Although one has never been built, Dr. Klaus Lackner from Columbia University has invented an artificial tree designed to do the job of plants. They wouldn't resemble a natural tree at all, but more importantly if built to scale, synthetic trees could help clean up an atmosphere grown heavy with carbon dioxide, the most abundant gas produced by humans and implicated in climate warming.

The synthetic tree would do the job of a real tree. It would draw carbon dioxide out of the air, as plants do during photosynthesis, but retain the carbon and not release oxygen. Dr Lackner is serious about developing a working model. His efforts suggest the wide net of ideas cast by scientists as they face the challenge of mitigating climate change. Dr Lackner believes that carbon sequestration technology must be part of the long-term solution. Global reliance on fossil fuels would not decrease any time soon, he said, and developing countries cannot be expected to wait until alternatives are available.

He estimated that 250,000 synthetic trees worldwide would be needed to soak up the 22 billion tonnes of CO2 produced annually.

THE FACTS

He predicts that one synthetic tree could remove 90,000 tonnes of CO2 in a year - the emissions equivalent of 15,000 cars.