Carbon dioxide and a wide variety of other industrial gases, including methane, ozone, and feron, trap a portion of the earth's thermal radiation that would otherwise escape into space. This radiative trapping of energy produces the heating of the atmosphere popularly labeled the greenhouse effect. Detailed observations from remote stations show that the carbon dioxide concentration of the atmosphere has increased from 316 parts per million by volume (ppmv) in 1958 to 350 ppmv in 1986. The exponential growth in carbon dioxide levels parallels the increased worldwide use of carbon-based fuels. Methane concentrations are increasing at a rate of one to two percent per year, lower atmosphere ozone at a somewhat smaller rate, and freons at a current rate of five percent per year. Calculations of the expected increase in the average temperature of the earth's surface since 1900 lead to a value of about 0.5 °C if the moderating effect of the earth's oceans is taken into account. Calculations are based on models that range in complexity from simple energy balance considerations to detailed three-dimensionsl calculations that strain the capacity of current digital computers. Detailed analysis of tens of millions of surface-temperature observations indicate an average warming of about 0.5 °C since the turn of the century and a greater warming of 2 °C in high latitudes. Major climatic shifts can be expected as the warming proceeds at an increasing pace. The rate of anticipated warming is historically unpercedented.
