ban ki moonSEOUL, South Korea —U.N. Secretary-General Ban Ki-moon said Monday that climate change is the greatest challenge facing a world beset by crises and called on governments to reach a deal on the environment at a meeting in Denmark later this year.

Ban said the world has “less than 10 years to halt (the) global rise in greenhouse gas emissions if we are to avoid catastrophic consequences for people and the planet.”

“It is, simply, the greatest collective challenge we face as a human family,” Ban said, referring to climate change, in a keynote speech at a gathering in Seoul of the World Federation of U.N. Associations.

He said, however, there was cause for hope. Referring to a December meeting in Copenhagen, he said “we have a chance to put in place a climate change agreement that all nations can embrace, which will be equitable, balanced, comprehensible.”

The Copenhagen meeting is meant to negotiate a new U.N.-brokered climate treaty to succeed the 1997 Kyoto Protocol that expires in 2012. Ban called it a “once-in-a-generation opportunity.”

He also called on governments to “seal the deal in the name of humankind” through a “renewed multilateralism, a compassionate multilateralism.”

Ban said he expects more than 100 heads of state and government to participate in a U.N. summit on climate change at the global body’s New York headquarters on Sept. 22, and called for them to pressure their negotiators so a deal can be concluded in Copenhagen.

Though identifying climate change as the world’s biggest problem, Ban said it faces other serious issues as well, including the proliferation of nuclear weapons and four problems that carry serious weight given their timing.

“We are living through an age of multiple crisis,” Ban said. “Fuel, flu and food, and most seriously, financial. Each is something not seen for years, even for generations. But now they are hitting us all at once.”

Ban also discussed nuclear weapons, saying he took heart in efforts by the U.S. and Russia to find ways to cut their nuclear arsenals and cited work by the Conference on Disarmament — a multilateral global forum — for agreeing to a program “that can move the world away” from nuclear weapons.

“Let us convince leaders, once and for all, of the danger posed by nuclear weapons,” Ban said, saying the abbreviation WMD should stand for “we must disarm,” rather than weapons of mass destruction.

Ban, a former South Korea foreign minister who took over leadership of the U.N. in 2007, did not mention efforts to rid North Korea of nuclear weapons.

In a separate speech, Hans Blix, the former chief U.N. weapons inspector and currently president of the World Federation of U.N. Associations, decried what he said was “our addiction to excessive armaments.”

He noted that last year world military spending amounted to about $1.4 trillion, of which he added the U.S. accounted for about half.

Still, like Ban, he said there is room for optimism.

“Fortunately, a drive for disarmament has emerged in the last few years,” he said.