Common Wealth Economics for a Crowded Planet By Jeffrey D. Sachs 386 pages. $27.95. The Penguin Press. The timing for Jeffrey D. Sachs's new book on how to avert global economic catastrophe couldn't be better, with food riots in Haiti, oil topping $120 a barrel and a gnawing sense that there's just less of everything - rice, fossil fuels, credit - to go around. Of course, we've been here before. In the 19th century, Thomas Malthus teased out the implications of humans reproducing more rapidly than the supply of food could grow. In 1972, the Club of Rome published, to much hoopla, a book titled "Limits to Growth." The thesis: There are too many people and too few natural resources to go around. In 1978, Mr. Smith, my sixth-grade science teacher, proclaimed that there was sufficient petroleum to last 25 to 30 years. Well, as Yogi Berra may have said, "It's hard to make predictions, especially about the future." And yet. Even congenital optimists have good reason to suspect that this time the prophets of economic doom may be on point, with the advent of seemingly unstoppable developments like climate change and the explosive growth of China and India. Which is why Sachs's book - lucid, quietly urgent and relentlessly logical - resonates. Things are different today, he writes, because of four trends: human pressure on the earth, a dangerous rise in population, extreme poverty and a political climate characterized by "cynicism, defeatism and outdated institutions." These pressures will increase as the developing world inexorably catches up to the developed world. By 2050, he writes, the world's population may rise to 9.2 billion from 6.6 billion today, an increase of 2.6 billion people, which is "too many people to absorb safely." The combination of climate change and a rapidly growing population clustering in coastal urban zones will set the stage for many Katrinas, not to mention "a global epidemic of obesity, cardiovascular disease and adult-onset diabetes." Sachs smartly describes how we got here, and the path we must take to avert disaster. The director of the Earth Institute at Columbia University and the author of "The End of Poverty," Sachs is perhaps the best-known economist writing on developmental issues (or any other kind of issues) today. And this is Bigthink with a capital B. "The very idea of competing nation-states that scramble for markets, power and resources will become pass