A quickly cooling Atlantic Ocean could dampen hurricane threats from the Pacific
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Over the past three months, the shift from hot to cool temperatures in the equatorial Atlantic Ocean has happened at record speed. This emerging “Atlantic Niña” pattern comes just ahead of an expected transition to a cooler La Niña in the Pacific Ocean, and these back-to-back events could have ripple effects on weather worldwide.
The swing towards cooler temperatures in both oceans is a welcome change after more than a year of record heat at land and sea,…
After over a year of record-high global sea temperatures, the equatorial Atlantic is cooling off more quickly than ever recorded, which could impact weather around the world
A jacaranda tree outside the Los Angeles courthouse
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Air pollution in Los Angeles from cars and human activity is getting a boost from the city’s plants, some of which emit chemicals in response to rising temperatures and drought.
“Since it’s hard to control the plant emissions, it’s even more important to control the [human-caused] part,” says Eva Pfannerstill at Forschungszentrum Jülich, a research institute in Germany.
From jacaranda trees in bloom to fragrant eucalyptus, many plants emit a class of compounds called terpenoids. For the plants, these act as chemical signals and can serve as antioxidants. But in the atmosphere, such volatile organic compounds (VOCs) react with other pollutants to produce harmful ozone and particulate pollution called PM2.5.
In places where human sources of air pollution have declined thanks to cleaner vehicles and power generation, emissions from plants have come to play a larger role. But how large is unknown.
Pfannerstill and her colleagues measured VOC emissions in Los Angeles by flying a plane above the city over several days in June 2021. The researchers used an on-board mass spectrometer to identify concentrations of more than 400 types of VOCs in the air. Simultaneous 3D measurements of wind speed enabled them to isolate the molecules rising from the city from those blowing in from elsewhere.
The researchers found terpenoids dominated VOC emissions in many parts of the city. This was especially true in places with the most vegetation, and on days with the hottest temperatures. When temperatures breached 30°C (86°F), terpenoids dominated emissions even downtown, where there are fewer plants and more people.
Exactly why plants would emit more terpenoids under hotter temperatures is unclear, but it could be a response to heat or water stress, says Pfannerstill. Probably due to a higher rate of evaporation, hotter temperatures also increased VOC emissions linked to human sources – like gasoline, paint and even scented personal care products such as deodorant and hair spray.
The contribution of these personal care products specifically jumped with population density, suggesting a small but direct link between the city’s smog and its citizens’ beauty routines. “It’s measurable,” says Pfannerstill.
This observed link between heat and emissions also implies a route by which climate change will add to air pollution. In Los Angeles, the effect of VOCs on ozone formation could as much as double with the 3°C of warming projected for the city by the middle of the century, the researchers found. The effect on PM2.5 pollution could increase by 40 per cent.
“Having this direct observation is crucial to building the right models to predict what’s going to happen with air pollution tomorrow or years from now,” says Matthew Coggon at the US National Oceanic and Atmospheric Administration. The rising emissions from plants also underlines the importance of further reductions in the human sources of air pollution that react with the VOCs, such as nitrous oxides from burning fossil fuels, he says.
Which species are planted in cities also has an impact, says Roisin Commane at Columbia University in New York, an important consideration as more cities pursue urban greening programmes. “The vegetation matters,” she says.
A scorching day in Bucharest, Romania in June 2019
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Future city dwellers could beat the heat with clothes made of a new fabric that keeps them cool.
The textile, made of a plastic material and silver nanowires, is designed to stay cool in urban settings by taking advantage of a principle known as radiative cooling – the natural process by which objects radiate heat into space.
The material selectively emits infrared radiation within the narrow band of wavelengths that can escape Earth’s atmosphere. At the same time, it blocks the sun’s radiation and infrared radiation emitted by surrounding structures.
Po-Chun Hsu at the University of Chicago in Illinois and his team designed this material to “try to block more than half of [the radiation] from the buildings and the ground”, he says.
Some cooling fabrics and building materials already rely on this radiative cooling principle, but most of those designs do not account for radiation from the sun or infrared radiation from structures like buildings and pavement. They also assume the material would be oriented horizontally to the sky like panels on a rooftop, rather than the vertical orientation of material in clothes worn by a person.
Those designs work well “when you are facing a cooler object such as the sky or an open field”, says Hsu. “However, that’s rarely the case when you are facing an urban heat island.”
Hsu and his colleagues designed a three-layer textile. The inner layer is made of a common clothing fabric like wool or cotton, and the middle layer consists of silver nanowires that reflect most radiation.
The top layer is made of a plastic material called polymethylpentene, which doesn’t absorb or reflect most wavelengths, but emits a narrow band of infrared radiation.
