Human life is facing one of the biggest challenges in its history. Rampant climate change, driven by industrial activity, threatens our entire civilisation. The destabilised currents, intensifying heat waves and increasingly frequent storms are a danger to all of us.
The undisputed solution is to reduce our emissions, which may have already passed their peak, although the rate of fall isn’t enough to avert the effects of a changing climate.
Yet there might be another approach to complement our sluggish efforts at emission reduction.
What if, as well as decarbonising our society, we used temporary measures to alter Earth’s climate and prevent some of the worst effects of climate change?
That’s the dream touted by those championing geoengineering, a term that refers to manipulating the environment to counteract human-caused climate change. It’s not a term that has always sat well with scientists.
“Geoengineering has been pretty taboo for a long time,” says Jessica Wan, a climate scientist at the Scripps Institution of Oceanography in the US. “It’s typically been seen as a way to deter mitigation efforts to cut emissions.”
Momentum, however, appears to be shifting.
In May 2025, the UK government’s Advanced Research and Invention Agency (ARIA), designed to fund high-risk and high-reward research, announced £56.8 million (almost $77m) in funding for 21 geoengineering projects over the next five years in a programme called Exploring Climate Cooling.
It followed a handful of other experiments in the US and Australia to investigate whether any geoengineering ideas might be viable.
“It’s important to conduct small-scale research,” says Michael Gerrard, a professor of environmental and energy law at Columbia Law School in the US.
So, what might the future hold and could a large-scale geoengineering project ever become a reality?
Brighter clouds
Various techniques fall under the umbrella of geoengineering. Perhaps the most well-known and least disputed is carbon dioxide removal.
The idea is to remove CO2 directly from the atmosphere to help reduce its impact on global warming. Work to develop such systems is already underway.
“Most climate analysts agree that CO2 removal is absolutely necessary at large scale,” says Gerrard. “There’s no way we can achieve our temperature objectives unless we remove enormous amounts of the CO2 that’s now in the atmosphere, in addition to producing much less of it.”
The projects being funded by ARIA and investigated elsewhere are more experimental. But due to the unease surrounding geoengineering, very little research has been carried out.
There is, however, increasing demand for cautious, small-scale experiments to explore these techniques.
Undertaking research like this, transparently and openly, and releasing the findings could prevent any countries or companies attempting to try a technique themselves, without knowing what the effects could be.
“There’s a need for a responsible actor to operate objectively, and in the public good in this space,” says Prof Mark Symes at the University of Glasgow in the UK, who leads ARIA’s Exploring Climate Cooling programme.
One technique is called marine cloud brightening (MCB).
As temperatures on Earth increase due to climate change, they pose a major problem to the oceans, in particular coral reefs.
Hotter temperatures and overexposure to sunlight can trigger coral bleaching, where the coral expels the algae it needs for food and becomes transparent, risking disease and starvation.
There are entire ocean ecosystems that rely on coral reefs to survive, so it can have devastating knock-on effects.
The effects of bleaching could be lessened with MCB. By brightening clouds above coral reefs during periods of hot weather, more sunlight could be reflected back into space, protecting the coral below.
Dr Daniel Harrison, an oceanographer at Southern Cross University in Australia, is currently investigating the technique.
His experiment, which has received funding from the Australian government as well as ARIA, is looking at whether fans could be used to spray seawater over the Great Barrier Reef.
As the seawater is expelled, the salt crystals in the water rise into the clouds and form tiny droplets. The more such droplets are added to the clouds, the better they reflect sunlight.
“Fundamentally, we’re trying to add extra cloud droplets by using sea salt,” says Harrison. The fan his team has developed takes in seawater and air, compresses them together and blows them out. “A single fan produces 1,000 trillion droplets per second,” says Harrison.
No one else has tried this before. “We’re the first,” says Harrison. “Somebody’s got to be first.”
Harrison and his team have built the technology and are working with the Great Barrier Reef Marine Park Authority to conduct an experiment over a section of the reef.
Modelling suggests that alongside a reduction in emissions, “it’s enough to really improve the trajectory of the reef into the future.”
Without that reduction, “you see a benefit for a couple of decades and then it’s overwhelmed by climate change,” even with MCB, Harrison says.
Another idea, investigated by Wan, could be to use MCB over sections of the ocean, such as the Pacific, to provide a cooling effect on nearby land.
Last year, she studied whether this technique could be used to reduce extreme heat waves in the western US. She found it could reduce the risk of heat exposure by up to 55 per cent in current conditions, although the effect is lessened or even reversed if the planet continues warming.
“You cool the air, and the winds and ocean currents transport the cooler air towards land,” says Wan. “The cooler air will eventually displace other air masses and then you get effects that are more on the interior of continents as well, not just the coastal regions.”
The side-effects of such a technique, if any, remain unclear without any small-scale experimental research, however.
The prospect of even considering attempting such a technique at scale remains decades away, though. Not only would there need to be strict governance and regulation, but public perception would be crucial too.
Efforts to conduct small-scale experiments in the past have been controversial. In May 2024, an MCB experiment on an aircraft carrier docked in San Francisco was halted before it began after local opposition.
“If you can’t get public buy-in, there’s no way any of this is ever going to become large-scale,” says Wan. “That’s the challenge.”
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Thicker ice
Another geoengineering technique that could be beneficial is sea ice thickening.
Arctic sea ice loss is a major effect of climate change. According to NASA, Arctic sea ice is shrinking at a rate of 12.2 per cent per decade. By 2040, it’s estimated that the Arctic could be completely devoid of ice during the summer months.
