The silver tsunami is approaching: Many countries, not all of them rich, are facing the challenges of an ageing population thanks to growing life expectancies and shrinking birth rates.

As global climate change affects livelihoods across the world, migration patterns are also changing. In a recent study published in Global Environmental Change, Clark Gray, Valerie Mueller, and I found that since the 1970s, climatic variations have been increasing internal migration across many South American countries, with few exceptions. And many people are headed to cities.