U.N. chief tells summit world is on "highway to climate hell" and nations must "cooperate or perish"

Sharm el-Sheikh, Egypt —  The only way to "put an end to all this suffering" from "a highway to climate hell" is for the world to cooperate or perish, dozens of leaders were admonished as they gathered Monday for international climate talks.

More than 100 world leaders will speak over the next few days to try to deal with a worsening problem that scientists call Earth's biggest challenge. Nearly 50 heads of states or governments started to take the stage Monday in the first day of "high-level" talks at this year's annual U.N. climate conference, known as COP27, with more to come in the following days.

Much of the focus will be on national leaders telling their stories of being devastated by climate disasters, culminating Tuesday with a speech by Pakistan Prime Minister Muhammad Sharif, whose country's summer floods caused at least $40 billion in damage and displaced millions of people.