S1, E1: Sir David Attenborough looks at the science of climate change and potential solutions to this global threat. We're just two degrees away from a climate catastrophe. If the rate of global warming continues, we'll reach the threshold for permanent environmental damage within 40 years. But we have the power to prevent it. Intimate stories get inside the lives of the people affected by climate change, and those fighting it. And world-leading experts reveal the developments that are redefining our horizons. This is the greatest challenge we've faced. And the human race can rise to it.