Bad Idea: Foresting the Sahara

A plan to turn the Sahara into a forest is not about
reducing carbon emissions at all

There's ambition, there's drive and then there's hatching a plan to combat climate change by turning the Sahara into a forest. The idea alone is enough to make your head ache. But Leonard Ornstein, a cell biologist at the Mount Sinai School of Medicine in New York, reckons he has worked out the details of how to afforest the world's largest desert - oh, and the Australian Outback as well.

His academic paper appears in the journal Climatic Change this month. In it, he envisages forests of eucalyptus and other heat-tolerant tropical trees, irrigated with seawater from neighbouring oceans. Desalination plants on the coast would supply usable water, a huge system of pumps and aqueducts would carry it into the desert, and "drip irrigation" - also known as plastic tubing around the base of the trees - would keep the soil moist and the plants lush.

Along with David Rind and Igor Aleinov, climate modellers at Nasa's Goddard Institute for Space Studies, Ornstein has calculated that areas of the Sahara would be cooled by as much as 8°C. The trees would increase rainfall and cloud cover, and the combined effect of the Australian and African forests would be to draw down about eight billion tonnes of carbon emissions a year - nearly one and a half times the amount the US produces annually.

So, is that it? Has someone just solved all our problems? Well, not if you are one of the 2.5 million people who live in the Sahara, or one of the 700,000 Australians living in the Outback. Even if you're not - and you're also not concerned at this creepily colonial approach - there are still a few little drawbacks.

The project's $2trn annual price tag aside, there is the problem of what to do with all the highly salty waste water created by the desalination process, as putting it straight back into the sea would create "hyper-saline, anoxic 'dead zones'". There's the iron-rich Sahara dust, which at present blows off the desert and into oceans, where it nourishes sea life, but which would no longer be going anywhere. And just in case the message about the dangers of playing God weren't quite clear enough, there are also the plagues of locusts, encouraged by increased moisture.

Biblical horrors aside, there is one other, small disadvantage to Ornstein's plan, which is that it is not actually about reducing carbon emissions at all. He sees this project being paid for by a tax on petrol, the cost of which he hopes can be offset in future by increasingly fuel-efficient car design. In short, the plan is to kick millions of people off the land and throw the ecosystems of entire continents into chaos so that the west can carry on guzzling gas. If anyone has a more daft idea, we'd love to hear it.