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Population and Climate

The population-climate connection is worth covering because -- whether they pay attention to it or not -- it will eventually affect the lives of people all over North America in serious ways.

Certainly there are local population-climate connections in various parts of the U.S. (for example, the fogs that result from irrigated agriculture in California's Central Valley). But when it comes to global climate change -- the greenhouse warming most scientists now regard as inevitable -- it is global population growth that is a critical variable.

There are many sources detailing the potential impacts of global climate change on the United States.An example is the "National Assessment" (http://www.usgcrp.gov/usgcrp/nacc/default.htm). But the focus of this backgrounder is how population growth interacts with climate.

Just about any expert discussion of the planet’s climate future tends to rely on a series of line graphs showing trend lines climbing steadily upward through the 19th and 20th centuries, then through the 21st and beyond. Rarely do we stop and ask why all these trend lines for fossil fuel consumption ... carbon dioxide emissions ... global mean temperature ... and sea level rise ... are climbing so inexorably upward.

One of the many answers is simple: population. And that is one trend that is not inevitable. The people of the world have it in their power to affect their own population destiny.

Perhaps another good reason to cover the population-climate connection is that there are many economic interests, political factions, and religious forces working energetically to keep journalists from covering it. Often, it is the uncomfortable or "suppressed" story that people need most to hear.

Story Ideas

1. Has climate change ever been disastrous for large human populations in the past? If you live in North America, you may find that this was true for pre-Columbian civilizations.

2. Has population growth in your locality or region had any localized climate impacts? Has anyone measured the "urban heat island effect" for your area?

3. Has anyone tried to calculate greenhouse gas emissions per capita for your area? How do they compare to those for the United States as a whole or for the world? As a starting point, check out EPA ’s greenhouse gas emissions inventory.

Background and Context

Population Growth and Climate Change

Most of the mechanisms by which humans affect global climate depend directly on the number of humans that populate the planet. It is common in political rhetoric for advocates to blame climate change on industrial- ization,on the energy-intensive lifestyles of nations like the U.S., or on economic development and higher technology generally -- but that misses some of the point. People cause global warming. This is true by definition, because it is anthropogenic global warming we are talking about. Other things being equal, more people will cause more global warming.

Carbon dioxide, the major man-made greenhouse gas, offers an example. It is formed when any number of fuels burn. Policy debaters pay the most attention to fossil fuel combustion, because that is a matter of taking carbon (coal,oil,methane) that has been in long-term storage beneath the earth and releasing it as carbon dioxide into the atmosphere (from which it was removed millions of years ago).

The amount of fossil fuel that a nation burns depends on a number of things. Imagine a place (like Massachusetts) where almost everyone uses fuel oil to heat their home during the winter. Of course, almost every resident burns a certain amount of fuel oil to keep from freezing to death. But some -- the poor -- cannot afford to burn more than a bare minimum, and they shiver through the winter, unlike the rich who burn all they want. There is another group -- let ’s call them the smart -- who have well- insulated homes and high-efficiency furnaces, who burn no more oil than the shivering poor, but bask as comfortably as the warmest rich.

That example is the basis for a famous formula theoretically describing the environmental impacts of resource use.Often called the IPAT formula, it was stated by Stanford biologist and population pessimist Paul Ehrlich and his colleague J.P.Holdren. It states that Environmental Impact (I) equals Population size (P) times Affluence, or consumption per person (A), times Technology, or damage per unit of consumption (T).

The point is that population is a multiplier of any human impact on the environment. Only by improving some other term in the equation can population be increased without proportional environmental impact.

The human impact on atmospheric concentrations of carbon dioxide occurs through many mechanisms, but most of them are population- related. It doesn’t make much difference whether the use of fossil fuel is for heating or for cooling -- or for industrial production, for fueling cars, or for the generation of electricity to light homes or streets or do a thousand other things. Of course the impacts will be greater in more affluent countries where people actually have air conditioners and can afford to run them.

Humans have also affected the global carbon balance by cutting down trees, which absorb and store carbon. Population pressures in countries like Brazil have led to the destruction of forests (and release of carbon) through slash-and-burn agriculture. But the harvesting of trees without replacing them -- whether for agriculture, homebuilding, or fuel -- negatively affects the climate in a number of ways. Only recently, for example, have scientists begun to appreciate how much carbon is stored in soils, which are changed by agricultural clearing and other human land-use changes. All of these things are connected to population.

Nor is carbon dioxide the only gas that makes a population-climate connection. Methane is another. Several of the most important causes of the post-industrial jump in atmospheric methane concentrations are directly linked to human population. Examples include rice agriculture and the digestive gas emissions of cattle and other agricultural ruminant animals -- not to mention the gas from decomposing trash in landfills. All of these things, likewise, are closely linked to population -- the number of people eating rice,drinking milk,or throwing away trash.

These connections are not merely theoretical. Between the years 1900 and 2000,the world’s population just about quadrupled, from 1.6 billion to 6.1 billion. During the same period, emissions of carbon dioxide grew 12-fold, from an estimated 534 million metric tons to 6.59 billion metric tons in 1997.

Technology: Problem or Solution?

"Technology" can be good or bad, environmentally. We can think of a nation’s technological progress as consisting of ever more and bigger cars per capita, which of course emit more carbon dioxide per mile. But we can also think of technological progress as the development of less- polluting and more energy-efficient cars, with the opposite impact.

