Fake Plastic Trees

William McDonough will often share with his audience a design challenge that requires incredible humility as a species – after all, he says, it took us 5000 years to put wheels on our luggage. The assignment: design a tree. In other words, design something that makes oxygen, sequesters carbon, fixes nitrogen, distils water, provides habitat for hundreds of species, accrues solar energy as fuel, makes complex sugars and food, changes colors with the seasons, creates microclimates, and self-replicates. Sure, he’s taking the best parts of many different trees, but the point is that we could not even come close. Still, should we be trying to?

With humanity’s recent foray into 400ppm territory, a level for atmospheric carbon dioxide not seen in more than 3 million years, much attention has been given to engineering solutions that mimic a single aspect of tree function: extracting CO2 from the air. Right on time, a few weeks ago I read about new resins that could absorb CO2 from the air. This was an update a story I had read previously about similar work. In both cases the articles chronicle the slow slog forward by researchers toward making a better tree – or at least a part of a tree. These materials do nothing for soil stability, habitat, shade provision, etc. The new resins act like a strong base binding with CO2 in the air. This is something lye does with CO2 to form baking soda. But unlike baking soda, which requires energy inputs to heat it up to 900˚C to release its CO2, the new resins can release their CO2 with only the addition of water.

The most recent article on these resins told the story of a piece that could absorb 700 kilograms in a day (about the amount exhaled by you and a dozen friends in that same time). This was a piece about the size of a pizza box, so you can imagine how much would be required to account for just the CO2 we’re letting out of our lungs which is the least of our problems. The estimates are that we need to absorb about 650B tons (650,000,000,000,000 kg) by 2011 to stay below 450 ppm. That’s a billion of these pizza boxes to stay at the highest concentration the Earth has seen since before humans evolved. At a pricetag of about $600 per metric ton of carbon dioxide captured, that racks up a bill of roughly $390 trillion. Other estimates say it could work for $300/metric ton; bringing the total to a much more manageable $195 trillion – still more than twice the global GDP last year.

Of course finding that much money and building these trees to capture that much CO2 is just part of the problem. Where do you put all these fake trees? (cut down real trees to put up expensive, less effective, CO2-sucking ones). Maybe we could coat our CO2 producing devices – our cars and buildings – but we’d need to get the CO2 out of the coatings everyday. Some developers of the technology say they’d need 10 million ‘trees’ to bring concentrations down 0.5 ppm/year. Experts say it would only take about 3 more decades of development and a century of use before we could start to see the effect we’re looking for. We don’t have that much time or money. Or power, these devices would require new fleets of energy sources for pumping CO2 from the membrane to someplace where it could be stored indefinitely. This is perhaps the most important question, where do you put all the carbon once you’ve sucked it out? The material’s ability to release CO2 with water means it can quickly be made anew and the captured CO2 can be pumped to underground sequestration while the ‘trees’ go back to sucking carbon. The US DoE estimates we have plenty of room underground to store this stuff, we just don’t know how to do it yet.

Still, considered against alternative (or additional) geoengineering ideas to cope with a problem that we know the main source of, this one is not too bad. The others include things shielding the Earth from incoming sunlight with mirrors in space or larger particles we would put into the atmosphere in large quantities. Sound familiar? Some ideas focus on changing the chemical composition of the ocean (more than we already are) to stimulate CO2 uptake by certain organisms.

Reading more about these ideas and innovations is more depressing than inspiring. The people working hardest on these projects will be the first to tell you this is just wheel spinning that might be doing more harm than good.

It’s actually still a question whether it will take more energy to capture CO2 then the CO2 associated with [fossil fuel] energy in the first place” – Howard Herzog of MIT (via Yale e360)

It makes little sense to capture CO2 from the air until these sources of pollution have been eliminated.” – Robert Socolow of Princeton (via Scientific American)

The tragedy is there’s no reason to be considering these options at all if we could just learn to cooperate [on reducing emissions…]” – Ken Caldeira of the Carnegie Institution of Washington at Stanford (via Yale e360)

This is time for big ideas and innovation, but where’s some of that humility Bill McDonough hinted at? We’re focusing solely on reinventing the wheeled luggage when we might do better to spend some time thinking about how to travel lighter.

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