*[Enwl-eng] Why is 1.5°C so important?
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No images? Click here  Almost every country agreed to try and limit global heating to 1.5°C at the 2015 Paris climate conference. The decision was hailed by small islanders and scientists who warned that devastation lay beyond this threshold. Nearly eight years later, meteorologists have confirmed that July 2023 was the hottest ever recorded – a month in which the air temperature at our planet's surface was 1.5°C hotter than the pre-industrial average. Have efforts to avert dangerous warming now officially failed? And what is so important about the 1.5°C target anyway? You're reading the Imagine newsletter – a weekly synthesis of academic insight on solutions to climate change, brought to you by The Conversation. I'm Jack Marley, energy and environment editor. This week, we're discussing life at 1.5°C. "The threshold was breached for a month before average temperatures dropped back. And July 2023 isn’t actually the first time this has happened either – the dubious honour goes to February 2016, where we broke the threshold for a few days," say Ailie Gallant and Kimberley Reid, climate and atmosphere scientists at Monash University. Then, as now, Earth was in what is called an El Niño event. This is the hot phase of a natural fluctuation in the climate which tends to last a few years and temporarily amplifies the background rate of warming caused predominantly by burning fossil fuels (animal farming and deforestation are also big sources of planet-warming greenhouse gases like CO₂ and methane). These two factors combined meant Earth exceeded the 1.5°C threshold for a whole month for the first time this summer. "But the climate is more than a single month," Gallant and Reid stress. The Intergovernmental Panel on Climate Change, the global authority on climate change, defines the threshold as the first 20-year period in which air surface temperatures average 1.5°C above what they were between 1850 and 1900 (referred to as the pre-industrial average). A study published earlier this year estimates that we could pass this point in the early 2030s. So what awaits us in this world made a degree-and-a-half hotter? Gallant and Reid describe "dangerous" levels of warming as that which threatens the stability of ecosystems, economies and agriculture and makes adapting very difficult or impossible. "Put simply, the 1.5°C threshold is the best estimate of the point where we are likely to find ourselves well up the proverbial creek, without a paddle," they say. And then there is the risk of triggering irreversible climate tipping points. These are self-sustaining shifts in the climate system that lock in devastating changes after a certain level of warming has occurred, such as the collapse of ice sheets or the rapid die-back of the Amazon rainforest. Both changes could accelerate the rate at which Earth is heating by reflecting less sunlight to space or releasing more carbon to the atmosphere. But a scientist studying these possible tipping points explains that passing 1.5°C is not necessarily "game over" for the climate. "Most scientists don’t expect the world to reach a slew of climate tipping points if El Niño causes the world to cross 1.5°C briefly," Stockholm University's David Armstrong McKay wrote in April. "Our estimates for climate tipping point thresholds are based on what would happen if global warming stayed at that level for many years. So a tipping threshold that is estimated to lie at 1.5°C won’t have been reached until global temperatures average 1.5°C for around a decade." If that sounds reassuring, McKay has a caveat: "Recent research I led judged that several of these climate tipping points become likely beyond 1.5°C and can’t be ruled out even at current warming of around 1.2°C." If dangerous shifts in Earth's climate are possible south of 1.5°C, why is so much hope and anxiety invested in it? "There’s nothing magic about this number," Gallant and Reid say. "Every increase worsens the impacts." '2°C is a death sentence' For much of the time countries have been debating Earth's rising temperature, 1.5°C was not the official goal at all. "Halting global heating at 2°C remained the horizon to which negotiators strived for nearly two decades," says Piers Forster, director of the Priestley International Centre for Climate at the University of Leeds. "And yet, you’re more likely to hear about the rapidly approaching 1.5°C temperature limit nowadays." That world leaders eventually agreed to revise down the acceptable level of climate damage is testament to the campaigning of a formation of island nations known as the Alliance of Small Island States (AOSIS), Forster says. At Copenhagen's 2009 climate summit, the world still lacked a scientific assessment of what a "safe" limit to warming looked like. But research had started to paint a picture of an Earth 2°C warmer: widespread coral bleaching, receding coastlines and increasingly erratic weather. Worse, it seemed sea-level rise would proceed more rapidly and violently than in earlier predictions. At stake was the survival of some small islands. "Only stopping global temperature rise well below 1.5°C would head off this catastrophe, AOSIS argued," Forster says. "As Mia Mottley, prime minister of Barbados, would later put it: '2°C is a death sentence.'" "The idea that a 'safe' level of warming could be achieved was subjective: current levels were already unsafe for those on the sharpest end of climate change," Forster adds. The story of the 1.5°C limit highlights that the only acceptable level of warming is that which humanity collectively decides, Forster says. So can the Paris signatories still keep their promise? Maybe, say Gallant and Reid. "We would need extremely aggressive cuts to emissions to have a chance. Failing that, we will likely exceed the Paris target within the next decade or so." "The closer we stay to the line – even if we cross it – the better. And there’s now good evidence that even if we overshoot 1.5°C, we could still reverse it by ending emissions and soaking up excess greenhouse gas emissions. "It’s like turning around an enormous container ship – it takes time to overcome the inertia. But the sooner we turn around, the better." Correction: last week's newsletter on invasive species referred to "rivers choked with [Japanese] knotweed". This behaviour is more accurately ascribed to Himalayan balsam. - Jack Marley, Environment commissioning editor Was this email forwarded to you? Join the 20,000 people who get one email every week about the most important issue of our time. Subscribe to Imagine.  We just blew past 1.5 degrees. Game over on climate? Not yet July was the hottest month on record – and took us past 1.5 degrees. But one month isn't the same as failing to meet our Paris Agreement goals.  What El Niño means for the world’s perilous climate tipping points The Pacific Ocean is entering the hot phase of its temperature cycle, an event that will turbo-charge global warming.  1.5°C: where the target came from – and why we’re losing sight of its importance There is no safe limit to global warming – there is only what people deem to be acceptable damage.  Every tenth of a degree makes climate change significantly worse.  How 1.5 became the most important number at the Paris climate talks 1.5 or 2 degrees? What matters is how we get there.  Not convinced on the need for urgent climate action? Here’s what happens to our planet between 1.5°C and 2°C of global warming Nations are signed up to limit global heating to well below 2°C, and to aim for 1.5°C. Limiting warming to the latter matters – the future of humanity and the living world is at stake. Latest from The Conversation on climate change
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