GENEVA — The United Nations hosted a conference on Monday to help Pakistan cope with the fallout of last summer’s devastating flooding, which the U.N. chief called a “climate disaster of monumental scale” that killed more than 1,700 people in the immediate aftermath. Pakistani Prime Minister Shahbaz Sharif was joining U.N. Secretary-General António Guterres in-person. “We need to be honest about the brutal injustice of loss and damage suffered by developing countries because of climate change,” Guterres told the gathering.