Given the power that the daily statistics of Covid deaths have exerted over us this year, it was only a matter of time before we started being bamboozled with terrifying figures of the estimated death toll from climate change. Sure enough, the latest issue of Nature Climate Change contains a widely-reported paper by the London School of Hygiene and Tropical Medicine and the University of Bern, which attempts to quantify the death toll from higher global temperatures. The scientists ran a simulation which they claim predicted what the weather would have been like in recent years had it not been for man-made climate change. They then reached the conclusion that man-made climate change was responsible for a third of heat-related deaths, leading to an extra 82 deaths a year in London, 141 in New York and 156 in Tokyo.
Let’s leave aside the argument of how much of the rise in temperatures over the past few decades can be attributed to human activity and how much is natural, and assume that all of it has been caused by greenhouse gas emissions. There are still two huge problems with the conclusion presented by this research.
Firstly, the outdoor shade temperature – i.e. the metric which is used to measure climate change – is a poor marker for the temperatures people are actually exposed to during a heatwave. What matters rather more is the temperature inside buildings, where people spend most of their time. Live in a well-designed building with air conditioning and protection from direct sunlight, and there is no reason why a heatwave should be any less comfortable than any other weather. On the other hand, if you live in a poorly-designed building with inadequate ventilation, which receives large amounts of solar radiation and from which heat cannot escape at night, then indoor temperatures can reach uncomfortable levels even when the temperature outside is not especially high. As Emily Hill wrote here in 2015, some of the worst buildings for overheating are modern flats designed and marketed as ‘eco-homes’. They are designed to cut carbon emissions but not, apparently, to adapt to rising temperatures. Her flat was reaching 24 Celsius in the middle of winter, even without the heating on. For three months during the summer, temperatures hovered between 28 and 32 Celsius. In Britain, those are considered to be heatwave temperatures – and yet inside the flat they were maintained for three months, day and night. If we want to protect people from excessive heat the fastest and surest way to do this is to design buildings which do not trap excessive heat.
The other obvious objection to the London School of Hygiene and Tropical Medicine study is that it doesn’t even try to compute the other side of the ledger: the number of lives which are presumably being saved by fewer days of very low temperatures. The closest we have are the figures for ‘excess winter deaths’ in the UK which are published by the Office for National Statistics. These show that in the five years to 1967/68 there were an average of 54,350 excess winter deaths in England and Wales. In the five years to 2017/18 there were an average of 32,058. It will be different in tropical countries, but in temperate climates like Britain's the cold is a far more significant killer than the heat.
If you are going to try to put a figure on the effect of climate change on mortality you surely ought to consider both effects: and try to compare extra deaths from the heat against fewer deaths from the cold. Yet the LCHTM study – along with several others in a similar vein published in recent years – makes no attempt to do this. Perhaps ‘thousands of Londoners’ lives saved by climate change’ doesn’t make such a good headline.