In outdoor tests, the textile stayed 8.9°C (16°F) cooler than a regular silk fabric and 2.3°C (4.1°F) cooler than a material that emitted radiation across a broad range. When tested on skin, the textile was 1.8°C (3.2°F) cooler than a cotton fabric.
Hsu says this small difference in temperature could theoretically increase the time someone could comfortably be exposed to heat by up to a third, although this hasn’t yet been tested.
“Making this stuff practical as a textile is always difficult,” says Aaswath Raman at the University of California, Los Angeles, adding the work is a good demonstration of translating the physical principle of radiative cooling to a usable material. Other materials with similar properties could also be used on the vertical surfaces of buildings, he says.
Hot temperatures can lead to ozone pollution, which irritates the airways of people with asthma
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Hot weather appears to be triggering more frequent hospital visits for children with asthma.
Symptoms of the lung condition, such as breathlessness and wheezing, are more commonly associated with cold weather. To better understand the impact of hot temperatures, Morgan Ye at the University of California, San Francisco (UCSF), and her colleagues studied electronic health data from UCSF Benioff Children’s Hospitals.
The data included records on asthma hospitalisations and the patients’ addresses. The researchers used information from PRISM Climate Group at Oregon State University to obtain temperature records at the patients’ homes every day from June to September between 2017 and 2020.
The researchers defined heatwaves in 18 different ways. By looking at the range of temperatures that occurred over these periods, they considered it a heatwave if it fell in the top 99 per cent of these temperatures, or the top 97.5 per cent, or the top 95 per cent, and so on.
Presenting their results at the American Thoracic Society conference in San Diego, California, this week, the researchers found that across all of the heatwave definitions, these temperatures were associated with 19 per cent higher odds, on average, of a child with asthma being admitted to hospital, compared with when there wasn’t a heatwave.
While further research is required, hot weather can contribute to smog and ozone pollution, which may inflame or irritate the airways, says Ye.
“As we continue to see global temperatures rise due to human-generated climate change, we can expect a rise in health-related issues as we observe longer, more frequent and severe heatwaves,” she says.
Children are particularly vulnerable to extreme heat, says Stephanie Holm at the UCSF’s Western States Pediatric Environmental Health Specialty Unit. Speaking of the researchers’ approach to defining heatwaves, she says: “The fact that their results were robust to different definitions of extreme heat is powerful.”
Last year’s marine heatwaves saw an unprecedented decline in the growth of phytoplankton and algae, which many animals in the oceans depend on for food
A blazing month-long heatwave has brought drought in Vietnam
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The world has recorded its hottest ever March, extending a streak of global temperature records that began in June 2023.
“March 2024 continues the sequence of climate records toppling for both air temperature and ocean surface temperatures, with the 10th consecutive record-breaking month,” Samantha Burgess at the Copernicus Climate Change Service said in a statement. It is the latest indication that Earth’s climate has entered uncharted territory.
The average surface air temperature was 14.14°C in March, 0.1°C above the previous high set in March 2016 and 1.68°C warmer than in pre-industrial times, Copernicus said in its latest climate bulletin.
Over the past 12 months, global average temperatures have tracked 1.58°C above the 1850 to 1900 average, the period used to represent pre-industrial levels.
Countries have collectively promised to limit the temperature rise to 1.5°C above this pre-industrial average.
One single year above this level won’t represent a breach of this promise, as the target is based on a long-term average. But each record-breaking year makes shooting past this goal ever more likely.
The unprecedented run of high temperatures in 2023 and 2024 has coincided with alarming climate impacts, from severe marine heatwaves to rapid glacier melt and intense tropical cyclones.
Human-caused greenhouse gas emissions are responsible for rising global temperatures. The latest spell of record-breaking warmth is also partly driven by El Niño, a natural weather pattern where sea temperatures in the Pacific Ocean are warmer than usual.
Global rules introduced in 2020 to cut aerosol pollution from ships may also be playing a role. Aerosols enable clouds to reflect more of the sun’s light and heat back out of the atmosphere. Reducing aerosol emissions improves air quality, but increases the amount of warmth entering the atmosphere.
Aerosols may provide short-term cooling benefits, but decarbonising the global economy is the only long-term strategy to halt climate change, scientists stress. “Stopping further warming requires rapid reductions in greenhouse gas emissions,” said Burgess.
Without dramatic action to curb greenhouse emissions, even high-latitude countries with cooler climates will suffer devastating, if indirect, financial losses as extreme heat disrupts global supply chains. The result could be the worst financial crisis the world has ever seen.
It is already well known that severe heatwaves have numerous health and economic impacts, including higher mortality rates, preventing people from working outside, destroying crops and disrupting industrial processes. But until now, little research has been done looking at the financial impact of heatwaves…
