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close this bookClimate Protection and the National Interest (WRI, 1997, 56 pages)
close this folder2. THE CLIMATE CHANGE PROBLEM
View the document(introduction...)
View the documentThe Cooling Effect of Air Pollution
View the documentSearching for the Signal of Global Warming
View the documentExpected Impacts of Global Warming
View the documentCoping with Climate Change


There is no doubt that Earth has a natural greenhouse effect. Without it, the world would be about 33°C (60°F) colder. Life as we know it would not be possible. The great French physicist Jean Fourier argued 170 years ago that Earth's atmosphere acts like the glass of a greenhouse by admitting the sun's light while impeding the escape of the earth's radiant heat (infrared radiation) back into space.


The buildup of carbon dioxide accounts for about two-thirds of the human sources of excess greenhouse warming from long-lived gases.5 (Figure 1 shows the history of global CO2 emissions.) Each year, the burning of fossil fuels and biomass, along with other activities such as cement making, releases over seven billion metric tons of carbon to the atmosphere in the form of CO2, raising the atmospheric concentration of the gas by about half a percent annually. Figure 2 shows CO2 emissions for the United States for the period 1980 to 1996 while Figure 3 shows the source of emissions for 1994 by sector and fuel. Note that electric-power production and transportation are by far the largest and fastest-growing sources. With current global emissions of some 6.3 billion metric tons per year (1995), fossil fuel combustion is the best quantified and the largest source of CO2 from human activity. Since preindustrial times, the global CO2 concentration has increased almost 30 percent, from 280 parts per million (ppm) to about 360 ppm today. (See Figure 4.) Carbon dioxide stays in the atmosphere 50 to 200 years.6

In 1896 - after performing at least 10,000 hand calculations - the Nobel-prize winning Swedish chemist Svante Arrhenius correctly reasoned that the quantities of water vapor and carbon dioxide (CO2) in the atmosphere absorb enough of the earth's outgoing heat radiation to warm the earth by nearly 33°C (60°F). Arrhenius concluded that a doubling of atmospheric CO2 would raise average global temperatures by 5 to 6°C (9 to 11°F) over the preindustrial temperature3 This is remarkably close to the range of 1.5 to 4.5°C (2.7 to 8.1°F) that climate experts now believe would accompany a doubling of atmospheric CO24.


Methane (the main component of natural gas) has both natural and human sources. Natural sources include peat bogs, termites, swamps, and other wetlands. Human sources include rice paddies, domestic animals, landfills, biomass burning, and the production and burning of fossil fuels. Fossil fuels account for about 20 percent of the total, including leakage from natural gas pipelines, oil wells, and coal seams.7 About 60 to 80 percent of all methane emissions are of human origin. Atmospheric methane concentrations have been increasing in the atmosphere at about 0.6 percent per year8 and have more than doubled from preindustrial levels. Methane stays in the atmosphere 12 to 17 years and accounts for about 20 percent of greenhouse warming from human sources.

Over the past century, human agricultural and industrial activities have led to the buildup of CO2 and other greenhouse gases, including methane, nitrous oxide, ozone, and the halogenated compounds (including the CFCs). These gases are trapping yet more of the earth's outgoing radiation, leading to an enhanced greenhouse effect and, eventually, to a warmer earth. (See the sidebars on pages 5 - 7 for a discussion of the sources, properties, and emission trends of the important greenhouse gases.)