Is there anyone who hasn't taken a good whack at corn ethanol over the past year? It's not just that, depending on how you measure things, the process of producing corn ethanol may actually create more greenhouse-gas emissions than gasoline does, once you take changes in land use and deforestation into account. There's also the fact that last year, thanks to various ethanol mandates, the United States alone gobbled up 23 percent of its corn crop to make just 5 percent of its car fuel supply, driving up food prices and making the whole enterprise look nigh unsustainable.

But does that mean all biofuels are doomed to fail? Not necessarily. Robert Langreth has a good piece in Forbes this week about companies that are researching the next generation of plant-based fuels—from cellulosic ethanol made from the non-edible parts of plants, to bioengineered microbes that can produce hydrocarbon molecules, to algae-based ethanol. It's all mildly exciting and in theory there's a lot of potential—if you had an incredibly efficient (and borderline magical) process to convert an entire plant into fuel, one BP biochemist argues that you could power the world's cars and trucks using just 1 percent of the planet's surface area.

Trouble is, we're very, very far from that utopia. There are precisely zero commercial cellulosic ethanol plants operating right now, and it's one of those technologies that's always "a few years away"—though one company profiled elsewhere in Forbes is vowing to commercialize a process to make ethanol from corncobs by 2011. We'll see. Also, any profitable biofuel approach runs the risk of giving people incentives the world over to clear away forests in order to grow fuel crops—which, again, risks making this method a net loser from a climate perspective. (One tricky point is that analysts are still wrangling over how best to calculate the life-cycle impact of biofuels.)

That means plug-in hybrids and electric cars still look like the cleanest, surest way to end our dependence on oil, though lest anyone think that's entirely cost-free from a sustainability standpoint, the BBC had a recent piece on analysts who are fretting about whether there's enough lithium in the world to make all those advanced car batteries. (One official from Mitsbuishi, which is unveiling an electric car soon, expects lithium demand to outstrip supply in less than ten years, unless new reserves are brought online.) Chile, for one, has been dubbed the Saudi Arabia of lithium—a light metal that's most easily harvested from the brine under salt flats—but the world's largest reserves may be in Bolivia. Yet Bolivia's president, Evo Morales, isn't terribly keen on welcoming in foreign mining companies to exploit the area, which could become a bone of contention for electric-car makers trying to keep battery prices down. Never a dull moment in the resource wars...

--Bradford Plumer