Every mile you drive your car releases about a pound of CO2 into the air. How many miles do you drive in a year? Now think about the natural gas that heats your home, the electricity that lights it ( mostly generated by the burning of fossil fuels). Your life is pumping an enormous amount of CO2 into earth's atmosphere.

And you are not alone. About 300 million other Americans are making similar contributions. In 2005 alone, the United States released 6 billion metric tons of carbon dioxide into earth's atmosphere from the burning of fossil fuels (5,973,000,000,000,000 pounds!).

Carbon dioxide has the unfortunate chemical property of absorbing sunlight and remitting it at a lower wavelength as heat, much as the glass windows of a greenhouse do. As more and more CO2 is added to the atmosphere, the earth is getting warmer -- as it turns out, a lot warmer. Global warming, once a controversial hypothesis, is now a clearly established scientific observation.

What can we do about it? While in the future hydrogen might provide an alternative, for now our cars are going to continue to run on chemical fuel and the best way to avoid contributing to global warming will be to switch to a different carbon-rich chemical, one that doesn't increase the atmosphere's load of CO2.

Ethanol, the same alcohol found in beer and wine, is such a chemical. Ethanol makes a good fuel: Burning a gallon of ethanol in your car releases about 80 percent as much car-powering energy as burning a gallon of gasoline.

Burning a fossil fuel like gasoline releases into the atmosphere stores of carbon dioxide that had been trapped for many centuries as oil buried deep in the earth. Burning ethanol releases carbon dioxide, just as burning gasoline does, but in this case the carbon dioxide released into the atmosphere has just been taken from it by photosynthesis. Our automobiles are simply returning to the atmosphere the CO2 recently extracted from it! No net increase in atmospheric CO2 occurs.

Think of the atmosphere as a fountain that recycles the water it shoots into the air. The level of water stays the same in the pool because the water added to the pool by the falling spray is recycled back to the pump to shoot up again. That is how ethanol works with regards to carbon dioxide emissions. Imagine now if a hose were placed into the pool, pumping in additional water. Eventually, the pool will fill completely and begin to overflow. That is what happens when fossil fuels are burned.

If ethanol is to replace gasoline in our cars, we are going to need a lot of it. Where could we get it? Brazil powers most of its automobiles with ethanol fermented by yeasts from sugarcane, in much the same way beer is made. But the United States doesn't grow much sugarcane. In the United States, commercial ethanol fuel is traditionally produced by fermenting sugars obtained from starch stored in corn kernels.

The United States produced nearly 4 billion gallons of ethanol from corn in this fashion in 2005. The ethanol is typically added to gasoline, rather than burned by itself. New cars called Flexible Fuel Vehicles (FFV) have redesigned engines that burn 85 percent ethanol-15 percent gasoline blends, called E85, as if they were 100 percent gasoline. This adoption of ethanol for automobile fuel is sensational news for combatting global warming.

Now consider that the starch used to make the ethanol in E85 fuel represents less than half of the biomass of a corn plant. The stalk, the leaves, the cob -- they aren't used to make ethanol, and are typically left to decay in the field. This biomass represents an enormous opportunity for future ethanol production.

Fully 80 percent of the stems and leaves of a corn plant is cellulose, the material of which newspaper is also made, and its close relative hemicellulose.

Focus on cellulose. Like starch, cellulose consists of chains of glucose sugars linked together. Why not use these sugars to make ethanol? Because there is a subtle but very important chemical difference between starch and cellulose. Each of the glucose sugar molecules in starch or cellulose has six carbon atoms arranged in a ring like a snake biting its tail.

In cellulose, the rings of the glucoe molecules are inside-out, as if the snakes bite their tails on the bottom rather than the top. Yeast enzymes do not attack links between these kinds of sugars. To use cellulose to produce ethanol, bioengineers have had to find a way to teach yeasts to break these links.

There are microbes with enzymes that can do this. Otherwise cows could not eat grass, nor termites wood. Using the sort of plant genetic engineering technology for which St. Louis is becoming famous, it is possible to "bioengineer" a yeast able to ferment cellulose. Researchers might for instance add to the yeast some DNA taken from plant-digesting bacteria in the gut of termites -- DNA containing the genes these bacteria use to break down cellulose to free sugars.

This approach is already succeeding overseas. In Spain a plant is today making commercial ethanol from biomass cellulose.

Nor is corn the only plant that can be grown to produce cellulose biomass. Fast-growing plants that could be dedicated to fuel production include switchgrass and trees such as hybrid poplar and willows. These plants can be grown on lands that are not suitable for row crops, especially erosion-prone soils, leaving fertile soil for consumable crops such as corn, soybeans and wheat. Other sources of cellulose from industrial and commercial waste, such as sawdust and paper pulp, could also be used to produce ethanol. So could leaves and yard waste, and the paper and cardboard that make up the bulk of municipal dumps.

It is difficult to imagine a more attractive long-term investment in our country's future than developing strains of ethanol-producing yeasts that ferment cellulose. President Bush has commendably restored cuts his administration had made in the funding of ENREL, the federal laboratory that carries out such research. The federal government should massively increase this funding. With a serious national commitment to developing biomass-to-ethanol technology, we might in the not-too-distant future be filling up our tanks with farm-grown rather than fossil fuels, to the world's great benefit.

Parts of this article appeared in the St. Louis Post-Dispatch,

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