Global warming is changing the Earth's climate so fast that influential scientists fear it is already outrunning our ability to prevent the planet from overheating. John Holdren, US President Barack Obama's chief scientific adviser, is only the latest to suggest radical geo-engineering measures may have to be considered to keep the Earth habitable. 'It's got to be looked at. We don't have the luxury of taking any approach off the table,' he said. He recently compared the crisis with being 'in a car with bad brakes driving towards a cliff in the fog'. Some suggestions for re-engineering the planet have gone way beyond even the imagination of science fiction writers. Among new ideas that are already being investigated: Wrapping Greenland's glaciers in blankets to protect them from the sun's rays. Dropping tens of thousands of seedlings from aircraft to reforest large tracts of land. Spraying micron-sized particles of sea water into the air to make clouds whiter so as to reflect more light. Developing a new wind turbine that will produce energy from winds 300 metres above sea level. Deploying wave-powered pumps in the North Pacific to revive the phytoplankton that convert carbon dioxide into living matter. Diffracting the power of the sun by placing trillions of lenses in space, in effect to create a 250,000 sq km sunshade. Sending thousands of satellites into space to gather the energy of the sun and beam solar energy to Earth as microwave energy, which can be collected by antennae on the ground and converted to electricity; this would aim for a double whammy of cutting carbon emissions and supplying never-ending power. Scrubbing carbon dioxide from the air with a giant 120-metre-high machine that will suck ambient air into one end, spray it with a sodium hydroxide solution and then expel clean air from the other end. Shooting particles into the air, in effect to create an artificial volcano. Creating artificial trees to suck carbon dioxide out of the air. Some scientists would like to go into space to solve the problem of our threatened environment by tinkering with the atmospheres of neighbouring planets such as Mars so as to make them habitable. Mars has very little carbon dioxide and an average temperature of minus 45 degrees Celsius - unlike Venus, which is closer to the sun, has a thick atmosphere containing 96 per cent carbon dioxide and an average temperature of 215 degrees. The Royal Society, Britain's national academy of science, is the world's oldest scientific body and is celebrating its 350th birthday. It is also taking geo-engineering seriously. It recently devoted an issue of its journal Philosophical Transactions to the topic, edited by Brian Launder, professor of mechanical engineering at Manchester University. All this sudden interest in extreme measures is a sign of increasingly desperate times. Only a few years ago, the Intergovernmental Panel on Climate Change dismissed geo-engineering as 'largely speculative and unproven, and with the risk of unknown side effects'. Professor Launder admitted as much. 'It's almost like talking about how we could stop world war two with an atomic bomb when we haven't done the research to develop nuclear fission,' he said. Martin Rees, president of the Royal Society, justified the august body's interest in the topic. 'It's not clear which of these geo-engineering technologies might work, still less what environmental and social impacts they might have, or whether it could ever be prudent or politically acceptable to adopt any of them. 'It is worth devoting effort to clarifying both the feasibility and any potential downsides of the various options. But none of these technologies will provide a get-out-of-jail-free card, and they must not divert attention from efforts to reduce emissions of greenhouse gases.' Professor Launder confessed to scepticism about even the best economic plans. 'I suppose it is that I am an engineer. I have little faith in economic strategies. I am someone that tends to look to engineering or scientific ways of overcoming the problem.' He had hopes for solar power. 'By which I mean large-scale solar power,' he said. 'Not these silly little photovoltaic cells that appear everywhere at 55 degrees north. I can envisage electricity plants going up in the Sahara. 'As far as storage is concerned, I don't see that as a major problem. During the day, you can use the electricity generated to produce hydrogen or whatever you use in other means. There are various other quasi-storage mechanisms, and I would have thought that converting to hydrogen is quite an attractive one. 'There are some proposals which are both actually and metaphorically too far out. I do not favour schemes involving putting into outer space mirrors, lenses and so forth. But more down-to-earth schemes certainly seem worth exploring, worthwhile economically and in ability to be developed in a relatively short time. 'I think one ought to favour carbon-capturing devices over sunlight reflection devices, because those are the options. If you are going to chuck lots of carbon dioxide out into the atmosphere, either you have to get it out of the atmosphere or you have to ensure that less energy reaches us from the sun to keep our temperature under control.' But, he cautioned, experience has shown there is often a huge gap between the grand ambitions and actual practice. He cited a plan to create artificial trees, which their makers said would each remove 10,000kg of carbon dioxide per hour, but which only managed to remove 50 grams a day when they built a prototype. Professor Launder the engineer recognised that real life does not meet the ambitions of imagination, and that initial success may trigger subsequent problems, requiring re-engineering of the re-engineering. This is the case with trying to get rid of carbon dioxide from the atmosphere by putting it in the ocean. 'How do you get it out of the atmosphere? The process is known as diffusion; you have got carbon dioxide in the atmosphere; you have got very low carbon dioxide in the ocean, so gradually it will diffuse into the ocean,' he said. 'However once it has diffused, the concentration in the ocean goes up, so less goes in - so what you want is some means of getting it into the surface layers of the ocean, and the idea is that you grow lots of plants, effectively growing the phytoplankton, and once the plants die they will sink, or maybe things will eat the plants and they'll die and sink.' One way of helping the process along is to go deep into the ocean to find nutrient-rich materials, then use a pump driven by the waves to force the nutrients to the top. Other scientists suggest fertilising the ocean with iron, which has been shown to make plankton bloom. Victor Smetacek of the Alfred Wegener Institute for Polar and Marine Research in Germany and Wajih Naqvi of the National Institute of Oceanography in India, plan to conduct experiments in the South Atlantic to see what happens when the ocean is fertilised with iron particles. In particular, they will look at the effects on diatoms, single-celled algae that seem to absorb most of the carbon dioxide when iron is added to the ocean. There is good reason for caution: fertilising the ocean with iron is not technically difficult, but planktonic algae are at the bottom of the planet's food chain, and there is always the risk that the resulting chain reaction might not be entirely benign. The alternative strategy of reducing the Earth's incoming sunlight also risks setting off perverse chain reactions. Professor Launder was quick to discount the extraterrestrial strategy. 'It would be frightening putting things into outer space, because if you suddenly find that, instead of 2.5 per cent of the incoming sunlight, you are deflecting 15 per cent of it, then you would have a disaster on your hands and would need somehow to work out how to get these things back,' he said. Other scientists advocate stratospheric seeding, in effect trying to imitate what happens in a big volcanic eruption, to lower the Earth's temperature. This would be perverse to the point of being malign because it would actually try to increase the amount of pollution in the atmosphere by increasing sulfur compounds, which governments have been trying to combat because they cause acid rain. Professor Launder said he preferred something at ground - or sea - level, and put forward a scheme devised by John Latham and Stephen Salter 'Latham suggested that if you could find a way to increase the number of water droplets in low-level maritime clouds, you could greatly enhance their reflectivity. By making lots of much smaller droplets, you then simply reflect more of the incoming sunlight back into space. What I like about this approach is that if something goes wrong with it, you just stop spraying these drops, and things will return to normal.'