The combined threat of global warming, balance of payments, high energy cost and security of supply have forced the consideration of a variety of ideas on alternative energy. Some of these ideas, however, can be rejected as wishful thinking. Here are three:

. In his Jan. 22, 2000, State of the Union address, President Clinton said, “Before you know it, efficient production of biofuels will give us the equivalent of hundreds of miles from a gallon of gasoline.” We asked the director of renewable energy for the U.S. Department of Energy: Where did that come from? The answer: “That came from the White House.” President Clinton just made it up. That’s what his polling and focus groups told him to say.

. Amory Lovins in 1976 predicted that by the year 2000, 30 percent of our total energy would come from hydro, biomass, solar and wind power systems. The actual figure is more like 3 percent – and most of that comes from highly subsidized biomass plants.

. The advocates of nuclear power were equally optimistic. The “too cheap to meter” quote – which came from Lewis Straus, a member of the government, not a utility executive – reflects that buoyancy.

Perhaps we can be more realistic about the future if we review the past and cite the events that brought us to the present energy and industrial posture. Between 1860 and 1920, the technology of electric power generation, the steam turbine, the internal combustion engine, inexpensive steel, explosives, synthetic fertilizers and electrical components were developed. In the 1890s, Sanford Moss wrote his doctoral dissertation at Cornell on the gas turbine. Aurel Stodola in the 1920s described the compound steam and gas cycles that now dominate the generation of electric power. Both Moss and Stodola would be completely at home with the thermodynamics of present power generation systems. Their amazement would focus on the computational power used to resolve problems in fluid mechanics.

A second and much smaller burst of technology came after World War II. The high-bypass jet engine matured along with the development of high-speed computing. No new prime movers have developed – not on a scale great enough to make any difference on a global basis. The fission reactor has come close. About 16 percent of worldwide electricity is fission generated, but political issues, weapons proliferation and economic considerations may prevent significant expansion.

Nothing on the current menu – wind, solar, biomass, hydrogen, geothermal – can come close to matching energy sources now in place. The Energy Information Administration, a nonpolicy branch of the U.S. Department of Energy, has over 400 professional employees and a budget of nearly $100 million. It publishes worldwide annual energy consumption data. The current total energy consumption figure is 500 quadrillion Btu per year. If we divide it by the world population and convert that consumption to watts, the result is more than 2000 watts per person. At the moment, each person – all 6 billion of us – is consuming, on average, 24-7, the energy equivalent of 20 100-watt light bulbs.

If we focus on just the United States, with 300 million people and 100 quadrillion Btu of energy, the consumption per person jumps by a factor of five: 100 100-watt light bulbs. To be sure, this energy is not consumed in the form of electricity, but in the form of gasoline, coal, hydro power, etc. Yet many people project that this magnitude of energy consumption can be sustained by energy sources such as solar collectors on roofs, biofuel from switchgrass, and wind farms. These people simply can’t do arithmetic.

Tree plantations and switchgrass plots can capture solar energy at the rate of about 1 watt for each square meter. Once converted to electricity or petroleum equivalent, that drops to 0.5 watts per square meter. The entire cropland area of the United States, if planed to short-rotation crops, could not supply even a small fraction of our current energy needs.

Much has been said of this biomass option. But converting foodstuffs such as corn to ethanol and soybeans to biofuels is a dubious proposition. It doesn’t make economic sense to convert foodstuffs to energy, and it raises moral issues as well. It is clear that use of lignocellulose is much preferred to the use of foodstuffs for energy, but converting all of the wood and crop residuals in the United States to ethanol or some alternative fuel will not make a dent in satisfying the country’s energy budget. Here in Maine, converting wood to ethanol is a shaky proposition at best but would help the forest products industry with an additional value-added product. This will not, however, solve the long-term energy problem that the country faces.

Then there is the hope that we can manage the continued use of fossil fuel by sequestration of the carbon dioxide formed during the combustion process. Currently, about 25 billion tons of carbon dioxide is put into the atmosphere each year from the combustion of fossil fuels. If, by some magic, we can separate carbon dioxide from all the other gases and compress 10 percent to a density of carbon dioxide liquid, we will then have about 5 billion cubic meters of carbon dioxide to sequester. The world is now approaching petroleum consumption of 100 million barrels per day, or a bit less than 5 billion cubic meters per year. The worldwide complex of pipes, wells, tanks, ships and trucks delivering that oil is mind-boggling. An equally complex infrastructure would be required to sequester just 10 percent of the world’s generation of carbon dioxide. This will not be done.

The horizon of the “foreseeable future” is closing in. To push back that horizon, we must learn to use fossil fuels more efficiently, expand the nuclear option, and concentrate our efforts on conservation. There is no magic that will keep the future like the past.

Richard C. Hill is professor emeritus of mechanical engineering at the University of Maine. Dr. Joseph Genco from the university’s department of chemical engineering helped write this commentary.