UN chief: Climate change is "most important issue we face" By FRANK JORDANS and MONIKA SCISLOWSKA, Associated Press KATOWICE, Poland (AP) — 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. Guterres, who spoke at the opening