The Global Nature of Greenhouse Warming
Greenhouse warming is global in at least two respects. First, greenhouse gases released anywhere in the world disperse rapidly in the global atmosphere. Neither the location of release nor the activity resulting in a release makes much difference. A molecule of CO2 from a cooking fire in Yellowstone or India is subject to the same laws of chemistry and physics in the atmosphere as a molecule from the exhaust pipe of a high-performance auto in Indiana or Europe. Second, the anticipated climatic effects include changes in the global circulation of air and water. Global average temperature is often used as an indicator of the various climatic effects. Climate change, however, has many facets: seasonal cycles and annual fluctuations of temperature and precipitation, wind speed and direction, and strength and direction of ocean currents. Although the results of climate change will differ from place to place, they derive from global processes.
Greenhouse Gas Emissions from Human Activities
Greenhouse warming is complicated in another, more fundamental way. The amounts released vary, of course, but virtually every form of human activity contributes some amount of greenhouse gas to the atmosphere or removes some from the atmosphere. Subsistence agriculture contributes its bit, as does modern industry and the consumption and use of modern goods and services. Growing trees remove CO2 from the atmosphere, but burning wood for heating and cooking releases CO2 into the atmosphere. Rice paddies and cattle contribute CH4. Industrial activities include releases of all the
greenhouse gases to varying extents. In most societies the burning of fossil fuels for electricity and transportation is a major contributor.
Since releases of greenhouse gases are connected to most economic activity, significant reductions in their emission may affect the economic competitiveness of individuals, firms, and nations. Avoiding additional greenhouse warming may be costly, it may create economic winners and losers, and it may alter trade balances.
The Effects of World Population and Economic Growth
The world's population today is 5.3 billion, and it is expected to continue to grow at about 1.7 percent per year at current rates of fertility. Figure 2.1 shows historical population growth and an estimate for 2000. This increasing population is one of the major factors affecting trends in greenhouse gas emissions. More people create greater demand for food, energy, clothing, and shelter. Producing such products emits greenhouse gases.
Economic growth also produces more greenhouse gas emissions. If population grows with constant per capita income, more resources are used for food, clothing, and shelter. If per capita income grows in a constant population, the demand for goods also grows, particularly for health and education services, transportation, and housing. Most nations in the world have policies to reduce population growth rates, but all nations seek to achieve rapid growth in per capita income. The reduction of greenhouse gas emissions is well served by the first objective (reducing population growth) but, depending on the means used, can be in conflict with the second (growth in per capita income).
The detailed links between population growth and greenhouse gas emissions are complex and not well understood. The developing countries that have reduced their population growth rates within the last 30 years did so only after rapidly increasing their standards of living. This often was accompanied by environmental degradation. Perhaps it will be possible to rapidly raise living standards without resulting in traditional patterns of pollution. Unfortunately, there are few examples to guide us. What is needed is a breakthrough in strategies for development, especially with respect to energy supply and demand. Developing countries experiencing rapid economic growth will need effective mitigation programs if they are to avoid substantial increases in their greenhouse gas emissions. Implementing new strategies will require funds that will probably be scarce if populations grow rapidly. Nevertheless, at any given per capita rate of greenhouse gas emissions, a smaller population means fewer emissions, as well as less stress on the environment in general.
Trends in Human Activities Affecting Greenhouse Gas Concentrations
Table 2.1 presents emission estimates for five greenhouse gases (CO2, CH4, CFC-11, CFC-12, and N2O) that accounted for about 87 percent of the increase in the heat-trapping capacity of the atmosphere in the 1980s and about 92 percent of the increase over the previous 100 years. The table presents estimated 1985 emissions (in million tons per year) and converts non-CO2
TABLE 2.1 Estimated 1985 Global Greenhouse Gas Emissions from Human Activities
NOTE: Mt/yr = million (106) metric tons (t) per year. All entries are rounded because the exact values are controversial.
aCO2-equivalent emissions are calculated from the Greenhouse Gas Emissions column by using the following multipliers:
Numbers in parentheses are percentages of total.
bTotal does not sum due to rounding errors.
SOURCE: Adapted from U.S. Department of Energy. 1990. The Economics of Long-Term Global Climate Change: A Preliminary AssessmentReport of an Interagency Task Force. Springfield, Va.: National Technical Information Service.
TABLE 2.2 Carbon Dioxide Emission Estimates
gases into CO2-equivalent emissions so that their respective contributions can be compared. These projections necessarily involve uncertainties. (Note that throughout this report tons (t) are metric; 1 Mt equals 1 million metric tons.)
The United States is the world's largest contributor of greenhouse gas emissions. Table 2.2 shows total and per capita CO2 emissions (the dominant greenhouse gas emitted by human activity) for the United States and several other countries from 1960 to 1988, in order of their most recent per capita emissions. Two of the six countries with the largest total emissions are developing countries (People's Republic of China and India). Per capita
TABLE 2.3 Carbon Dioxide Emissions per Unit of Economic Activity (1988 to 1989)
emissions in 1988 are lower than those in 1980 in several countries, including the United States, suggesting that some actions to reduce greenhouse warming are already being taken.
It is also informative to compare emissions to economic activity. Table 2.3 shows CO2 emissions per unit of economic activity for recent emissions data. The table illustrates that some developing countries and centrally planned economies are large emitters of greenhouse gases per unit of
TABLE 2.4 Estimated Deforestation in the Tropics (thousand hectares)
economic activity and that the United States is in the middle of the field. It also shows France with low emissions per unit of economic activity, probably because of its extensive reliance on nuclear power as a source of electricity.
Table 2.4 shows recent estimates of deforestation in tropical forests for selected countries. About 80 percent of this wood is destroyed or used as fuel wood, and the remaining 20 percent is harvested for industrial or trade purposes. If the trees are burned, the CO2 they have stored is added to the air, and if they are replaced with plants that grow more slowly, less CO2 will be removed from the atmosphere.