The knock-on effects could be dramatic, including rising sea levels, a weaker jet stream that could disrupt weather patterns, and changing ocean circulations. There are concerns that there could be a tipping point at which the changes are irreversible, even if we reduce emissions.
“You can imagine cascades of tipping points where ice sheets melt, ocean circulations change and forests die back,” says Symes. “It’s critical that we pay more attention to these tipping points.”
Sea ice thickening could be one solution. Dr Shaun Fitzgerald, a climate scientist at the University of Cambridge, is leading a team to pump seawater out from below ice sheets and spread it over their surface, where it refreezes and provides an extra layer of insulation.
His team, with the help of local communities, has already begun small-scale experiments in northern Canada, pumping out about 1,000 litres (approx 250 gallons) of seawater a minute during the previous Arctic winter and thickening the sea ice by tens of centimetres (1–2ft) in a small area.
They’re now studying the area during the Arctic summer to see if the thicker ice persists, versus a control area where no pumping took place.
“It might have grown thicker, but did it actually last longer?” says Fitzgerald. “They’re related, but different questions.”
The goal is for the team to return in the winter and try the experiment again with help from funding by ARIA, and potentially scale it up in future to an area up to a kilometre (just over half a mile) across.
“The big idea is if you can increase the overall extent of sea ice in the Arctic summer, that’ll help with the overall radiation balance,” says Fitzgerald. “We’re seeing an ever-diminishing extent of sea ice, so this is a major concern.”
Atmospheric injection
What might be the most controversial geoengineering idea involves injecting particles into the atmosphere to reflect more sunlight.
Known as Stratospheric Aerosol Injection (SAI), the technique has received considerable opposition, not least because its side effects aren’t fully known.
“Solar-radiation management is extremely controversial,” says Gerrard. “It’s important that we know how it works, how well it works and whether it has negative effects.”
At its core, the idea involves depositing particles of a material, such as sulphur, calcium or even diamond dust, into the stratosphere, the region of the atmosphere that extends from about 6–50km (4–30 miles) above Earth’s surface.
These particles would increase the reflectivity of the stratosphere, reflecting more sunlight into space and cooling the planet.
The idea is similar to how volcanic eruptions have cooled Earth in the past, spewing large amounts of sulphur dioxide into the atmosphere. The 1991 eruption of Mount Pinatubo in the Philippines, for example, is estimated to have cooled the planet by half a degree the following year.
No SAI experiment has ever been conducted, although there have been attempts. One project funded by ARIA will perform a SAI experiment, of sorts, using weather balloons to loft equipment into the stratosphere to examine how different materials age in the stratosphere.
Nothing will be released into the stratosphere as part of the experiment. Instead, a tray containing samples will be exposed and the effects of the stratosphere on the samples will be studied on the ground.
“[The samples are] out sitting in the stratosphere where they’re subjected to UV, light, ozone and all the other harsh conditions that are up there,” says Symes. “That’ll give an idea of not only how they might behave in the stratosphere, but also what the impacts might be if they were ever used at scale.”
SAI, if employed on a large scale, could provide a temporary cooling effect either to particular regions or the entire globe. Aircraft could deposit aerosols into the atmosphere over months, which would mix across the entire stratosphere in a couple of years.
The aerosols would eventually fall out of the atmosphere if not replenished, but could be a temporary measure to provide a cooling effect on the ground.
“There’s significant evidence that some of these sunlight reflection methods could reduce climate change substantially, reducing human impacts for the most vulnerable,” says Prof David Keith, a climate scientist at the University of Chicago in the US.
Public perception of proposals like this remains a sticking point, but some surveys have shown that people would support research into SAI.
“The really big picture is that things are changing very quickly on this topic,” says Keith, with endeavours such as ARIA now taking tentative steps towards understanding SAI in more detail.
Space shades
A more far-fetched geoengineering idea would take place in space. Using large shades or mirrors, it might be possible to reflect some sunlight before it reaches Earth, providing a cooling effect for certain parts of the planet.
No experiment to attempt this idea is underway, although ARIA is funding a modelling study from the Planetary Sunshade Foundation in the US to look into the feasibility of it. How, or even if, this technique might work is something “we definitely don’t know,” says Symes.
The idea is that, somewhere between Earth and the Sun, a large shade or series of shades would be deployed, lessening the amount of sunlight reaching the planet.
The amount could be extremely small, so small that there would be no noticeable difference on Earth, but enough to lower temperatures in some parts of the planet.
“We’re talking about removing tiny percentages of incoming sunlight,” says Symes. For the moment, the idea remains extremely speculative. “We might have a better idea after the project has completed the modelling,” says Symes.
Even if such an idea remains a pipe dream, it highlights the growing desire of scientists to see research into geoengineering take place, even if it ultimately amounts to nothing.
The field is “definitely growing,” says Wan, “because there’s this urgency to do something with climate change.”
The overall goal remains to reduce emissions. But if some effects of climate change can’t be averted before we do so, might it be worthwhile to carry out temporary measures that could potentially save millions of lives? At the very least, research into such measures is vital.
There’s also currently little global regulation on geoengineering, meaning that knowing the effects of different techniques is particularly important if any country or company were to attempt one of them. “This is a totally ungoverned area,” says Gerrard.
“A concern I have is that a rogue state, or even a billionaire, could do this on their own and wouldn’t require anybody’s approval.”
We may start to see the first peer-reviewed publications from ARIA’s projects in the next year or two, alongside other work taking place elsewhere.
“We’re trying to be as transparent as we can,” says Symes, “so that people can see these [projects] aren’t scary. They’re really small, they have well-defined aims and they have expert [scientists] who have spent their whole careers researching these phenomena.”
Will geoengineering save the planet? We may find out in the years to come.
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