Human-generated carbon dioxide is produced mainly through the combustion of fossil fuels for electricity, heat, transportation and industrial processes. Houghton graphs global energy-usage levels over time in gigatons of oil equivalent consumed per year. During 1860, the start of his calculations, annual usage stood at about one-tenth of a gigaton per year. Between 1900 and 1940, energy consumption rose from roughly one to 1.5-2.0 gigatons a year. During the 1940s, usage began to increase more rapidly, passing 3.0 gigatons about 1960, 5.0 about 1970, and more than 8.0 gigatons by the late 1980s.
Energy consumption is skewed widely by region.
Energy consumption per person in the United States is more than twice what it is in Europe, and roughly 15 times the amount used in sub-Saharan Africa. The largest factor in this difference is the pervasiveness in any given area of private automobiles and other motorized vehicles. Having examined the evidence relating rising carbon-dioxide levels and temperatures, Houghton then speculates on what all of this means for the future of humankind. The prospects are not pretty. Deaths from extreme heat also will increase, especially in large urban areas, Houghton writes.