| Climate change is one of the greatest challenges facing humanity today. Its effects are already being felt – from strengthened storms and rising sea levels to changing temperature and weather patterns – and they will only grow worse. Urgent action is needed to reduce emissions and to mitigate and adapt to these changes. Everyone will be impacted by climate change, especially those who are poor, vulnerable and lacking the resources to adapt. All communities will need to build resilience and sustainability. And with migration and urbanization taking place on an unprecedented scale, this will require understanding how populations are changing, and then planning to address people’s current and future needs. UNFPA is working with governments and other partners to better understand population dynamics, how they affect the changing climate and how people can become resilience in the face of these changes. Only with this knowledge can policymakers take on this gravest of challenges.