Cold Weather Deaths: What the Evidence Shows
Key takeaways · 11 min read
- Cold is linked to far more deaths than heat: 7.29% of deaths against 0.42% in a 13-country study.
- About 4.6 million deaths a year worldwide are associated with cold, against about 489,000 with heat.
- Most cold-related deaths happen on moderately cold days, not in extreme freezes.
- Researchers disagree about how much winter mortality is caused by cold rather than by infections and season.
In this article
Heatwaves get the headlines. They are sudden, visible and increasingly common, and their death tolls are reported in real time. Cold weather rarely gets the same attention, except when something dramatic happens, such as the Texas power grid failing in February 2021.
Yet in most of the world, cold kills far more people than heat. A study of 74 million deaths in 13 countries, published in The Lancet in 2015, found that cold was linked to about 17 times as many deaths as heat. A global analysis in 2021 put the number of cold-related deaths at about 4.6 million a year.
Those numbers are not as simple as they look. Researchers disagree about how much of the winter rise in deaths is caused by cold itself, and about whether climate warming will reduce it. This article looks at what the evidence shows, where the uncertainty lies, and what is known about who is most at risk.
How many deaths are linked to cold?
The most influential study is by Antonio Gasparrini and colleagues in the Multi-Country Multi-City Collaborative Research Network. They analysed 74,225,200 deaths in 384 locations across 13 countries, including Australia, Canada, China, Japan, the UK and the USA, and modelled how the risk of death changed with daily temperature over the following three weeks.
They estimated that 7.71% of all deaths were attributable to temperatures above or below the level at which mortality was lowest. Of those, cold accounted for 7.29% of all deaths and heat for 0.42%.
Qi Zhao and colleagues extended the approach to the whole world in The Lancet Planetary Health in 2021, using data from 750 locations in 43 countries. They estimated that about 5.08 million deaths a year between 2000 and 2019 were associated with non-optimal temperatures, 9.43% of all deaths. About 4.59 million were linked to cold and about 489,000 to heat, a ratio of roughly nine to one.
Share of all deaths attributable to cold and heat
384 locations in 13 countries, 1985 to 2012.
Gasparrini A and colleagues, The Lancet, 2015. Bars scaled to the cold figure.
Deaths linked to non-optimal temperatures worldwide
Estimated deaths per year, 2000 to 2019.
Zhao Q and colleagues, The Lancet Planetary Health, 2021. Data from 750 locations in 43 countries.
It is not mostly the extreme cold
One of the most important findings in Gasparrini’s study is easy to miss. Extreme temperatures, both hot and cold, accounted for only 0.86% of all deaths. Most temperature-related deaths happened on days that were moderately cold, not on the rare days of severe frost.
The reason is frequency. Each moderately cold day adds only a small amount of risk, but there are many such days every winter. A cold snap raises risk more sharply, but it lasts a few days. Over a year, the many ordinary cold days add up to more deaths.
This has practical consequences. Public warnings and emergency responses are usually triggered by extreme events. If most cold-related deaths happen outside those events, then warnings alone will miss most of the problem.
It also explains why heat and cold behave differently. The risk from heat rises steeply once temperatures pass a threshold, so a heatwave concentrates deaths into a few days. Cold risk rises more gradually and lasts longer, with deaths from heart disease and respiratory illness often following a cold spell by days or weeks.
Most temperature-related deaths are not on extreme days
Share of all deaths attributable to non-optimal temperatures.
Gasparrini A and colleagues, The Lancet, 2015. Extreme means below the 2.5th or above the 97.5th percentile of local temperature.
How cold harms the body
Hypothermia, a fall in core body temperature, is the most direct way cold kills. But it accounts for only a small share of cold-related deaths in most countries.
Most of the excess comes from heart attacks, strokes and respiratory disease. Cold makes blood vessels near the skin constrict, which raises blood pressure. Blood becomes thicker and more likely to clot. Breathing cold air can irritate the airways and worsen chronic lung disease, and respiratory infections spread more easily in winter when people spend more time indoors.
William Keatinge, Gavin Donaldson and colleagues in the Eurowinter study, published in The Lancet in 1997, compared regions across Europe from Finland to Greece. They found that mortality rose more for each degree of cold in regions with mild winters than in regions with harsh ones. People in colder places tended to heat their homes more, wear more clothing outdoors and spend less time outside without protection.
That finding has shaped much of the thinking since. It suggests that cold-related deaths depend less on how cold a place gets than on how well people are protected from the cold they experience. It is also one reason why countries with mild winters and poorly insulated housing, such as the UK, Ireland and Portugal, have often recorded larger seasonal rises in deaths than Scandinavian countries with much harsher winters.
Homes, heating and who is at risk
Older people carry most of the risk. The body’s ability to sense and respond to cold declines with age, and older people are more likely to have the heart and lung conditions that cold makes worse.
