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The idea that you can save the natural world by increasing the efficiency of agriculture is very appealing. This writer is far from convinced

INTENSIFYING agriculture is never going to be the new rock 鈥榥鈥� roll, but the idea is pretty fashionable right now. Last week a major study led by the UK government鈥檚 chief scientist John Beddington warned that the only way to feed the world is to produce more food from the same amount of land.

Some say that misses the point: we already produce enough food to feed 10 billion people, if only we didn鈥檛 waste so much. But there is another argument for intensifying agriculture: to save the rainforests. At last December鈥檚 climate conference in Canc煤n, Mexico, many delegates called for investment in farming to be included in , the fund that will pay tropical countries to protect their rainforests and the carbon they lock away.

The argument runs like this. As demand for food increases, farmers 鈥� already the biggest destroyers of forest 鈥� are likely to chop down yet more trees. So to prevent further destruction, we urgently need to intensify agriculture. As climate economics guru Nicholas Stern put it in Canc煤n: 鈥淐attle pasture in Brazil has only one animal per hectare. Raise that to two and you can save the Amazon rainforest.鈥� The Brazilian government鈥檚 strategy is based on exactly that premise. The World Bank, which will run the fund, made the same pitch.

The idea that intensifying agriculture relieves pressure on land is sometimes called the Borlaug hypothesis after Norman Borlaug, the pioneer of the green revolution, who first articulated it. But before we go ahead we had better be sure that it is true.

The counter-argument is that farmers don鈥檛 clear forests to feed the world; they do it to make money. So helping farmers become more efficient and more productive 鈥� especially those living near forests 鈥� won鈥檛 reduce the threat. It will increase it.

Tony Simons, deputy director of the World Agroforestry Centre in Nairobi, put it this way in Canc煤n. 鈥淏orlaug thought that if you addressed poverty in the forest border, they鈥檇 stop taking their machetes into the forest. Actually, they get enough money to buy a chainsaw and do much more damage.鈥�

One recent study seems to bear out this contrarian view. Thomas Rudel of Rutgers University in New Brunswick, New Jersey, compared trends in national agricultural yields with the amount of land under crops since 1990. If Borlaug was right then where yields rose fastest, the rise in cropland should be least. It might even go into reverse.

No such luck. Mostly, yields and cultivated area rose together. Rudel compared the finding to the Jevons paradox, named after the 19th-century economist William Jevons who found that increasing the efficiency of coal burning led to more, not less, coal being burned ().

That鈥檚 not to say intensification isn鈥檛 needed 鈥� the world has to be fed, after all. But it won鈥檛 necessarily save the forests. Any climate protection scheme that assumes it does is likely to be handing out money for nothing.