Effects of climate change on human health
affects human health in many ways, including an increase in heat-related illnesses and deaths, worsened air quality, the spread of infectious diseases, and health risks associated with extreme weather such as floods and storms. Rising global temperatures and changes in weather patterns are increasing the severity of heat waves and extreme weather events. These events in turn have direct and indirect impacts on human health. For example, when people are exposed to higher temperatures for longer time periods they might experience heat illness and heat-related death.
In addition to direct impacts, climate change and extreme weather events cause changes in biomes. Certain diseases that are carried and spread by living hosts such as mosquitoes and ticks may become more common in some regions. Affected diseases include dengue fever and malaria. Contracting waterborne diseases such as diarrhoeal disease will also be more likely.
Changes in climate can cause decreasing yields for some crops and regions, resulting in higher food prices, less available food, and under nutrition. Climate change can also reduce access to clean and safe water supply. Extreme weather and its health impact can also threaten the livelihoods and economic stability of people. These factors together can lead to increasing poverty, human migration, violent conflict, and mental health issues.
Climate change affects human health at all ages, from infancy through adolescence, adulthood and old age. Factors such as age, gender and socioeconomic status influence to what extent these effects become wide-spread risks to human health. Some groups are more vulnerable than others to the health effects of climate change. These include children, the elderly, outdoor workers and disadvantaged people.
Overview of health effects and pathways
The effects of climate change on human health can be grouped into direct and indirect effects. Extreme weather, including increased storms, floods, droughts, heat waves and wildfires can directly cause injury, illness, or death. The indirect impact of climate change happens through changes in the environment that change the Earth's natural systems on a large-scale. These include worsening water quality, air pollution, reduced food availability, and faster spread of disease-carrying insects. Recent research highlights that these direct and indirect health impacts are increasingly interlinked, as climate change contributes simultaneously to worsening food and water insecurity, undernutrition, and infectious disease burdens across diverse populations. The World Health Organization likewise reports that climate change is already contributing to increases in undernutrition, vector-borne diseases, and heat-related mortality, with disproportionate impacts on vulnerable populations.Both direct and indirect health effects vary across the world and between different groups of people according to age, gender, mobility and other factors. For example, differences in health service provision or economic development will result in different health risks and outcomes, with less developed countries facing greater health risks. In many places, the combination of lower socioeconomic status and gender roles result in increased health risks to women and girls as a result of climate change, compared to those faced by men and boys.
The various health effects that are related to climate change include cardiovascular diseases, respiratory diseases, infectious diseases, undernutrition, mental illness, allergies, injuries and poisoning.
The provision of health care can also be impacted by the collapse of health systems and damage to infrastructure due to climate-induced events such as flooding. Therefore, building health systems that are climate resilient is a priority. The World Health Organisation has called climate change the biggest global health threat of the 21st century.
Health risks from extreme weather and climate events
is increasing the frequency and intensity of some extreme weather events. Extreme heat and cold events are the most likely to increase and worsen followed by more frequent heavy rain or snow and increases in the intensity of droughts.Extreme weather events, such as floods, hurricanes, heatwaves, droughts and wildfires can result in injuries, death and the spread of infectious diseases. For example, local epidemics can occur due to loss of infrastructure, such as hospitals and sanitation services, but also because of climate changes creating a more suitable weather for disease-carrying organisms.
Heat
Since the 1970s, temperature on the surface of Earth has become warmer each decade. This increase happened faster than in any other 50-year period over at least the last 2000 years. Compared to the second half of the 19th century, temperature in the 21st century show a warming of 1.09 °C.Extreme heat is a direct threat to health, especially for people over 65 years, children, people living in cities and those who have already existing health conditions. Rising global temperatures impact the health and well being of people in multiple ways. In the last few decades, people all over the world have become more vulnerable to heat and experienced an increasing number of life-threatening heatwave events. Extreme heat has negative effects on mental health as well, raising the risk of mental health-related hospitalizations and suicidal.
