The government will increase research into the possible impacts of climate change on the world's most vulnerable people, including deeper poverty and conflict, the international development minister said.
Secretary of State Douglas Alexander said his department will spend 20 million pounds a year over the next five years, a tenfold increase, to pinpoint where global warming will hit hardest and show how to proof development against more extreme weather and rising seas.
"Climate change is a defining global social justice issue," Alexander said on Wednesday.
Droughts and heatwaves from Kenya to Australia and southern Europe have been blamed on global warming which is happening already. Six of the first seven years this century were among the seven hottest since reliable records began in 1850, says the World Meteorological Organisation (WMO).
Poor countries will be hit hardest because they have the least resources to cope when crops fail or storms wreak havoc.
Rich countries' efforts to help developing nations are not entirely altruistic, as concern rises that climate change may trigger more conflict, for example over water, and migration.
"By the middle of this century there could be as many as 200 million people forced from their homes because of rising sea levels, heavier floods and more intense droughts. Where will they go?" said Alexander.
"If today's image of climate change is the polar bear tomorrow's could be the AK47."
The extra funding announced on Wednesday was separate from 800 million pounds that Britain last year pledged to support developing countries' fight against climate change, through a World Bank fund expected to be detailed at the Group of Eight leaders' summit in Japan in July.
Japan presented a $10 billion (5.1 billion pound) package last month to help emerging countries tackle climate change.
The United States said in January it would commit $2 billion over the next three years to promote clean energy technologies and help developing nations fight climate change.
