Irrigate and Forest the Desert and Cool the Planet. (September 15, 2009)

Available online the journal Climatic Change, has published as open access simulations predicting the effect of converting the Sahara desert and central Australia to a forested expanse in order to mitigate global warming^§.

Leonard Ornstein*, a cell biologist at New York's Mount Sinai School of Medicine, together with climate modellers David Rind and Igor Aleinov of NASA's Goddard Institute for Space Studies show the feasibility of desert forestation with sufficient desalination of ocean waters and using aqueducts and pumps together with drip irrigation immediate to the trees to minimize water loss to evaporation and seepage into sandy soils.

Dr Ornstein told ScienceNow Daily News: "Eucalyptus grandis and a large number of other tropical tree species are heat-tolerant, so long as they have an ample supply of water in the root zone."  In addition the simulations indicate the tree cover would bring more rain -- about 700 to 1200 millimetres per year -- and clouds, which would help to reflect the sun's rays back into space. The scheme could also work for the arid Australian outback.

Dr Ornstein went on to say that if most of the Sahara and Australian outback were planted with fast-growing trees like eucalypts, the forests could draw down about 8 billion tons of carbon a year -- nearly as much as people emit from burning fossil fuels and forests today. As the forests matured, they could continue taking up this much carbon for decades.

All up Dr Ornstein and his colleagues estimate costs would run to about US$2 trillion per year. However, according to ScienceNow: "The price would be roughly comparable to that of capturing carbon dioxide at power plants and storing it underground, which would eventually cost about US$200 per ton of carbon, according to a recent study from Harvard University's Belfer Center for Science and International Affairs, compared with about US$400 per ton of carbon for the forests. 'Any solution to climate change has to be a multitrillion-dollar project,' Ornstein says. 'The issue is what the payback is.' In several decades, the forests could be sustainably harvested as a source of fuel for wood-burning power plants, making them a nearly carbon-neutral energy source, Ornstein argues."

As to side effects ScienceNow notes: "The increased moisture could trigger plagues of locusts in Africa, just as the odd wet year does now. It could also dampen existing soils, stopping iron-rich dust from blowing off the Sahara and into the Atlantic Ocean, where it nourishes sea life, the study points out."

Nevertheless, Richard Anthes, president of the University Corporation for Atmospheric Research in Boulder, Colorado says the Ornstein, Rind, Aleinov model: "is incredibly important and definitely worth taking seriously and looking into further. The benefits could be enormous and go well beyond carbon sequestration."

Would desalinating enough seawater be affordable? Dr Anthes says: "This paper suggests that it is."

The Abstract from the paper:

 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 is shown to stimulate considerable rainfall over these forests, 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, near-term route to complete control of green-house-gas-induced, global warming.

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[Note added September 17:

It's hard to evaluate the personal impact of a multi-trillion dollar price tag, without having a feel for what the size of the 'gross global product' might be. In our paper, we mainly frame the problem in terms of how large might be a 'carbon tax' on a gallon of gasoline, to 'compensate' for the CO2 it will turn in to, if that tax would be used to build and support such forests.
     It turns out that at 'worst', it would be about $1. If the forests stimulate sufficient rainfall to reduce the required irrigation by half (and the GCM runs suggest they would), that drops to about $0.50. And if you take into account that those forests are huge sources of sustainable and renewable carbon, to replace our non-renewable and dwindling fossil carbon (used for fuels and petrochemicals), that $0.50 is also buying something presently 'priceless'!

Leonard Ornstein]

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^§ The paper: Irrigated afforestation of the Sahara and Australian Outback to end global warming by Leonard Ornstein, Igor Aleinov and David Rind

and an Editorial essay by Dr Ornstein are available for free download.

*According to the Mount Sinai School of Medicine commemorative sesquicentennial publication: "1959 -- Dr Leonard Ornstein develops the polyacrylamide gel electrophoresis method for separating proteins."