Boi, frango e porco: USP analisa movimentos de pre?os das carnes concorrentes e reflexos da estiagem em agosto
Protect Arctic from 'dangerous' climate engineering, scientists warn.txt
Protect Arctic from 'dangerous' climate engineering,magico da blaze scientists warn2 days agoShareSaveMark PoyntingClimate and science reporter, BBC NewsShareSaveGetty ImagesPlans to fight climate change by manipulating the Arctic and Antarctic environment are dangerous, unlikely to work and could distract from the need to ditch fossil fuels, dozens of polar scientists have warned.These polar "geoengineering" techniques aim to cool the planet in unconventional ways, such as artificially thickening sea-ice or releasing tiny, reflective particles into the atmosphere.They have gained attention as potential future tools to combat global warming, alongside cutting carbon emissions.But more than 40 researchers say they could bring "severe environmental damage" and urged countries to simply focus on reaching net zero, the only established way to limit global warming.Geoengineering - deliberately intervening in the Earth's climate system to counter the impacts of global warming - is one of the most controversial areas of climate research.Some types are widely accepted - removing planet-warming carbon dioxide from the atmosphere via planting trees or using machines, for example, are recognised parts of net zero efforts.Net zero means balancing the amount of planet-warming "greenhouse" gases produced by human activities with the amount being actively removed from the atmosphere. But some more radical geoengineering ideas, like reflecting sunlight "are dealing with the symptoms of climate change rather than the causes," said lead author Martin Siegert, professor of geosciences at the University of Exeter.For supporters, it is worth exploring techniques which could help rein in rapidly rising temperatures, which are already bringing severe impacts for people and ecosystems around the world.But for opponents, the risks are simply too great – particularly for the fragile polar regions, about which much remains unknown.The 'insane' plan to save the Arctic's sea-iceConspiracy theories swirl about geo-engineering, but could it help save the planet?UK experiments to reflect sunlight one step closerThe scientists behind the new assessment, published in the journal Frontiers in Science, reviewed the evidence for five of the most widely discussed polar geoengineering ideas.All fail to meet basic criteria for their feasibility and potential environmental risks, they say.One such suggestion is releasing tiny, reflective particles called aerosols high into the atmosphere to cool the planet.This often attracts attention among online conspiracy theorists, who falsely claim that condensation trails in the sky – water vapour created from aircraft jet engines – is evidence of sinister large-scale geoengineering today.But many scientists have more legitimate concerns, including disruption to weather patterns around the world.With those potential knock-on effects, that also raises the question of who decides to use it – especially in the Arctic and Antarctic, where governance is not straightforward.If a country were to deploy geoengineering against the wishes of others, it could "increase geopolitical tensions in polar regions", according to Dr Valerie Masson-Delmotte, senior scientist at the Université Paris Saclay in France.Another fear is that while some of the ideas may be theoretically possible, the enormous costs and time to scale-up mean they are extremely unlikely to make a difference, according to the review.One idea BBC News recently looked at was a plan to pump seawater over the surface of Arctic sea-ice in winter to thicken it, giving the ice a better chance to survive the summer.But to cover 10% of the Arctic could require about 10 million seawater pumps, one estimate suggests.A more fundamental concern is that these types of projects could create the illusion of an alternative to cutting humanity's emissions of planet-warming gases."If they are promoted… then they are a distraction because to some people they will be a solution to the climate crisis that doesn't require decarbonising," said Prof Siegert."Of course that would not be true and that's why we think they can be potentially damaging."BBC/Jemma CoxOne suggestion to save Thwaites Glacier, one of the most vulnerable Antarctic glaciers, is to install a giant sea "curtain" to stop warm water melting it more quickly - but the new study says this would be extremely costly and unlikely to workEven supporters of geoengineering research agree that it is, at best, a supplement to net zero, not a substitution."The need for emissions reductions comes first… almost anything we do is futile without it," according to Dr Shaun Fitzgerald, director of the University of Cambridge's Centre for Climate Repair, which has been involved in some of the projects highlighted.The assessment raises "very valid concerns" about some of the ideas, but they need to be balanced against the risks from "the perilous state of the climate," he argued.Like many other supporters of geoengineering research, Dr Fitzgerald does not support deploying it on a large scale yet, and acknowledged that further investigation might indeed find that the ideas are "bonkers".But he argued that more research would allow society to make "more informed decisions" about whether they could help or hinder in the fight against climate change.A UK government-backed agency recently announced nearly ￡60m of funding for such research, though the government says it has no plans to deploy them.But the authors of the new assessment view these projects as so unrealistic that efforts would be better directed towards decarbonisation and polar research."There are some basic home truths that don't need an awful lot of research to come to a conclusion that they're not really viable," argued Prof Siegert.A UK government spokesperson said: "Our priority is to reduce greenhouse gas emissions from human activities and to adapt to the unavoidable impacts of climate change."A simple guide to climate changeFour ways climate change worsens extreme weatherWhat is net zero and is the UK on track to achieve it?Sign up for our Future Earth newsletter to keep up with the latest climate and environment stories with the BBC's Justin Rowlatt. 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