This scenario is a plausible extrapolation from what is known: it reflects both the magnitude of the possible risks courted by industrial humanity, and the inadequacy of the global managerial perspective when circumstances go beyond what is viewed as industrially acceptable. However, even if this scenario is completely accurate, industrial managers can always point to enough uncertainty at each step to justify inaction.

Global warming is the result of the release into the atmosphere of "greenhouse gases," i.e., gases that are relatively transparent to the passage of energetic short-wave solar radiation (sunlight) and, at the same time, reflect back much of the longer wave infrared (or heat) radiation generated when sunlight strikes the earth. The most significant greenhouse gas is CO:, which has been released into the atmosphere in huge quantities as a by-product of burning fossil fuels in automobiles, power plants, and industrial processes such as steel production, and by wood burned for fuel and forests burned for land-clearing. In 1950, 1.62 billion metric tons per year of carbon (gigatons carbon or GTC) were released from burning fossil fuels; by 1991, this figure had increased to 5.854 billion tons per year.

To get some sense of the significance of this number, we need to know that the preindustrial atmosphere contained an estimated 580 billion tons of carbon. Thus, we are now adding about 1 percent of the preindustrial carbon total to the atmosphere yearly. Current atmospheric carbon levels are 750 GTC, a 29 percent increase from preindustrial levels. In only thirty-two years since 1959, when continuous record keeping of atmospheric carbon dioxide began, concentrations have increased 12 percent from 316 parts per million (.0316 percent) to 355 parts per million (.0355 percent). Other greenhouse gases include methane (CH4), a product of natural decay and fermentation released in large quantities from concentrated livestock production, and the chlorofluorocarbons (CFCs) that are also responsible for the destruction of the ozone layer.
The precise global dynamics and possible effects, both long-and short-term, of huge increases in greenhouse gases are unclear. There is a natural cycle that keeps CO2 concentrations relatively balanced. Huge amounts of CO2 are dissolved in the oceans, 39,000 GTC with about 90 GTC exchanged each year between atmosphere and ocean. (CO2 in water forms carbonic acid-this is why steam heating condensate pipes often corrode unless the boiler water is deaerated.) Huge amounts of carbon are also locked up in submarine methane hydrates, ice-like solids made up of water crystals and trapped methane gas, on the Arctic continental shelf.

Carbon is also found in the bodies of all living things, from giant redwoods to microscopic creatures (an estimated 750 GTC in land plants and 1,500 GTC in soils; annually 100 GTC is exchanged between the atmosphere and land plants.) The normal carbon-based system includes the use of CO2 by plants, which release oxygen as a by-product that is then used for animal respiration (which, in turn, yields CO2 as its by-product). The carbon taken up in the bodies of living creatures is also released in the form of methane as they die and decay.

Atmospheric scientists argue that climate stability can likely be sustained if levels of human CO2 production are somewhat below the emission levels seen in the 1950s. At present rates, by the middle of the 21st century, most climate scientists predict substantial increases in global temperature.

How significant these increases will be, and the nature of their impact, is the question. Jeremy Leggett warns that such global warming may disturb major sinks for carbon in Arctic tundra and, through a complex series of interactions, result in runaway warming that would continue even if human CO2 and all other greenhouse gas emissions dropped to zero.

Leggett's "putative" logical chain of events includes: