This weeks short read

[SteamyTea]

Melting of Greenland ice could cause European heat extremes this year

When lots of freshwater from Greenland pours into the North Atlantic Ocean, it triggers feedback loops that lead to hotter and drier weather in Europe, according to a study of the past 40 years

By Michael Le Page

28 February 2024

 

 

 

The melting of ice in Greenland could be worsening weather extremes across Europe

REDA &CO srl/Alamy

 

The 10 hottest and driest summers in Europe in the past 40 years have all followed the release of particularly large amounts of freshwater from Greenland’s ice sheet, and it may mean an especially hot summer is coming in southern Europe this year.

The link happens because the extra meltwater triggers a series of amplifying feedbacks that affect the strength and position of the atmospheric jet stream over Europe, according to Marilena Oltmanns at the National Oceanography Centre in Southampton, UK.

“2018 and 2022 were the most recent examples,” she says. In 2022, there was extreme heat and many wildfires across Europe, with parts of the UK hitting 40°C (104°F) for the first time.

These feedback effects mean Europe is going to get even hotter and drier in coming decades as the melting of Greenland’s ice sheet accelerates, in addition to the underlying warming trend due to fossil fuel emissions, says Oltmanns.

“This occurs on top of the warming that we already have because of increased greenhouse gases,” she says.

Although hotter heatwaves and drier droughts are expected as the planet warms, in some regions such as Europe, recent heatwaves and droughts have been even more extreme than climate models projected. Several studies have linked these extremes to the changes in the strength and position of the northern polar jet stream, a belt of high-level winds whose position and strength have a big influence on the weather.

 

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But it hasn’t been clear what is causing these changes, says Oltmanns. Now she and her colleagues have analysed weather observations over the past 40 years, which they say show that the weather extremes are ultimately a result of periods of increased melting of Greenland ice.

“The statistical links based on the observations are very robust,” she says.

The extra meltwater leads to a shallow layer of freshwater spreading south in the North Atlantic Ocean. Because this layer is less likely to mix with the warmer, saltier water below, in winter the sea surface becomes colder than usual.

This leads to a more extreme gradient between this cold water and the warmer waters further south, which strengthens the weather front above. That in turn strengthens wind patterns, which push warm water flowing north – the North Atlantic current – even further north than usual. This amplifies the temperature gradient even further.

“These fronts that get created between the regions where we have cold freshwater and regions where we have warmer ocean water are the main energy source for storms,” she says.

In a 2020 study, Oltmanns suggested that this process is leading to increased storminess during some winters.

Now Oltmanns’s team is suggesting that these winter changes have lasting effects in the following summers. “We still see significant signals two years after the freshwater anomaly has occurred,” she says.

The stronger temperature gradient leads to a stronger jet stream across Europe, leading to hotter and drier weather in southern Europe, the team found. Then, as the abnormally cold water recedes, the jet stream shifts north, bringing hot, dry weather to northern Europe.

“Individual links in this feedback chain have been discussed before,” says Oltmanns. “What we have done in this study is put these links together.”

This chain of feedbacks has been missed in computer models because they don’t include factors such as the big variation in meltwater from year to year, she says.

“The proposed link in this study between Atlantic freshwater anomalies and subsequent summer weather over Europe is intriguing and relevant to current scientific research on long-range prediction of summer weather, particularly if the relationship holds in future summers,” says Adam Scaife at the UK Met Office, the country’s national weather service, who works on long-range forecasting.

“I think the study is somewhat convincing,” says Fei Luo at the Centre for Climate Research Singapore. But looking at meltwater in the previous year won’t be as good as looking at winter weather conditions when it comes to forecasting summer weather, says Luo.

 

Vikings left Greenland after growing ice sheet caused sea level rise

The increasing mass of the Greenland ice sheet caused local sea level to rise more than 3 metres after Vikings colonised Greenland, flooding many settlements and contributing to their abandonment of the place

 

Oltmanns, however, is confident enough to predict that, because of increased melting of Greenland ice during the summer of 2023, Europe is in for more heatwaves and droughts in the coming years. “I think this summer we’ll have strong heat anomalies over southern Europe,” she says.

These could be even stronger in 2025, and will then start to affect northern Europe. “We estimate that we will have another strong heatwave and drought not this year in northern Europe but in the coming years.”

 

Journal reference

Weather and Climate Dynamics DOI: 10.5194/wcd-5-109-2024

 

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[SteamyTea]

Quantum quirk explains why carbon dioxide causes global warming

A phenomenon called the Fermi resonance, which affects how molecules vibrate, is responsible for a large part of carbon dioxide’s planet-warming effect

By Alex Wilkins

13 February 2024

 

 

 

Carbon dioxide emissions are warming the planet

Rupert Oberhauser / Alamy

 

Carbon dioxide is uniquely suited to cause global warming because of a coincidental quirk of quantum mechanics.

Global warming is largely caused by carbon dioxide and other gases absorbing infrared radiation, trapping heat in Earth’s atmosphere – known as the greenhouse effect.

The most accurate climate models use precise measurements of the amount of radiation CO₂ can absorb to calculate how much heat will be trapped in the atmosphere. These models are excellent at predicting future changes in Earth’s climate, but they don’t provide a physical explanation for why this gas can absorb so much radiation, which can make their predictions difficult to explain.

Robin Wordsworth at Harvard University and his colleagues have now shown how CO₂’s heat-trapping properties can be explained in terms of quantum mechanical effects, in particular a phenomenon called the Fermi resonance.

“Rather than just a narrow range of radiation getting absorbed, as you would naively expect, it becomes much broader,” says Wordsworth. “It’s this broadening which is really critical to understanding why carbon dioxide is an important greenhouse gas.”

The Fermi resonance describes how the different directions and patterns in which molecules vibrate can influence each other and make them vibrate more. This is similar to how two pendulums, connected by a shared string, can increase the amplitude of each other’s swinging.

A molecule of CO₂ consists of two oxygen atoms bonded to one carbon atom. Two of the molecule’s vibrations influence each other to make it absorb more light: a side-to-side stretching of the oxygen atoms, and a sidewinder snake-like zigzagging of these atoms.

Wordsworth and his colleagues came up with equations to describe how much radiation CO₂ can absorb based on its physical properties, with and without the Fermi resonance. They found that its light-absorbing features and its warming effect on Earth’s atmosphere could only be reproduced when the resonance was included.

The Fermi resonance was responsible for nearly half of the total warming effect. “Even things that are happening on the scale of our planet are determined, ultimately, by what’s going on at the micro scale,” says Wordsworth.

While it was already known that CO₂ had a particularly large Fermi resonance, having an equation that links this to the greenhouse effect could be useful for quick calculations without running a full climate model, says Jonathan Tennyson at University College London. This could also help physicists model the climate of exoplanets, which can require large amounts of computing power to fully simulate.

Something that Wordsworth and his team couldn’t explain is why CO₂ vibrates in such a unique way – a question that might never be answered without a theory of everything. “There doesn’t seem to be a clear reason why this resonance occurs in CO₂,” says Wordsworth. “One could imagine a different universe where it was slightly different, and carbon dioxide might not have the same effects.”

 

Reference:

arXiv DOI: 10.48550/arXiv.2401.15177