On the eastern edge of Kolkata, Dulu Bibi, a 25-year-old mother of four, worries about the cost of treating her two sick boys. Her husband earns 80 rupees to 90 rupees (Dh6.5 to Dh7.3) a day. The family's basic diet is low in the essential micro-nutrients that children need to thrive. Mrs Bibi's two sons, aged three and one, are weak and feverish, lack appetite, and cry a lot. "If I have to spend 150 to 200 rupees on medicine," she asks, "what will I eat and feed my children with?"
Mrs Bibi's story is heartbreaking - and heartbreakingly common - in the developing world: three billion people survive on diets that lack micro-nutrients like vitamin A and zinc, and are at increased risk of illness from common infections like diarrheal disease, which kills nearly two million children annually.
Micro-nutrient deficiency is known as "hidden hunger". This is a fitting description, because it is one of the global challenges that we hear relatively little about in the developed world. It draws scant media attention or celebrity firepower, which are often crucial to attracting charitable donations to a cause.
But there is a larger point here: billions of dollars are given and spent on aid and development by individuals and companies each year. Despite this generosity, we simply do not allocate enough resources to solve all of the world's biggest problems. In a world fraught with competing claims on human solidarity, we have a moral obligation to direct additional resources to where they can achieve the most good. And that is as true of our own small-scale charitable donations as it is of governments' or philanthropists' aid budgets.
In 2008, the Copenhagen Consensus Centre, which I direct, asked a group of the world's top economists to identify the "investments" that could best help the planet. The experts - including five Nobel Laureates - compared ways to spend $75 billion on more than 30 interventions aimed at reducing malnutrition, broadening educational opportunity, slowing global warming, cutting air pollution, preventing conflict, fighting disease, improving access to water and sanitation, lowering trade and immigration barriers, thwarting terrorism, and promoting gender equality.
Guided by their consideration of each option's costs and benefits, and setting aside matters like media attention, the experts identified the best investments, which included increased immunisation coverage, initiatives to reduce school dropout rates, community-based nutrition promotion, and micro-nutrient supplementation.
This last initiative, which could do so much to help Dulu Bibi's family in Kolkata, is extraordinarily cheap. Providing vitamin A for a year costs as little as $1.20 per child, while providing zinc costs as little as $1.00.
By highlighting the areas in which even small investments can accomplish a great deal, the project influenced philanthropic organisations and governments. This month, the Copenhagen Consensus Centre releases the Guide to Giving (www.copenhagenconsensus.com) so that those of us without a government treasury or charitable foundation at our disposal can also consider how to use the experts' lessons.
Often we hear catch phrases like "without an education there is no future" or "without water one cannot survive", as if it is obvious that we should focus first on one or the other. But many people go without proper education and access to clean drinking water. The difficult task that the expert panel undertook was to look at the extra good that an additional donation - even as little as $10 - could achieve with respect to many good causes.
The contrast between saving lives today and aiming at tomorrow becomes clear when efforts to tackle global warming are included in the comparison. How could $10 best be spent? Should we, say, buy carbon offsets, or donate to a charity providing micronutrient supplements?
One lesson we can draw is that while global warming may exacerbate problems like malnutrition, communities bolstered by adequate nutrition will generally be less vulnerable to climate-based threats. Overall, we can typically best help through direct interventions, including micro-nutrient supplements, fortification, biofortification, and nutritional promotion.
There are billions of stories like Mrs Bibi's and billions of other stories that demand our attention. By embracing simple lessons from economics, all of us - individuals, governments and philanthropies - can ensure that our generosity yields the greatest benefit possible.
Bjorn Lomborg is the head of the Copenhagen Consensus Center
© Project Syndicate 2011