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land to feed the same number of people. In practice this trade-off is fatal: Land use counts as a planetary boundary, as the next chapter will show, because the health of terrestrial ecosystems depends on only a small proportion of land being devoted exclusively to sustaining humans. If we were to try to use organic agriculture to feed the entire world’s population at current levels of nutrition, remaining terrestrial natural ecosystems would be devastated by the massive required expansion in plowed farmland.

This conundrum has been demonstrated in microcosm by studies of British organic farming. One piece of field research, conducted by ecologists at Leeds and York universities, demonstrated that although butterfly populations were higher on organic farms thanks to more wildlife-friendly farming practices, crop yields were typically much lower.31 In practice, the researchers concluded, it might be better to farm conventionally (using chemicals) on smaller parcels of land, produce the same quantity of food overall, and devote the spare farmland to nature reserves—which would be much better for butterflies and other wildlife even than organic farms overall. “If ‘sharing’ our farmland with wildlife means that more total land will be taken into production to produce our food, then there may be a hidden cost of hurting wildlife somewhere else,” says author Professor Bill Kunin of Leeds University.32 A second study, also published in 2010, confirmed that while organic farms tended to harbor 12 percent more wildlife on average, they produced less than half the yield.33 “Our results show that to produce the same amount of food in the UK using organic rather than conventional means, we’d need to use twice the amount of land for agriculture,” says Professor Tim Benton, also at Leeds University.34 This trade-off will also apply internationally: British consumers may already be compensating for underproductive domestic organic farms by buying crops grown on land abroad, leading to a more damaging effect on biodiversity overall as rain forests and grasslands are plowed up overseas.

Nor is organic farming necessarily better for the climate, despite the dependence of intensive industrialized-country farms on oil-guzzling heavy machinery. Researchers based at Stanford University in the U.S. recently calculated that the widespread use of mechanization and artificial fertilizers between 1961 and 2005 avoided the emissions of 161 billion tonnes of carbon that would otherwise have been released through land-use change.35 (Yes, this is a net figure: Carbon dioxide exhaust from all the tractors has been subtracted, as have agricultural nitrous oxide and methane emissions.) In other words, had farms been run organically during the period, huge areas of forest and savannah would have been brought into production to keep people from starving, destroying, and releasing the stocks of carbon stored in trees and soils. During the 1961–2005 period, global cropland area did increase by 27 percent—but total yields rose 135 percent, a jump in productivity that spared vast areas of natural land from the curse of the plow. The amount of additional land that would have been needed to produce this quantity of food at 1961 levels of yields and inputs is truly vast: 1,761 million hectares, an area larger than Russia.

Given that humanity cannot do without nitrogen fertilizer for our crops without running the risk of starvation, the most sensible strategy to try and meet the nitrogen boundary is to use what we need as efficiently as possible. That means aiming to design crops that are much more efficient in their uptake of nitrogen added by farmers to the soil. At the moment only a third of nitrogen applied to fields actually ends up in the grain. Given that cereal crops are dosed with two-thirds of the global total of 128 million tonnes of fertilizer, that is an awful lot of nitrogen left to wash down rivers or add to the growing stock of nitrous oxide in the atmosphere.36 There are ways that farmers can waste less fertilizer, but the key long-term strategy