Measuring Population's Impact

There is no easy way to measure the overall impact of human activities on the environment. Nevertheless, several approaches have been developed, as follows:

Environmental resource accounting attempts to place an economic value on “environmental goods and services” used—natural resources that conventionally have been regarded as free and used in common. These include unpolluted freshwater, clean air, ocean life, forests, and wetlands. A recent study by Robert Costanza of the University of Maryland estimated the total value of ecosystem services and products at US$33 trillion per year—an amount that exceeds the total value of the global economy as conventionally measured (US$29 trillion in 1998) (41, 163).

Some economists argue that the value of environmental goods and services should be incorporated into estimates of Gross Domestic Product (GDP), as are manufactured assets. Unlike manufactured capital, which depreciates in value over time, environmental capital (such as forests, fisheries, and unpolluted air and water) currently is not considered to depreciate, and no charge is made against current income as it is used. “A country could exhaust its mineral resources, cut down its forests, erode its soils, pollute its aquifers, and hunt its wildlife and fisheries to extinction, but measured income would not be affected as these natural assets disappeared,” notes Robert Repetto of the World Resources Institute (98, 192).

If natural resources were valued in the same way that manufactured assets are valued, it might help economies learn to use them more efficiently and to conserve them in order to assure continued use in the future. Such valuations also might help indicate the economic benefits of protecting the environment, as well as the ecological benefits. In other terms, instead of continuing to draw down their “environmental capital” until it is gone, economies could begin to live on its interest, maintaining the capital for use indefinitely in the future (90).

The equation I = PxAxT represents another effort to describe the overall impact of humanity on the environment. In the equation:

• I is environmental impact,
• P is population (including size, growth, and distribution),
• A is the level of affluence (consumption per capita), and
• T is the level of technology.

Despite its limitations—for instance, inability to assign actual values to each component or to depict changes in the factors over time—the equation is valuable. In particular, it emphasizes that developing countries with large and rapidly growing populations affect the environment, even though their levels of affluence may be low, while at the same time countries in the developed world with little or no population growth have a substantial environmental impact because consumption per capita is so high (54, 55, 92, 212).

The equation makes clear that slowing population growth is a key part of any strategy to reduce humanity's impact on the environment. For example, even if per capita resource consumption (A) declined or technologies (T) improved enough to reduce the environmental impact (I) of humanity by 10%, this gain would be wiped out in less than a decade because world population (P) is growing at over 1% per year (92, 240). Since per capita consumption of resources is expected to increase as living standards rise, protecting the environment requires more efficient production technologies, less waste, and ultimately a stable world population size (245, 247).

In 1997, as part of the five-year review of environmental conditions following the Rio Earth Summit, the Earth Council of Costa Rica sponsored a major “Ecological Footprints of Nations” study. The chief researcher was Mathis Wackernagel of the University of Anahuac de Xalapa in Mexico.

Wackernagel's study calculated, nation by nation, the biologically productive areas needed to provide the resources consumed by the population and to absorb their wastes, given prevailing levels of technology. As Wackernagel explained, “Everybody has an impact on the Earth, because they consume the products and services of nature. Their ecological impact corresponds to the amount of nature they occupy to keep them going. In other words, we calculate the `ecological footprints' of these countries” (249).

Wackernagel and his group calculated the ecological footprints of 52 nations containing 80% of the global population and accounting for 95% of the World Domestic Product. The researchers concluded that the world's people are using about one-third more of the earth's biological productivity than can be regenerated (249).

The term “carrying capacity” refers to the number of people the earth can support. Logically, population growth must stop at some point, or the earth would become overcrowded and its resources eventually would be depleted. But what is this maximum human population?

This question has been debated since 1798, when English economist Thomas Malthus predicted that population growth inevitably would outstrip the food and water supply at some point. Since then, estimates of carrying capacity have varied a great deal depending on what assumptions are made about technology, consumption levels, and other factors that are not easily forecast (38). Some have even argued that the earth's carrying capacity may already have been exceeded in the sense that that the world could support only 2 billion people if the entire world consumed at the rate that Americans and Western Europeans consume (42).

