Try counting the treesStill Pictures

THE human impact of climate change “is difficult to assess reliably”, say the authors of a new report from the Global Humanitarian Forum, a think-tank run by Kofi Annan, a former United Nations secretary-general, aided by a raft of eminent folk. But they make a stab, reaching the conclusion that 325m people around the world are seriously affected by climate change every year and that this number could more than double, to around 660m, by 2030.

As in so many reports of this kind, the trend looks plausible, but there seems little basis for the exact numbers. 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.”

On slightly firmer ground, the authors elaborate on the familiar point that most of the damage from a changing climate will be felt in poor countries. Warmer temperatures are actually leading to increased crop yields in some parts of North America and Russia. But areas where yields are falling because of climate change include sub-Saharan Africa and South Asia, where the victims are small farmers eking out an already meagre living. And the countries seen as most vulnerable to climate change are all poor: they include Somalia, Burundi, Niger, Eritrea, Afghanistan and Chad.

Nor are people in those countries well placed to adapt to change. As their livelihood vanishes, they are more likely to fuel the ranks of the temporarily or permanently displaced. The eminent writers duly propose a huge (nay, hundredfold) boost in funding to help the poor cope with a shifting climate—through drought-resistant crops, for example.

In another haphazard estimate, the authors of “Human Impact Report: Climate Change—Anatomy of a Silent Crisis” say 26m people have already been displaced by climate change. But here again, accuracy is impossible. Should Cyclone Aila, which hit Bangladesh and India on May 25th and affected hundreds of thousands of people, be classified as a climate-change event? Even if scientists could agree on the contribution of global warming to the rising frequency of such disasters, it would still be hard to classify the causes of any given catastrophe. Nor is it easy to disentangle the effects of climate change from those of avoidable failures in policy.

In South Asia, for example, climate change is likely to bring more water to a perennially thirsty region. A blessing in disguise, then? No, because so little progress has been made on ways to trap and use this water when it cascades down in a short space of time. Given that governments have missed so many obvious tricks, is there any reason to assume that more money thrown at the problem will be spent wisely? Coping with climate change will certainly cost money—it is anyone's guess how much—but plenty of wisdom will be needed too.