A Planet Under Pressure

In 2023 a committee of scientists proposed that we mark a new chapter in the Earth's own geological record, an epoch defined not by an asteroid or an ice age but by us, and they pointed, as its marker, to a small Canadian lake whose yearly layers of mud carry, from about 1950 onward, the unmistakable signature of a single species remaking a whole planet: the fallout of nuclear tests, the fly ash of burned coal, the pollen of felled forests, the first plastics.

Whatever the geologists finally decide to call it, the fact it points at is not in dispute, and it is the plainest way to say where the living planet now stands. Since roughly 1950, almost every measure of human activity, our numbers, our energy, our water and fertilizer and invention and consumption, has bent sharply and all together upward, in what its students call the Great Acceleration, and the Earth's own systems have bent along with them. The carbon dioxide in the air is higher than it has been in at least eight hundred thousand years, and the planet is measurably warmer for it. The ocean, which has quietly swallowed much of that extra carbon and heat, is growing warmer and more acidic, its coral reefs bleaching pale, its chemistry turning against the shells and skeletons of the creatures that depend on it. The plastic we met in an earlier chapter, the plastic now in the deepest sea trench and the Arctic snow and the falling rain and human blood and the unborn child, is not a forecast but a present measurement, the mark of a species whose reach has quietly exceeded a threshold it never meant to cross. Insects are thinning out of the long-running traps. The wild populations of vertebrate animals have fallen, on average, by well over half within a single human lifetime. Of nine planetary boundaries that scientists have proposed as the safe operating limits for a civilization, most are now judged to have been crossed.

The honest way to hold all of this is neither the shrug nor the scream, and this book has earned the standing to say so. It is not "the end of the world," a phrase that is both lazy and, worse, paralyzing. The Earth has taken far heavier blows than us, as Part II showed in its five great extinctions, and life itself will certainly outlast our species whatever we do to it. What is genuinely at stake is narrower, and more serious, than the planet: it is the particular, temperate, improbably generous set of conditions under which human civilization actually grew up, the mild climate and the full oceans and the dense living web that we, specifically, evolved to need. We are not in danger of destroying the Earth. We are spending down the unusually kind conditions that made us possible, faster than they can renew, and we are doing it, exactly as the cyanobacteria did when they first poisoned the ancient air with oxygen in Part II, largely as a side effect of how we make our living. The single difference, and it is the whole of the difference, is that unlike the cyanobacteria we can see it happening, and can, in principle, choose otherwise. Whether we will is one of the questions the last stretch of this book must hand to you.