While nobody can know how many people the earth could support, few would want to find out the hard way—by reaching this theoretical limit. Calculating the maximum number of people who could exist on earth seems less important than determining how resources can be used wisely and managed sustainably to improve living standards without eventually destroying the natural environment that supports life itself.

Cities at the Forefront

The rapid growth of cities in the developing world puts them in the forefront of the struggle for improved living standards and protection of the environment. Since 1950 the urban population has more than tripled, from just over 750 million to about 3 billion (171). By 2030 some 5 billion people will live in cities (239, 243). In the developing world the urban population is projected to double from 1.9 billion in 2000 to be just under 4 billion by 2030 (165, 239).

Worldwide, about three-fourths of all current population growth is urban (222, 239). Cities are gaining an estimated 55 million people per year—over 1 million new residents every week from in-migration and natural population increase within cities. In developing countries many cities are growing two or three times faster than population growth for the country as a whole (58, 84). As cities grow ever larger, their impact on the environment grows exponentially (249).

The UN coined the term megacities in the 1970s to describe cities with 10 million or more residents. As recently as 1975 there were only five megacities worldwide. Currently, there are 19 megacities, of which 15 are in developing countries. By 2015 the number of megacities will grow to 23 (239) (see Table 4). "Megacities have captured public interest because cities this large are unprecedented in history, and because of the popular perception that human well-being will decline in such dense concentrations of people,” writes demographer Martin Brockerhoff (273).

Millions of people move from the countryside to the city to seek a better life, but they often find that their lives become more difficult. In many cities 25% to 30% of the urban population live in poor shanty towns or squatter settlements, or they live on the streets (85, 222). Of Rio de Janeiro's 10.6 million residents, for example, 4 million live in squatter settlements and shanty towns, some perched precariously on steep hillsides (215). Nevertheless, cities in developing countries continue to attract more and more people.

Cities occupy only 2% of the world's land surface, but city populations have a disproportionate impact on the environment. For example, London requires roughly 60 times its land area to supply its 9 million residents with food and forest products (171). Because commerce and trade have spread dramatically in recent years, city residents consume resources not just from surrounding areas but, increasingly, from around the world (171, 191). Urban areas also export their wastes and pollutants, affecting environmental and health conditions far from the cities themselves.

In the long run, slowing population growth would help ease the pressure on cities, buying time to make improvements in technology. Municipalities also can take a number of steps now—building better transportation systems, promoting recycling, and encouraging water conservation.

Public transportation. One of the best investments that cities can make—both environmental and economic—is an efficient mass transportation system. In many cities people waste great amounts of time and fuel going nowhere because traffic congestion is severe. In many urban areas vehicular exhausts account for 50% to 70% of polluting emissions. Curbing the number of motor vehicles by offering transportation alternatives would save energy and reduce pollution. Some cities—for example, Amsterdam and Copenhagen—have helped ease the transportation crisis by creating special traffic lanes for bicycles and by urging bicycle use.

Recycling. Recycling mountains of urban waste into new resources makes sense both environmentally and economically. Recycling saves natural resources and reduces the amount of trash deposited in landfills or dumped into rivers, lakes, and the ocean. Also, for every million tons of solid waste, about 1,600 recycling jobs could be created in developed and developing countries alike (271).

Water conservation. Urbanization dramatically increases per capita freshwater use, as millions of households gain access to piped water, as industry increases, and as large-scale irrigated agriculture replaces subsistence farming. Cities everywhere need to adopt water conservation measures.

Global Warming: Worrisome Signs

Scientists increasingly agree that the earth's atmosphere is becoming warmer. A long-term rise in the global climate could cause sea levels to rise around the world and bring a number of other adverse consequences (62). Reliance on fossil fuels as an energy source and the widespread destruction and burning of forests are chiefly responsible for the carbon emissions—the so-called greenhouse gasses—that lie behind global warming (20, 69, 110, 140, 167, 213, 264).

One indication of global warming is that over the past 40 years the ocean surface (the top 1,000 feet) has warmed an average of half a degree Celsius (168, 209). The US National Oceanic and Atmospheric Administration (NOAA) has reported that tropical waters in the Northern Hemisphere have been warming up even faster—in fact, 10 times faster than the measured global rate—because tropical oceans retain heat more readily than other areas (168).

