Terraforming the Sahara

Spot the dune...

An interesting paper in Climatic Change: Irrigated afforestation of the Sahara and Australian Outback to end global warming by Leonard Ornstein, Igor Aleinov and David Rind Doi: 10.1007/s10584-009-9626-y. (Mason Inman has a nice write up with some background and comment over at ScienceNow; [update] and corresponding author Len Ornstetin chronicles the idea’s rocky research road on his own site). The central idea is that with enough irrigation you can turn big deserts into big forests: forests big enough to suck up a large part of total carbon dioxide emissions for decades or even centuries. I think that you can take this notion as a serious plan, a thought experiment, a jeu d’esprit, a warning or a jumping off point, depending on predisposition. Aspects of all that in what follows.

Here are the basic numbers: The Sahara is about a billion hectares in area, on which you could fit a trillion eucalyptus trees. Those trees, if working flat out, could each put on twenty kilos of biomass a year. If roughly half that biomass is carbon, that would mean a net annual sink on the order of ten billion tonnes of carbon. That’s about the amount that humans currently emit.

To create such a forest in a century, you would have to plant as many hectares of trees every year as are currently lost to deforestation worldwide. And, even harder, you’d have to provide them with what they need to order to grow. You need a great many things to turn a desert into a forest — soil nutrients, microbiota, possibly pioneer plants, a compelling reason for doing the work, and so on — but the biggest hurdle, pretty obviously, is water. Eucalyptus, the authors say, needs about a metre of rainfall  a year. For a billion hectares, that’s 10 trillion tonnes of water. The authors assume, reasonably for all that I know, that if you have smart irrigation getting the water to just where it is needed you can get away with half that amount. Even so, even the vast aquifers beneath the Sahara don’t contain the amount of water required, so it will have to come from desalination plants on the and be pumped it up to where it is needed (the average elevation of the Sahara is about 450m). The size of this undertaking — more than 50 new Niles, flowing in reverse — may explain why the authors feel they need to use that fine old-school term “terraforming” for their undertaking.  The power requirement, if I’m reading their figures right (4.04kWh/m^3 fresh water delivered), is a bit to the north of 2.2 terawatts, about 40% of it for desalination by reverse osmosis and about 60% for pumping.

The world’s electricity generators currently provide about 18,000 TWh of energy, which averages out at 2TW of constant supply. So in energy terms the desalination and pumping needed for the Sahara forest would use a bit more electricity than the world currently generates for every other purpose.  This unavoidably sounds nutty. But that is at least in part because of the nuttiness of the situation, rather than its proposed solution — the nutty situation in which we burn fossil carbon at tens or hundreds of thousands of times the rate at which it is sequestered over geological time. If humanity insists on putting so much carbon dioxide into the air every year that it would take a brand new forest the size of the Sahara to suck it all up, then that’s where the madness starts. That creating such a forest would have to be a large undertaking — large in terms of  the whole world economy — is just a consequence of the initial folly.

And in practice the investment would be smaller. A nice thing about forests is that they can go some way to creating their own weather, and the authors have looked at this effect with some climate modelling work. If a forest with irrigation dampened soil is imposed on the Sahara, rain begins to fall, in some places as much as a metre of it every year. This rainfall doesn’t obviate the need for irrigation, because it is strongly seasonal — basically an extension of the West African monsoon of April to November. But it might significantly reduce the irrigation requirements. Maybe you could get away with just a terawatt…

The Sahel, to the south of the Sahara, also gets damper in those enhanced and extended monsoon rains, which is definitely a plus, I’d guess, and the African Easterly Jet, a feature which is driven in large part by the temperature contrast between the desert and surrounding land, seems to more or less vanish. Since a large number of Atlantic hurricanes get their starts as kinks in the AEJ, that might be a pretty significant change, too. Beyond that, the rest of the world seems pretty much unaffected. In particular, the authors say that their models show no additional warming that might be laid at the door of the change of albedo which comes with replacing light desert with darker trees. (I think this fits with the 2007 Bala et al paper in PNAS, which suggested that warming associated with afforestation would be due to changes in boreal, rather than tropical, forest cover).

