The recent surge in world food prices is already creating havoc in poor countries, and worse is to come. Food riots are spreading across Africa, though many are unreported in the international press. Moreover, the surge in wheat, maize and rice prices seen on commodities markets have not yet fully percolated into the shops and stalls of the poor countries or the budgets of relief organizations. Nor has the budget crunch facing relief organizations such as the World Food Program, which must buy food in world markets, been fully felt.

What should we do about climate change? The question is an ethical one. Science, including the science of economics, can help discover the causes and effects of climate change. It can also help work out what we can do about climate change. But what we should do is an ethical question.

A grassroots approach alone won't make the earth stop warming.

Weighing our own prosperity against the chances that climate change will diminish the well-being of our grandchildren calls on economists to make hard ethical judgments.

Cities worldwide are promoting environmentally "green' roofs to mitigate several urban problems. Ground cover, shrubs and other flora planted across a building's roof can reduce storm water runoff, easing the burden on local sewers and water treatment systems. And the vegetation can keep the roof cooler in summer, lowering interior air-conditioning costs and therefore peak demand on area power plants.

Plans are afoot to reuse spent reactor fuel in the U.S. But the advantages of the scheme pale in comparison with its dangers.

Africa needs a green revolution. Food yields on the continent are roughly one metric ton of grain per hectare of cultivated land, a figure little changed from 50 years ago and roughly one third of the yields achieved on other continents. In low-income regions elsewhere in the world, the introduction of high-yield seeds, fertilizer and small-scale irrigation boosted food productivity beginning in the mid-1960s and opened the escape route from extreme poverty for huge populations. A similar takeoff in sub-Saharan Africa is both an urgent priority and a real possibility.

The Aral Sea in Central Asia was the fourth-largest lake on the planet in 1960. By 2007 it had shrunk to 10 percent of its original size. Widespread, wasteful irrigation of the deserts along the Amu and Syr rivers, which feed the Aral, cut the freshwater inflow to a trickle. Nevertheless, a dam built in 2005 has helped the northernmost lake expand quickly and drop substantially in salinity.

Firms seek greener ethanol from wood chips and agricultural waste. Scientists and engineers are working on dozens of possible biofuel-processing routes, reports Charles Wyman, a chemical engineer at the University of California, Riverside, who is a founder of Mascoma Corporation in Cambridge, Mass., a leading developer of cellulosic ethanol processes.

Unscientific assumptions in economic theory are undermining efforts to solve environmental problems.