The two defining challenges of our time are managing climate change and overcoming world poverty. We cannot succeed on one without succeeding on the other. With international collaboration and sound policies, we can achieve that success by launching a new era of low-carbon economic growth while adapting to the climate change that is on the way. ... Unmanaged climate change would so transform the planet that by the end of this century hundreds of millions of people would need to move, probably leading to severe and extended conflict. Poor countries and communities are the most vulnerable and have done the least to create the problem. Rich countries have a clear obligation to provide additional resources.