The day Hurricane Sandy slammed into the East Coast, I was in Mali, a country in West Africa’s Sahel region. As a native New Yorker, I was stunned and dismayed to see pictures of the flooded streets and tunnels of Manhattan, of destroyed homes and schools on Staten Island, and of thousands of my fellow New Yorkers displaced and in shelters. But I was even more struck by the indiscriminate nature of what I was witnessing both in Mali (one of the world’s poorest countries) and the United States (one of its richest): massive humanitarian emergencies resulting from more extreme weather.