A true count of climate deaths

This story was originally published by WIRED and appears here as part of the Climate Desk collaboration.

Climate change can kill people in all kinds of ways. There are the obvious ones — wildfires, storms, and floods — yet rising temperatures may also lead to the increased spread of deadly diseases, make food harder to come by, and increase the risk of conflict.

Although we know about these wide-ranging but equally terrifying risks, attempts to pinpoint the number of deaths caused by climate change have been piecemeal. One recent study estimated that climate change was to blame for 37 per cent of heat-related deaths over the past three decades. In 2021, Daniel Bressler, a PhD student at Columbia University in New York, estimated that every additional 4,400 metric tons of carbon dioxide emitted will cause one heat-related death later this century. He called this number the “mortality cost of carbon.”

Putting a number on climate deaths isn’t just an academic exercise. People are already dying because of extreme temperature and weather events, and we can expect this to become more common as the planet continues to heat up. If governments want to put in place policies to prevent these deaths, they need a way of accurately measuring the deaths and ill health linked to warming. The search is on for the true mortality cost of carbon.

As part of this search, the U.K. government has made its first attempt at putting a number on climate change deaths. The U.K. Office for National Statistics (ONS) — an independent government agency responsible for producing official data — has for the first time reported climate-related deaths and hospital admissions in England and Wales. The report covers the years 2001 to 2020, but future reports will be released annually, revealing for the first time detailed information about the impact that climate change is having on health in the two nations. (Statistics for Scotland and Northern Ireland are recorded separately.)

The main finding from this investigation is counterintuitive. The report found that the number of deaths associated with warm or cold temperatures actually decreased between 2001 and 2020. On average, 27,755 fewer people were dying each year due to unusually warm or cold temperatures. In other words, climate change might have actually prevented over half a million deaths in England and Wales over this period. In 2001, there were 993 climate-related deaths per 100,000 people in England and Wales. By 2019, that figure had fallen to 771.

But let’s not get ahead of ourselves. There are a number of reasons why the net number of temperature-related deaths appeared to decline over this period, says Myer Glickman, head of the epidemiological, climate, and global health team at the ONS. For a start, statisticians took a relatively narrow definition of climate-related deaths. They only included deaths from conditions where scientists had previously found a clear link between temperature and disease outcome, and they also excluded any health condition where their own analysis showed no link between temperature and outcome.

This means that the mortality data doesn’t include deaths from violence or natural forces (such as storms, landslides, or flooding).

The analysis also excluded deaths from air pollution, which Public Health England estimates is equivalent to between 28,000 and 36,000 deaths each year in the U.K. Glickman says that there is no accepted way to separate out the effect that temperature increases have on air pollution. Add all these caveats together and it’s likely that the ONS analysis is a little on the conservative side.

Then there is the big reason why climate change has not led to more deaths in England and Wales: the very mild climate. Although average temperatures in the U.K. have increased by 0.9 degrees compared to the period from 1961 to 1990, its residents are not some of the three billion people who face unlivable conditions if greenhouse gas emissions increase rapidly. And while deaths linked to cold weather were down in England and Wales, on warmer days there was a net increase in hospital admissions linked to warmer weather. This was particularly true when it comes to injuries, which may be because more people do outdoor activities when it’s warmer or might be linked to the increases in violence and mental health problems that are associated with warmer temperatures.

The lower rate of deaths might also be a sign that our attempts to fight back against cold weather are working. Widespread flu vaccinations, support for people to pay their heating bills, and increases in home insulation mean that the coldest days didn’t hit as hard as they might have without these mitigations in place, Glickman says. And warmer homes might be a good thing now, but as summers in the U.K. get hotter and air-conditioning remains rare, it may start to become a problem.

The ONS will now release this data on a yearly basis, but Glickman’s next project is to look more closely at how temperature changes affected different areas.

“We’re going to drill down to a local level temperature,” he says. “That’s going to give us a lot more resolution on what’s happening and who it’s happening to.” The impact of climate change might depend on how wealthy an area is, for example, or whether its residents have easy access to health care or community support.

Glickman also wants to explore indirect impacts of climate on health. “What will be a big interest in the coming years is the lower-level health impacts of things like flooding,” he says. If someone’s home is flooded, it might increase their vulnerability to respiratory disease or worsen their mental health. Researchers from the U.K. have already found that people with mental illnesses are more at risk of death during hot weather. We don’t know why that is exactly, but researchers think it might be because people with mental illnesses are more likely to be socially isolated or already have poorer health, which makes them more vulnerable when temperatures rise.

The team behind the ONS report is also part of a wider effort to create a global system to count climate-related health impacts. “What we don’t have is a robust set of statistics to categorize the impact of climate on health,” says Bilal Mateen, a senior manager of digital technology at Wellcome Trust, the health charity funding the new climate change health impact initiative.

The first year of the project will be spent identifying countries to partner with before developing and testing different ways of measuring climate change deaths that work for specific countries, says Mateen. The idea is to use this data to help countries devise policies that lessen the health impact of climate change. “We can begin to tease out what works, what doesn’t, and what adaptation and mitigation interventions we should be supporting,” Mateen says.

If it’s true that warmer homes and flu vaccines helped reduce climate change deaths in England and Wales, it’s a sign that populations that are healthier on the whole might be better at surviving the ravages of a heating world. Other countries may want to take note.

“All policies are health policies,” says Mateen. “There is a clear need to support job stability, to address fuel poverty and every other policy that’s outside the mandate of the health minister because we know that those social determinants of health have a downstream impact.”