Cold weather kills far more people worldwide than heat does, but that does not mean packing up and moving to the tropics will add years to your life. A massive global study covering 2000–2019 found that roughly 5 million deaths per year were linked to non-optimal temperatures, and cold accounted for about nine times more of those deaths than heat did.1The Lancet. Global, regional, and national burden of mortality associated with non-optimal ambient temperatures from 2000 to 2019: a three-stage modelling study The relationship between climate and longevity is shaped by cardiovascular stress, infectious disease patterns, sunlight exposure, infrastructure, behavior, and how well a population has adapted to its local weather. Warm places have real advantages, but they come with their own costs.
Cold Is the Bigger Killer, and It Is Not Close
When researchers tally deaths attributable to temperature extremes across the globe, cold dominates. Of the roughly 5 million annual temperature-related deaths identified in the 2000–2019 study, about 8.5% of all global deaths were cold-related compared to under 1% from heat.1The Lancet. Global, regional, and national burden of mortality associated with non-optimal ambient temperatures from 2000 to 2019: a three-stage modelling study A separate analysis of disability-adjusted life years across 204 countries found that cold exposure accounted for about 68% of the total temperature-related health burden.2PubMed Central. Burden of environmental heat and cold exposure and its attributable risk factors in 204 countries and territories (1990-2021) These are not just deaths from hypothermia during blizzards. The vast majority of cold-related mortality comes from the chronic, low-grade cardiovascular stress that winter weather puts on the body day after day.
The seasonal pattern of cardiovascular disease has been recognized for decades. Heart attacks, strokes, and sudden cardiac deaths spike during winter months in temperate and cold climates.3PubMed. Cold and the risk of cardiovascular diseases. A review When your body is exposed to cold, blood vessels near the skin constrict to conserve heat. That drives up blood pressure, forces the heart to work harder, and in people with existing coronary artery disease, can reduce oxygen delivery to the heart muscle itself.4PubMed Central. Cardiovascular diseases, cold exposure and exercise Cold also triggers the sympathetic nervous system and the renin-angiotensin system, promotes dehydration, and sparks systemic inflammation, all of which raise the risk of a cardiovascular event.5PubMed Central. Cardiovascular response to thermoregulatory challenges For someone with mild hypertension or clogged arteries, a cold snap can be genuinely dangerous even if they never set foot outside without a coat.
Heat Has Its Own Deadly Mechanisms
If cold kills more people overall, why not just recommend warm climates and call it a day? Because heat is not benign. Extreme heat stresses the cardiovascular system through a different but equally damaging pathway. When you overheat, your body pushes blood toward the skin to dump heat, forcing the heart to pump harder and faster. Dehydration thickens the blood, raising the risk of clots and heart attack. The kidneys take a hit too, as reduced blood flow and low fluid volume can lead to acute kidney injury. At the cellular level, extreme heat triggers inflammation, oxidative damage, and the death of heart muscle cells.6BMJ. Effects of extreme heat on physiology, morbidity, and mortality under climate change: mechanisms and clinical implications
There is also a ceiling on the human body’s ability to cool itself, and it is lower than many people assume. The long-cited figure of 35°C wet-bulb temperature as the upper survivability limit turns out to be optimistic. Laboratory studies of young, healthy adults found that the actual critical wet-bulb temperature averaged around 30.5°C in humid conditions, and it dropped even further in hot, dry environments where the skin absorbs heat faster than sweat can carry it away.7PubMed Central. Evaluating the 35°C wet-bulb temperature adaptability threshold for young, healthy subjects (PSU HEAT Project) Follow-up work confirmed that above a person’s individual threshold, core body temperature rises continuously and could reach heatstroke levels within about 10 hours.8PubMed Central. Validating new limits for human thermoregulation These limits matter for the tropics and for anywhere that experiences extreme heatwaves, because humid heat is the combination most dangerous to human survival.