Although heat itself is not a direct threat to health on its own, a combination of factors of rising temperatures can detriment one's health. The effects of heat on an individual's health is influenced by temperatures, humidity, exercise, hydration, age, pre-existing health status and also by occupation, clothing, behavior, autonomy, vulnerability, and sense of obligation.
Physical exercise is beneficial for reducing the risk the many illnesses and for mental health. At the same time the number of hours per day when the temperature is dangerously high for outdoor exercise has been increasing. The rising heat also impacts people's ability to work and the number of hours when it is not safe to work outdoors has also increased.
It is estimated that between 1960 and 1990, climate change has put over 600 million people outside the human climate niche which is the average temperature range in which people have been able to thrive in the past 6,000 years. Unless greenhouse gas emissions are reduced, regions inhabited by a third of the human population could become as hot as the hottest parts of the Sahara within 50 years. The projected annual average temperature of above 29 °C for these regions would be outside the biologically suitable temperature range for humans.
Heat-related health effects for vulnerable people
Exposure to extreme heat poses an acute health hazard, especially for people deemed as vulnerable. Vulnerable people with regard to heat illnesses include people with low incomes, minority groups, women, children, older adults, people with chronic diseases, disabilities and multiple long-term health conditions. Other people at risk include those living in urban environments, outdoor workers and people who take certain prescription drugs.Climate change increases the frequency and severity of heatwaves and thus heat stress for people. A 2022 global study found that heat-related deaths increased significantly between 2000 and 2019, particularly in tropical and low-income countries, underscoring the growing health burden from rising temperatures.
Human responses to heat stress can include heat stroke and overheating. Extreme heat is also linked to acute kidney injury, low quality sleep, and complications with pregnancy.Furthermore, it may cause the deterioration of pre-existing cardiovascular and respiratory disease. Adverse pregnancy outcomes due to high ambient temperatures include for example low birth weight and pre-term birth.Heat waves have also resulted in epidemics of chronic kidney disease. Prolonged heat exposure, physical exertion, and dehydration are sufficient factors for the development of CKD.
The human body requires evaporation of sweat to cool down and prevent overheating, even with a low activity level. With excessive heat and humidity human bodies would no longer be able to adequately cool the skin. A wet-bulb temperature of 35 °C is regarded as the limit for humans. As of 2020, only two weather stations had recorded 35 °C wet-bulb temperatures, and only very briefly, but the frequency and duration of these events is expected to rise with ongoing climate change. Global warming above 1.5 degrees risks making parts of the tropics uninhabitable because the threshold for the wet bulb temperature may be passed. A wet-bulb temperature of 31 degrees is already considered dangerous, even for young and healthy people. This threshold is not uniform for all and depend on many factors including environmental factors, activity and age. If the global temperature will rise by 3 degrees, temperatures will exceed this limit at large areas in Pakistan, India, China, sub-Saharan Africa, United States, Australia, and South America.
People with cognitive health issues are more at risk when faced with high temperatures and ought to be extra careful as cognitive performance has been shown to be differentially affected by heat. People with diabetes and those who are overweight, have sleep deprivation, or have cardiovascular/cerebrovascular conditions should avoid too much heat exposure.
The risk of dying from chronic lung disease during a heat wave has been estimated at 1.8–8.2% higher compared to average summer temperatures. An 8% increase in hospitalization rate for people with chronic obstructive pulmonary disease has been estimated for every 1 °C increase in temperatures above 29 °C.
In urban areas
The effects of heatwaves tend to be more pronounced in urban areas because they are typically warmer than surrounding rural areas due to the urban heat island effect. This results from the way many cities are built. For example, they often have extensive areas of asphalt, reduced greenery along with many large heat-retaining buildings that physically block cooling breezes and ventilation. Lack of water features are another cause.Extreme heat exposure in cities with a wet bulb globe temperature above 30 °C tripled between 1983 and 2016. It increased by about 50% when the population growth in these cities is not taken into account.
Cities are often on the front-line of climate change due to their densely concentrated populations, the urban heat island effect, their frequent proximity to coasts and waterways, and reliance on ageing physical infrastructure networks.