Five scientists, working in different parts of the world, bear witness to some of the dramatic changes to our planet that have occurred in their lifetimes, as the global climate warms. 4. In May 2004, Professor Jennifer Leaning of Harvard University's FXB Center for Health and Human Rights, led a two-person human rights investigation into the reported widespread attacks and killings against agrarian villagers in Darfur, in Western Sudan. The villagers became refugees in neighbouring Chad. Jennifer Leaning explains how this trip lead her to realise that climate change has a crucial part to play in human migration. Produced by Anna Buckley for the BBC Radio Science Unit. First broadcast on Thursday 24 May, 2018.