Astronomers, astrobiologists, and science fiction writers have long dreamt of terraforming planets and their moons — converting barren and alien wastelands into lush habitats for humans and other creatures. These scientific and creative thinkers point to the numerous advantages of distributing life to other planets, solar systems, and eventually other galaxies, if possible. Furthermore, they argue that such a bold agenda is actually necessary for humans to pursue, if only to ensure the survival of our species and any others that we wish to save from the unavoidable death of our sun. (Our star, like any other, will go through known stages of its existence, eventually converting from hydrogen to helium as its primary fuel source, causing it to expand and destroy at least the first three planets.)
Yet if greater biodiversity on other worlds holds so much promise, why are we not pursuing it more on planet Earth, for which the feasibility is so much greater, and the costs so much lower — at least, compared to such operations in space? Why are we not transforming our deserts into lush grasslands, forests, and jungles? Surely this would increase the amount of life on our planet, as well as the odds of survival of all species, including those at the brink of extinction. In addition, it would significantly cool a planet that is supposedly suffering from global warming, and it would absorb a huge amount of carbon, which is the fundamental building block of all life on Earth. On the other hand, critics question where we could possibly obtain the fresh water and minerals needed for growing vast tracts of greenery.
Scientists are now taking those ideas from daydreams to drawing boards, as they begin to seriously consider whether it would be wise, or even viable, to try to transform Earth's largest deserts into vast forests of heat-resistant plants, such as eucalyptus. Details can be found in an article titled "Forest a Desert, Cool the World" and published on 14 September 2009 by ScienceNOW (the online daily news service of the journal Science). A group of three scientists believe that it is possible to terraform the deserts of Australia and the Sahara, by desalinating nearby ocean water, distributing that water via aqueducts and pumps, and watering the forests using drip irrigation to minimize water loss from evaporation and from seepage into sandy soil.
Like any massive disruption of Earth's ecosystem — planned or otherwise — any such project would have tremendous consequences — not all of them positive, intended, or even foreseeable. Benefits include increased rainfall (roughly 700 to 1200 millimeters per year, in the Sahara), cooling of the Earth's atmosphere (up to 4 to 8 degrees Celsius) because of the increased cloud cover, and natural and ongoing sequestration of carbon (8 billion tons per year, assuming both Australia and the Sahara are fully forested). One advantage not mentioned in the article is the potential moderation of any increases in sea level as a result of the current melting of icebergs and the ice caps at the poles. Known downsides include the cost of developing and maintaining these forests: $2 trillion per year, which is equivalent to $400 per ton of carbon — approximately double the cost of underground sequestration. Unknown pitfalls include potential plagues of locusts in Africa, and moist soil no longer being blown as dust into the ocean, where its iron is essential for sea life. Other possible natural disasters include huge forest fires, to which eucalyptus is quite prone. Imagine the terrible bush fires of 2009 in the Australian state of Victoria, multiplied hundreds fold. In that case, all of the carbon would be right back in the atmosphere.
The science fiction authors may have been correct from the start: We should perhaps first try these experiments on another planet, before risking our only home.