UN chief: Climate change is ‘most important issue we face’

In this photo taken Wednesday, Oct. 3, 2018, a bird flies past as smoke emits from the chimneys of Serbia's main coal-fired power station near Kostolac, Serbia. The COP 24 UN Climate Change Conference is taking place in Katowice, Poland. Negotiators from around the world are meeting for talks on curbing climate change. (AP Photo/Darko Vojinovic)
UN Secretary General Antonio Guterres addresses during the opening of COP24 UN Climate Change Conference 2018 in Katowice, Poland, Monday, Dec. 3, 2018. (AP Photo/Czarek Sokolowski)
Actor Arnold Schwarzenegger delivers a speech during the opening of COP24 UN Climate Change Conference 2018 in Katowice, Poland, Monday, Dec. 3, 2018.(AP Photo/Czarek Sokolowski)
In this image taken with a slow shutter speed, vehicles move on a road in Belgrade, Serbia, Monday, Dec. 3, 2018. The COP24 UN Climate Change Conference is taking place in Katowice, Poland. Negotiators from around the world are meeting for talks on curbing climate change. (AP Photo/Darko Vojinovic)
UN Secretary General Antonio Guterres delivers a speech WLduring the opening of COP24 UN Climate Change Conference 2018 in Katowice, Poland, Monday, Dec. 3, 2018.(AP Photo/Czarek Sokolowski)

KATOWICE, Poland — U.N. Secretary-General Antonio Guterres issued a dramatic appeal to world leaders Monday to take the threat of global warming seriously and to act boldly to avert a catastrophic rise in temperatures before the end of the century.