Quotes of the Day

If you had $75 billion to spend, how would you save the world? Would you invest it all in alternative energy research, to fight global warming? Would you revamp America's border and port security, to fight terrorism? Would you sign Kobe Bryant, Paul Pierce and Tim Duncan for the Philadelphia 76ers? (My personal choice.) Most of us might would make such a decision based on emotions — witnessing the pain of hunger, or experiencing the fear of nuclear terorrism. But what if there were a way to calculate the exact value of global priorities, a way to figure out just how much human suffering we could alleviate per dollar spent?

That's how the Copenhagen Consensus works. Over the past two years, some of the world's top economists have been crunching the numbers on the most efficient way to spend that $75 billion, roughly the sum total of global foreign aid budgets. Led by Bjorn Lomborg — an idiosyncratic author best known for his skeptical views on global warming — the organization last month gathered eight major economists, including five Nobel Prize winners, to come up with an answer. The results are surprising. According to the numbers, the biggest problem facing the world isn't global warming or terrorism. It's malnutrition in the developing world, and it can be sharply reduced for as little as $60 million a year, by supplying basic micronutrients for 112 million kids who lack essential vitamins. According to the Copenhagen Consensus's figures, that $60 million would pay back more than $1 billion in benefits — better health, fewer deaths, more worker productivity. "It's a matter of cost and benefit," says Lomborg. "These are the best problems with the best solutions." (Hear Lomborg talk about the Copenhagen Consensus and climate change on this week's Greencast.)

In its work, the Copenhagen Consensus poses a useful question: what if instead of trying to tackle the world's myriad problems in a piecemeal fashion, we focused our efforts tightly on where we could get the most value for our dollar? It's a very economist — and unglamorous — way of looking at the world. So one of the group's top global priorities is salt iodization for the poorest regions of South Asia, Africa and Eastern Europe. (An estimated two billion people in the world suffer from iodine deficiency, which can lead to goiter and which can be prevented with iodized salt.) For $19 million, this problem can essentially be solved. Delivering salt to the developing world isn't as dramatic as saving the polar bear, but the benefit of reducing human suffering is real. "It shouldn't be about who has the cutest animal," says Lomborg. "It's about the value of life."

Lomborg says the Copenhagen Consensus tends to focus on problems that have clear, applicable and economical solutions — which explains why climate change, despite its potential for long-term catastrophe, ranks beneath threats like parasitic worms and malaria on the group's list. To Lomborg — who says he believes in global warming but is skeptical of its severity — fighting climate change just isn't a good way to spend our money. We know for certain that supplying vitamins to impoverished children will save lives — but we don't know for sure that spending billions to reduce carbon emissions will have the same clear effect. One is a sure thing, and the other is a bit of a gamble — and since the world has limited resources for doing good, the thinking goes, best to opt for the sure thing when lives are at stake. It's a position that's earned Lomborg the enmity of the mainstream environmental community — the green website Grist.org once called him "Bjorn Loser" — but he's unshakable. "You give the most to the solutions that do the most good," says Lomborg, who believes that more effort needs to be put on adapting to climate change, rather than simply trying to stop it. "There's definitely a case of hype and one-sidedness on the climate debate."

To some degree, Lomborg is right. It would be a mistake to let fears over warming in the future overwhelm the endless list of ills today, and at times it does seem as if environmentalists care more about climate in the abstract than real human suffering. But not every threat can be broken down in terms of dollars and cents. Climate change is a unique challenge because if the dire predictions turn out to be right, our planet — and our civilization — might no longer be recognizable. We remain frustratingly incapable of nailing down how much warming we'll experience over the next century, or what the exact effects of climate change will be. But we know more every day, and the evidence, while not flawless, is frightening. By all means spend the money to halt malnutrition, or improve reproductive rights, or clean up water sanitation. But if I were asked to come up with the world's most pressing challenge, I wouldn't need to crunch the numbers. It's climate change — because we only have one Earth.

• Bryan Walsh