Housing has also been a major focus, especially in the UK. The Marmot Review Team, in a 2011 report for Friends of the Earth, estimated that 21.5% of excess winter deaths in England and Wales could be attributed to the coldest quarter of homes, almost three times as many as if deaths were spread evenly across housing.
But the evidence at the individual level is less clear-cut than that estimate suggests. Peter Tammes and colleagues, in the British Journal of General Practice in 2018, used primary care records to study who died on colder days in England. Each 1°C fall in the three-day average temperature raised the risk of death by about 1.1%. They found no clear modifying effect of sociodemographic characteristics or the energy efficiency of people’s homes, although risk was higher in northern England.
The overall picture is that cold homes plausibly contribute to winter deaths, but that the effect of housing is harder to measure than the broad population estimates imply.
The debate about winter deaths
Not everyone accepts that the large cold-related death figures reflect cold itself.
Patrick Kinney and colleagues, in Environmental Research Letters in 2015, looked at 36 US and 3 French cities. Winter mortality was about 16% higher than summer mortality across all of them, whether their winters averaged below freezing or above 20°C. There was no relationship between how cold a city’s winter was and how many extra deaths it had. They also showed that if a model does not control well for season, cold effects look much larger than they are.
Philip Staddon and colleagues, in Nature Climate Change in 2014, found that in England and Wales excess winter deaths had stopped tracking the number of cold days, and that year-to-year variation was better explained by influenza. They argued that climate warming would not reduce winter mortality.
Others disagree. Donaldson and Keatinge, in the BMJ in 2002, estimated that only 2.4% of excess winter deaths in south-east England over a decade were due to influenza, and argued that cold stress was the main driver. Shakoor Hajat and Gasparrini, in Epidemiology in 2016, argued that the common measure of excess winter deaths, which compares December to March with other months, is itself biased. It misses cold-related deaths that happen outside those months and counts deaths that are seasonal for other reasons.
The disagreement matters for climate policy. If cold causes most winter deaths, warming will save many lives in cold regions, partly offsetting the rising toll from heat. If winter deaths are mainly driven by infections and other seasonal factors, those savings will be smaller.
Is winter mortality really about cold?
Studies that reach different conclusions.
| Study | Finding | Implication |
|---|---|---|
| Kinney and colleagues, 2015 | Similar winter excess in cold and warm cities | Cold effect may be overstated |
| Staddon and colleagues, 2014 | Winter deaths no longer track cold days | Warming may not cut winter deaths |
| Donaldson and Keatinge, 2002 | Influenza only 2.4% of excess winter deaths | Cold stress is the main driver |
| Hajat and Gasparrini, 2016 | Winter death index is biased | Need temperature-based methods |
Environmental Research Letters; Nature Climate Change; BMJ; Epidemiology.
When the power goes out: Texas, 2021
The most dramatic recent example of cold-related death in a wealthy country came in February 2021, when Winter Storm Uri brought record cold to Texas. The state’s power grid failed, leaving millions of people without electricity or heat for days.
The official state death toll, revised in January 2022, was 246 people in 77 counties, ranging in age from infants to a 102-year-old. Most died of hypothermia. Others died in road accidents, falls and house fires, from carbon monoxide poisoning while trying to heat their homes, with at least 19 such deaths, or after losing power to oxygen machines and other medical equipment. Independent analyses of excess deaths suggested the true toll was higher.
Texas was an extreme event in a place unused to extreme cold, which fits the Eurowinter finding that people in milder climates are less protected. It also showed that the main danger in a modern cold disaster is often the loss of heat and power, not the outdoor temperature alone.
Winter Storm Uri, Texas, February 2021
Official state count of storm-related deaths.
Texas Department of State Health Services, revised January 2022, as reported by NPR.
What reduces the risk
Because most cold-related deaths are spread across ordinary winter days, the measures with the best supporting evidence are also ordinary ones.
Public health guidance in England, including the National Institute for Health and Care Excellence guideline on cold homes, published in 2015, focuses on identifying people at risk, particularly older people and those with heart or lung disease, and helping them keep their homes warm. That includes referral to heating and insulation schemes and checking that people can afford to heat their homes.
Since 2023 the UK Health Security Agency and the Met Office have issued cold-health alerts in England, graded by the expected impact on health services rather than by temperature alone. The idea follows directly from the research: the aim is to prompt action by health and care services before and during cold spells, not only in the most extreme weather.
Seasonal flu and COVID-19 vaccination also matter, whichever side of the cold-or-infection debate one takes, because respiratory infections contribute a share of winter deaths. And in places where cold is rare, such as Texas, the evidence from 2021 points to resilient power and heating systems as the first line of protection.
What the evidence does not show
It does not show that every death attributed to cold was caused by cold. The estimates come from statistical models, and results depend on how they handle season and other factors.
It does not show that climate warming will produce a large net fall in temperature-related deaths. Some studies expect savings in cold regions; others argue winter deaths will change little, while heat deaths will rise.
