The World Without Us

This chapter focuses on the Korean Demilitarized Zone (DMZ), a strip of land 151 miles long and 2.5 miles wide separating North and South Korea. The DMZ has been devoid of humans since the 1953 end of hostilities in the Korean War because it’s full of land mines, and it has become an important refuge for endangered Asian wildlife. An international coalition of scientists is now trying to persuade the North and South Korean governments to make it a “peace park”; the high cost of mine removal would be easily surpassed by tourism revenue, they contend. However, encroaching development threatens this option, and Weisman is pessimistic about the prospects of preventing development within the DMZ if it is opened to human use:

[I]f land mines can be swept for tourists, real estate mongers will scheme for the same prime property. If a compromise results in developments surrounding a token history-nature theme park, the only viable species left in the DMZ will likely be our own (190).

If humans suddenly vanished, however, megafauna would rapidly spread out from the DMZ and devour most livestock. Species that are the product of extensive selective breeding, such as horses, would quickly evolve back to their wild origins. One way or another, all domesticated plants, crops, and animals would be gone in a matter of centuries according to the eminent biologist E. O. Wilson, a leading advocate of the DMZ peace park.

Not much more than a century ago, the North American passenger pigeon was probably the most abundant bird on Earth: “Its flocks, 300 miles long and numbering in the billions, spanned horizons fore and aft, actually darkening the sky” (192). Nevertheless, the last one died in 1914, thanks to massive over-hunting and habitat destruction. This tragic outcome inspired a successful movement to conserve habitat, but today birds face novel threats that are harder to combat.

One of these is collision with radio, television, and cell-phone transmission towers, which probably kills at least 500 million birds a year in America. Millions more are electrocuted by power lines, and an estimated 60 to 80 million die from crashing into fast-moving cars on the highway. Because birds don’t recognize windows as obstacles, as many as 1 billion deaths annually may result from collision with plate-glass windows and mirrored high-rise buildings. Hunting accounts for another 120 million deaths. In the tropics, incessant land clearing and wetland drainage for agriculture cause even greater reductions in bird populations, although these impacts are harder to quantify.

Many of these human-caused threats would be eliminated immediately after human extinction, but one that would persist is predation by domestic cats, which in America probably accounts for billions of deaths every year. Introduced by European colonists, cats immediately began hunting the continent’s songbirds “not only for sustenance, but also seemingly for the sheer pleasure of it” (197). Cat population growth has also far outpaced that of humans, and unlike most other domesticated animals, cats would most likely do just fine without people around to take care of them. Cats are not the only exotic bird-predators humans have introduced into ecosystems; in the Pacific islands, for example, exotic pigs, rats, mongoose, and snakes have caused the extinction of many bird species. The rapid proliferation of these exotic species is currently limited only by the programs humans have established to eradicate them, but these efforts would end with us, allowing those species to run wild.

Weisman questions what would become of the roughly 30,000 intact nuclear warheads humans would leave behind if humanity suddenly vanished. The likelihood of any bombs exploding on their own is almost zero, but the structures housing them would eventually corrode, releasing their radioactive contents into the environment, where they would linger for a very long time: “It would take 250,000 years before the levels [of plutonium] were lost in the Earth’s natural background radiation” (202). Until then, the plutonium would continuously emit alpha particles, killing anything that inhaled them.

In the 1980s an international treaty banned the use of chlorofluorocarbons (CFCs) after they were found to be destroying the atmospheric ozone layer that makes life on Earth possible by limiting ultraviolet radiation from the sun. Ozone destruction has slowed since then, but the hydrochlorofluorocarbons (HCFCs) that replaced CFCs have similar (if somewhat less severe) effects, and humans haven’t yet found a replacement. If humans disappeared, the production of these substances would cease, but they would still be leaking out of millions of old appliances.

Another source of lingering radioactivity would be the almost 13,000 tons of spent fuel produced annually by the planet’s 441 functioning nuclear power plants. Spent fuel is far more radioactive than when it is fresh, and humanity has not figured out how to store it safely. The United States has only one permanent waste storage facility, constructed inside of underground salt domes similar to those in Houston, but it is designed to contain relatively mildly radioactive material such as discarded gloves, not spent fuel. Even so, the Department of Energy “is legally required to dissuade anyone from coming too close for the next 10,000 years” (209). At every other site in the US, spent fuel is contained in temporary structures that would eventually be breached by fire. At some facilities, high-level waste is melted in furnaces with glass beads and transformed into radioactive glass that could endure for a very long time. However, these facilities rely on air-conditioning, and if the power went off permanently, the radioactive material would eventually generate enough heat to cause an explosion. Elsewhere, spent fuel rods are “mummified” in steel canisters. Without humans to maintain them, the nuclear reactors themselves would eventually overheat, causing either a fire or a meltdown of the reactor core, and radioactivity would continue leaking into the air and water for millions of years.

The Chernobyl nuclear power plant, which in 1986 exploded in the world’s worst nuclear disaster, provides a real-time illustration of nature’s response to massive radioactive fallout. Barn swallows returned the following spring, but some had patches of albino feathers. Pine forests resprouted, but the trees had elongated, irregular branches and needles of various lengths. Four miles south of the plant, the population and diversity of birds has significantly expanded. Yet the Chernobyl fallout “will significantly irradiate [the] soils and food chain until at least AD 2135” (216). In a posthuman world, similar circumstances would unfold many times over. Rates of genetic mutation would increase greatly, with unknowable consequences. Some “successful” mutations might yield increased tolerance of radiation, while others would cause extinctions.

If humans disappeared, we would no longer be extracting and burning fossil fuels, but the greenhouse gases we have already produced would continue to warm the planet. If the climate warmed enough to deeply melt the permafrost in northern Canada, billions of tons of frozen methane deposits would be released, which could heat the planet to its hottest temperature in 250 million years. To mitigate global warming, companies are attempting to sequester carbon dioxide by injecting it into saline aquifers or abandoned gas wells, but these technologies are speculative. As environmental attorney David Hawkins puts it: “We know that nature can engineer leak-free gas storage: there’s been methane trapped for millions of years. The question is, can humans?” (223)

Weisman notes that it’s very hard for humans to imagine our own disappearance but says we can learn from civilizations that have already disappeared, like the Maya of Peru: “For at least 1,600 years, about 6 million Maya lived in […] a flourishing megalopolis of city-states” (224), yet the entire civilization collapsed within a century and was rediscovered only a thousand years later. Mayan society appeared to be remarkably stable and peaceful until the eighth century CE, when leaders in the city of Dos Pilas started conquering other lands. The rapacious elites amassed “fabulous wealth” but also provoked counterattacks, which forced residents to barricade themselves in city centers and abandon outlying fields. Population grew as the empire expanded, but agriculture struggled to keep pace on this diminishing acreage; what’s more rain forest soils are quickly depleted by intensive cultivation. According to the archaeologist Arthur Demarest, the Mayan collapse demonstrates how quickly single changes can lead to societies breaking down.

The geologic record is full of extinctions followed by the evolution of new life forms. During the Permian Extinction, 250 million years ago, 95% of living things died, possibly due to sustained volcanic activity in Siberia and/or an asteroid strike. Worms and snails became super-abundant before being killed off by creatures like crabs. Active predators took over, eventually transforming the planet “from near nothingness to the lush kingdom of dinosaurs” (231). Mammals took center stage after the next asteroid hit, 150 million years later. Humans will eventually go extinct, too, and we cannot know how this will impact the evolution of other species.