With the world set to blow past 1.5°C of warming, researchers are increasingly studying possible methods of cooling the planet by modifying the atmosphere or the oceans. More geoengineering research is planned in 2025, such as projects aiming to make clouds reflect more sunlight and efforts to remove carbon dioxide from the atmosphere by tweaking ocean chemistry.
Such tests have long been controversial. Opponents of research on geoengineering – itself a loaded term – see it as a from pressing efforts to slash greenhouse gas emissions, and fear unintended consequences of large-scale interventions in the planet’s climate. They view research on geoengineering to be on a slippery slope towards actual deployment.
Until recently, this made geoengineering a taboo subject to study using computer models or in the lab, let alone to test in the field. But escalating climate impacts and the fact that emissions cuts aren’t on track to avoid dangerous levels of warming have increasingly opened the door to research on the efficacy and consequences of geoengineering as a way to reduce climate risks and buy time to cut emissions.
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“It’s becoming less and less defensible to argue that we shouldn’t talk about this in case we affect people’s willingness to mitigate [emissions],” says at Cornell University in New York, who leads a project to model the climate effects of geoengineering. “That train seems to have left the station.”
In October, for instance, the American Geophysical Union released a on how to ethically conduct research on what it calls climate intervention, citing “rapidly growing interest” in such research. Dozens of studies were published this year modelling the climate effects of different methods of reflecting more sunlight away from the planet, for instance by releasing aerosols into the stratosphere. In December, the Intergovernmental Panel on Climate Change whether to include such interventions in its influential climate assessments.
This year also saw some small-scale field tests of what is sometimes called solar radiation management. For instance, researchers at the University of Washington in Seattle briefly tested spraying salt into the air in the San Francisco Bay to brighten marine clouds and thus reflect more sunlight, but the project was halted by the local government.
A provocative start-up called Make Sunsets has also been launching weather balloons that release small amounts of reflective sulphur dioxide into the stratosphere since 2022. The company this has now offset the warming effect of more than 80,000 tonnes of CO2 and it has sold “cooling credits” on this basis, although there is no direct way of measuring the potential cooling effects.
2025 will see even more research and tests, no doubt with their own battles. In May, Cape Town in South Africa will host what is billed as the largest ever conference focused exclusively on solar geoengineering, with a particular focus on research from lower-income countries. “If SRM works well to reduce climate risks, it is climate-vulnerable countries of the Global South that have the most to gain. If it goes wrong, it’s these countries that will be most harmed,” says at the Degrees Initiative, the non-profit organising the conference.
The UK’s Advanced Research and Invention Agency is also expected to announce next year the first recipients of more than £50 million in funding for a programme called , which may include “small, controlled, outdoor experiments”. Separately, a UK company called Real Ice is developing ways to thicken sea ice by pumping water over the top of it. At large scales, more ice would also reflect more sunlight away from Earth.
Storing carbon in the oceans
A wide array of methods of removing CO2 from the atmosphere, which some consider to be a form of geoengineering, have also seen a flurry of activity, although their effect on the climate remains negligible. The most hotly contested ideas involve altering marine ecosystems or tweaking ocean chemistry to accelerate the natural removal of CO2 by the sea.
One approach in particular known as ocean alkalinity enhancement (OAE) has seen a surge of interest, with researchers and companies around the world testing various ways of making seawater more alkaline so it will take up more CO2. For instance, a start-up called Planetary Technologies, which adds alkaline minerals to wastewater streams, ran tests in Halifax, Canada, and Chesapeake Bay, US, in 2024. Next year, it aims to restart efforts in Cornwall, UK, where an earlier test ended after sustained protests.
What would have been among the first tests of OAE in open water was planned to happen off the coast of Cape Cod, Massachusetts, in 2024. But the experiment – known as the LOC-NESS Project – was delayed till next year after researchers at the Woods Hole Oceanographic Institution in Massachusetts were unable to secure the necessary permits from regulators in time.
The many submitted to the US Environmental Protection Agency about that proposed experiment capture the ongoing debate about geoengineering: some were strongly in support of it, given the urgency of addressing climate change; others were strongly opposed for the same reason. One said simply: “Stop messing with mother earth. Thanks.”