It does not settle how much cold homes matter. Population estimates are large, but individual-level studies have found weaker or inconsistent effects of housing quality.
And it does not mean heat is unimportant. Heat deaths are concentrated in time, rising, and more sensitive to climate change.
Questions people ask
Does cold kill more people than heat?
In most places, yes. A study of 74 million deaths found cold linked to 7.29% of deaths and heat to 0.42%.
Do most cold deaths happen in severe cold snaps?
No. Most occur on moderately cold days, which are far more common. Extreme temperatures accounted for 0.86% of all deaths.
What do people actually die of in cold weather?
Mostly heart attacks, strokes and respiratory disease. Hypothermia is a small share of cold-related deaths.
How many people died in the 2021 Texas winter storm?
The official toll is 246, most from hypothermia. Independent analyses suggest the real figure was higher.
Will climate change reduce winter deaths?
Researchers disagree. Some expect fewer cold deaths as winters warm; others find winter deaths no longer track cold and may not fall much.
The short version
- Cold is linked to far more deaths than heat: 7.29% of deaths against 0.42% in a 13-country study.
- About 4.6 million deaths a year worldwide are associated with cold, against about 489,000 with heat.
- Most cold-related deaths happen on moderately cold days, not in extreme freezes.
- Researchers disagree about how much winter mortality is caused by cold rather than by infections and season.
- The 2021 Texas storm killed at least 246 people, most from hypothermia after the power grid failed.
This article summarises published research on cold-related mortality. It is not medical advice. If you are worried about an older relative or someone with heart or lung disease during cold weather, their doctor or a local public health service can advise on keeping warm safely.
Further reading. Gasparrini and colleagues, ‘Mortality risk attributable to high and low ambient temperature’, The Lancet, 2015, is the foundation of most current estimates and is open access. Kinney and colleagues, ‘Winter season mortality: will climate warming bring benefits?’, Environmental Research Letters, 2015, is the clearest statement of the sceptical view.
- The Heat Will Kill You First, Jeff Goodell (2023). A journalist on heat as a health risk, useful for understanding why heat and cold behave so differently.
- Not the End of the World, Hannah Ritchie (2024). A data scientist on climate and environmental trends, including how temperature-related deaths are estimated.
- Weathering, Arline T. Geronimus (2023). A public health researcher on how social disadvantage wears down the body, relevant to who is most vulnerable to cold.
Sources
- Gasparrini A, Guo Y, Hashizume M, and colleagues. Mortality risk attributable to high and low ambient temperature: a multicountry observational study. The Lancet, 2015;386(9991):369–375. doi:10.1016/S0140-6736(14)62114-0.
- Zhao Q, Guo Y, Ye T, and colleagues. Global, regional, and national burden of mortality associated with non-optimal ambient temperatures from 2000 to 2019. The Lancet Planetary Health, 2021;5(7):e415–e425. doi:10.1016/S2542-5196(21)00081-4.
- The Eurowinter Group. Cold exposure and winter mortality from ischaemic heart disease, cerebrovascular disease, respiratory disease, and all causes in warm and cold regions of Europe. The Lancet, 1997;349(9062):1341–1346. doi:10.1016/S0140-6736(96)12338-2.
- Kinney PL, Schwartz J, Pascal M, and colleagues. Winter season mortality: will climate warming bring benefits? Environmental Research Letters, 2015;10(6):064016. doi:10.1088/1748-9326/10/6/064016.
- Staddon PL, Montgomery HE, Depledge MH. Climate warming will not decrease winter mortality. Nature Climate Change, 2014;4(3):190–194. doi:10.1038/nclimate2121.
- Donaldson GC, Keatinge WR. Excess winter mortality: influenza or cold stress? Observational study. BMJ, 2002;324(7329):89–90. doi:10.1136/bmj.324.7329.89.
- Hajat S, Gasparrini A. The excess winter deaths measure: why its use is misleading for public health understanding of cold-related health impacts. Epidemiology, 2016;27(4):486–491. doi:10.1097/EDE.0000000000000479.
- Tammes P, Sartini C, Preston I, Hay AD, Lasserson D, Morris RW. Use of primary care data to predict those most vulnerable to cold weather: a case-crossover analysis. British Journal of General Practice, 2018;68(668):e146–e156. doi:10.3399/bjgp18X694829.
- Marmot Review Team. The Health Impacts of Cold Homes and Fuel Poverty. Friends of the Earth and the Marmot Review Team, 2011.
- National Institute for Health and Care Excellence. Excess winter deaths and illness and the health risks associated with cold homes. NICE guideline NG6, 2015.
- UK Health Security Agency. Weather-health alerting system: cold-health alerts. 2023 onwards.
- Texas Department of State Health Services. February 2021 winter storm-related deaths, Texas. Revised January 2022; as reported by NPR, 3 January 2022.
