At least, that's what a group of economists said.

There isn't an unlimited amount of money to be spent on every problem, so choices have to be made. The question addressed by the Copenhagen Consensus Center is what investments would do the most good for the most people. The center's blue-ribbon panel of economists, including five Nobel laureates, weighed more than 40 proposals to improve the world by spending a total of $75 billion over the next four years.

What would do the most good most economically? Supplements of vitamin A and zinc for malnourished children.

Number two? A successful outcome to the Doha Round of global free-trade talks. (Someone please tell Barack Obama.)

Global warming mitigation? It ranked 30th, or last, right behind global warming mitigation research and development. (Someone please tell John McCain.) The nearby table lists other rankings.

"It's true that trade doesn't immediately save lives," explains Bjorn Lomborg, the political scientist who heads the Copenhagen Consensus Center. "But it's proven that when people have more money" – as tends to be the case when trade barriers fall – "they improve their health, their education and so on." The resulting prosperity reduces such problems as malnutrition and disease, while improving education. All three of those ranked high on the priority list.

The benefits of freer trade were estimated in a paper presented by Professors Kym Anderson and Alan Winters. They found that a successful Doha Round could generate up to $113 trillion in new wealth during the 21st century, at a cost of $420 billion or less from inefficient industries going bust. If you like ratios, that's a return of $269 for every $1 of cost. A less conservative projection puts the gains three times higher. More than 80% of this global windfall would go to the world's poorest countries.

Meanwhile, providing vitamin A and zinc would help some 112 million children in sub-Saharan Africa and South Asia for merely $60 million a year. The minerals would help prevent blindness and stunted growth – increasing lifetime productivity by an estimated $1 billion. Similar if not quite so bountiful returns apply to investments in iron supplements, salt iodization and deworming, all low-cost measures that the economists in Copenhagen ranked highly. A private charity would be smart to seize on these opportunities, the way that Rotary International led the fight to all but eradicate polio in the 20th century.

No doubt there is room to debate these priorities, and that was the point of the Copenhagen sessions. But it's also instructive that the rich world's political cause du jour, global warming, fell well down the list. Research into low-carbon energy technologies, at No. 14, was the only climate-related proposal to reach even the middle of the priority list.

As Mr. Lomborg recently explained, the costs of mitigating climate change would be enormous for what are highly speculative benefits. He prefers research on new technologies, rather than a global cap-and-trade regime that would raise energy prices and thus reduce overall economic growth. Meanwhile, societies that are wealthier due to free trade will be better able to cope with the consequences of warming, if it occurs.