Developing nations have argued, in the Kyoto climate treaty talks, that since the rich industrialized nations have put most of the carbon dioxide into the atmosphere (by virtue of affluence and technology), the industrialized nations should bear the burden of reductions. The developing nations, believing rich nations have already committed the planet to climate change, resent now being asked to forego their own economic development.

That is why some nations have paid so much attention to Kyoto provisions like the "clean development mechanism." Through CDM projects, industrialized nations can help poor nations speed economic development by selling them cleaner and more energy-efficient technology. That way, everybody wins.

Impacts: Populations Bear the Brunt

Often (but not always) nations where population is densest and growing fastest are also those where economic development is lower or slower and where people are most vulnerable to climate change. Bangladesh is a good example.

Bangladesh’s population is the eighth highest in the world, with 130 million people in an area the size of Wisconsin. It is also desperately poor, with per capita income averaging $370. Many of its people live in the low-lying alluvial plain next to the Bay of Bengal, which floods often, killing tens of thousands of people. The sea-level rise that will accompany global warming -- along with a possible increase in frequency and intensity of storms many climate scientists fear -- will make the flooding more frequent and more deadly, and ultimately deprive the nation of farmland it needs to feed its population.

The connections between population growth/density and vulnerability to climate change are many, complex, and sometimes indirect, but real nonetheless. Places where population growth has outstripped economic development are places where people are forced to live at the margin of what natural resources will sustain.

One point of connection is water. In the United States, for example, many of the states with the greatest population growth (Nevada, Arizona, California, and Florida) are also the ones where water resources are the most stressed. This is a matter of even greater concern in the parts of the world where basic sanitation and health services are wanting. The World Health Organization recently estimated that some 1.5 billion people worldwide lack access to clean drinking water and 3 billion lack basic sanitation. One result is that 5 million to 12 million people die each year from dirty-water diseases -- a problem that gets worse when populations are crowded together.

Another point of connection is land and food. Even today,as recurring famines in sub-Saharan Africa have shown, even short-term variations in climate can mean failure of the food supply for millions of people. Human history and pre-history seem to offer example after example of major populations or civilizations vanishing when climate change took away their food supply. The examples range from the Indus Valley thousands of years ago to the Anasazi in the American Southwest only a few hundred years ago.

Issues

1. What is the U.S.government’s population policy? How is this policy formed? Are environmental issues such as climate considered in forming U.S. population policy?

2. Should the administration withhold the $34 million Congress appropriated for the U.N.Population Fund this year, on the grounds that it allegedly encourages forced abortions and sterilizations in China? Will withholding the money -- as the administration now has decided to do -- cause more abortions than it might prevent as critics assert?

Players and Sources

Intergovernmental Panel on Climate Change: Climate Change 2001: The Scientific Basis (New York,2001), Cambridge University Press.This is an authoritative and up-to-date compilation of consensus science on the physical processes involved in climate change.(http://www.ipcc.ch/pub/tar/wg1/index.htm)

Population Reference Bureau: An established source of objective and authoritative information on population matters. Press contact:Ellen Carnevale,(202)939-5407, ecarnevale@prb.org, (http://www.prb.org/). The group’s collects population-related links online (http://www.popnet.org/).

Center for International Earth Science Information Network (CEISIN): Based at Columbia University’s Lamont-Doherty Earth Observatory, CEISIN is a good source of information about the social and economic impacts of climate change. Press contact: W.Christopher Lenhardt, (845) 365-8988, clenhardt@ciesin.columbia.edu. Washington, D.C. Office: (202)314-3822,(http://www.ciesin.org/)

PlanetWire: This is a free and ultra-cool electronic news service focused on population and environment, including backgrounders, a broad-based daily clip service (subscribable by e-mail), and more. Press contact: Kathy Bonk or Cecilia Snyder, Communications Consortium Media Center (CCMC), (202)326-8711, csnyder@ccmc.org, (http://www.planetwire.org/)

World Resources Institute: An established and academically respected think tank on world resources issues, with a focus on sustainability. Press contact: Adlai Amor, (202)729-7736, aamor@wri.org, (http://www.wri.org/)

Worldwatch Institute: Another respected think tank with an even more pronounced slant toward sustainability. Press contact: Leanne Mitchell, (202) 452-1992 ext.527, lmitchell@worldwatch.org, (http://www.worldwatch.org/)

Population Connection (formerly Zero Population Growth): An advocacy group focused on population issues. Press contact: Mark Daley, (202)745-3179, Mark@PopulationConnection.org (http://www.populationconnection.org/)

Population Action International: An advocacy-oriented policy shop with lots of solid information, especially on population-environment connections. Press contact: Sally Ethelston, (202) 557-3400, sae@popact.org, (http://www.populationaction.org/)

United Nations Population Fund: The U.N.’s official population organization. Especially helpful is its publication, Footprints and Milestones: Population and Environmental Change -- The State of World Population 2001. Press contact: William Ryan, (212) 297-5279, ryanw@unfpa.org, (http://www.unfpa.org/)

American Association for the Advancement of Science (AAAS): An especially useful reference is the AAAS Atlas of Population and Environment, by Paul Harrison and Fred Pearce (Berkeley, 2000), University of California Press. Press office: (202) 326-6440, media@aaas.org, (http://www.aaas.org/news/) Available also from CCMC, above.