The Bodele depression

The Bodélé depression (pic by Charlie Bristow)

There is, however, a fly in the ointment. The Bodélé depression in Northern Chad is only a small part of the Sahara, but it is the world’s greatest source of mineral dust, with the winds drawing some 700,000 tonnes a day off the surface. According to  Koren et al in ERL, 2007 40 million tonnes of dust a year travels from the Bodélé to the Amazon rain forest, half the total annual mineral inputs into the forest basin (the dust fertilises the mid Atlantic, too, and it may play a role in abating hurricanes too — Jim Giles wrote a lovely piece on this for Nature some time back). There’s a real chance that this dust is crucial to maintaining the soil fertility of the forest, and even if the Bodélé itself were left unirrigated and unforested, the increase in precipitation all round it, and the wetter atmosphere downwind of it, would probably shut it down as a dust producer. If growing a forest in the Sahara hurts the one we already have in the Amazon it obviously becomes a less attractive proposition (though if we are going to lose the Amazon forest anyway, things might look different…). That said, if you are pumping trillions of tonnes of water across continental scales, thenpaying to air dump a few tens of millions of tonnes of fine-particle mineral fertiliser upwind of where you want it is hardly going to break the bank.

Something the authors don’t look into is that the higher the CO2 level in the atmosphere gets, the easier this all becomes. Higher carbon dioxide levels make plants more water efficient, all other things being equal. All other things are not, necessarily, equal — higher CO2 also makes things hotter, which plants don’t much care for. In a world with some solar radiation management, though (such as aerosols in the stratosphere) all things might indeed be kept equal, or at least temperature might be. Martin Claussen has been working for some time on the idea that the Sahara is a “tipping element” in the climate regime, one that can be pushed from a dry state to a wetter one relatively easily. In a more carbon rich but not-too-hot world the circumstances might be right for it to tip the other way, and it might take rather less than a 50-Nile terraforming project to nudge it over.

In the final analysis, I don’t think I take this paper very seriously as a practical proposition. Doubling global electricity generation for a single project seems far fetched. For such a thing to be put anywhere near the top of one’s list of African infrastructure investments would require that a great many other large and important development initiatives (provision of power, water, roads, cold chains, vastly improved agronomical advice, etc to the vast majority of the population, for starters) would already have had to have been put in place. But it’s kind of nice to imagine a world in which we were wealthy and together enough to have actually taken the pressing need for those changes to heart, and were thus in a position to consider greening a great desert too.

Bahrains Tree of Life -- a limited pilot project...

Bahrain's Tree of Life -- a limited pilot project?

And regardless of practicalities I think there’s real value in taking the analysis further. A big idea like this throws off many fascinating questions that force you to look at the earth, and what we know about it, in new ways (or old ways but with a new twist):

What polycultures would you build the new forest with? (all-eucalyptus-all-the-time is fine for first calculations, but doesn’t sound like anyone’s idea of a proper landscape. Baobabs? Laurels? And what fauna might be good, or bad?)

What  genetic engineering — reduced flammability, higher albedo leaves, more refractory soil carbon, who knows what else — might help?

How much bioenergy with carbon capture could be built into the scheme, perhaps initially to power some of the inland the pumping stations?

Can biochar help? (and a million other soil-creation questions)

What are the best silvicultural ways to make the new woodlands pay, as that is something people by and large like their environments to do, and can there be room for some agriculture too?

How could local people best be convinced this was a good idea? And what are the property title reforms that would be prerequisite?

If the AEJ stops, do hurricanes stop too? Or does some other mechanism initiate them, maybe somewhere else? And does the dust really have an effect?

When the Sahara was wetter and less dusty in the past, did the Amazon actually suffer from lack of nutrients? (I think there is actually some research already out there on that — but can’t offhand think where)

How can the transformation be made stunningly beautiful?

What regions and landforms do you want to keep as monuments/heritage sites/national or world parks? There  would undoubtedly be a real aesthetic/biodiversity loss in the removal of the desert, not to mention risks to some utterly wonderful buildings.

How to stop the Fremen becoming soft and decadent now that Arrakis has become a land of milk and honey?

and so on.

In particular, it would be nice to see some analysis of halfway houses; where in the Sahel and points north might merely huge, as opposed to planet-sized, afforestation be attempted, and what would be the costs and benefits? It is possible to transform land on very large scales, if not quite this large: 40m hectares of the Brazilian cerrado have been brought into agricultural production over the past fifty years. Can afforestation/silvicultural interventions on such scales ever make sense? And where else might be suitable for such things?

And on the topic of where else: My apologies to any Australian readers for not going into the paper’s analysis of foresting the Outback in addition, or as an alternative, to the Sahara. Basically the arguments are largely the same but the costs and effects are a bit smaller. There’s also a risk of interfering with El Nino that would definitely merit further attention. If anyone wants to blog more on that aspect of the subject send me a link and I’ll post it up here.

