*[Enwl-eng] Behind 'shocking' September heat
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No images? Click here  Has the beginning of autumn felt more like the middle of summer to you? Even scientists who have monitored Earth's climate for decades were shocked by global temperature data for September, which was 0.93°C warmer than the average for the month between 1991 and 2020. In fact, September 2023 was a whole half-degree celsius hotter than the previous record, set in 2020. 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 why September was sweltering – and what accelerating climate change means for the world. This year was already proving to be particularly warm before the September temperature spike. With it, scientists estimate that 2023 is now on track to be the hottest year ever recorded. The biggest driver of the increasing rate at which Earth is heating remains emissions of carbon dioxide and other greenhouse gases, which have yet to peak globally. The burning of coal, oil and gas is the overwhelming source. "Overall, humanity’s effect on the climate has been a global warming of about 1.2°C," says Andrew King, a senior lecturer in climate science at the University of Melbourne. "The record-high rate of greenhouse gas emissions means we should expect global warming to accelerate too." But there is another big influence on global temperatures this year says King: El Niño, the warm phase of a natural cycle centred on the Pacific Ocean. "During El Niño we see warming of the surface ocean over much of the tropical Pacific. This warming, and the effects of El Niño in other parts of the world, raises global average temperatures by about 0.1 to 0.2°C," he says. Paulo Ceppi and Piers Forster, climate scientists at Imperial College London and the University of Leeds respectively, point out that the current El Niño is still building and will amplify global heating even more in the months to come. "After years of excess heat flowing into the ocean, the current El Niño is causing the release of some of this to the atmosphere," they say. That's not all, though. Some forms of air pollution, like sulphur dioxide from coal furnaces or the engines of container vessels, help cool the climate system by reflecting some of the Sun's radiation back to space. Low sulphur rules imposed on the shipping industry by the International Maritime Organization in 2020 have reduced global emissions of sulphur dioxide by 10%. Cleaner air has unfortunately meant a smaller cooling effect. "It’s likely this is contributing to the extreme high global temperatures – but only on the order of hundredths of a degree. Recent analysis suggests the effect of the 2020 shipping agreement is about an extra 0.05°C warming by 2050," King says. On top of this, the Sun's intensity (which varies in 11-year cycles) is peaking, say Ceppi and Forster. "Two additional effects, both likely to be small, come from the Hunga Tonga–Hunga Ha’apai volcanic eruption in January 2022, which injected large amounts of water vapour (a potent greenhouse gas) into the stratosphere, plus a recent decrease in the amount of Saharan dust being blown onto the Atlantic ocean, allowing more sunlight to reach and warm the ocean surface, possibly contributing to the exceptional North Atlantic sea surface temperatures recorded this year," they add. Searing heat so late in the year will affect crops which ripen in the autumn, like hops, which are predominantly grown in Germany, the Czech Republic and Slovenia. A study published this week found that European beers are likely to taste worse and cost more as a result of these seasonal changes. More alarming is the implication that Earth's average temperature anomaly for September was 1.7°C above the pre-industrial average. This is well above the 1.5°C threshold scientists have urged countries to limit long-term global heating to in order to prevent worsening and potentially irreversible effects – and close to the Paris agreement's upper limit of 2°C. Research suggests that even briefly exceeding this latter temperature limit could cause permanent damage to our planet's teetering ecosystems. Temporary overshoot, permanent damage Climate change has already made the ocean uncomfortably hot and increasingly breathless for a vast array of marine life. The warmer the water, the less dissolved oxygen it can hold. If global warming exceeds 2°C temporarily (which is possible even with substantial cuts to emissions according to one analysis), the effect on ocean ecosystems would endure over several human lifetimes – long after CO₂ levels in the atmosphere have peaked and declined. That's according to new research by Tilo Ziehn and Andrew Lenton at CSIRO and Yeray Santana-Falcón at CNRM. "Our study findings raise concerns about shrinking habitats. For example, species like tuna live in well-oxygenated surface waters and are restricted by low oxygen in deeper waters," the team say. "Their habitat will be compressed towards the surface for hundreds of years, according to our study." A study published last year examined the consequences of overshooting 2°C on land. "The results suggest that a temporary overshoot would cause waves of irreversible extinctions and lasting damage to tens of thousands of species," say Joanne Bentley, Alex Pigot, Andreas L. S. Meyer and Christopher Trisos, ecologists at the University of Cape Town and UCL. "This is what the world can expect if humanity fails to make deep emission cuts this decade, and relies instead on future technologies to remove emissions later." Smaller contributors to global heating will vary in strength over time but it is greenhouse gas emissions – and therefore, humanity – that is firmly in the driver's seat say Ceppi and Forster: "Only by rapidly reducing emissions of greenhouse gases towards zero can the level of global warming be limited." - 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.  6 reasons why global temperatures are spiking right now The preliminary global-average temperature anomaly for September is a shocking 1.7°C. These are the drivers of current record-breaking heat.  Here’s what’s driving the record autumn heat (it’s not just carbon emissions) On top of rising greenhouse gas emissions, aerosol pollution which would normally cool Earth has fallen.  Even temporary global warming above 2℃ will affect life in the oceans for centuries A climate overshoot that creates warmer oceans with lower oxygen levels will reduce the suitable habitat for many marine species long after CO₂ levels have peaked and declined.  Climate crisis: even temporarily overshooting 2°C would cause permanent damage to Earth’s species Species will endure intolerable conditions long after the global average temperature stabilises.  Hotter, drier summers will make European craft beers less ‘hoppy’ – new study By 2050, the chemicals which make craft beers 'hoppy' could decrease by a third.  One of 2023’s most extreme heatwaves is happening in the middle of winter Parts of Argentina and the Chilean Andes experienced some of their highest temperatures on record. Latest from The Conversation on climate change
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