Science is now unequivocal as to the reality of climate change. However, one facet - its human face - has been dangerously neglected. Until now. Given what the science tells us about global warming, how many people around the world will be affected, in what way, and at what cost?
These are the questions that a major new report attempts to answer for the first time. Its findings indicate that hundreds of millions of people are already permanently or temporarily affected, and half a billion are at extreme risk now. Because of climate change, each year hundreds of thousands lose their lives. All these figures are set to increase rapidly in as little as 10-20 years.
This publication, from the Global Humanitarian Forum, of which I am a board member, constitutes the most plausible estimate of the human impacts of climate change today. The scale of devastation is so great that it is hard to believe the truth behind it, or how it is possible that so many people remain ignorant of this crisis.
Four main factors have contributed to the silence. First, while the world has been coming to terms with the science of climate change, the problem has moved from being a future threat to a current danger. Climate change is an evolving concern, affecting people now.
Second, 99% of the casualties linked to climate change occur in developing countries. Worst hit are the world's poorest groups. While climate change will increasingly affect wealthy countries, the brunt of the impact is being borne by the poor, whose plight simply receives less attention.
Third, and worse, climate change hides its influence among a wide range of today's key global problems. It impacts heavily on nutrition and diseases such as malaria, and increases poverty. But that impact can be lost among the many contributing factors.
That is why a fourth major challenge is the current inability to separate the impacts of climate change in specific situations. It is impossible to say, for example, how much the severity of any hurricane is due to climate change.
It is time, however, to break the silence. It may not be possible to pin-point specific situations, or to achieve unequivocal global consensus. It took the Intergovernmental Panel on Climate Change (IPCC) 19 years to accomplish a consensus on the science in its 2007 report. But the general changes in the global climate system are clear: the number and intensity of extreme weather events, such as major floods and storms, has increased steadily in the last 30 years. Temperature changes show similar patterns, as do cyclone trajectories and rainfall patterns. From these changes it is possible to make good estimates about their global impacts on people.
That tells us who is worst affected: the poor, who are largely unprepared, and unable to cope with climatic change. Of course, wealthy countries are affected: long-term drought in Australia has caused certain crop yields to plummet. But the poor lack the resources to prevent disasters or adapt to changed conditions. Many already subsist on the mere threshold of survival.
Next week a series of UN talks will take place in Bonn - one of the last stepping stones in the effort to reach international agreement on how the world should tackle climate change, at the Copenhagen summit in December. Any post-Kyoto agreement must take into account the tremendous scale of suffering already being caused today.
There is a great responsibility for major polluters to protect the poorest populations from a problem for which they cannot be held responsible. Their silent suffering must serve as a warning signal of the greater suffering that lies in store for the rest of us if we fail to tackle climate change together.