A s global heating escalates, the US government has set out a plan to further study the controversial and seemingly sci-fi idea of redirecting the sun's rays before they hit Earth. A growing group of scientists don't like the idea of solar engineering.

The White House wants to conduct research into climate interventions over the next five years. Sending a phalanx of planes to spray reflective particles into the upper reaches of the atmosphere is one method of blocking incoming sunlight.

The work needs to be done by congress. It is not new research but a report that highlights some of the key knowledge gaps and recommendations of priority topics for relevant research.

Several American researchers, somewhat reluctantly, want to explore options to tinker with the climate system to help restrain runaway global heating, even as they acknowledge many of the knock on risks aren't fully known Chris Field, who chaired a National Academies of Sciences report last year that recommended at least $100 million be spent researching the issue, said that until recently he thought it was too risky.

There are still a lot of concerns and I don't think we should deploy it yet. Climate change is costing lives and hurting the economy. We are in a tough situation and need to know more.

Diagram showing three potential solar geoengineering methods.

There have been previous attempts to run experiments for solar radiation management. Last year, an exploratory flight in Sweden of a high- altitude balloon, led by Harvard University researchers, was stopped after objections by environmentalists and Indigenous leaders.

At least one US startup is trying to improve the efficiency of the sun.

Make Sunsets was launched in October. It claims to have run two internal test flights for its plan to inject sulphur through balloons into the sky.

The venture, named after the deep red sunsets that would occur if particles were seeding into the sky, says itsshiny clouds will prevent catastrophic global warming and help save millions of lives. It says on its website that any human-caused release of carbon dioxide isgeoengineering. We messed up the atmosphere and now have a moral obligation to fix it.

Make Sunsets claims that it can return the world to its pre-industrial temperature for $50 billion a year. He says that most researchers don't want to deploy a last-ditch option.

The risks in researching solargeoengineering have been overblown, and the US is probably the boldest leader on this. If we have a research program, it would be a huge step forward.

The likelihood that a nation will make a serious effort on solar engineering over the next 30 years is about 90 percent. It is likely that some major nation will consider its citizens to be suffering climate harms that are intolerable as impacts get worse.

The prospect horrifies opponents of solargeoengineering Growing calls for research in this area are a cause for alarm due to an unknown set of ramifications that will have different consequences in different parts of the world.

Frank Biermann, an expert in global governance at Utrecht University, said that he is disturbed by the idea that governments will ease off efforts to cut emissions and fossil fuel companies will use it as cover to continue business as usual. If the world is to avoid dangerous levels of global heating, planet-heating emissions need to be halved this decade.

This debate threatens to derail current climate policies. It’s a huge risk.
Frank Biermann, global governance expert

Biermann believes the US is an outlier because of its large per-capita emissions and inconsistent adherence to global agreements.

Everyone who is dependent on coal, oil and gas will jump on the solar engineering bandwagon and say, 'we can continue for 40 years with fossil fuels' now. Climate policies are at risk of being derailed by this debate. It's a big risk.

Biermann likes to compare research on blocking sunlight to the movie Don't Look Up, in which researchers who warn of a catastrophic incoming meteoroid are overlooked in favor of an outrageous plan to deal with it. He said that it was the only way to find out if it worked.

Is it possible that 8 billion people will sit in their living rooms waiting for their last meal and hope that elite western universities get it right, that the Americans won't mess it up?

White cumulus fluffy clouds in the sky.

The WTO head says climate engineering needs to be regulated.

There is no international governance around solargeoengineering at the moment. Critics worry that if one part of the world benefits from the change in the climate, another may suffer from the same problem.

Any disruption, either intentional or otherwise, would cause a sort of "termination shock", where bottled up warming would be unleashed.

Lili Fuhr is a Climate and Energy expert at the Center for International Environmental Law. The systems that sustain life on Earth are at stake. Imagine if India and Pakistan disagreed over whether or not to weaponize it.

This doesn't turn bad ideas into good ones and we need to do more than just emissions cuts.

The UN secretary general, António Guterres, at the UN biodiversity conference (Cop15) youth summit in Montreal, Canada, earlier this month

The UN head says the climate goal of 1.5C is breathing a sigh of relief.

Recalibrating the world's climate to deal with heat-trapping emissions isn't new. In 1965, a group of scientific advisers to Lyndon Johnson warned him about the dangers of global warming.

As countries continue to dawdler over emissions cuts and as an internationally agreed limit of 1.5C of global warming looms into view, calls for intervention have grown.

To make clouds more reflective of sunlight, for example, or to place ice particles in high-altitude clouds to stop them trapping so much of the heat that bounces off Earth, are some of the methods proposed.

The most high-profile method is firing a reflective substance such as sulphur or chalk dust from nozzles into the sky, where the particles would then circulate around the world. The professor of applied physics and of public policy at Harvard believes that injecting 2 million tons of sulphur a year into a fleet of 100 high-flying aircraft would cool the planet by 1C.

It would cost billions of dollars a year and provide a quick drop in temperatures. Various carbon capture technologies can take a long time and involve a lot of infrastructure. The idea that climate change can be solved with emissions cuts alone is dangerous.

We have lost so many easy paths to limit the harms of climate change that we only face worse options.
David Keith, professor of applied physics and of public policy at Harvard University

The basic physics of doing this is well understood, likening it to the eruption of Mount Pinatubo in the Philippines in 1991, an event that caused global temperatures to drop by about half a degree.

There have been studies that show that it can be done and that most people didn't notice. We don't know how it should be done, and the environmental aspects and governance are concerns. We have lost so many easy paths to limit the harms of climate change that it would be foolish to just deploy this now.

Some people think that spraying sulphur into the sky could deplete the ozone layer and make the sky white.

One recent novel based on the topic, The Ministry for the Future by Kim Stanley Robinson, depicted India embarking upon solar geoengineering to save itself from deadly heatwaves while another, Termination Shock, had India.

The debate over how much we should interfere with the climate is likely to intensify as the climate gets hotter. They won't back down. Biermann thinks that solargeoengineering should be considered a banned weapon by governments.

He said this was one of the ones on the list. You don't have the freedom to sit in your back yard and make a chemical bomb if you want to.