Image credits: Eucalyptus trees at the top from Big Lands Brazil, who would like to sell you some…; Bodele  from Charlie Bristow, reused with permission; Tree of life from Flickr user Solvo under Creative Commons license

Two-tier tree
June 18, 2009, 8:50 am
Filed under: Trees
Willow and fruit tree, near Grana, Utaly

Willow and fruit tree, near Grana, Utaly

Just cool: One tree growing atop another. From AtlasObscura, via BoingBoing: original source the  Bricc e Foss bed and breakfast

Can't help thinking this is good for Gondor

Cosmic Jacks of the Forest
April 6, 2009, 2:25 pm
Filed under: Trees

Here’s an interesting jeu d’esprit of extreme conservation (via Gary):

My favourite long-term solution is simply to aim for not just a post-industrial civilization but a post-biological one. We can currently roughly foresee how we could go about it. We would fixate our brains (presumably when near biological death), scan them in detail, reconstruct the functional structure and recreate it as software. The successor version would then go on living in virtual reality, with occasional visits to the physical world using a robot, android or just remote controlled human body.

How efficient could a postbiological civilization be? The current IBM roadrunner does 376 million calculations per watts. If we take my mid-range estimates of computing needs, 10^22 to 10^25 FLOPS, then a single emulation would need 10^13 to 10^16 watts. The total insolation of Earth is about 10^17 watts, so this won’t do – there would be space for just a few minds on the entire planet. But current research on zettaflops computing suggest we can do much better. A DARPA exascale study suggests we can do 10^12 flops per watt, which means “just” a dozen Hoover dams per mind. Quantum dot cellular automata could give 10^19 flops per watt, putting the energy needs at 200-2000 watts.

That is between 2 and 20 times the current wattage of a current human. However, we bio-humans get our energy through the inefficient method of having plants collect sunshine (at about 3%) efficiency, then we either harvest them and eat a small part of them (expending a lot of agricultural energy) or have animals eat them (at a few percent efficiency) and finally we eat the result, again with a few percent efficiency. A brain emulation of this type would just need a few square meters of solar panels (plus night-time energy storage). In terms of area and energy required, these postbiological humans would have far smaller material requirements than we do. They could also run slower to save energy.

How much matter would go into this system? Using [quantum dots], each gate would be on the order of a nanometer. Each floating point operation would require about 20,000 gates. These gates would be re-used every 0.1 millisecond timestep, so a full 10^25 flop emulation would need a volume of 0.02 cubic meters. This does not take the rest of the infrastructure into account. Let’s scale it up to one cubic meter. 6.7 billion people would then require the same volume, or a cube with side 1885 meters if bunched together into the ultimate datacenter. That is unlikely to work if the energy use is on the orders of many watts per person, since cooling would be hard (not to mention the vulnerability of having everybody in the same spot). A more likely solution would be smaller centres distributed close to energy sources: a single hydroelectric dam would supply several million people with energy, a square kilometre of 20% efficiency solar panels would supply 150,000-1.5 million people. A 100×100 kilometre area would be enough to run all of posthumanity. And if the reversible computing works, the energy collection infrastructure could be 10,000 times smaller.

Maybe the most sustainable thing we could do would be to aim at a future ensconced in cold datacenters under the subtropical deserts of Earth. Humanity would largely look like a forest of quiet semiconductor trees. We would indeed have become plants.

It reminds me a little, among other things, of this passage from Eating the Sun:

The simplest, and perhaps the most profound, of the differences between those that eat light and those that eat others … stems from the fact that sunlight is, at the efficiencies photosynthesis is capable of, a rather dilute source of energy. To appreciate how insufficient it would be to animal needs, imagine the Green Man of forest folklore. Let us assume that his greenness is due to chlorophyll through which he feeds himself. Given the surface area of his skin—and the fact that at any given time some of it will inevitably be averted from the sun—such a green man would have about as much energy on which to run his metabolism as someone restricted to a diet grown in a couple of square metres of garden. All he could eat in a day would be what his little plot could grow in a day. A few leaves for breakfast, maybe a morsel of root for supper: berries for Sunday lunch.

On the sunshine equivalent of this meagre diet, our Jack of the Forest has no energy for moving, or for thinking—nerves and muscles use a lot of energy. He lacks the energy to breathe in or out, or to keep his body any warmer than the outside air. He’s not good for much except sitting there repairing the daily entropic wear and tear to his body. Indeed he doesn’t really have enough energy for that; quite a lot of him will rot away. The prognosis for the Green Man is vegetable.

Plants simply don’t have the energy to rush around like animals, pumping blood and flapping wings and flashing nerve impulses hither and thither along their limbs. So they eschew the compactness of muscle and opt for the looseness of leaf. The lines of their lives do not rush back and forth across the landscape—instead they are recorded in their shoots and limbs and twigs. Plants have shape where we have behaviour; their history is recorded in their form. Where the swoop of the sparrowhawk falling on the pigeon is gone in an instant, the tree’s decision to grow its twigs this way or that, depending on the light, is written in wood and lasts the rest of its life—or at least until some rough wind or uncouth animal snaps the relevant limb off.

