"The urgency of this report, presented by the world's top scientists, should be matched with an equally urgent response by governments," said Hans Verolme, director of the World Wildlife Fund's global climate change programme.

"There's no escaping the facts: global warming will bring hunger, floods and water shortages. Poor countries that bear the least responsibility will suffer most -- and they have no money to respond."

The report by the UN's Intergovernmental Panel on Climate Change (IPCC) said that up to 30 percent of animal and plant species will be vulnerable to extinction if global temperatures rose by 1.5-2.5 C (2.7 F to 4.5 F).

It said the world's have-nots would be worst hit by the climate change, predicting greenhouse gases would change rainfall patterns, intensify tropical storms, accelerate the melting of Arctic ice and mountain glaciers, and amplify the risk of drought, flooding and water stress.

"This is a glimpse into an apocalyptic future," said Greenpeace International campaigner Stephanie Tunmore. "The earth will be transformed by human induced climate change, unless action is taken soon and fast."

The Friends of the Earth asked the world's rich nations to cut emissions to avert a looming "humanitarian catastrophe."

"Unless we take action ... far worse is yet to come, condemning millions in the poorest parts of the world to loss of lives, livelihoods and homes. Climate change is no longer just an environmental issue," said Catherine Pearce, the group's climate campaigner.