The science is clear: the climate crisis is existential, and humanity is still not doing enough to prevent catastrophe. A new report from the United Nations warns that at our current rate, the world is set for disastrous overheating of 2.5 degrees Celsius by the end of the century – way higher than the goal of 1.5. This weekend, world leaders will gather in Sharm el-Sheikh, Egypt for the COP27 summit, where once more they will try to agree on a way to reverse this. Simon Stiell is the United Nations’ climate chief and speaks to Christiane ahead of this vital summit.  Also on today's show: Two-time Oscar-winner Genna Davis; Joan Donovan & Emily Dreyfuss, co-authors of Meme Wars.To learn more about how CNN protects listener privacy, visit cnn.com/privacy