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from the atmosphere. This would enable crops to produce only as much nitrogen as they need, rather than farmers having to spread reactive nitrogen liberally and wastefully on the soil surface. But achieving this breakthrough, even with a technology as powerful as genetic engineering, will be far from easy. For a start, even legumes don’t actually fix their own nitrogen in their tissues: The task is performed by microbes living symbiotically in a plant’s specially created root nodules. To complicate things further, these nodules only work because they can somehow maintain the anaerobic (oxygen-free) conditions the microbes need to perform their nitrification miracle. At the moment, even the best plant scientists speak about getting nitrogen-fixation genes into major food crops as “at least a ten-year effort.”58 It may take even longer.

It seems almost impossible, right now, to imagine ways in which scientists could accomplish the trick. But then it seemed equally impossible, back in the days of William Crookes, to imagine that “through the laboratory” the starvation that seemed to threaten at the end of the nineteenth century could be turned into a century of plenty. But back then the optimists were right and the pessimists wrong. Creating new strains of rice, wheat, and corn that fix their own nitrogen could achieve in the twenty-first century what the Haber-Bosch breakthrough managed for the twentieth, and without the serious environmental drawbacks of industrial ammonia production. Environmentalists should not be scared of this prospect; they should welcome it. There can be no more important task than feeding people while protecting the planet. We must use the best of science and technology to help us to achieve this vital aim.

BOUNDARY FOUR

LAND USE

Consider humanity’s most serious planetary impacts covered so far. From climate change to biodiversity loss to nitrogen pollution, our unwitting changes to the Earth system have been extensive, mostly damaging, and often irreversible. But they have also been largely subtle, long-term, and imperceptible, and therefore easy to ignore or deny. The subject of this chapter, on the other hand, is not at all invisible—because it is taking place right in front of our eyes. No one can plausibly deny the utterly transformative impact we have had on the land.

The vast majority of the planet’s ice-free land surface—83 percent according to one study1—is now influenced by humans in some way or another. This may seem surprising, shocking—or perhaps merely stating the obvious. Where I live, in the British Isles, no part of the landscape is totally unaltered by people. Even “wild” areas like national parks look very different today to their natural prehuman state. The Lake District, for example, if left ungrazed by sheep, would revert to dense woodland on all but the highest peaks. Throughout the entire United Kingdom, the only species that have survived into the modern era are those that are able to coexist with human domination of the land: Others, from beavers to wolves, have been extirpated entirely.

Human impacts on land may be much greater than is obvious at first sight. Roads, for example, appear to directly affect only a relatively small strip of land, but they also cut ecosystems in half, altering the survival prospects of species living on either side of them. With an estimated 1 million animals killed every day on America’s road network, the effect of this constant removal of predators and prey is felt over much wider areas.2 A seminal 2002 study of the ecological effects of a busy four-lane highway in Massachusetts found impacts—varying from wetland drainage to noise—across a broad 600-meter corridor. The consequent nationwide effects over the United States’ entire 6.2-million-kilometer road network can only be guessed at.3

While busy paved roads are a recent phenomenon, general human transformation of the land surface has been accelerating for millennia. The Roman Empire deforested large areas around the Mediterranean, contributing to soil erosion and declining fertility.