Marvellous madness?

The team braving temperatures of -45C in the Arctic CircleAn imaginary line drawn around the most northern part of the world. It is one of the two very cold areas of the Earth near the poles. are short of support. "The vast majority of polar scientists think this is never going to work out," says University of Exeter glaciologist Professor Martin Siegert.

"It is quite insane in my opinion," says polar climate scientist Professor Julienne Stroeve, from the University of Colorado Boulder. According to environmental lawyer Lili Fuhr¹, from Germany's Centre for International Environmental Law, geoengineeringDeliberate attempts to intervene in the Earth's natural processes to counteract climate change on a large scale. comes "with enormous uncertainties" and creates "novel risks for ecosystems and people".

The three are criticising a project by Cambridge University's Centre for Climate Repair. Its aim is to thicken Arctic sea ice enough to stop it melting, and perhaps even reverse that process.

The project is a form of geoengineering - an attempt to alter Earth's climate system to compensate for the damage caused by human activity.

It involves drilling a hole in the ice and pumping 1,000 litres of water per minute from the sea on to the surface. There the water freezes rapidly and in so doing thickens the ice.

"The idea is that the thicker the ice is [at the end of winter], the longer it will survive when we go into the melt season," says one of the team, Andrea Ceccolini. In the small area where the Cambridge team is working, the ice, it claims, has increased in depth by more than 30cm.

To do this for just 10% of the Arctic, however, would require 10 million wind-powered pumps. And even the team leader Dr Shaun Fitzgerald says he is not sure the idea is a good one.

His critics warn that geoengineering could have unpredictable consequences and do far more harm than good. According to Professor Siegert, "people with vested interests will use it as an excuse to keep burning fossil fuels". Some experts want geoengineering banned altogether.

But its advocates are undeterred. Here are some other ideas being explored:

Beneficial beads Spreading a thin layer of tiny glass beads across the Arctic ice to reflect the sun's rays and prevent it from melting.

Guarding glaciers Building underwater walls to protect glaciers from warmer water. However, protecting the Greenland ice sheet would require a wall 107m high and almost 5km long.²

Paint power Scientists have come up with a new type of white paint which reflects 98.1% of sunlight.³ They say that it could cool streets and save energy use in buildings by ending the need for air conditioning.

Softening sunlight Releasing tiny particles into the atmosphere which reflect the sun's light might also reduce global warming. Some scientist favour calcium carbonate particles while others favour sulphur. An even more ambitious idea is to send particles or mini-spacecraft with reflective umbrellas into orbit around the Earth.

Fabricating forests A professor at Arizona State University has designed a 10m-high "mechanical tree". The steel structure contains filters to take carbon from the atmosphere. He hopes to create "tree farms" which will capture as much as 1,000 tonnes of carbon a day.

Encouraging algae Pipes in the ocean could bring nutrient-rich water from the sea floor to feed algaeA simple plant that grows in or on water. on the surface. These would absorb carbon from the atmosphere and then sink with it to the sea bed.

Do we need more crazy ideas?

Yes: We have no choice. Global warming is increasing, extreme weather is becoming more frequent and governments are not doing nearly enough to fight it. We need radical solutions to make a difference.

No: Trying to tamper with the environment in this way is incredibly dangerous and could make the situation much worse. Even the people suggesting these ideas are far from certain about the outcome.

Or...  We need internationally agreed regulations to govern these or any other attempts at geoengineering. Since they could affect the entire planet, every country should have the power to veto them.