Saving Earth's Carbon Dioxide

Heading toward twice the CO2 in the atmosphere by 2100

By Brad Lemley|Monday, October 24, 2005

Wallace Broecker, Newberry professor of Earth and Environmental Sciences at Columbia University, has some advice for global warming activists to follow over the next 100 years or so: Get real. Ecologists, he argues, have wrongly focused on developing power-generating technologies that don’t use fossil fuels and don’t spew carbon dioxide, which can trap solar radiation and warm the planet. “But we are a very long way from being able to get 30 or 40 percent of our energy from solar power,” Broecker says. “If we bank on that, and it does not happen, we will be stuck.” In his view, no carbon-free technology—including nuclear, wind, geothermal, and tidal—is likely to be deployed quickly enough to head off increasing accumulations of the greenhouse gas.

Even if easy-to-access oil begins to run out in a few years, as some geologists predict, Broecker says nations will simply switch to other relatively cheap fossil fuels. “The Athabasca tar sands in Canada are being mined and converted to petroleum at a cost of about $20 a barrel,” he says. As long as oil prices remain at more than $50 a barrel, that’s irresistibly profitable. “The next step would be to make petroleum out of coal, much like the Nazis did in World War II when their supply was cut off. It might double the price of gasoline, but that would still be cheaper than other alternate forms of energy.”

Broecker adds that what the developed wealthy world will do is largely irrelevant, because China, India, and much of the third world will grow increasingly wealthy and thirsty for fossil-fueled growth. “Since there are a billion and a half of us, and 5 billion people in the poorer parts of the world, it is more what they do to increase their fossil-fuel usage than what we do to decrease that matters,” he says.

In short, there is simply no realistic way to clamp down on carbon-generating technologies before they fill the skies with high levels of carbon dioxide. Atmospheric CO2, measured in parts per million, has been climbing steadily for more than 150 years and threatens to keep doing so. “We are headed toward 900 parts per million early in the next century,” or more than double the current level of 380 ppm, Broecker says. “That would mean four to five Fahrenheit degrees of warming for the world as a whole, raising sea levels by a meter or more.” And it won’t stop there, he says. Sea levels might eventually even rise five meters, submerging the world’s low-lying lands, including most of Florida.

The answer? “We need to work out a way to take CO2 out of the air and bury it,” Broecker says. He points to Klaus Lackner, a Columbia University geophysicist, and Alan Wright, an engineer formerly with the Biosphere 2 project, who are designing and building the first atmospheric CO2 extraction machine. Gary Comer, founder of the Lands’ End clothing company, is funding the project. Although he won’t divulge exact figures, Broecker says “the cost of development is peanuts. If it turns out that the models that predict warming are not right, we can leave the technology on the shelf. But if we need it, it will be there.”

Klaus Lackner is a geophysicist at the Earth Institute at Columbia University and codeveloper of the synthetic tree, a device designed to remove carbon dioxide from the air. By Lackner’s calculations, one synthetic tree could absorb 1,000 times more CO2 than a living tree.

How would the synthetic tree remove carbon dioxide from the air?
L: The device itself would look something like goalposts with venetian blinds. It would be equipped to use liquid sodium hydroxide, which converts to sodium carbonate as it pulls CO2 from the wind stream.

How much could one tree remove?
L: The unit, which has a collection area of 50 meters by 60 meters, could gather 90,000 tons of CO2 a year. That means one synthetic tree could handle an amount equivalent to the annual emissions of 15,000 cars.

How many of these synthetic trees worldwide would be needed to soak up the 22 billion tons of CO2 produced annually from fossil fuels?
L: About 250,000.

To make this process efficient, you need to recycle the sodium hydroxide, which means you need to take the absorbed carbon back out. How do you do that?
L: You percolate the liquid sodium carbonate over solid calcium hydroxide, and the calcium catches the carbon. So you have taken the carbon out of your sodium hydroxide, and you can use it again. But then you have to get the carbon out of the calcium so that you can repeat the process. You do this by heating the calcium carbonate to 900 degrees Celsius, and it lets loose the CO2. So now we have the CO2 back in hand as a concentrated stream, with which we can do whatever we want.

What do you suggest?
L: It can be sequestered underground. The question is, is there enough capacity? Short term, it will work, but for the long term we need to develop other alternatives. I have proposed mineral sequestration. There are entire mountain ranges made of magnesium silicates that over millions of years would naturally turn into magnesium carbonate. We could speed up that process in an industrial fashion. We could make a stable, harmless solid.

What percentage of the energy in, say, gasoline would be consumed in the process of cleaning it up?
L: About 40 percent. People say 40 percent is a big hit. But it’s not, compared with producing hydrogen from coal, which I think is the most likely way large quantities of hydrogen would be made. Those guys also have a 40 percent energy hit, if not larger. So in a sense, the cleanup will cost that much, whether it is converting hydrogen from coal or pulling carbon dioxide from the air. In one case, you pay for the energy upstream; in the other you pay for it downstream.

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