Human Populations and Biodiversity

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Human population growth affects biodiversity in two main ways: massive numbers of people change the environment—global warming is the primary example—and urban areas expand into less developed areas. Expansion into rural land brings with it the hallmarks of city life: roads, congestion, pollution, noise, and wastes.

Humanity affects biodiversity in a general sense because of its impact on the earth and the atmosphere. Developed societies are also industrialized societies with a high level of consumerism, so they exert a larger ecological footprint on the planet than nonindustrialized societies. An ecological footprint is the amount of land and water needed to support one person and absorb that person’s wastes. The amount of cropland, grazing land, forests, and fishing grounds plus carbon-based fuel and nuclear fuel consumption factors into a single ecological footprint. For instance, a typical U.S. resident has a footprint of about 24 acres (0.1 km2); a typical resident of India has a footprint of less than 2 acres (0.01 km2). Subtle things also contribute to ecological footprint because not all industrialized nations have footprints equal to that of the United States. Germany’s is about 11; France’s and the United Kingdom’s are each less than 14.

Carbon footprint is a component of ecological footprint and equals the amount of carbon-based fossil fuels used and the waste made by burning those fuels. Environmental organizations such as the Nature Conservancy calculate carbon footprint as follows: the amount of forestland needed to remove from the atmosphere the end-products of burning a unit of fossil fuel. The Nature Conservancy’s online calculator determines the carbon footprint for any household by answering questions on energy use, vehicle type and daily travel, diet, and waste recycling. The calculator
then automatically determines an individual’s or household’s carbon footprint as tons of carbon dioxide equivalents produced per year. Equivalents means that all greenhouse gases have been converted to an equivalent amount of carbon dioxide based on the degree of global warming they cause. Ecologists have determined that carbon footprint makes up almost half of a typical ecological footprint, and it has grown faster than any other component, especially in countries with a high level of consumerism. For example, the world carbon footprint is 2.64 acres (0.01 km2) per person, ranging from nonindustrialized countries such as Peru and Somalia that produce a carbon footprint of 0 acres compared with that in the United States, 13.6 acres (0.05 km2) per person. The United States owns the third-highest carbon footprint, behind the United Arab Emirates (22 acres [0.09 km2]) and Kuwait (16 acres [0.06 km2]). Watching television, buying clothes, visiting a gym, and spending a day at the beach provide a short list of examples of carbon-emitting activities. Euan Murray, strategy manager of the Carbon Trust in Great Britain, told Britain’s Independent in 2006, “This piece of work [calculating carbon footprint] is about making people aware that everything they do involves carbon emissions and not just flights and heating their homes.” The term carbon footprint shows up increasingly in the media, but as Murray suggests, how does a large carbon footprint affect ecology?

The continued growth of ecological and carbon footprints puts animals and plants in peril because Earth’s biota can no longer support the current number of people. Since about 1988 the ecological footprint of Earth’s human population has exceeded the planet’s capacity to support it. This attribute is called biocapacity, and as humans continue to stress biocapacity, other species will lose hold on their natural habitats. This scenario may be altered, however, if people make major changes in their relationship to natural resources. The purpose of green technologies is to find ways to preserve biocapacity by conserving natural resources.

Almost every human activity affects biodiversity in a negative way. All types of industries, agriculture, recreation, and general consumption lead in some way to ecosystem degradation. Furthermore, the natural world seems to have become a foreign concept to many. Each year people are injured or killed because they did not understand animal behavior in nature. It is not unusual, for example, to see visitors at national parks leap from their cars and rush too close to bears, elk, moose, coyotes, and other wildlife. National Geographic writer John G. Mitchell once observed while visiting Tennessee’s Great Smokey Mountains National Park, “Enthralled visitors often assume—mistakenly—that roadside creatures are too tame to be dangerous.” Urbanization has simply disconnected people’s lives from nature. Many city residents go weeks, months, or even years without experiencing a day free from human influence.

The natural world is everywhere disappearing before our eyes— cut to pieces, mowed down, plowed under, gobbled up, replaced by human artifacts.

—Edward O. Wilson

Climate change, or specifically global warming, symbolizes the dangers wrought on the environment by human activities. Earth has always possessed natural rhythms consisting of long periods of colder temperaxvitures and long periods of warmer temperatures. This has led some people to believe that global warming results from a natural cycling of temperature rather than a continuous and increasing phenomenon. Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research in Boulder, Colorado, told the New York Times in 2008, “Too many think global warming means monotonic relentless warming everywhere year after year. It does not happen that way.” Today’s combination of greenhouse gases in the atmosphere and deforestation has caused, nevertheless, a dramatic rise in the average of year-to-year global temperatures than at any other time in Earth’s history. Greenhouse gases—volatile organic compounds, ozone, methane, and carbon dioxide and other exhaust emissions—trap the Sun’s heat in the atmosphere like a glass greenhouse


The rapid increase in the world’s human population since the 1800s has been the root of today’s threats to the environment and to biodiversity.

holds heat. At the same time, deforestation leaves fewer trees to absorb carbon dioxide, the most abundant greenhouse gas. In 2007 the Intergovernmental Panel on Climate Change released a report, “Climate Change 2007: Synthesis Report,” that was the product of six years of work plus research on previous studies by hundreds of researchers from more than 100 nations. It stated, “Warming of the climate system is unequivocal, as is now evident from observations of increases of global average air and ocean temperatures, widespread melting of snow and ice and rising average global sea level.” Put another way, there should no longer be any question of whether climate change is real and caused by humans.

Much of the damage to the Earth’s biomes from global warming may be irreversible, but two technologies exist for rescuing the remains of habitats in peril: restoration ecology and reconciliation ecology. Restoration ecology comprises the activities for returning a damaged habitat disturbed to its original state. Reconciliation ecology comprises the actions that make a habitat suitable for sharing between humans and native species. The case study “The Everglades” discusses how these methods work.