Studies project that by 2100 the earth's surface temperature could increase between 1.0 and 3.5 degrees Celsius (110). If the highest projection were reached, Greenland's ice sheet probably would melt. As a consequence, the global sea level gradually would rise as much as seven meters (176).

Computer models project that this rise in sea level would take more than a millennium. Some climatologists, however, think that sea levels could rise much faster, pointing to dramatic shrinkage of the Arctic ice cap over the past 30 years (138).

Even a rise of one meter in sea level—which could occur by 2080, according to the computer models—would inundate many low-lying coastal areas around the world. For instance, much of the Nile River Delta of Egypt would disappear. A one-meter rise in global sea levels also would inundate close to 20% of the coastline of Bangladesh and displace millions of people (111, 130).

Rising global temperatures also would carry adverse health consequences. As temperatures warmed and episodes of droughts and floods became more frequent, the incidence of water-borne diseases and a resurgence and spread of infectious diseases carried by mosquitoes and other disease vectors probably would increase (62).

Warmer global temperatures also would magnify the effects of human activities on the environment, including more pollution and habitat destruction. Climate change might even cause some ecosystems to exceed critical thresholds, leading to their irreversible decline (166).

In 1988, to help study and focus attention on the issues, the Intergovernmental Panel on Climate Change was created under the auspices of the World Meteorological Organization and the United Nations Environment Program. The panel has involved as many as 2,000 scientists from around the world. In 1996 a panel report concluded firmly that global climate change is a reality and not just a possibility (110).

After reviewing the evidence, the panel determined that:

• Evidence for the link between climate change and human activities is compelling. Already, increases in carbon dioxide and other climate-changing gasses have upset the balance of the earth and its atmosphere.
• The earth's surface has become warmer; the number and severity of storms have increased; and the global sea level has risen by 10–25 cm over the past century.

Because the warming trend is a global problem, solutions must be global in scope, the panel concluded (110).

Over the last 150 years burning of fossil fuels has released some 270 billion tons of carbon into the atmosphere in the form of heat-trapping carbon dioxide gasses (210). Since 1950 annual worldwide carbon emissions have increased fourfold, reaching 6.3 billion tons in 1997 (69). Other emissions that contribute to climate change include methane (mainly from domestic livestock and agriculture), nitrous oxide, and chlorofluorocarbons (262).

Atmospheric concentrations of carbon dioxide reached 363 parts per million in 1998, the highest level since the time of massive volcanic activity over 160,000 years ago, based on examination of ice cores in Antarctica and in the Arctic. If current trends continue, atmospheric concentrations of carbon dioxide would double during this century (69).

About three-fourths of the huge increase in carbon emissions over the past half-century is due to increased energy consumption per capita; about one-quarter is due to population growth (21). Western industrialized countries account for nearly half of atmospheric carbon emissions, but developing countries are producing a growing share as industrial activity increases and populations grow. China is now the world's second largest carbon emitter, after the US (69, 71).

The earth's forests are carbon sinks that currently soak up an estimated one-third of the carbon dioxide released into the atmosphere (see Chapter 6). When forests burn, whether naturally or when people clear the land, they not only release more carbon into the atmosphere but also diminish the amount of carbon-absorbing forest cover remaining.

Some scientists are concerned that droughts caused by global warming will increase the number of forest fires, thus contributing further to carbon emissions in the atmosphere. For instance, the six months of extensive forest fires that occurred in Asia in 1997 and 1998 released more carbon into the atmosphere than Western Europe emits in a year (21). Burning trees for land clearance in the tropics releases about 1 billion tons of carbon into the atmosphere annually (71).

As more carbon fills the atmosphere, scientists worry that forests will become saturated and no longer play their role as carbon sinks. Instead, they will start to release carbon themselves. As Will Steffen of Sweden's Royal Academy of Sciences has said, “Forests are temporary reservoirs that can buy valuable time to reduce industrial emissions, not permanent offsets to these emissions” (177).

Moreover, models developed by the Hadley Centre for Climate Prediction and Research in the UK project that, as the world warms, vast swaths of tropical forest—especially in the Amazon River Basin—could begin to dry out. If so, many tropical forests would die out. Their loss would mean even less ability to soak up carbon dioxide from the atmosphere, a trend that could accelerate global warming (176).

