In April last year a group of environmentalists shut down EON’s coal-fired power station in Ratcliffe-on-Soar, northern England. The goal: to reduce carbon dioxide emissions and, in their words, “save lives”. On Feb 25 judge Morris Cooper presented a 20-page judgment accepting there was an “urgent need for drastic action”, but convicted them of aggravated trespass, saying their defence, that their crime was necessary to save lives, could not be substantiated.

In the trial, for which I was an expert witness, crucial questions were how many people does climate change kill, and what proportion is the UK responsible for? I was surprised to discover that nobody knows. Scientists such as myself are involved in programmes to measure CO2 emissions, air temperatures, sea-ice loss and the much more complex impacts on birds, rainforest trees and coral reefs. We know that climate change-related events are killing people, yet there is no comprehensive global monitoring program to document the lives lost due to climate change. There is no official climate-change body count. Admittedly, the impact of climate change on human health and mortality is difficult to quantify.

The WHO publishes the only global estimate of the number killed by climate change - about 150,000 annually. Worryingly, this estimate comes from a single modelling study in 2002, and includes only four impacts of climate change (deaths from one strain of malaria, malnutrition, diarrhoea-type diseases and flooding). It is, as the authors point out, a highly conservative first estimate and, by now, considerably out of date. Why are we relying on a single, limited, out-of-date study for our information on the numbers of people killed by climate change? This is not a criticism of the WHO; the real question is why they are apparently alone in this effort.

The core of the climate-change community, of course, is that group studying the atmosphere. Their questions therefore don’t often relate directly to human health. The medical profession is obviously more interested in saving lives now than in the slower and longer term effects of climate change, and so have been late in engaging with the question. Naturally, funding influences which questions are answered. Politicians have not asked for a body count. But why not?

Such an understanding is essential for two quite different reasons. First, it is a basic issue of justice. The dead should be remembered and their families and friends should understand the factors involved in their deaths. Second, it seems likely that the numbers of people killed by climate change has been significantly underestimated.

This means that in addition to issues of the morality of equating human lives with the time spent

waiting in airport queues, such cost-benefit analyses used to shape government policy with major climatic impacts, such as building a new runway at Heathrow, are likely to be biased by underestimating the cost in human lives of such decisions. — The Guardian