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  • High hopes for new carbon capture device currently in development
  • Designer says the machine works much like a tree but is far more efficient
  • Question marks remain over the wisdom of the geological CO2 sequestration
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By Matthew Knight for CNN
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LONDON, England (CNN) -- The idea of intervening to modify the earth's climate is not a new one. As early as 1836, American meteorologist James Pollard Espy proposed enhancing precipitation by lighting huge fires, which earned him the nickname 'The Storm King'.

The Intergovernmental Panel on Climate Change (IPCC) believe that CO2 capture and storage could contribute to mitigating climate change.

More recently the U.S. National Academy of Sciences has suggested that erecting a vast bank of mirrors in space -- to reflect and block out sunlight -- would lower temperatures.

And Nobel Prize winning Dutch chemist Paul Crutzen thinks that blasting rockets laden with sulfur into the stratosphere would create a protective and cooling 'blanket' for the earth.

But whilst space mirrors and sulfurous skyrockets are still far out, far off and potentially catastrophic for the earth's climate, there are some more down to earth projects and trials currently in operation. Carbon capture and storage is just one of these.

One way of achieving effective CO2 capture and storage might be to suffuse vast swathes of the oceans with iron ore, thus increasing the levels of plankton which not only capture CO2 but after dying fall to the ocean depths taking the CO2 with them.

But the long term consequences of iron fertilization remain unknown, and sea trials currently underway are proving controversial.

Less divisive, however, is the idea of carbon capture straight from the air. The basic technology for achieving carbon capture from major sources -- gas flues and power stations -- is now established and trials continue apace.

Another idea is to take CO2 from the air we breathe by using 'synthetic trees'.

The proposal to replicate nature's lungs is the brainchild of Dr. Klaus Lackner, a Professor of Geophysics at Columbia University in New York.

Dr. Lackner's interest in carbon capture was inspired by an experiment his daughter performed in a chemistry lesson at school. By blowing carbon dioxide through a solution containing sodium hydroxide, she was able to capture half of the CO2 as sodium carbonate.

The early sketches of the 'synthetic tree' which have been variously described as a giant fly-swatter or a goal post with a Venetian blind were bold and futuristic in appearance.

Since 2003 Dr. Lackner has been developing a prototype with Global Research Technologies (GRT), a technology research and development company based in Arizona.

The design is smaller and less striking than Lackner's original concept, but GRT hopes that it is the first step towards a commercially viable carbon capture device.

CNN spoke to GRT President Allen Wright about the development of the carbon-extraction machine christened ACCESS (Atmospheric Carbon CapturE SystemS) and how it works.

"In simple terms there is a portion of the device which is in contact with air," Wright said. "The CO2 has an affinity for the surfaces that run along the collector."

Initially GRT were using sodium hydroxide surfaces to collect the CO2, but due to the excessive amounts of energy that were required, they have since migrated to operating with sodium carbonate and sodium bicarbonate.

"Once these surfaces get loaded up we wash them with a liquid sorbent which takes the CO2 off to a separator," Wright said. "The CO2 is then removed from that solution and produced as a pure gas."

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Speaking to National Public Radio (NPR) earlier this year, Lackner explained that a surprising amount of CO2 can be pulled out of the air this way and although the device works much like a normal tree, it is far more efficient.

"The device will be probably on a scale of capturing a ton of CO2 a day," Wright explained. "We have chosen that number because the machine that size can produce a significant amount of CO2 per day but is not so big that it can't be mass-manufactured."

The device is currently at the pre-prototype stage, but GRT are hopeful that the technology they've developed can be deployed on a large scale -- similar to a wind farm -- in the future.

Although storing CO2 is outside the scope of the GRT project the pros and cons are a source of much debate amongst energy experts.

Carbon is naturally stored in the oceans and in trees, but scientists and governments are turning their attentions to geological storage, which range from depleted oil and gas wells to coal seams and saline aquifers (underground saltwater deposits).

On the face of it, this appears to be not only an attractive environmental option but a profitable one as well, especially for energy companies. But even oil giant Shell concede on their website that: "questions remain about whether CO2 stored underground could eventually leak out."

Their view is echoed by Professor Stefaan Simons, director of the Center for CO2 Technology at University College London (UCL).

"I have reservations about the geological storage of carbon dioxide," Professor Simons told CNN. "Is it going to stay down there? And what problems are we storing for future generations?

"Once you've drilled into a chamber you have compromised it. Presumably there are cracks around the hole. I'd be keen to see more work done on the long term complications of CO2 storage."

Professor Simons heads up a UCL team dedicated to developing technologies for the large scale reduction, removal and sequestration of carbon dioxide. His current focus is on converting flue gas CO2 into carbonates.

"Geological storage is an obvious route to take if you want to carry on as normal," he said. "But it is hiding the issue of reducing emissions and says that we can carry on emitting because it can be stored underground."

According to Simons, an interesting addition to the environmental energy debate has been put forward in the 2006 book, 'Beyond Oil and Gas: The Methanol Economy' by George Olah, Alain Goeppert and G.K. Surya Prakash.

The authors propose to convert CO2 from industrial exhausts and in the atmosphere into liquid methanol for fuel use.

"Methanol is much easier to use than hydrogen because it's a liquid," Professor Simons said.

"Quite frankly, we're going to have to carry on reducing emissions," he said. "And the big issue is transport. It is a problem for society to grapple with because there isn't really an alternative to fossil fuels." E-mail to a friend E-mail to a friend

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