The British government is expected to approve new experiments in the coming weeks aimed at dimming sunlight as a potential solution to curb global warming — despite the fact that England averages just 58 sunny days a year. 

The field trials, which may involve techniques like injecting aerosols into the atmosphere or brightening clouds to reflect sunlight — perhaps using sulphur dioxide, a major contributor to acid rain–are being explored as part of geoengineering strategies to prevent climate change. 

For America, such geoengineering experiments are not likely to move forward any time soon. “The first few months of 2025 saw a sharp rise in the number of US states considering proposals to ban solar geoengineering,” one climate group wrote. Some 22 states have moved to ban the very experiments the U.K. is proposing. 

In April 2024, Tennessee became the first state to “prohibit the intentional injection, release, or dispersion, by any means, of chemicals, chemical compounds, substances, or apparatus within the borders of this state into the atmosphere with the express purpose of affecting temperature, weather, or the intensity of the sunlight.”

Earlier this week, Lee Zeldin, the administrator of the Environmental Protection Agency, demanded that information from a U.S. company called “Make Sunsets,”  which sells “cooling credits” in return for releasing sulphur dioxide from latex balloons into the stratosphere.

“The idea that individuals, supported by venture capitalists, are putting criteria air pollutants into the air to sell ‘cooling’ credits shows how climate extremism has overtaken common sense,”  Mr. Zeldin said in a press release. “Based on Make Sunsets’ responses to our information request, we will look into all our authorities to ensure that we continue maintaining clean air for all Americans.”

Back in the U.K., the Advanced Research and Invention Agency, the government’s funding body for cutting-edge scientific projects, has allocated $66 million to support the initiatives. The agency is expected to announce its selected projects soon.  

“We will be announcing who we have given funding to in a few weeks, and when we do so, we will be making clear when any outdoor experiments might be taking place,” Mark Symes, program director for ARIA, told The Telegraph.

He emphasized that the experiments would be safe and conducted with strict controls. “Everything we do is going to be safe by design. We’re absolutely committed to responsible research, including responsible outdoor research. We have strong requirements around the length of time experiments can run for and their reversibility, and we won’t be funding the release of any toxic substances into the environment,” Mr. Symes said.

Geoengineering, which involves artificial manipulation of the climate, has long been a controversial topic. Critics argue that such interventions could have unforeseen and harmful consequences and distract from efforts to reduce carbon emissions.  

Sunlight Reflection Methods are emerging as a prominent area of geoengineering research. These methods include Stratospheric Aerosol Injection, in which tiny particles are released into the stratosphere to bounce sunlight back into space, and Marine Cloud Brightening, which involves spraying sea-salt particles into the atmosphere to make clouds more reflective.  

Evidence supporting sunlight reflection methods comes from natural phenomena and past human activities. “If you inject small particles into clouds, you can brighten them, hence reflecting more sunlight back out to space,” Jim Haywood, a professor of Atmospheric Science at the University of Exeter, said, The Telegraph reported.

Mr. Haywood pointed to two key examples. Ship emissions, which release pollutants into the atmosphere, have been observed to create brighter clouds along shipping routes. Similarly, the 2014 volcanic eruption in Iceland released large amounts of sulfur dioxide, which increased cloud brightness and temporarily cooled the planet. 

“What we need to do is some form of field experiments,” Mr. Haywood said.  

Other geoengineering ideas include modifying cirrus clouds, high-altitude clouds that trap heat in the atmosphere. By thinning these clouds through seeding techniques, more heat could escape into space.  

If successful, these early experiments could pave the way for large-scale implementation within the next decade. Alongside open-field tests, ARIA will also invest in computer modeling, indoor trials, climate monitoring, and public perception studies to ensure comprehensive research.  

While the debate over geoengineering continues, experts agree that further data from real-world trials is essential. “One of the missing pieces in this debate was physical data from the real world,” Mr. Symes said. “Models can only tell us so much.”  

Geoengineering can be risky. A 2018 study from Rutgers University in New Jersey found that suddenly ending a project could have severe impacts on Earth’s climate. “Rapid warming after stopping geoengineering would be a huge threat to the natural environment and biodiversity,” study coauthor professor Alan Robock said.

“If geoengineering ever stopped abruptly, it would be devastating, so you would have to be sure that it could be stopped gradually, and it is easy to think of scenarios that would prevent that. Imagine large droughts or floods around the world that could be blamed on geoengineering, and demands that it stop. Can we ever risk that?” the professor said.

Other efforts to cool the planet are underway, including a trial program to vacuum carbon dioxide out of the air with huge fans, “ocean fertilization,” a process that adds key plant nutrients to the upper ocean to spur growth, and planting trees in denuded areas.