Higher carbon dioxide levels in the atmosphere would extend the agricultural growing season and promote forest growth in the short-run but would have potentially negative effects on crops and forests in the long run (110). Because the world's grain belts would become less productive, an additional 350 million people would go hungry by the middle of this century (279). Major droughts have been projected for sub-Saharan Africa as climatic patterns shift, reducing rainfall and drying out soils for longer periods (208).

In 1999 NOAA projected that by the middle of this century soils in agricultural regions of the central US, Central Asia, and the areas surrounding the Mediterranean Sea would likely experience substantial reductions in soil moisture during the summer growing season because evaporation rates would be higher. Such reductions in soil moisture would make these areas “particularly vulnerable,” according to the study (167).

Others point out that, ironically, global warming could produce colder temperatures in northern Europe and Russia, reducing crop yields in these regions as well (51, 176, 207). This change would occur because the huge amounts of arctic freshwater from melting ice caps would make the water less dense. Such a change would interrupt the “conveyor belt” effect of the North Atlantic Drift, the ocean current that transports warm tropical water from the Gulf Stream to Scandinavia and northern Europe.

What is the prospect for reducing emissions of carbon dioxide into the atmosphere? The United Nations Framework Convention on Climate Change was opened for signature at the Rio Earth Summit in 1992. It was promptly signed and ratified by most low-lying island states and countries with extensive coastal areas. The Convention established a framework and a process for agreeing on specific actions later on; it asked signatory states to take preliminary action to reduce greenhouse gas emissions; and it encouraged scientific research on climate change.

The Convention, however, was not binding and did not set targets or deadlines (231). Consequently, in December 1997 representatives of nations around the world met in Kyoto, Japan to negotiate a binding agreement. The Kyoto Protocol committed developed countries to individual emissions targets for the period 2008–2012. The projected overall result would be a 5% reduction in emissions by those countries from 1990 levels by no later than 2012 (238). So far, however, only 14 countries—all from the developing world—have ratified the Protocol. It cannot take effect until at least 55 countries have ratified it (6, 238).

The next round of negotiations is scheduled for late 2000, to be held in The Hague, Netherlands. Can progress be made at this meeting? If too little is done, some experts worry that climate change trends could become irreversible (167, 199).

D. Hinrichsen

Many low-lying coastal areas, such as this mangrove forest in Kenya, would be submerged if sea levels rise as much as scientific models project based on trends in global warming. Even a rise of one meter would displace millions of people.

Five Extinctions and Counting

We live in the period of the greatest extinction of plant and animal species since the extinction of the dinosaurs some 65 million years ago (9, 56, 143, 246). The history of life on earth has included at least five periods during which huge numbers of species vanished forever, primarily due to changes in climate and sea level. Some scientists worry that a sixth extinction has begun because of humanity's gross misuse of the earth's resources (56).

First extinction: End-Ordovician. About 440 million years ago. This was the second-most severe extinction yet discovered. About 85% of all species were wiped out.

Second extinction: Late Devonian. About 365 million years ago. Marine species were particularly hard-hit in an extinction that took place in two waves a million years apart.

Third extinction: End-Permian. About 251 million years ago. With an estimated extinction of 96% of all species, this is the largest mass extinction of all. It dealt a near fatal blow to mammal-like reptiles that had ruled life on land for 80 million years. The dinosaurs stepped into their place as the dominant species.

Fourth extinction: End-Triassic. About 205 million years ago. An estimated 76% of all species, mostly marine creatures, vanished.

Fifth extinction: End-Cretaceous. About 65 million years ago. This is the most famous mass extinction of all because it signaled the end of the dinosaurs, which had dominated the land for 140 million years. Probably between 75% and 80% of all species disappeared during this time.

Sixth extinction? Since 1950 some 600,000 species have disappeared (164), and nearly 40,000 more currently are threatened (116). The pace of extinction may increase under the weight of human consumption and pollution of natural resources and, with global warming and resulting rising sea levels, take on alarming proportions.