The Temperature Sweet Spot Shifts With Local Climate
Researchers use a concept called the minimum mortality temperature, the daily temperature at which death rates in a given population are lowest. The striking thing about this number is that it is not fixed. It shifts depending on where people live, because populations physiologically and behaviorally adapt to their local climate. A multicountry study of over 400 locations found that the minimum mortality temperature ranged from about 13°C in alpine regions up to roughly 26.5°C in the tropics.9PubMed Central. Geographical Variations of the Minimum Mortality Temperature at a Global Scale: A Multicountry Study In absolute terms, the minimum mortality temperature generally tracks higher as you move toward the equator and lower as you move toward the poles.10Nature Communications. Mapping the increased minimum mortality temperatures in the context of global climate change
What this means in practice is that people living in warm climates are not simply “safer” because cold kills more people globally. Their bodies and habits are tuned to warm conditions, and they become more vulnerable to cold snaps that residents of Stockholm would barely notice. The reverse is equally true: people adapted to cold climates tolerate winter far better than their physiology would suggest, but a summer heatwave can overwhelm them. This adaptation happens both at the individual level, where repeated heat exposure over days or weeks lowers resting core temperature, improves sweating efficiency, and reduces cardiovascular strain, and at the population level through housing design, behavioral norms, and infrastructure.11PubMed. Adaptations and mechanisms of human heat acclimation: Applications for competitive athletes and sports
Why Temperature Swings May Matter More Than Average Temperature
A factor that often gets overlooked in “warm vs. cold” debates is day-to-day and within-day temperature variability. The gap between daytime highs and overnight lows, known as diurnal temperature range, turns out to be a meaningful health risk in its own right. A nationwide prospective study found that for each 1°C increase in diurnal temperature range, the risk of death from all causes rose by about 13%, and cardiovascular disease risk rose by about 12%.12PubMed Central. Long-Term Impacts of Diurnal Temperature Range on Mortality and Cardiovascular Disease: A Nationwide Prospective Cohort Study A meta-analysis focusing on hospital admissions found smaller but consistent effects: each 1°C increase in diurnal temperature range was associated with about a 1.5% increase in cardiovascular hospitalizations, with older adults and men at higher risk.13International Journal of Cardiology Cardiovascular Risk and Prevention. Diurnal temperature range and hospital admission due to cardiovascular diseases: A systematic review and meta-analysis study
Desert climates often have enormous diurnal swings, sometimes 20°C or more between afternoon and predawn hours. Some tropical climates, by contrast, stay relatively stable around the clock. A place with a moderate average temperature but wild daily fluctuations could be harder on the body than a place that is consistently warm. Stability, not just warmth, seems to matter for long-term cardiovascular health.
Sunlight, Vitamin D, and Cardiovascular Benefits
One genuine longevity advantage of warmer, sunnier climates has less to do with temperature itself and more to do with ultraviolet light. Solar UV-B radiation is the main source of vitamin D for most people, and vitamin D status is strongly influenced by latitude, season, and how much time you spend outdoors. A significant portion of the population in northern Europe and North America has vitamin D levels in the deficient range, and large studies have found that people with deficient vitamin D concentrations face roughly double the cardiovascular mortality risk of those with adequate levels.14PubMed. Sun, vitamin D, and cardiovascular disease
But the sunlight story is more interesting than just vitamin D. Epidemiological data show that higher sun exposure correlates with lower blood pressure and reduced cardiovascular death even after accounting for vitamin D status. In fact, multiple trials of oral vitamin D supplementation have failed to reproduce the cardiovascular benefits associated with actual sunlight exposure, suggesting that UV radiation has protective effects through pathways independent of vitamin D.15PubMed. Sunlight Has Cardiovascular Benefits Independently of Vitamin D One likely mechanism involves UV-triggered release of nitric oxide from skin stores, which dilates blood vessels and lowers blood pressure. If you live at a high latitude where winter daylight is scarce, a vitamin D pill may not fully replicate what an hour of midday sun provides.
Infectious Disease Tradeoffs
Cold and dry air favors the transmission of influenza. Experiments using guinea pig models demonstrated that aerosol spread of influenza virus increases at both low temperatures and low humidity, with conditions around 5°C and 20% relative humidity being most favorable for transmission.16PLoS Pathogens. Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature This helps explain why flu season tracks with winter in temperate zones. Warmer climates largely avoid the annual respiratory virus crunch that hits colder regions every year, which is a real advantage for older adults and people with chronic conditions.
The tradeoff is that warm, humid environments harbor their own disease threats. Mosquito-borne illnesses like malaria and dengue are endemic in many tropical areas year-round, and tick-borne diseases thrive in regions with mild winters, where vectors survive longer and reproduce more readily.17PubMed Central. Climate Crises and Developing Vector-Borne Diseases: A Narrative Review Warmer winters are expected to expand the geographic range of these vectors in the coming decades. So while you may dodge the flu in a tropical climate, you pick up exposure to a different basket of infectious risks. Whether the net effect favors warm or cold climates depends heavily on local public-health infrastructure and mosquito control.
Air Conditioning and the Infrastructure Question
Much of the longevity advantage or disadvantage of a given climate comes down to how well the built environment buffers people from temperature extremes. Air conditioning is the clearest example. A U.S. study estimated that household AC averted roughly 5,300 heat-related deaths annually, cutting heat-attributable mortality by more than half.18PubMed Central. Impact of household air conditioning usage on heat-related mortality in the USA When AC prevalence increased from low to moderate levels across counties, the death risk at extreme temperatures dropped substantially. Above moderate prevalence, the benefit plateaued, suggesting there is a point of diminishing returns.
This matters because it means the health impact of living in a hot climate is vastly different depending on whether you have reliable AC. A retiree in air-conditioned Scottsdale is in a fundamentally different risk category from an outdoor laborer in a poorly insulated home in the same city. Overviews of systematic reviews on heat adaptation have found that while air conditioning provides strong individual-level protection against heat-related death, its sustainability is limited by energy costs, grid reliability, and the carbon emissions that drive further warming.19PubMed. Adaptation and mitigation approaches to reduce heat-related health risks: An overview of systematic reviews Central heating in cold climates performs a parallel function: it makes harsh winters survivable and even comfortable. The places where cold kills most effectively are not the coldest places on Earth, but rather places where people lack adequate heating and housing insulation.
