President Xi Jinping made a big surprise announcement on Tuesday - that China is committing to cut its net carbon emissions to zero by 2060. But why has President Xi decided to take such a bold unilateral step? Will China's actions match his words? And how will other countries respond, not least the US? To answer these questions, Justin Rowlatt speaks to two people who have been at the top table of international climate diplomacy. Todd Stern was US President Barack Obama's representative in the Paris Agreement negotiations. And Rachel Kyte was an advisor on sustainable development to the United Nations Secretary General. Plus, Li Yan of Greenpeace in China explains what to look out for next year in the country's new five-year plan as proof that Beijing is serious about tackling carbon emissions. Producer: Laurence Knight (Picture: China's President Xi Jinping; Credit: Ed Jones/AFP via Getty Images)