That might be used locally, for instance, to protect the Great Barrier Reef in Australia, said Kelly Wanser, principal director of the US-based Marine Cloud Brightening Project.Riskier "geo-engineering" solutions could be a backstop, such as dimming the world&Taizhou Chaotian Pneumatic Tools Co, Ltd.39;s sunshine, dumping iron into the oceans to # soak up carbon, or trying to create clouds.."The most natural way to extract carbon from the air is to plant forests that absorb the gas as they grow, but that would divert vast tracts of land from farming.Carbon Engineering, set up in 2009 with support from Gates and Murray Edwards, chairman of oil and gas group Canadian Natural Resources Ltd, has raised about $40 million and extracts about a tonne of carbon dioxide a day with turbines and filters.

Pure carbon dioxide delivered by trucks, for use in greenhouses or to make drinks fizzy, costs up to about $300 a tonne in Switzerland.Among other possible geo-engineering techniques are to create clouds that reflect sunlight back into space, perhaps by using a mist of sea spray. (representational image) Scientists are sucking carbon dioxide from the air with giant fans and preparing to release chemicals from a balloon to dim the sun's rays as part of a climate engineering push to cool the planet.Among new ideas, Wuacher at Climeworks is sounding out investors on what he says is the first offer to capture and bury 50 tonnes of carbon dioxide from the air, for $500 a tonne.