Half-Earth: Our Planet’s Fight for Life

This chapter focuses on the Sixth Extinction. The primary driver of the Sixth Extinction is human activity, making humans “the most destructive species in the history of life” (54). Conservation scientists use the acronym HIPPO to describe these activities: habitat destruction, invasive species, pollution, population growth, and overhunting. Human population growth is the most politically charged of these activities. Wilson argues that reproduction, while necessary, has caused populations around the world to balloon to unsustainable numbers. Population growth also results in consumption increases; the latter trend further adds to “humanity’s ecological footprint” (58). Wilson defines ecological footprint “as the amount of space required to meet all of the needs of an average person” (189).

In the pre-human era, one extinction occurred every three million years. Scientists suggest that 99% of all species that have existed throughout Earth’s history have gone extinct. Wilson emphasizes that these extinctions were not true die-outs, since many evolved into other species. With the arrival of modern humans 200,000 years ago, the rate of extinction is now occurring up to 1,000 times faster than during the pre-human era. Conservation efforts, including conservation organizations and government regulations, are helping to stabilize species threatened with extinction. These efforts have not returned the extinction rate to pre-human levels.

Wilson describes four “facts about global biodiversity to keep in mind while trying to save it” (60). First, multiple human activities are usually impacting an ecosystem; when combined, they intensify the extinction rate. Also, tropical climates have greater biodiversity than temperate climates, and there is a relationship between the richness of species in an area and their geographical range. Tropical climates have a higher concentration of species, but these species have much smaller ranges compared to species living in temperate environments. This fact makes tropical species more vulnerable to extinction. Finally, invertebrate species are just as vulnerable to extinction as vertebrate species.

Since the mid-18th century, which was the beginning of the Industrial Revolution, humans have been “using the atmosphere as a carbon dump” (65). Human activities, including burning fossil fuels, deforestation, agriculture, and decomposition of wastes, have increased greenhouse gases in the atmosphere, such as methane and carbon dioxide. These gases prevent heat from leaving the atmosphere and result in global warming. Global temperatures should not increase more than 2°C (3.6°F) above pre-Industrial Revolution temperatures. Wilson reminds us that temperatures have already risen to nearly half of this threshold. Effects of this warming include longer and more intense heat waves, more severe storms, the melting of glaciers in Antarctica and Greenland, rising sea levels, and mass coral reef bleaching. These effects will continue to worsen if the global temperature continues to rise.

According to Wilson, governments have been slow to act, in part due to the “tragedy of the commons” (67), a term coined by the ecologist Garrett Hardin in 1968. The tragedy of the commons refers to a situation in which a shared resource is overused and ultimately depleted. This situation occurs because individuals consume a resource without considering the common good of all users. One classic example is the collapse of fisheries. Fishing is often weakly regulated or, in some places, not regulated at all. The result is overharvesting of fish (and other marine species).

Mass extinction of most ocean species is rare because their territory is significantly larger than that of land animals. The exception is coral reefs, “often called the ‘rainforests of the sea’” (68). Wilson notes that they are particularly vulnerable to climate change. Sea temperature rises result in increased acidity of oceans, which causes the catastrophic process of coral bleaching.

The conservation movement began in the United States during the 19th century. The movement “came late, but mercifully not too late to save what is left of our flora and fauna” (73). Local, state, and national parks were established to conserve large areas of land and all organisms within. Organizations such as the Nature Conservancy have also set aside reserves. Other parts of the world adopted this form of conservation, and most countries now have government-protected parks. This movement has not been successful in slowing the rate of extinction. To Wilson, the conservation movement gave rise to what he believes is the most dangerous worldview: the “Anthropocene worldview,” or “new conservation” for anthropocentrists. 

A growing group of revisionist environmentalists hold this Anthropocene worldview, in which “humans completely dominate Earth and surviving wild species and ecosystems are judged and conserved for their usefulness to our species” (71). Extreme advocates even suggest that humans’ ruling over nature was preordained. New conservationists posit several ideas for how to preserve biodiversity in this new age. First, they argue that invasive species will help balance the extinction of ongoing native species by filling in the niches left behind in the ecosystem. Interbreeding between invasive and native species, which creates new hybrid species, will also increase species’ numbers. They argue dramatic increases in new species followed past mass extinctions; Wilson points out that the emergence of new species often took at least five million years. Finally, many believe that modern technology can bring extinct species back to life, but this belief ignores the reality that their niches may no longer exist within the ecosystem.

Wilson strongly refutes new conservation and refers to it as “anti-conservation.” He believes that this worldview stems from not having experienced the “magnificent biodiversity” found across the planet.