The Earth appears to have the capacity to absorb carbon dioxide emissions at a level of 3 gigatons per year, although the exact level of tolerance and absorption is uncertain. Today’s emissions total about 9 gigatons, about two-thirds of which is due to fossil fuels. The remainder is the result of biomass burning.

Besides carbon dioxide emissions, fossil fuel mining and technologies for controlling emissions other than carbon dioxide to the air and water contribute to environmental degradation, which is often very severe in its local and regional impacts. Further, fossil fuel use in the present mode presents risks of climate change that are not yet well understood, but may be catastrophic and irreversible. Of the fossil fuels, natural gas provides the highest level of energy content per unit of carbon emissions. However, natural gas could not by itself fulfill global energy requirements with current technology, especially taking into account that the energy needs for a majority of the world’s population are unmet today. Moreover, natural gas (methane) leakage from pipelines contributes to global warming to a much greater (although not well understood) extent than carbon dioxide on a molecule-for-molecule basis.

Under today’s conditions, nuclear power has far lower routine emissions than energy from burning fossil fuels. However, it presents hazards of its own, notably the risk of accidents like Chernobyl, with severe, long-lasting consequences over huge regions. In addition, the security risks posed by large inventories of nuclear weapons-usable materials have no counterpart in fossil fuels.

Clearly, neither nuclear nor fossil fuel use is currently conducive to sound environmental and security policy. In addition, neither breeder reactors nor renewables (the two possible sources of an indefinite energy supply) are economical at present fuel prices so as to immediately constitute the basis of global energy supply. What are the options for a safe, sustainable, and ecological energy supply for the future? If fossil fuel use can be reduced and biomass burning done on a renewable basis so that emissions are below 3 gigatons per year of carbon, fossil fuels would be a sounder form of energy than nuclear, but would need to be accompanied by other energy sources. Economical, environmentally-sound carbon sinks, which would allow carbon dioxide to be absorbed and stored or disposed of without being released to the atmosphere as a gas, could also make fossil fuels a better energy source. Fossil fuels can be used at reduced levels as transition fuels to a renewable energy economy, or at higher levels if carbon sinks prove to be economical.

Natural gas could serve as a transition fuel to hydrogen derived from solar energy, since the infrastructure for use would be similar for the two gaseous fuels. Natural gas can be complemented by renewable energy sources such as solar energy, biomass fuels (renewably produced and used), and wind energy. Wind energy and solar energy are economical under some circumstances (such as areas with high wind speed or high insolation and low precipitation). The resource base for these technologies could extend to the indefinite future under &quotpresent economics” with a reduction in the cost of these technologies or an increase in uranium or coal and oil prices. Moderate fossil fuel use (with engineering measures to prevent releases of carbon dioxide gas into the atmosphere) and renewable energy sources joined with increased energy efficiency measures provide the best alternative for economical, sustainable energy in the future.

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