This is a tragicomic situation. The movement toward biofuels in the European Union has the best motivation: the desire to increase the fraction of its transportation fuel that comes from renewable sources. Unfortunately, to meet the growing demand for palm oil (which is also desirable in cosmetics and for shelf-stable processed foods), suppliers must grow more oil palm trees. They find the land to do so by clearing rain forests. Rain forests worldwide play a large role in recapturing carbon dioxide from the atmosphere and sequestering methane from decaying biomatter.
Deciding between a renewable fuel supply and a vital component of the world's ecosystem is a terrible dilemma.
We are at the point, if we haven't already passed it, of running up against hard limits on our ever-expanding population.
The subject of overpopulation has a long and, to its critics, dubious history, starting in the 18th century with Thomas Malthus. Humanity seems to blow right past the supposed upper limits for a supportable population every time someone declares such a limit to exist, making Malthus and these other prophets of doom sound foolishly alarmist.
Nevertheless, I think the palm-oil dilemma is a sign that today's large human population is going to have more negative than positive consequences in the not too distant future.
Any species' population is as great as its food supply, predators, and diseases allow. Humans in societies don't have any predators of consequence, so our population has been limited only by the availability of food and the incidence of disease. Technology has allowed us to produce more food and to resist more diseases, to the point where today, there are a previously unimaginable six billion of us alive.
However, the scale and effect of human activities has been multiplied by technology, too. We in the United States think nothing of traveling thirty miles to shop at a particularly desirable store, for instance. Yet to do so requires burning gasoline or other fuel (unless you use a bicycle), which results in the release of carbon dioxide and other combustion byproducts. The release of those byproducts has consequences we never thought about until some forty years ago. We had to think about them because we suddenly realized that the output of one car was trivial, but the output of millions was significant. (The same principle applies if you take a bus or a train, of course.)
The complexity of our civilization practically guarantees we're never going to have a perfect understanding of the impact of our activities. Our knowledge will increase with time, of course, but so will the complexity. So how should we try to minimize the likelihood of really large-scale problems caused by the irreconcilable demands of our civilization, like the tug of war between the desire for more palm oil and the desire for breathable air and a not unduly hot environment?
How about reducing the size of that civilization, by reducing the number of ... us?
A couple of formidable objections come to mind. One is that attempts to control population growth have been regarded as dictatorial, and the idea is highly unpopular. The other objection is that in a world of contending nation-states, nations with smaller populations tend to be conquered by nations with larger populations unless the smaller nation has a significant strategic advantage.
I don't have answers to these objections. I wouldn't want to be subject to the simple but draconian population controls imposed by the People's Republic of China, even though they seem to have been successful by some measures. And North Korea's success in preserving the stalemate on the Korean Peninsula demonstrates the continuing value of threatening to unleash human waves in battle (if they're backed by a sufficiently technologically sophisticated army, anyway).
Yet I also don't think we can sustain a world of six billion people, even if not all of them aspire to lead as resource-hungry a lifestyle as those of us in the U.S.
[EDIT: spelling fix: "availabilty" --> availability]