Can we assume that life on earth as we know it can continue no matter what the environmental conditions? Or are we setting the stage for an eventual sixth extinction—our own?

An Agenda for Change

The Rio Declaration on Environment and Development, adopted at the 1992 UN Conference on Environment and Development—the Earth Summit—expressed concern about the deteriorating status of the environment and established goals for improvement. The Earth Summit's “Agenda 21” publication set forth recommendations for change agreed to by the 179 countries participating. As the following excerpts from “Agenda for Change,” a “plain-language version” of the Earth Summit document illustrate (125), the world community has endorsed ambitious and far-reaching goals. It now remains to adopt policies and take actions to reach them.

Population and sustainability. The world's growing population, combined with unsustainable production and consumption patterns, is putting increasing stress on air, land, water, energy, and other essential resources.

• Development strategies will have to deal with the combination of population growth, ecosystem health, technology, and access to resources. Meeting the unmet need for family planning and reproductive health services should be part of national sustainable development strategies.
• The world needs to do a better job of forecasting the possible outcomes of current human activities, including population trends, per capita resource use, and wealth distribution.

Protecting the atmosphere. The atmosphere is under increasing pressure from greenhouse gasses that threaten to change the climate and from chemicals that reduce the ozone layer. Governments need to:

• Modernize existing power systems to gain energy efficiency and develop new and renewable energy sources.
• Promote national energy efficiency and emission standards and develop efficient, cost-effective, and less polluting mass transit systems.

Combating deforestation. Forests worldwide are threatened by uncontrolled degradation and conversion to other uses because of increasing human pressure.

• There is an urgent need to conserve and plant forests in developed and developing countries to maintain or restore the ecological balance and to provide for human needs.
• Governments need to work with business, scientists, local community groups, indigenous people, and the public to create long-term conservation and management policies for every forest region and watershed.

Sustainable agriculture and rural development. Hunger is already a constant threat to over 800 million people, while the world's ability to continue meeting growing demand for food and other agricultural products over the long term is uncertain. Soil erosion, salinization, waterlogging, and loss of soil fertility are increasing in all countries.

Agriculture has to meet rising needs mainly by increasing productivity, because most of the world's best croplands are already in use. At the same time, further encroachment on land that is only marginally suitable for cultivation must be avoided.

• Sustainable agriculture and rural development will require major adjustments in agricultural, environmental, and economic policies in all countries and at the international level.

Conservation of biological diversity. The loss of the world's biological diversity continues, mainly from habitat destruction, over-harvesting, pollution, and the introduction of foreign plants and animals (known as exotics). This decline in biodiversity is largely caused by human activity and represents a serious threat to our development.

Urgent and decisive action is needed to conserve and maintain genes, species, and ecosystems:

• Develop national strategies to conserve and sustainably use biological diversity and to make these strategies part of overall national development efforts.
• Implement fair sharing of the benefits between providers and consumers of biological resources.
• Protect natural habitats. Promote the rehabilitation of damaged ecosystems.

Protecting and managing the oceans. Oceans are under increasing environmental stress from pollution, over-fishing, and degradation of coastlines and coral reefs. About 70% of marine pollution comes from sources on land. Countries should commit themselves to control and reduce degradation of the marine environment. They should:

• Build and maintain sewage-treatment systems and avoid discharging sewage near shell fisheries, water intakes, and bathing areas.
• Develop land-use practices that reduce run-off of soil and wastes to rivers and thus to the seas. Use environmentally less harmful pesticides and fertilizers.
• Control and prevent coastal erosion and silting, due to land uses such as unplanned construction.

Protecting and managing freshwater. In many parts of the world there is widespread scarcity, gradual destruction, and increased pollution of freshwater resources. The causes include inadequately treated sewage and industrial waste, loss of natural water catchment areas, deforestation and poor agricultural practices, which release pesticides and other chemicals into the water. The following approaches are key:

• The way to provide all people with potable water and basic sanitation is to adopt the approach “some for all rather than more for some.” This approach can be achieved through low-cost services built and maintained at the community level.
• Nations need to identify and protect water resources and see that water is used on a sustainable basis. They need effective water pollution prevention and control programs. There is a particular need for appropriate sanitation and waste-disposal technologies for low-income, high-density cities.