I must admit, I don’t like the idea of the disembodied, emulated life. Although my own is not the finest specimen, I am all for embodiment, not least for the existential constraints it provides; I like my consciousness to come with an off switch. That caveat aside, I have the feeling that given its premises Anders‘ vision is oddly conservative. The idea that such power would be allocated to emulations of individuals seems a little traditionalist; if this trick can be pulled off, then surely it would be to create worlds where consciousness was far less confined, new universes of thought and distributed experience. And having the thinking trees rooted in the Earth seems peculiar; it is a harsh and vulnerable place for such things. As Freeman Dyson has argued on various occasions, places like the Oort cloud seem much more hospitable for life of this type, and indeed of other types.

And why on earth or off it do this in real time? Surely once the clock rate is semi-arbitrary one would either want to go really fast, so as to cram the most in, or — another Dyson idea — very slow: To watch the milky way turn like a waxing moon, to see the quasars redden like leaves in the fall, to tell stories around campfires of thought after the last stars gutter out. And to find out what spring, if any, comes after.

Image from Indium‘s solar materials science blog, used under a Creative Commons licence

A rephotography project in waiting
March 28, 2009, 12:47 am
Filed under: Artworks, Trees

The Forestry Commission has unknowingly thwarted a David Hockney project. Sometime in the past month or so the commission cut down a small stand of beech trees (at the private owners request) in Yorkshire. Here’s the before and after on that:

What the woodsmen didn’t know was that David Hockney had painted the copse twice, in winter and in summer, and had wanted to complete the whole four season set. As it is, that ain’t going to happen. He gave the whole story to the Guardian, including repro rights on the two pictures involved.

On the radio later I heard someone from the Forestry Commission apparently taking the fairly reasonable position that one couldn’t leave trees standing when people wanted to fell them on the off chance that a major artist was going to paint them. In retrospect it would probably have been a good idea if Hockney had let the owners know about his project. That’s not to blame him — but it’s worth remembering, in England, that most pretty stuff you see in the countryside is someone’s property and responsibility, and often their pride and joy too.

Anyway, the Guardian story quotes Hockney saying he may do some sort of follow up painting anyway.

Though he still mourns the lost trees [on returning yesterday he] was impressed by the patterns of the massive stacked trunks.

“I think now this is my next painting of the wood. It will be very different – but the piles of wood are quite beautiful in their own right, simply because wood can’t help being beautiful.”

I’d be big on that. I’m something of a Hockney fan; there was a time when he was occasionally visiting the gallery downstairs from our flat, and I wish I’d known that he had been. A retrospective in Paris that had some of the Grand Canyon pictures in it was quite an influence on one of the chapters of Mapping Mars. I’m sorry he won’t complete the set — but not too sorry, as he’ll surely use the time for something else. And his unfinished project provides scope for other eyes and hands to undertake a companion project he wouldn’t necessarily be able to see through to maturity. It seems to me that someone, or some collective, should adopt this little copse on the corner as a phenology/rephotography project, or more, and record what regrowth there is, or isn’t, as a tribute to Hockney. If I had visual skills and lived nearby I might even do it myself. Anyway, if anyone’s interested I’m pretty sure this is the spot in question in Google Maps.

Update: More on the story in the Mail.

All images except the Google one from David Hockney, used with great respect but no permission

Copenhagen: Has the Amazon tipping point tipped?
March 12, 2009, 12:01 am
Filed under: Global change, Trees

It appears that the action on Wednesday afternoon was where I was not: in the session on tipping points. Chris Jones of the Met Office’s Hadley Centre presented some studies of the Amazon (abstract in pdf) that have caused a big media stir. The studies suggest that a) there is a threshold level of warming beyond which much of the Amazon forest is committed to die back (probably being replaced by savanna) and b) that for significant parts of the forest that threshold is alarmingly low. Indeed it is quite possibly either unavoidable in the near future or already dwindling in the rear-view mirror. As I understand it from people who saw the presentation, models in which all the warming already in the pipeline (ie with no further emissions) is realised leave the forests pretty much committed to some dieback, and modest further warming seals  the deal. I wasn’t  able to check that with Jones himself, but it seems to fit with what he and his colleagues write:

We present results to show a possible climate threshold beyond which some dieback is committed and this commitment rises dramatically for global temperature rise above 2 degrees C, a threshold often used by policy makers in their definition of dangerous climate change. Any subsequent recovery is on such a long timescale as to make the dieback effectively irreversible on any pragmatic level.

