MATTHEW GREEN and KATE ABNETT WORLD leaders should declare states of "climate emergency" in their countries to spur action to avoid catastrophic global warming, U.N. Secretary-General Antonio Guterres said in opening remarks to a climate summit. More than 70 world leaders were due to address the one-day virtual gathering aimed at building momentum for much steeper cuts in planet-warming emissions on the fifth anniversary of the 2015 Paris climate accord. "Can anybody still deny that we are facing a dramatic emergency?" Guterres said via video. "That is why today, I call on all leaders worldwide to declare a State of…