Lord Stern: Deal with climate change or prepare for "extended world war"

"[Temperature change above 2 degrees Celsius would] transform where people can live [...] People would move on a massive scale. Hundreds of millions, probably billions of people would have to move if you talk about 4-, 5-, 6-degree increases [...And that would mean extended global conflict] because there's no way the world can handle that kind of population move in the time period in which it would take place."