Desert Greening

17 December 2018

For atmospheric CO2, there’s two basic options on how to reduce it: not emitting in the first place and putting it in the ground. Many of the big ideas that humans have (agriculture, vaccination, etc.) are based on harnessing things mother nature does and modifying it for human use. In that same way, we can look at the ways that nature sequesters CO2 and modify it. Hopefully from the title you can tell where I’m going with this, but before we get to desert greening, lets talk the chemical and biological processes of CO2 sequestration. The main chemical process of sequestration is turning CO2 into rock, called carbonates, most commonly calcium or magnesium carbonate. There have been intermittent news stories about large formations of rock in Oman that could be suitable candidates for such sequestration. The second way is biological processes, where organisms take CO2 from the air to do things with it (produce energy, build structures, etc.). When those organisms die, the carbon isn’t released back into the air, sealing it away for tens of thousands of years.

There are two further subdivisions of the biological process of carbon sequestration. We can make more organisms and/or we can make them more efficient at storing carbon. The second one is very interesting, and you could imagine how the recent advances in genetic engineering could make that method very possible. However, I’m going to be talking about the first one. We can make more organisms either in the ocean (via ocean fertilization) or on land. On land there are again, to methods. Either reclaim habitats that have been destroyed by humans, or make brand new habitats. Reclaiming land is hard because it’s being used, and people (and corporations) don’t like it when their land is taken from them. But creating new habitats is much easier, because usually nobody lives there. I’m specifically thinking of creating new habitats in the desert, as it’s usually the most underdeveloped.

The well known “green Sahara” is the idea that about 10,000 years ago the Sahara had dense vegetation and was a habitat for a bunch of different animals. Research by the meteorologist John Kurtzbach provides evidence for the Orbital Monsoon Hypothesis of the green Sahara, which says that the tilt of the earth (precession and obliquity) is the main driver of the Sahara being cycled between savannahs and deserts. More specifically, the tilt of the earth changed the North African Monsoons to be stronger and dump more water onto the Sahara. The tilt difference between the maximums and minimums was only 2 or so degrees, which both is and isn’t a big deal.

The types of things that come up when you search for “desert greening” in Wikipedia are all interesting and have merit in their own rights, but they’re not going to get us back to the green Sahara that’s necessary to put a massive dent in climate change. Y Combinator’s post about desert greening is a more interesting idea involving desalination and piping water to create oases. In the article’s own words, it would be the largest infrastructure project ever undertaken. Another way we could theoretically green the Sahara would be to manipulate the Earth’s climate to be more like the Holocene Wet Phase, the most recent period where the green Sahara existed. You could conceive of a scenario where some people throw a bunch of mirrors into orbit and adjust them such that the North African Monsoon becomes wetter and greens the Sahara, drawing down a lot of CO2. This has a timing issue though. Even if we do this in a few years, it may take several hundred to a thousand years to see the effects, as it takes time for currents and rain patterns to overcome their inertia and change to be how we want it. In a hundred years, we may have the technology to overcome this issue, but by then there’ll probably be a better solution given the technology (but maybe that’s just my inner techno-optimist speaking). Regardless, we don’t really have a hundred years.

So where does that leave us other than an unsatisfying ending to a blog post? Well, we could keep trying the current methods of desert greening like managed intentional rotational grazing (which is fascinating, but won’t solve climate change) or flood control, but neither of them have the pure scalable power necessary to make a global impact. I guess that leaves us with the Y Combinator post’s idea of desalinating and piping in water to make oases, but that seems like it’ll take a lot of energy and it’s unclear how exactly it’ll make money. They could buy land in the desert and sell it after it’s green, but that seems like a lot of capital for too little profit. Or I could be wrong and one of the current methods is actually really scalable or there’ll be some desalination break through that makes the oasis plan promising. Or maybe the deserts will just stay mostly deserts and desert greening isn’t actually a good way to go about sequestering carbon. Either way, there doesn’t seem to be a clear cut answer to this question.