Climate change is already killing 300,000 people a year in a “silent crisis” that is seriously affecting hundreds of millions more, an influential humanitarian group warned today.

A report by the Global Humanitarian Forum, led by Kofi Annan, the former UN Secretary-General, says that the effects of climate change are growing in such a way that it will have a serious impact on 600 million people, almost ten per cent of the world’s population, within 20 years. Almost all of these will be in developing countries.

“Climate change is the greatest emerging humanitarian challenge of our time, causing suffering to hundreds of millions of people worldwide,” Mr Annan said.

“As this report shows, the first hit and worst affected are the world’s poorest groups, and yet they have done least to cause the problem.”

The report claims that 90 per cent of the deaths are related to gradual environmental degradation caused by a warming climate, which exacerbates existing threats — mainly malnutrition, diarrhoea and malaria. The rest are said to be the result of weather disasters.

The study has been reviewed by leading experts including Rajendra Pachauri, chairman of the Intergovernmental Panel on Climate Change.

It estimates that the economic cost of climate change is currently $125 billion (£77 billion) a year, greater than the total amount of aid given to the developing countries every year.

The report forecasts that by 2030 this figure will treble to $340 billion (£210 billion) annually and that half a million people will be dying each year.

About 99 per cent of the casualties will be in developing countries, the report suggests — yet the 50 poorest countries are responsible for only one per cent of global emissions.

Developing countries do not have the capacity to cope will the threat and need a hundredfold increase in mitigation efforts, the report warns.

Mr Annan lamented that in industrialised countries, climate change was seen as a distant environmental problem, “a viewpoint reinforced by pictures of glaciers and polar bears — not human beings,” he said. “We testify here to the human face of a dangerous problem.”

The populations most at risk are a half billion people living in Africa, central Asia, South and south east Asia and in small island nations, according to the study.

However, it says that developed countries are also being affected by drought, forest fires and flooding.

Mr Annan criticises current political leadership on the issue as “weak” and said world leaders must do better when they meet in Copenhagen later this year to agree a successor to the Kyoto Protocol.

“Copenhagen needs to be the most ambitious international agreement ever reached,” he said. “As this report shows, the alternative is greater risk of starvation, migration and sickness on a massive scale.”

At the launch of the report, Barbara Stocking, chief executive of Oxfam, said that climate change was a “gross injustice” as well as a human crisis.

The research was carried out by Dalberg Global Advisers, a consultancy firm, who collated all existing statistics on the human impacts of climate change. The report acknowledges a “significant margin of error” in its estimates.

Mr Annan said the report could never be as rigorous as a scientific study, but said: “We feel it is the most plausible account of the current impact of climate change today.”

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