Much of the world is unprepared for the mounting threats of climate change.

That was the conclusion of top scientists in a new U.N. report released Monday in Japan.

It said global warming is affecting food and water shortages, economic livelihoods and raising the risk of wars.

The effects of climate change may be irreversible and billions of people could be affected.

(SOUNDBITE) (English) INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE CHAIRMAN, RAJENDRA PACHAURI, SAYING:

"The one message that comes out very clearly is that the world has to adapt and the world has to mitigate and the sooner we do that the less the chances of some of the worst impacts of climate change being faced in different parts of the world."

Outside the venue on Sunday, climate activists presented mock life preservers and urged world leaders to take urgent action.

(SOUNDBITE) (English) GLOBAL CALL FOR CLIMATE ACTION COMMUNICATIONS DIRECTOR, CHRISTIAN TERIETE, SAYING:

"This