This is not just a humanitarian imperative; it is in all our interests to act. In the globalised 21st Century conflicts are not easily contained by borders. As the Stern Review made clear, tackling climate change will ultimately be cheaper than allowing it to proceed unchecked. But it is the human cost of these crises, the children of Gaza, the homeless Philippines and the South Sudanese families who do not know where their next meal is coming from that really demand our action. The UK public have shown they are up to the task; it is time for world leaders to do likewise.