As an extreme year for hurricanes, wildfires and heat waves comes to an end, the head of the United Nations challenged world leaders to make 2021 the year that humanity ends its “war on nature” and commits to a future free of planet-warming carbon pollution. “The state of the planet is broken,” U.N. Secretary-General Antonio Guterres said in a speech at Columbia University. “Humanity is waging war on nature. This is suicidal.”