Sheer lunacy?

"Moonteam One to control," says the space captain, looking up from the Moon's surface. "We are firing now." Taking a deep breath, he presses the button. The ground shakes as thousands of tons of moondust hurtle towards the Sun.

This is the scene imagined by three astrophysicistsThe branch of astronomy looking at the physical laws of space. at Harvard University. It is a type of geoengineering, which means changing the Earth's natural systems to combat climate change.

The plan is to mine millions of tons of dust from the Moon and fire them into space. There they would deflect the Sun's rays, lowering the Earth's temperature.

It would be a major project, possibly involving a new space station which would help spread the dust.

The firing would need to happen on a regular basis to maintain the dust cloud. If the cloud suddenly dispersed, the Earth could heat up again rapidly.

But there is a lot of opposition to all plans like this. "I would say the majority of scientists believe this is a crazy idea for a variety of reasons," says Frank Biermann, a professor at UtrechtA city in the Netherlands. University.

One worry is that it would get in the way of efforts to reduce carbon emissions. People who want to carry on using coal, oil and gas might say, "It is OK to stick with fossil fuelsFuels made from decomposing plants and animals, including coal, natural gas and oil. These fuels release carbon dioxide, causing global warming. because moondust will solve the problem of climate change."

An open letter signed by over 380 scientists calls for solar geoengineering to be banned.

The scientists argue that no one can be sure what the effect of plans like Bromley's might be: "There are uncertainties about the effects on weather patterns, agriculture and the provision of basic needs of food and water."

They also worry about governments going ahead without other countries' agreement. If this resulted in some parts of the world benefiting while others suffered, it could even lead to wars.

Yes: There are too many variables. The dust cloud could end up in the wrong place and be completely ineffective. Or it could be much more effective than anticipated, with catastrophic consequences.

No: With governments dragging their feet over reducing emissions, a radical alternative is needed. Even if solar geoengineering did not solve the problem completely, it would buy us vital extra time.

Or... A better solution would be to inject sulphur into the Earth's atmosphere to reflect the Sun's rays. Professor David Keith of Harvard University estimates that this could cool the planet by 1C.