In 2008, the Copenhagen Consensus Center, 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.