Bill Gates likes ethanol.

Ethanol, the gasoline additive derived from agricultural crops, is the current leader among biofuels–the latest objects of scrutiny in the rush to replace fossil fuels with alternative energy sources.

Microsoft founder Bill Gates recently joined that rush by investing $84 million in Pacific Ethanol, which will be constructing several ethanol producing facilities to benefit from the U.S. mandate that ethanol production increase from the 4 billion gallons of 2006 to 7.5 billion gallons in 2012.

Biofuels like ethanol are an alternative energy source created from “biomass”, a generic term for a variety of organisms ranging from plants to the byproducts resulting when the plants are broken down–hence the “mass”–like cow manure.

Among their advantages over fossil fuels as alternative energy sources are their renewability, biodegradability, and cleaner burning. And they even help, as growing plants which remove carbon dioxide from the atmosphere, to offset the carbon dioxide resulting when fossil fuels are burned. So they are not only providers of alternative energy; they are weapons in the fight against global warming.

And, while some forms of alternative energy–solar, hydroelectric, or wind, for example–can only be used to create electricity, biofuels like ethanol can be added to gasoline as “extenders”, reducing some of the demand for petroleum. About forty percent of the energy we currently consume is in the form of liquid petroleum products.

On the down side, as the price for a barrel of petroleum continues to climb, the economics of biofuel production are becoming more attractive. As a result, land cultivation of already fragile ecosystems has increased; in Malaysia and Indonesia great tracts of rainforest have been transformed into oil palm plantations–the oil palm seed being the world’s richest source of seed oil—and possibly of alternative energy–in the world. And the Amazon rainforest is experiencing similar agricultural expansion.

So, Bill Gates’ joining the biofuel alternative energy movement may have its positives, as a sign that alternative energy development is no longer the exclusive domain of tree-huggers.

And, ironically, the trees in the rainforest of the world are suffering for it.