Division of Energy
Global Climate Change: The Facts - The Projections
The Report of the Missouri Commission on Global Climate Change and Ozone Depletion (1991) states, climate change has been ongoing as the earth's present environment developed, but until now such change has occurred very slowly and without human intervention. Data produced within the last decade suggest that global climate change is now being induced by human activity and may occur at an unprecedented pace which could challenge natural and human adaptation. Whether significant response occurs by 2030, 2050 or some other year is less important than the understanding that the continued accumulation of greenhouse gases will alter the environment.
While the greenhouse effect is real and greenhouse gases in the earth's atmosphere are being increased by human activities, projections of global warming are still theoretical. However many scientists believe that rapid global warming or some other form of climate change is likely in the next century and serious economic and environmental impacts could occur. Still, there may not be scientific consensus for decades on whether global climate change is a reality, nor on the environmental consequences of such a change. Specific regional consequences are even harder to predict. Thus, some aspects of the issue are well accepted facts while others are inferences or projections based on incomplete data and complex computer models.
The greenhouse effect due to water vapor and other trace gases in the atmosphere such as carbon dioxide (CO2), chlorofluorocarbons (CFCs), methane (CH4), and nitrous oxide (N2O) is a well established phenomenon. These gases allow incoming solar radiation to reach the earth but block outgoing infrared radiation. This results in a warming of the atmosphere. Consequently, these infrared-absorbing gases are sometimes called greenhouse gases. Without this greenhouse effect the earth would be uninhabitable because the average surface would be -19 degrees Celsius (-3 degrees Fahrenheit) instead of its actual 14 C (57 F), i.e., 33 C (60 F) cooler. At the height of the last ice age (18,000 years ago), the earth was only 3-5 C (5.4-9 oF) cooler than the present temperature.
During the 160,000 years prior to the beginning of the Industrial Age (which started in the late 18th century), CO2 levels in the atmosphere fluctuated between 200 and 300 parts per million (ppm) and the changes in the levels of CO2 paralleled changes in average temperature.
As increase in the carbon dioxide level from 272 to 353 ppm since the onset of the Industrial Age is an accepted scientific fact. At this rate, atmospheric levels of CO2 will double preindustrial concentrations during the latter part of the next century. Levels of other greenhouse gases are also rising. (Some recent measurements indicate that these increases in CO2 and the other greenhouse gases may be slowing.) Most of this modern increase in CO2 is due to the burning of fossil fuels in industrial countries and, more recently, to deforestation in tropical countries because both of these activities release large amounts of stored carbon to the atmosphere.
Temperature records are plagued by many problems of inaccuracy and incompleteness. Demonstrating a global temperature change is complicated because of this incomplete and distorted data, but a review of the historical record strongly suggests an increase of 0.5 to 1.1 F in the average global surface temperature since 1900. Some scientists believe that the increased warming is producing more clouds and thus producing higher temperatures at night but not in the daytime. New temperature data coming from weather satellites will greatly improve our understanding of global temperature changes in the next decade.
Future Warming Projections and Impacts
Increasingly sophisticated computer models called general circulation models are being used to assess the effect of a continued increase of atmospheric CO2 and other greenhouse gases on temperature. Most models suggest that a doubling of atmospheric CO2 levels will probably produce a global warming from 1.7 to 4.5 C (3 to 8 F) before the end of the next century, sometime between the years 2030 and 2080. This is a greater change than seen over the past 10,000 years, since the last ice age. Although a great deal of controversy exists regarding these computer models, most scientists agree that the potential for substantial and accelerated global warming exists. This consensus is Documented in the Report of the International Panel on Climate Change (1990).
However, many scientists believe that these global climate models are not yet useful because the data base is inadequate and because they do not understand how these global systems function and interact. As a result the models do not adequately account for factors such as the role of clouds, the oceans, variations in solar output, volcanic emissions, and the response of living systems in influencing global climate.
Another factor is the possibility of increased natural releases of CH4 and CO2 as a result of global warming because of increased decay of organic matter in northern latitudes. We don't understand well enough the negative or positive feedback mechanisms which can lessen or amplify climatic effects. Super computers are becoming more powerful and climate models and their data inputs are being improved, but it may be a decade or more before there is scientific agreement on their usefulness.
It is reasonably well established that a temperature rise of 3-8 F would significantly alter world climate and weather patterns. Many scientists predict more frequent hurricanes, hotter and dryer summers in continental interiors resulting in severe droughts, and rising sea levels with subsequent destruction of coastal cities, beaches and wetlands. Some regions could be more severely impacted than others. Other scientists predict more benign consequences because of the increased cloud formation that would occur. Again, it may be a decade or more before there is a consensus on the reality or the potential impacts of global warming.