Energy supply and demand implications of CO2

It may become necessary to try to limit the concentration of atmospheric CO₂. Consideration of temperature rise as a surrogate for the ensemble of possible adverse effects of increased CO₂ suggests a concentration limit in the range of 1.5–2.5 times the present concentration (? 338 ppmv in 1980). Although the lower limit, even in the absence of restrictions on fossil fuel use, would probably not be reached for 50 years, that limit may nevertheless prove difficult to avoid because of long lead times required for major changes in energy demand and supply. The higher limit is not presently restrictive. In either case, intensive development of non-fossil energy sources appears warranted and improved efficiency of energy use will provide more time to make the transition.