*[Enwl-eng] Behind 'shocking' September heat

[enwl]

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      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


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      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.

      Read more


       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.

      Read more

       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.

      Read more

       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.

      Read more

       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.

      Read more

       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.

      Read more


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      From: Imagine newsletter
      Sent: Wednesday, October 11, 2023 9:02 PM
      Subject: Behind 'shocking' September heat


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