Installed: 8/22/09------------------------------Updated 3/20/10
As noted on the Irristat page, and in Tenuous but Contingent Connections to Technical Treasures ruminations about its applications led me to think about using it to make deserts bloom.
At the time, (about 1979) concern about Anthropogenic Global Warming (AGW) was just beginning to be taken seriously. I thought, "What would the consequences be if the Sahara Desert were planted with appropriate evergreen trees, irrigated with efficient devices, like the Irristat - or other drip/trickle technology, using the vast fossil aquifers that are known to exist beneath the Sahara? Would such a forest change the climate sufficiently to increase rainfall, and make the forest self-sustaining?
So, in 1979, I got in touch with Jule Charney, at MIT. He had recently published 2 papers about what he named, biogeophysical feedback, to explain the sensitivity of the Sahel, the southern margin of the Sahara Desert, to wide fluctuations in rainfall. He suggested that overgrazing of grasslands led to increased surface albedo (increased reflection of sunlight), decreased soil moisture and decreased surface roughness, all leading to further drought; while in the absence of overgrazing, the albedo was lower, the soil moister, and the surface roughness greater, tending to increase precipitation and move further from desert-like conditions. He told me his colleague, Peter Stone, and Jim Hansen, the new Director of the Goddard Institute for Space Studies, in NYC were just starting to test a new Global Climate Model (GCM) which might allow us to explore such questions.
I then contacted Jim, and began an off again - on again collaboration with him and his group.
In the early '80s, the GCM had developed to a stage where we thought we could run an appropriate simulation. David Rind prepared an appropriate file that redescribed the 8º by 10º 'cells' that are used to describe the Sahara Desert region of Africa in the GCM - changing the albedo, soil-wetness and surface-roughness to match that of a tropical rainforest. We then ran a simulation. The rainfall over the Sahara increased, but not enough to make the forest self-sustaining. Eventually the fossil aquifers would be drained dry, and the forest would die!
Well, so much for a good idea!
I kept in touch, as they improved the GCM. A few years ago, they developed an educational version of essentially the same model GCM as we had used in the '80s, (EdGCM) but which could now run on a laptop, rather than on a main-frame computer. For at least nostalgic reasons, I decided to try to repeat the Sahara simulation again, on my laptop. It turned out I had to change the equivalent Sahara files again (albedo, soil wetness, roughness, etc.), and Jim Hansen encouraged Mark Chandler and his crew to help, since this capability was not available in the EdGCM 'client' software.
I got essentially the same results after runs which tied up an Apple iBook for a couple of weeks of steady crunching. But the new graphics software is particularly user friendly, and so it was much easier to explore what had been going on. I discovered that the soil moisture that we programmed in, was rapidly consumed. Whereas the GCM held albedo and roughness constant with time, soil moisture responds to the trees' demands. The changes DID NOT simulate constantly irrigating to replace consumed water! My first reaction was to suppose that I had not really repeated the '80s experiment. I asked David Rind just what he had done to simulate irrigation in those eary runs? It turned out that we had made the same error then!
So it became clear to Jim Hansen, Peter Stone, David Rind and I that it might be worth re-doing the experiment, but with the latest version of the GCM, ModelE, with 4º by 5º resolution. Igor Aleinov, who with Nancy Kiang, was working on a dynamical vegetation module for ModelE, was recruited to develop appropriate software. At each time step, it would check the soil moisture of each 'Sahara cell', and if it had dropped below the prescribed moisture level, add just enough water to restore it to the prescribed set-point (just like an Irristat!).
We made a few such runs and VERY SUBSTANTIAL increases in rainfall were induced - but only during a season from about March through October. During the rest of the year, the trees would die without irrigation! At that point (the summer of 2006), a paper was published in Science 313, page 1088, that reviewed the latest results wiith reverse osmosis (RO) desalination of seawater. Below I quote a sentence from page 1089 that struck me as phenomenal:
"In one such plant, which started up last fall in Ashkelon, Isreal, for example, isobaric chambers have helped lower the cost of desalinated seawater to $0.527 cents (sic) per m3 , among the cheapest ever by a desalination facility." I did NOT notice the typographical error, and interpreted the statement as saying that a cubic meter of pure water could be extracted from seawater for 0.527 cents! At that price, irrigating the Sahara forever would be economical.
It took me a week to spot the typo. But by then, I had made pertinent calculations that made it clear that even at 52.7 cents per cubic meter, the irrigation of the Sahara forest was economically feasible. Had Science not made the typo, I might have ignored this possibility!
The rest, I hope, is history. Two papers, stemming from these studies have just been published online in the journal, Climatic Change:
Here are abstracts:
Irrigated afforestation of the Sahara and Australian Outback to end global warming (free pdf)
Leonard Ornstein · Igor Aleinov · David Rind
Received: 14 January 2008 / Accepted: 28 April 2009
© The Author(s) 2009. This article is published with open access at Springerlink.com
Abstract Each year, irrigated Saharan- and Australian-desert forests could sequester amounts of atmospheric CO2 at least equal to that from burning fossil fuels. Without any rain, to capture CO2 produced from gasoline requires adding about $1 to the per-gallon pump-price to cover irrigation costs, using reverse osmosis (RO), desalinated, sea water. Such mature technology is economically competitive with the currently favored, untested, power-plant Carbon Capture (and deep underground, or under-ocean) Sequestration (CCS). Afforestation sequesters CO2, mostly as easily stored wood, both from distributed sources (automotive, aviation, etc., that CCS cannot address) and from power plants. Climatological feasibility and sustainability of such irrigated forests, and their potential global impacts are explored using a general circulation model (GCM). Biogeophysical feedback (Charney 1975) is shown to stimulate considerable rainfall over these forests, (see animations) reducing desalination and irrigation costs; economic value of marketed, renewable, forest biomass, further reduces costs; and separately, energy conservation also reduces the size of the required forests and therefore their total capital and operating costs. The few negative climate impacts outside of the forests are discussed, with caveats. If confirmed with other GCMs, such irrigated, subtropical afforestation probably provides the best, nearterm route to complete control of green-house-gas-induced, global warming.
Replacing coal with wood: sustainable, eco-neutral, conservation harvest of natural tree-fall in old-growth forests (free pdf)
An editorial essay
Received: 17 May 2008 / Accepted: 28 April 2009
© The Author(s) 2009. This article is published with open access at Springerlink.com
Abstract When a tree falls in a tropical old-growth forest, the above ground biomass decays fairly rapidly and its carbon is returned to the atmosphere as CO2. If the trunk of that tree were to be harvested, before decay, and were stored anoxically, or burned in place of coal, a net of about 2/3 of that amount of CO2 would be prevented from entering the atmosphere. If the ash-equivalent of each tree trunk (about 1% of dry mass) were recycled to the site of harvest, the process would be indefinitely sustainable and eco-neutral. Such harvest of the undisturbed old-growth forests of Amazonia and Equatorial Africa could effectively remove about 0.88 to 1.54 GtC/yr from the atmosphere. With care, additional harvest of adjacent live trees, equaling up to two times the mass of the fallen trees, might be similarly collected, just as sustainably, and with almost as little ecological impact. This very large contribution to the mitigation of global warming is discussed - with caveats. It could result in substantially reduced coal emissions, but without closing down many presently coal-fired power plants - and at much lower cost and lead-time than carbon capture and sequestration (CCS).
And here are my "How To Quickly Lower Climate Risks At 'Tolerable' Costs?".
“Irrigated Afforestation of Deserts for Thermostatting the Earth, to End Global Warming and Provide Enormous Sustainable Sources of Wood to Replace Non-renewable Fossil Fuels”.
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