Artist’s rendering of what a “synthetic tree” might look like. Resin filters on top would capture CO2 from the ambient air. The CO2 is then removed at the bottom using a series of moisture and compression steps, according to one of the concept’s developers. Deploying technology on a grand scale to alter the planet and combat global warming — that is, the concept of geoengineering — has had scientists brainstorming for some time. Ideas vary, from spraying reflective particles into the atmosphere, to seeding the oceans with iron, to launching a giant reflective sunshade into space.
A more modest geoengineering concept is to build “synthetic trees” — essentially high-tech towers with special absorbents that scrub carbon dioxide from moving air, and then hold it until it can be processed and stored.
Klaus Lackner, a geophysicist at Columbia, is leading the effort to bring such synthetic trees to market. The technology is expensive, but it exists now, Mr. Lackner said, suggesting that the first synthetic trees could be up and collecting within two years.
Their economic viability, he added, might be enhanced by their ability to supply CO2 for commercial use in places where the gas is difficult to obtain.
Green Inc. caught up with Mr. Lackner recently to discuss his project and its global implications. Excerpts from that conversation follow.
You have been working to develop a system that captures carbon dioxide from the air for many years. What’s the latest news on your project?
We have reached a point where we can collect CO2 from the air and recover it … at a low cost. Now it’s a production issue, rather than an “inventing new things” kind of issue.
I would say that in relatively short order, we can get to the point where we can undercut the commercial price of C02 in some locations. Our advantage is that we can produce C02 onsite. We will not compete right next to an ammonia plant [which produces commercial C02], but 200 or 300 miles away, we might look quite good.
This is sort of a way of introducing the concept, and then as we get better, I think our prices come down. I think in current dollars, we might drive prices down into the range of $30 per ton of C02.
In a previous interview, you referred to your project as “The C02 collector of last resort,” and then said, “I’m convinced we will need one.” Why is that?
I would argue that if you build a modern, brand-new coal-fired power plant, you can probably collect that C02 more cheaply than I can, because you have it in concentrated form. It seems silly to me to let it out in the air and then chase after it.
On the other hand, you may have an old power plant, lets say inside Manhattan, and you have no practical way of building a pipeline to get the C02 away from the plant. In that case, collecting an equal amount somewhere in the Nevada desert would cancel out your emission.
Another example is if you drive a car. In the car, it’s virtually impossible to collect the C02 onboard, because the C02 weighs three times as much as the gasoline you started with. For an airplane, it’s physically impossible; the airplane couldn’t lift the C02 it will make during a long flight. So the bottom line is, there are a number of options where air capture is really the obvious method of choice. Right now, roughly half of all emissions are not from the big sources.
Why do we need carbon capture and not just clean, renewable energy instead?
I’m absolutely convinced if we want to stop climate change, we will have to stop net emissions. We cannot stabilize at some level and keep emitting C02. And I have a hard time seeing us completely giving up on liquid hydrocarbon fuels. In order to deal with them, we need air capture.
Liquid hydrocarbon fuels have enormous advantages. A battery has approximately half a megajoule per kilogram, and that’s a high-tech battery. Gasoline has 50 megajoules per kilogram. So it’s about 100 times as much energy as a battery. That’s what makes it so convenient. So, if you can eliminate the C02 problem of liquid fuels, liquid fuels are the perfect storage device for carrying energy in an easily manageable transport environment.
In March, a new study was released that documents 6,000 square miles of ultramafic rocks in the Sierra Nevada and Appalachian Mountain ranges — rocks that are ideal for sequestering carbon in a mineral form. Why are these rocks significant?
The best way of storing carbon dioxide is to actually chemically bind it and form a carbonate. That’s what nature does in the long term. So we looked for rocks that can do that, and ultramafic rocks can do that.
My view is that ultramafic rocks can take up more C02 than we can ever make. What’s nice about it is, though, yes, you make big piles, you know it stays in there. Once you form a carbonate, it doesn’t want to go back. The biggest ultramafic deposit in the world happens to be in Oman. Those ultramafic rocks alone could take the world’s CO2. You could imagine having air collectors in the desert of Oman and putting C02 directly into mineral carbonates.
You claim that your first synthetic trees will collect one ton of carbon dioxide per day and will cost about $30,000 to build. How many of these things would be needed to make a difference?
If you were to install 10 million of them, you would pull back on the order of 3.6 gigatons of C02 a year. The world right now produces 30 gigatons of C02 a year. In 2006, the world made 73 million cars. They are comparable in size, and ultimately comparable in cost.
Compared to some other geoengineering ideas that have been proposed, are synthetic trees less risky in terms of potential unintended consequences?
Synthetic trees are quite different from the others, because I’m not trying to say, “O.K., I push the system here to do something, and now I’m over here changing it to compensate for that change.” In a sense, people say, “O.K., C02 emissions make it warmer, let me figure out how to make it cooler again.” You are asking for trouble, and I think it’s fundamentally unstable too, because you can’t, under that umbrella, keep letting C02 get higher and higher and higher, because you have to push back harder and harder and harder.
What we do is to actually remove the problem we put into the air. We are not trying to manipulate a parameter which is naturally what it is and change it in order to compensate for something else. We are saying we as humans are responsible for having put too much CO2 into the air, and we as humans take it back out.
Now, you should never say never with whether there are unintended side effects, but I can’t see one. The absorbents are benign, and the air right behind one of our collectors still has as much CO2 as it had in 1800.
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