Sweltering heatwaves can have lasting health impacts – accumulated exposure to hot-weather days appears to accelerate people’s biological ageing.

“We now have at least two prominent studies showing an impact of heatwave exposure on ageing, with these examining populations from two different countries,” says at Macquarie University in Australia. “We all need to take heatwaves seriously – not only looking after our own health but also that of others in our communities.”

The newest research comes from at The University of Hong Kong and her colleagues. First, the researchers used medical screening data from nearly 25,000 adults in Taiwan to determine the biological age of each person based on factors such as inflammation, blood pressure and organ functions. Next, they compared each individual’s biological age with their chronological age, to figure out if they were ageing faster or slower than normal.

“The physiological changes in the body associated with ageing can appear earlier and progress faster in some people than in others,” says Beggs, who was not involved in the research.

The team then calculated each person’s cumulative exposure to heatwaves – including the total number of heatwaves they lived through and the sum of temperatures across these periods – two years prior to their medical screening. The total number of heatwave days experienced ended up being the most significant factor for accelerated ageing in this Taiwanese population. The results aligned with another that investigated outdoor heat’s impact on ageing in older US adults.

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For the Taiwanese group, the ageing effect generally increased as the amount of cumulative heatwave exposure did. Each four-day increase in total heatwave duration was associated with a biological age increase equivalent to about nine days.

But the effect was even more pronounced for specific groups of people. For instance, manual workers experienced around three times as much accelerated ageing from the same amount of heat exposure compared to the group as a whole. Residents of rural communities also experienced greater ageing impacts, indicating access to air conditioners might be able to stave off heat’s ageing effects, the researchers say.

To avoid making climate change and heatwaves worse, however, the protective benefits of air conditioning will need to be complemented by more sustainable cooling solutions, says Beggs. “Air conditioners also directly add to the heat outdoors, making conditions for those without air conditioners even worse than they would have been,” he says.

Fingernail-size discs that levitate in sunlight could someday carry sensors through some of the thinnest and coldest reaches of the atmosphere. By flying higher than commercial aircraft or weather balloons can, such swarms could reveal new insights about Earth’s changing weather and climate patterns.

The levitating devices harness a phenomenon called photophoresis. It was first discovered more than 150 years ago when chemist William Crookes invented the radiometer, a device with black and white vanes that spin when exposed to sunlight. This happens because the vanes absorb the light and give off heat, and this heat boosts the momentum of gas molecules around them. Because the black sides of the vanes are hotter than the white ones, they transfer more momentum to the gas, making the air flow in one direction with enough force to turn the vanes.

“We’ve taken this obscure piece of physics and applied it to something that could actually impact a lot of people – and help us better understand how things like weather and climate are evolving over time,” says at Harvard University.

To develop the levitating discs, Schafer and his colleagues created a 1-centimetre-wide device made of two aluminium oxide sheets full of micro-scale holes. When exposed to light, the bottom sheet – which included alternating layers of chromium with the aluminium oxide – heated up more than the top sheet, like the black sides of a radiometer’s vanes. This also created a directional airflow, but moving upward instead of sideways.

Under white LEDs and laser light – set to intensities equivalent to about 50 per cent of natural sunlight – this lifting force levitated the device. That is an improvement on other solar-powered fliers, which require light intensities several times brighter than sunlight. But the demonstration also took place in laboratory conditions with air pressure several thousand times weaker than that at Earth’s surface.

Fortunately, those low air pressure conditions are common elsewhere – like the mesosphere, an upper layer of the atmosphere that extends 50 to 85 kilometres above the planet. The researchers say scaling up their discs to 3 centimetres would let them carry 10 milligrams of payload at an altitude of 75 kilometres, bringing sensors to a region so difficult to study it has been nicknamed the “ignorosphere”. Schafer co-founded the startup Rarefied Technologies to commercialise swarms of such high-flying devices for atmospheric monitoring and telecommunications.

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After the sun sets, computer modelling suggests the discs could stay airborne by harnessing heat radiating from Earth’s surface. “If you can stay aloft at night, that’s a big change from just settling or falling,” says at the University of Pennsylvania, whose lab is doing similar research.

An iron-air battery that stores and releases energy through a reversible rusting process has become the first of its kind to connect with a public electricity grid. On 30 July, the Dutch start-up Ore Energy announced its batteries had connected to the grid at Delft University of Technology in the Netherlands.

Batteries can help deliver a consistent supply of electricity by storing renewable energy from solar or wind farms, releasing it when necessary to ensure that a sudden change in sunlight or wind doesn’t mean an immediate drop in available electricity.

“You need to be able to store that excess energy when the wind is blowing and the sun is shining, to be able to deploy it when you need to during critical demand periods during the day,” says at The Faraday Institution, a battery research body in the UK. “Essentially, batteries can help to smooth out that power output to make it usable on the grid.”

Many grid-connected batteries are now lithium iron phosphate ones manufactured in China. But they typically hold power for just 4 to 6 hours and are prohibitively expensive, says Marie. In contrast, the iron-air batteries developed by Ore Energy can store power for 100 hours or longer and are made from cheap and widely available materials.

“Iron is the most mined metal in the world, it’s incredibly cheap,” says Marie. “And when you combine that with air, which is literally all around us and basically free, those are almost the two cheapest components that you could find.”

The system charges and stores energy by using electricity to convert iron oxides – a form of rust – into metallic iron. The iron can then discharge or release its stored energy by chemically reacting with oxygen from the air to form rust again.

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“When the battery is discharging, we are actually taking the iron and turning it into a special type of rust,” says , CEO of Ore Energy. “And when we are charging the battery, we are taking the rust back into iron, and we do this over and over again [while] the battery is breathing in and out the oxygen from atmospheric air.”

The batteries are stored in standard 12-metre shipping containers and can store multiple megawatt-hours of energy – with 1 megawatt-hour being enough to supply more than a month of electricity to a typical US home.

Separately, the Massachusetts-based company Form Energy has several iron-air battery projects in the works in the US. They are slated for installation in New England and the Midwest.

In addition to iron and air, such batteries incorporate water-based electrolytes that are also cheap and abundant – not to mention greatly reducing the risk of battery fires. “I wouldn’t want to be the one to say never, but you can’t set fire to water,” says Marie.

But the main goal of the battery technology is to help renewable power sources replace fossil fuels in electricity grids.

“Energy companies still rely a lot on gas-fired [power] generation to provide the flexibility needed when wind and solar are not sufficient,” says , business development manager at Ore Energy. “But in the long term we will need a different type of flexibility, and that is where our battery really excels – to provide this multi-day flexibility.”