How human demands are outstripping the earth's capacities—and what we need to do about it.

Ever since 9/11, many have considered al Queda to be the leading threat to global security, but falling water tables in countries that contain more than half the world's people and rising temperatures worldwide pose a far more serious threat. Spreading water shortages and crop-withering heat waves are shrinking grain harvests in more and more countries, making it difficult for the world's farmers to feed 70 million more people each year. The risk is that tightening food supplies could drive up food prices, destabilizing governments in low-income grain-importing countries and disrupting global economic progress. Future security, Brown says, now depends on raising water productivity, stabilizing climate by moving beyond fossil fuels, and stabilizing population by filling the family planning gap and educating young people everywhere.

If Osama bin Laden and his colleagues succeed in diverting our attention from the real threats to our future security, they may reach their goals for reasons that even they have not imagined.