Introduction

Information in this unit, particularly that relating to future energy options, draws heavily on a Science article by Hoffert et al (2002). The reader is encouraged to consult this article for more details.

Current rates of increase in uses of fossil fuels will create atmospheric concentrations of 550 to 950 ppm of CO₂ by the end of the 21st century. This compares with the pre-industrial value of about 275 ppm and exceeds atmospheric CO₂ levels in the Earth's atmosphere in the last 400,000 years and perhaps the last 2 million years. The current atmospheric CO₂ level is about 370 ppm and rising at about 1 ppm per year. Supplying future global energy needs with reduced contributions to atmospheric CO₂ requires a combination of more efficient energy use and major advances in non-fossil-fuel sources of energy.

The change in global temperatures produced by 550 ppm would be comparable to but opposite sign with the magnitude of cooling that created the last ice age. A ceiling of 450 ppm is needed if we expect to prevent major bleaching of global ocean coral reefs, shutdown of global ocean thermohaline circulation, and sea level rise from disintegration of the West Antarctic Ice Sheet.

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