2007 Hot Issue

>HOT GIZMO: Mechanical Trees

Watch out, trees. Your job as air purifiers may be threatened. To better combat global warming, Columbia University geophysics professor Klaus Lackner has invented what he calls "atmosphere scrubbers": 300-foot-tall steel posts bearing giant air filters that chemically simulate photosynthesis. They may look more like oversized fly swatters than Ponderosa Pines, but what they lack in aesthetic appeal, they make up for in efficiency. The scrubbers can remove CO2 from the atmosphere a thousand times faster than natural trees -- 90,000 tons a year, the emissions equivalent of 15,000 cars.

How do these mechanical trees work? Their "leaves," resembling Venetian-blind slats, are coated with a chemical that absorbs CO2; the trapped molecules are then converted into waste that can be buried underground. Lackner believes that a "forest" of 250,000 of these trees placed in an area the size of Arizona could completely offset humanity's current annual CO2 output.

The projected cost is up to $20 million a tree. But before Lackner can prove the trees have commercial potential, he has several glitches to address: First, so far only a nine-foot-tall model exists. He's scrambling to develop a full-size prototype but says it won't be completed for two years (critics predict it will take decades). Another glitch: The process of prying the CO2 loose from the filter's chemical membrane and storing it underground requires lots of electricity, and critics say unless that power comes from carbon-free sources, these trees could give off more CO2 than they remove. Green activists have a bigger gripe: The invention would prolong the use of polluting fuels and delay the shift to cleaner, greener energy sources like wind and solar. "It's treating the climate crisis superficially, not curing its root cause," says Kert Davies of Greenpeace, "like taking NyQuil for pneumonia."

Lackner admits his invention extends the use of fossil fuels -- in fact, he thinks of that as one of the selling points. "This will enable us to keep the door open to the world's use of oil, coal and natural gas," he says, "the cheapest and most reliable energy sources we've got." It will take decades to wean humanity off its fossil-fuel addiction, he reasons, and global warming could wreak havoc much sooner. Says Lackner, "We need a contingency plan." --A.G.L.

Click here to watch Columbia Scientist Klaus Lackner demostrate how mechanical trees work.