Climate change kills about 315,000 people a year through hunger, sickness and weather disasters, and the annual death toll is expected to rise to half a million by 2030, a report said on Friday.
The study, commissioned by the Geneva-based Global Humanitarian Forum (GHF), estimates that climate change seriously affects 325 million people every year, a number that will more than double in 20 years to 10 percent of the world's population (now about 6.7 billion).
Economic losses due to global warming amount to over $125 billion annually — more than the flow of aid from rich to poor nations — and are expected to rise to $340 billion each year by 2030, according to the report.
"Climate change is the greatest emerging humanitarian challenge of our time, causing suffering to hundreds of millions of people worldwide," Kofi Annan, former U.N. secretary-general and GHF president, said in a statement.
"The first hit and worst affected are the world's poorest groups, and yet they have done least to cause the problem."
The report says developing countries bear more than nine-tenths of the human and economic burden of climate change, while the 50 poorest countries contribute less than 1 percent of the carbon emissions that are heating up the planet.
Annan urged governments due to meet at U.N. talks in Copenhagen in December to agree on an effective, fair and binding global pact to succeed the Kyoto Protocol, the world's main mechanism for tackling global warming.
"Copenhagen needs to be the most ambitious international agreement ever negotiated," he wrote in an introduction to the report. "The alternative is mass starvation, mass migration and mass sickness."
The study warns that the true human impact of global warming is likely to be far more severe than it predicts, because it uses conservative U.N. scenarios. New scientific evidence points to greater and more rapid climate change.
The report calls for a particular focus on the 500 million people it identifies as extremely vulnerable because they live in poor countries most prone to droughts, floods, storms, sea-level rise and creeping deserts.
Africa is the region most at risk from climate change, home to 15 of the 20 most vulnerable countries, the report says. Other areas also facing the highest level of threat include South Asia and small island developing states.
To avoid the worst outcomes, the report says efforts to adapt to the effects of climate change must be scaled up 100 times in developing countries. International funds pledged for this purpose amount to only $400 million, compared with an average estimated cost of $32 billion annually, it notes.
"Funding from rich countries to help the poor and vulnerable adapt to climate change is not even 1 percent of what is needed," said Barbara Stocking, chief executive of Oxfam in Britain and a GHF board member.
"This glaring injustice must be addressed at Copenhagen in December."