Here’s the coverage from the Times and here’s some from The Guardian. Worth noting that it’s a single study, that there are error bars to consider and that people have in the past suggested that the Amazon is often more vulnerable in the Hadley Centre model than in most others. But still very worrying; all the more so if it were to be spun as a counsel of despair on efforts to stop deforestation on the basis that there’s no point preserving a forest that’s already doomed.

I’ll see if I can find Chris Jones, or some Brazilians, or both to talk about this with on Thursday.

Cross posted at Climate Feedback

Tim Knowles — Tree drawings
July 30, 2008, 9:46 am
Filed under: Artworks, Nature writing, Trees



Tim Knowles (via Patrick Appel standing in on The Dish) is an artist who lets his trees do the drawing, and I wish I had known of him before, for example when he had an instillation at The Economist building earlier this year. Natural movements of the branches and well positioned canvases make the trees into devices that record movements of which they have no knowledge. Recursively, he photographs the set-up, too, apparently for parallel display. Here’s his online gallery

I think I would absolutely love this work. It certainly sets my mind whirring about nature and the unintended and their connection. One thing it reminded me of was a microcosmic reprise of David Nash’s Wooden Boulder (documented on his gallery’s site, though you have to click around to find it), in which the eponymous object rolled down a Welsh river and into an estuary and out to sea over many years; the natural movement shapes the artform. That thought led me to Google and via Plinius’s Some landscapes (a great resource to which you may be sure I will be returning) I came to this comment by Nash in an interview in Sculpture magazine

I think Andy Goldsworthy and I, and Richard Long, and most of the British artists’ collectives associated with Land art would have been landscape painters a hundred years ago. But we don’t want to make portraits of the landscape. A landscape picture is a portrait. We don’t want that. We want to be in the land.

At one level you could see Knowles as continuing this process by enabling natural self portraits; not self portraits by the tree, but self portraits of the tree-wind process. But that obviously doesn’t really tell the story, because the invisible intervention of Knowles himself is obviously also part of the subject, in the way that it permits the powerful orthogonality in the display — the record of movement on one side, the captured-moment stillness of the photo on the other. (I’d put in a quote about the meaning of the space between frames here, but I seem to have leant my copy of Understanding Comics to someone…)

I suppose one way to read the works is as post-situationist “happenings” — very post, in that the set up, the game, is defined without any overt reference to society and then highly aestheticised, and I suspect from a position of very little knowledge that situationists would have disapproved of both those things. Another way in would be to see them in the context of Bruno Latour’s notion of the inscription device, nicely outlined by George Goodall on his blog Facetation — but here, this being art not science, the inscription device is not made invisible, but re-rendered in parallel. 

I would, pretty obviously, love to see these pieces — and much of his other work, a lot of which also works on the basis of the unintended: movements of the wind, postal delivery services, etc. Here, for example, is a picture of the full moon reflected in the Serpentine on a long exposure.

More on Inhabitat, Le Territoire des sens

Image by Tim Knowles used under “fair use” for purposes of review. 

Wordling the Sun
June 18, 2008, 9:34 am
Filed under: By, with or from EtS, Trees

My excellent colleague Daniel, who blogs for us at Nature’s Great Beyond, has brought Wordle to my attention, and I now bring it to yours. It’s a tag cloud generator, and a very elegant one, I think, made by Jonathan Feinberg (who also, very coolly, used to drum for They Might Be Giants). I’ve used it on the three parts of Eating the Sun, in part to see if there are differences in the clouds that can have any meaning ascribed to them, in part because it is fun and pretty and easy.

The three parts, for those who have yet to buy or read the book, deal with the subject in three ways: the first looks at the recent scientific history of photosynthesis, the second looks at the impact of photosynthesis on the history of the earth, and the third looks at photosynthesis in the context of the current carbon/climate crisis. Some patterns are indeed there to see in the wordles: energy is an issue in the recent history and the implications, for example, but not so much in the section on the earth, where oxygen comes to the fore. Carbon becomes more and more dominant as the book goes on. 

That aside, they are quite pretty, though not as good as Daniel’s wonderful “Origin of Species”, which has T-shirt written all over it, or vice versa, or whatever. You can click through for higher res. Wordle clouds aren’t automatically generated with a vaguely tree-ish shape, by the way: there’s been some unnatural selection in the process.

EtS Part 3, wordled

Images: generated by me using Wordle, and available under a creative commons license

Update: I’ve added another Wordle tag-cloud to the entry “What’s ‘Eating the Sun’ about?” that shows how reviewers have answered that question