What Happens While You Sleep
Nighttime temperature is an underappreciated piece of the puzzle. Your bedroom environment affects sleep quality, and sleep quality affects just about every system in the body. A study of older adults found that bedroom temperatures above 24°C (about 79°F) were associated with disrupted autonomic nervous system function and increased heart rate during sleep, consistent with a shift toward sympathetic dominance and heightened physiological stress. The effect grew more pronounced as temperatures climbed higher.20PubMed Central. Effect of nighttime bedroom temperature on heart rate variability in older adults: an observational study In hot climates without AC or adequate nighttime cooling, this chronic sleep-related cardiovascular strain could chip away at long-term health, particularly for the elderly.
Tropical and subtropical regions often maintain high overnight temperatures, especially in urban areas where concrete and asphalt absorb daytime heat and radiate it back at night. If you cannot cool your sleeping environment below that threshold, the cardiovascular cost accumulates night after night. This is one reason why heatwave mortality tends to spike when nighttime temperatures stay elevated, not just when daytime highs are extreme.
Temperature, Physical Activity, and Behavior
Climate shapes how much people move, and physical activity is one of the strongest predictors of longevity. Research using accelerometer data from Chinese adults found an inverted U-shaped relationship between temperature and moderate-to-vigorous physical activity, with a peak around 26°C. At both temperature extremes, activity dropped, with extreme cold reducing overall activity by about 13% and extreme heat reducing it by about 4.5%.21PubMed. Short-term effects of temperature on physical activity and sedentary behavior in Chinese adults: An accelerometer-based analysis A longitudinal study of Australian adults found a similar pattern: people were generally less active and more sedentary during weather extremes, and they slept less as temperatures rose.22PubMed Central. Weather associations with physical activity, sedentary behaviour and sleep patterns of Australian adults: a longitudinal study with implications for climate change
Mild, warm climates with moderate humidity probably offer the best conditions for year-round outdoor activity. Places with brutal winters or scorching summers both push people indoors and onto couches. If you live somewhere with three months of ice and darkness, you are fighting an uphill battle to maintain the walking, cycling, or gardening habits that keep cardiovascular and metabolic systems in good shape. A place where the weather is comfortable for outdoor movement most of the year gives you a structural advantage, assuming you actually use it.
Heat and Mental Health
The mental health dimension of warm climates rarely comes up in longevity conversations, but it probably should. A narrative review of the mechanisms linking heat to psychiatric outcomes found that heat exposure can worsen symptoms in people with schizophrenia, bipolar disorder, and anxiety disorders, and is associated with increases in suicidal behavior. The pathways involve neurotransmitter disruptions, physiological stress responses, and sleep disturbance.23PLOS Climate. The mechanisms underlying the effects of heat on mental health: A narrative review People on certain psychiatric medications, including antipsychotics and some antidepressants, are also at elevated risk during heat events because these drugs can impair the body’s ability to thermoregulate.
Meanwhile, seasonal affective disorder and the winter mood dip are well-documented costs of living at high latitudes with limited winter daylight. It is not clear which direction the net mental health balance tips, and it almost certainly depends on the individual. But the assumption that warm weather is universally good for mental well-being does not hold under scrutiny, particularly as extreme heat events become more frequent.
How Climate Change Is Reshaping the Equation
Whatever the current balance between heat and cold risks, it is shifting. A panel data study estimated that a 1°C increase in average annual temperature is associated with a decline of about half a year in life expectancy at birth, after controlling for other factors.24PLOS Climate. A panel data study on the effect of climate change on life expectancy Projections suggest that at 1.5°C of global warming, heat-related mortality will rise by about 0.5%, and at 3°C, by about 2.5%. Cold-related deaths were expected to decrease as the planet warms, but population aging largely counteracts that benefit: older people are more vulnerable to both heat and cold, and the global population is getting older fast enough that cold-related deaths are projected to increase slightly even in a warmer world.25PubMed Central. Impact of population aging on future temperature-related mortality at different global warming levels
The regional picture is uneven. Northern Europe, East Asia, and Australia are projected to experience a temporary net reduction in temperature-related deaths as milder winters offset modest heat increases. But already-hot regions face a sharp surge in heat mortality that overwhelms any cold-related improvements. Under high-emission scenarios, Southeast Asia could see excess mortality climb by roughly 13%, and southern Europe by about 6%.26The Lancet Planetary Health. Projections of temperature-related excess mortality under climate change scenarios The warm-climate advantage that currently exists in some regions may erode or reverse entirely within decades, especially in places that lack the infrastructure or economic resources to adapt.
For anyone thinking about where to live for a longer life, the honest answer is that mild, stable climates with good infrastructure and ample sunlight probably offer the best package today. But “warm” and “healthy” are not synonyms, and the margin is narrower than intuition suggests.