How Earth-Scale Engineering Can Save the Planet

Carbon dioxide wasn´t always public enemy number one. For the past 400,000 years, the concentration of CO₂ in the atmosphere has fluctuated between about 180 and 280 ppm (parts per million, the number of CO₂ molecules per million molecules of air). But in the late 1800s, when humans set about burning fossil fuels in earnest, atmospheric CO₂ began to increase with alarming speed-from about 280 ppm to the current level of almost 380 ppm, in a scant 100 years. Experts predict that CO₂ could climb as high as 500 ppm by 2050 and possibly twice that by the end of the century. As CO₂ levels continue to rise, the planet will get hotter. “The question now,” says Ken Caldeira, an atmospheric scientist at Lawrence Livermore and one of the world´s leading authorities on climate change, “is what can we actually do about it?” Here are some of the geoengineering schemes under consideration.

1. Store CO₂ Underground
Feasibility: 10
Cost: $$
RISK: 4
In the southeastern corner of Saskatchewan, just outside the town of Weyburn-the “Opportunity City”-a steel pipeline descends 4,000 feet below the prairie at the edge of a 70-square-mile oil field. Into this subterranean cavern, petroleum engineers are pumping 5,000 tons of pressurized, liquefied carbon dioxide every day. The aim is twofold: Use high-pressure CO₂ to drive oil from the porous rock in the reservoir to the surface, and trap the carbon dioxide underground.

Welcome to the world´s largest carbon-sequestering operation. Dubbed the Weyburn Project, it began in July 2000 as a partnership between EnCana, a Canadian oil and gas company, and Canada´s Petroleum Technology Research Centre. With $13 million in funding from more than a dozen sponsors, including the U.S. Department of Energy, engineers have already socked away six million tons of carbon dioxide, roughly the amount produced by burning half a billion gallons of gasoline.

The Timeline
Unlike other geoengineering schemes, this one is already happening, with more than half a dozen major projects under way. The problem, says Howard Herzog, a principal research engineer at MIT´s Laboratory for Energy and the Environment, is that concentrated CO₂ is in short supply. There´s too much of the gas floating around in the air, but actually capturing, compressing, and transporting it costs money. In the U.S. and most other nations, there are no laws requiring fossil-fuel-burning power plants-the primary source of CO₂ emissions-to capture a single molecule of the gas.

The Promise
By 2033, the Weyburn Project will store 25 million tons of carbon dioxide. “That´s like taking 6.8 million cars off the road for one year,” says project manager Mike Monea, “and this is just a pilot test in a small oil reservoir.” Saline aquifers, giant pools of saltwater that have been trapped underground for millions of years, could hold even more CO₂. Humans dump about 28 gigatons of CO₂ into the atmosphere every year. Geologists estimate that underground reservoirs and saline aquifers could store as much as 200,000 gigatons.

The Perils
Before CO₂ is injected into the ground, it´s
compressed into what´s called a supercritical state-it´s extremely dense and viscous, and behaves more like a liquid than a gas. In this form, CO₂ should remain trapped underground for thousands of years, if not indefinitely. The danger is if engineers accidentally “depressurize” an aquifer while probing for oil or natural gas. There´s also a risk that carbon dioxide could escape slowly through natural fissures in subterranean rock and pool up in basements or cellars. “If you walked down into a basement [full of CO₂],” Keith says, “you wouldn´t smell it or see it, but it would kill you.”

2. Filter CO₂ from the air
Feasibility: 4
Cost: $$$
RISK: 4
Klaus Lackner is accustomed to skeptics. They´ve doubted him since he first presented his idea for extracting carbon dioxide from ambient air in March 1999, at an international symposium on coal and fuel technology. “The reaction from everyone there was utter disbelief,” recalls Lackner, a physicist with the Earth Engineering Center at Columbia University.

He called for the construction of giant filters that would act like flypaper, trapping CO₂ molecules as they drifted past in the wind. Sodium hydroxide or calcium hydroxide-chemicals that bind with carbon dioxide-would be pumped through the porous filters much the way antifreeze is circulated through a car´s radiator. A secondary process would strip the CO₂ from the binding chemical. The chemical would recirculate through the filter, while the CO₂ would be set aside for disposal.

The Timeline
Lackner is collaborating with engineer Allen Wright, who founded Global Research Technologies in Tucson, Arizona. Wright is developing a wind-scrubber prototype but remains tight-lipped about the project. He estimates that a completed system is at least two years away.

The Promise
Wind scrubbers can be placed wherever it´s convenient to capture carbon dioxide, so there´s no need to transport it. Lackner calculates that a wind scrubber designed to retain 25 tons of CO₂ per year-the average amount each American adds to the atmosphere annually-would require a device about the size of a large plasma-screen television. A single industrial-size wind scrubber about 200 feet high and 165 feet wide would snag about 90,000 tons of CO₂ a year.

The Perils
Some experts are dubious about the ease of separating carbon dioxide from the binding chemical, a process that in itself would require energy from fossil fuels. “CO₂ is so dilute in the air that to try to scrub from it, you have to pay too much for energy use,” Herzog says. And to capture all the carbon dioxide being added to the atmosphere by humans, you´d need to blanket an area at least the size of Arizona with scrubber towers.