Science, Policy, and Advocacy on Population and the Environment

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The world's population is on track to reach 7 billion people this year, just twelve years after reaching 6 billion. In the meantime, global climate change, as a result of human activities, is having unprecedented effects on the planet's sea level rise, weather patterns, species habitat and freshwater resources.

The United States uniquely demonstrates how these two issues – population and climate change – are inextricably linked. The U.S. role within the global context is especially significant: it is the third largest country in the world in terms of population, and contributes disproportionately to the planet's climate change because it is responsible for a quarter of the world’s energy use. The U.S. uses more energy than any other country, is the biggest carbon dioxide (CO2) greenhouse gas emitter of all the industrialized nations, and second only to China in overall global emissions. It is also the largest and fastest growing developed nation worldwide.

This unique combination - of America's high population numbers and rapid growth, and, high per-capita energy consumption and carbon dioxide (CO2) emissions (the greenhouse gas primarily responsible for global warming) - makes the U.S. pivotal in the global climate change debate.

We've all heard the facts - with just 5% of the global population, Americans consume 25% of the world’s energy, and generate 5 times the world's average per-capita of CO2 emissions. Americans are high energy and resource consumers in a country with a large, rapidly growing population base. As a result the U.S. has a much bigger "per-person" link to global climate change than any other nation.

And, with 8,000 people added daily and 3 million people added each year in the U.S., there’s real potential to reach 1 billion high-energy-consuming Americans by 2100.

Meeting the energy demands of this large and rapidly growing population that consumes elevated levels of energy and resources - while at the same time reducing the greenhouse gas emissions contributing to climate change - is the challenge before us now.

But how do U.S. "population" factors (such as growth, density, movement, age/income, or per-capita resource use) relate to climate change? There are several key linkages, relating both to the causes and effects of climate change:

  • Population is associated with the causes of climate change mainly through high per-capita energy use and the associated greenhouse gas emissions. This is from large numbers of people burning fossil fuels for vehicle use, high energy consuming households and appliances, and widespread sprawl land development to accommodate the growth (resulting in increased vehicle use and fossil fuel burning, and deforestation which decreases the amount of trees used as carbon "sinks").

  • Population is linked to climate change’s effects when there is high population density and rapid population growth in the areas most vulnerable to climate change-related sea level rise, severe weather patterns, drought conditions including reduced snow-pack, seasonal changes, and habitat alteration that increases people's exposure to vector-borne diseases. Also, U.S. demographic trends such as the high and fast increasing numbers of people living along the U.S. coasts or in the arid West all exacerbate climate change's effects.

Understanding U.S. population trends and the associated per-capita energy and resource use is critical to addressing climate change effectively, especially as the world's policy makers work to mitigate and adapt to the inevitable changes to the planet's climate. This web site shows how the U.S., its regions, and each of the 50 states compare in terms of population and climate change factors. To see how they stack up, click on the map or graphs to the right.

Sources: Population Reference Bureau; UN Intergovernmental Panel on Climate Change; US Census Bureau; US Energy Information Administration; World Resources Institute; Center for Environment and Population (CEP) U.S. Population, Energy & Climate Change, 2009.


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