The world needs to prepare for millions of people being driven from their homes by the impact of climate change, the United Nations (UN) High Commissioner for Refugees said on Tuesday.

Speaking at the World Economic Forum, Filippo Grandi said a UN ruling this week meant those fleeing as a result of climate change deserved international protection, and that it had broad implications for governments.

The UN Human Rights Committee made the landmark ruling on Monday in relation to Ioane Teitiota, from the Pacific nation of Kiribati, who brought a case against New Zealand after authorities denied his claim of asylum.

"The ruling says if you have an immediate threat to your life due to climate change, due to the climate emergency, and if you cross the border and go to another country, you should not be sent back, because you would be at risk of your life, just like in a war or in a situation of persecution," Grandi said.

"We must be prepared for a large surge of people moving against their will," he said. "I wouldn't venture to talk about specific numbers, it's too speculative, but certainly we're talking about millions here."

Potential drivers include wildfires like those seen in Australia, rising sea levels affecting low-lying islands, the destruction of crops and livestock in sub-Saharan Africa and floods worldwide, not least in parts of the developed world.

Yet the convention relating to the status of refugees, signed in 1951, made no provision for climate change as a reason for people to flee their country and seek asylum elsewhere. As climate impacts grow, legal questions become more complicated.

(If you want to contribute and have specific expertise, please contact us at nature@cgtn.com.)