous contribuons à ce changement. Les concentrations atmosphériques de dioxyde de carbone augmentent continûment, ce qui est lié à la combustion des ressources fossiles et à l’utilisation des sols. Puisque le dioxyde de carbone joue un rôle significatif dans l’équilibre thermique de l’atmosphère, il est raisonnable de penser que son augmentation continue affectera le climat. »

    La lecture du rapport Charney nous rappelle, a expliqué en substance l’océanographe Carl Wunsch, professeur au MIT, qui en fut l’un des auteurs, que le diagnostic du réchauffement anthropique ne repose pas sur des modèles numériques complexes. Il tient à une physique simple, déjà maîtrisée il y a trente, voire quarante ans. L’estimation de la sensibilité du climat à un doublement du CO2 atmosphérique était grosso modo la même en 1979 qu’aujourd’hui : entre 1,5 °C et 4,5 °C d’augmentation de la température moyenne de la basse atmosphère.

    Mais « le plus important » est, selon Raymond Pierrehumbert, que la science de la fin des années 1970 avait déjà anticipé que les premiers effets du réchauffement mettraient des décennies à être décelables. « Les auteurs écrivaient que, vu l’inertie du système, si on attendait de voir les premiers effets du réchauffement avant d’agir, alors une grande quantité de réchauffement supplémentaire serait inévitable », dit le chercheur.

    Une fois remis, le rapport Charney est tombé dans l’oubli. « Les décideurs politiques ont du mal à tenir compte des prévisions, ils ne réagissent qu’à ce qu’ils voient se produire (...), pas à ce qui est prévu », conclut M. Pierrehumbert. Le rapport commandé par Jimmy Carter aura eu son utilité. Parmi ses auteurs, un certain Bert Bolin (1925-2007) allait cofonder, moins d’une décennie plus tard, le GIEC et en être le premier président.

    Stéphane Foucart

    #Climat #Rapport_Charney #GIEC #Science_et_politique