The study, carried out by Dalberg Global Development Advisers, estimates that climate change kills about 315,000 people a year through hunger, sickness and weather disasters, with the annual death toll expected to rise to half a million by 2030.

More than 90 percent of those deaths relate to environmental deterioration caused by the gradual onset of climate change, including a reduction in farm land, creeping deserts and sea-level rise, and only a tiny proportion are caused by sudden disasters.

The report also calculates that climate change seriously affects 325 million people every year, a number that will more than double in 20 years to 660 million, or around 10 percent of the world's population. And it says that 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.

More than nine-tenths of the economic and human burden of climate change is borne by developing countries, which are the least responsible and least able to cope, it says.

In many respects, these numbers are welcome, because the estimates often used by the humanitarian community are out of date. The aid world has been crying out for some new statistics on which it can build a stronger case for helping the world's poorest communities adapt to climate change.

But articles in two well-respected media outlets - the Economist and the New York Times - have poured cold water on the GHF's efforts to provide those figures.

"As in so many reports of this kind, the trend looks plausible, but there seems little basis for the exact numbers," says the Economist. "For example, the authors attribute two-fifths of an expected increase in weather-related disasters to climate change and use this as a basis for all their other sums. But they offer no convincing rationale for this approach, and admit with refreshing candour that 'the real numbers may be significantly lower or higher'."

In a news release, GHF says the study, carried out by Dalberg Global Development Advisers, collates "all relevant information and current statistics relating to the human impact of climate change".

"Within the limitations of existing research, the report presents the most plausible estimate of the impact of climate change on human society today," it says.

The sources of data, models and scenarios used in the report include the World Health Organisation, the Intergovernmental Panel on Climate Change (IPCC), the World Bank and the Stern Review on the Economics of Climate Change.

The report attributes 40 percent of weather-related disasters since 1980 to climate change based on an analysis of data from Munich Re, which it then uses as an approximation for deaths and the number of people seriously affected. And it references a WHO study in calculating that 4 percent of cases of people whose health is harmed by environmental degradation are down to climate change.

The authors admit the human impact "is still difficult to access with great accuracy because it results from a complex interplay of factors" and recommends that the report's estimates "should be treated as indicative rather than definitive".

They also warn that the true human impact of global warming is likely to be far more severe than they predict, because the report uses conservative IPCC scenarios. New scientific evidence points to greater and more rapid climate change.

But, despite the caveats, the academic gloves are most definitely off. According to an article by Andrew C. Revkin in the New York Times, the GHF study has been dubbed "a methodological embarrassment" by Roger A. Pielke Jr., a political scientist at the University of Colorado who studies disaster trends. He says there's no way to distinguish deaths or economic losses relating to human-induced global warming from those caused by wider factors such as population growth and economic development in vulnerable areas.

He goes so far as to tell the newspaper that the report "will harm the cause for action on both climate change and disasters because it is so deeply flawed".

Development economist Jeffrey Sachs - one of 12 experts who reviewed the report - acknowledges that some of its conclusions are oversimplified, but still endorses its message, according to the New York Times.

SILENT CRISIS

For those who do humanitarian and development work in the world's poorest countries, where they are witnessing the most harmful impacts of climate change, it's a message that matters.

They need all the weapons they can muster to highlight how changing weather and climate patterns are already hurting vulnerable communities, as well as the desperate need for more funds to help protect them from growing risks in the future.

"These are the people for whom daily life is already a hard struggle. They live on the margins. They are the ones who are the least resilient and unable to respond to this crisis," Annan said at a press conference to launch the report in London.

"Up until now, the scope of their plight has gone largely unnoticed. It is why we are saying the human impact of climate change is a silent crisis. It is time we gave them voice, it is time we focused on their issues."

Barbara Stocking, the chief executive of Oxfam in Britain, told reporters how she'd visited displaced survivors of northern Uganda's brutal conflict and been asked by an elderly man there whether recent floods, the like of which he'd never seen before, had happened because of the war.

"That made me feel very sad - that people who are trying to cope with climate change have no idea what is happening to them. It is disempowering," she said.

Both she and Annan emphasised the need for greater knowledge and understanding of the impact of climate change at all levels - whether it be among policy makers talking tough at U.N. negotiations, or a Bangladeshi woman who's trying to reduce the risk of flooding in her village.

If the GHF study - irrespective of its alleged imperfections - draws attention to the gaps in what we know and manages to convey the message that the poorest and most vulnerable should get more of a say in the international climate policy arena, it will be of value to the humanitarian community.

Suffering in silence until all the facts about climate change are 100 percent certain just isn't an option for a small farmer who's struggling to grow enough maize or rice to feed her hungry children.

What do you think? For more information, here's a video produced by GHF about the report.

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