The New York Times has recently taken some flack as the result of Nicholas Dawidoff’s New York Times Magazine profile of Princeton physicist Freeman Dyson. Times science blogger Andrew Revkin has also received some less than favorable reviews of a post he wrote about the article. The bulk of the criticism revolves around the treatment given to Dyson’s views on climate change, and is well warranted.
Neither Dawidoff nor Revkin apparently thought it necessary or desirable to subject any of Dyson’s views or proposals to any sort of reality check. This is at least somewhat strange. Dyson’s views are aggressively opposed to the strong scientific consensus on the issue, and yet he has not been very involved in research in the field. At the same time, some of the ideas that he proposes for climate change mitigation are outlandish, to say the least.
There are times when the perspective of someone outside a particular field can come up with an insight into a problem that has baffled those who have worked on the issue for years, and Dyson’s clearly a pretty bright guy. Luis Alvarez’s work on the Cretaceous-Tertiary mass extinction is a fantastic example of this, and it’s clearly important to keep that possibility in mind. It’s also important to remember that, just like every inventor who gets laughed at is not a Fulton, the distinguished scientist from the other field is not always going to be right.
When the distinguished scientist in question is suggesting specific ideas, it’s not always all that hard to do a quick back-of-the-envelope check to see just how feasible – or not – the idea is. That’s certainly the case with Dyson’s Magic Trees.
I’m referring, of course, to Dyson’s idea that sometime in the next few decades, we will “almost certainly” have genetically engineered “carbon eating” trees within the next 50 years. These trees will suck up the excess carbon dioxide from the atmosphere, and global warming (which Dyson thinks is an overstated problem to begin with) will be solved – once we’ve replaced 1/4 of the world’s trees with the carbon-eating variety.
Just on the surface, that idea looks to be just plain nuts. It’s the kind of thing that works well in sci-fi novels, not in reality. But let’s give it a chance for just a minute or two, and take a (semi-)serious look at it.
We’ll set aside the fact that we don’t currently know how to create a biological process to convert carbon into a form that’s not readily usable by other life forms. We’ll also set aside the difficulties involved in getting numerous species of trees to accept some sort of genetic modification that will get them to use that process. We’ll also ignore the logistical issues involved in getting that modification spread into 25% of the trees living on the planet.
Instead, let’s just look at how much inert carbon these trees will have to somehow output. In 2007, humans released an estimated 8.47 gigatons of carbon into the atmosphere. (Note: that’s the mass of the carbon, not the mass of the carbon dioxide.) That figure has been rising, and I’m just looking for round numbers, so I’m going to say that the last 10 years of output works out to around 80 gigatons.
If we’re looking for a way to store the carbon that’s not going to be readily degraded back into carbon dioxide, the best way is probably going to be to store it in as close a form to pure carbon as possible. Even giving out an enormous amount of the benefit of the doubt, I’m not prepared to say that we’re ever going to be able to make diamonds grow on trees, so that basically leaves graphite – the stuff that we call lead when it’s in a pencil. Graphite has a density that ranges from 2.09 to 2.23 grams per cubic centimeter, but for simplicity I’ll round that up to 2.25.
80 gigatons = 8.0 * 10^10 metric tones.
With a density of 2.25, that should work out to about 3.5*10^10 cubic meters.
If I’m doing the volume conversions correctly – and I’m fairly sure I did, since the first one’s easy – that works out to a 1 meter thick block of graphite that covers an area of 3.55*10^10 square meters, which works out to a bit more than 35,500 square kilometers, or a 10 centimeter thick chunk that covers 355,000 square kilometers.
In terms that are easier to grasp than numbers alone, that’s a 10 centimeter thick sheet of graphite that’s large enough to cover the entire state of New Mexico, with enough left over to cover Delaware and Maryland, and probably still supply the world with pencil lead for a few decades. And that’s just from the last decade of emissions.
We really do burn a lot of carbon-based fossil fuels, don’t we?
And that’s in a solid block form. It’s pretty clear that you’re not going to get a lot of vegetation growth on top of a block of solid graphite, and unless we’re really, really, really good at genetic engineering 50 years from now, the trees probably won’t be able to walk away and plant themselves somewhere else. They’d have to produce the graphite in a form that could mix into the surrounding soil without winding up in such high concentrations that it kills things off. That kind of rules out the single, 10 cm thick block thing. As a 1 cm block of graphite, you’re talking about more than twice the area of Texas, and you still won’t be able to grow anything on it.
I haven’t got to the whole issue of how to figure out what adding that much inert carbon to the soil will do to the ecosystem, or what happens when the trees suck the carbon down to pre-industrial levels – how do you stop it before the level drops too far?
No matter how much slack you cut Dyson, the Magic Trees idea is simply insane. Yet, for reasons beyond understanding, the New York Times seems to have decided to treat it as a serious suggestion from a serious person.