3 News: The United Nations delivered its sharpest warning to date about climate change today. It says we need to stop burning fossil fuels by the end of the century, or face catastrophic consequences. It's being called the most important ever document on climate change and the prognosis for humanity is grim: stop burning fossil fuels by 2100, or risk catastrophic warming that's a global rise in average temperatures of up to 5degC. "If greenhouse gas emissions continue to rise at the current rate, we...