Climate change has been identified as the biggest health threat of the 21st century, with the potential to reverse years of improvements in global health and increase the pressure on health systems. Climate change is linked to human health through multiple and complex pathways.

Climate change increases the frequency, magnitude and duration of extreme climate and weather events such as heatwaves and heavy rainfall. Excess heat places additional pressure on the heart, brain and lungs, increasing the death rate from cardiovascular, cerebrovascular and respiratory diseases, particularly for those with pre-existing health conditions. Elderly people are particularly vulnerable to heat-related illnesses and children under 1 to the health risks of heat and dehydration. In the last 20 years climate-related heat mortality in elderly people is estimated to have increased by 54 per cent, driven by both climate change and growing numbers of elderly people living in hotter locations, according to the Lancet Countdown on health and climate change.

Heat stress also poses a significant risk to the health of those working outdoors, due to exposure both to direct sunlight and high temperatures. For example, a combination of heat stress and dehydration appears to be contributing to an increased prevalence of chronic kidney disease in outdoor manual workers, including those working in agriculture and construction. These sectors employ varying proportions of women and men and therefore there is likely a gender dimension to these impacts. The extent of the impact of heat on physical health and labour productivity is illustrated by the example of China, where the associated economic costs reached an estimated 1.35 per cent of GDP in 2020. 

Extreme heat and drought due to climate change are also linked to increasing risk and spread of wildfires. Wildfire smoke and ash increase illness and death related to air pollution through the release of harmful ground-level ozone and particulate matter pollutants, which can damage the heart and lungs. Fires can also reduce opportunities for exercising outdoors.

The Intergovernmental Panel on Climate Change has found robust evidence of increasing rainfall extremes in Europe, North America and Asia, which can lead to an increased frequency of flooding. Drowning accounts for 75 per cent of deaths in flood disasters and the risk increases particularly in low- and middle-income countries where people are more likely to live in flood-prone areas and where evacuation or warning systems may be inadequate.

Through higher temperatures, altered precipitation and sea level rise, climate change is altering the climate suitability and distribution of disease vectors (which carry and transmit infectious pathogens), especially mosquitos. This is increasing the incidence of diseases such as malaria, dengue and vibrio cholera. Malaria, which is particularly life threatening for children and women, is increasing in highland areas of Sub-Saharan African and Pacific countries as temperatures warm. Changing weather patterns are increasingly creating a favourable environment for bacterial growth in contaminated drinking water, resulting in greater transmission of cholera.

Environmental and land degradation, extremes of temperature and precipitation, and increasing droughts associated with climate change all have negative impacts on food production and water supply. Additionally, ocean acidification and coral bleaching are reducing fishery and aquaculture productivity. These factors are jeopardising food security, people’s ability to obtain a safe, affordable, reliable and healthy food supply.

Disease and lack of good sanitation in turn lead to increased levels of undernutrition, due to the impact on food utilisation – the ability of the body to absorb nutrients. Being undernourished, caused primarily by an inadequate intake of dietary energy, makes people more vulnerable to disease. The health burden from undernutrition falls disproportionately on low- and middle-income countries, and is particularly dangerous for children under 5, accounting for about 45 per cent of deaths among young children. The links to climate change are complex, but wasting appears linked to poor sanitation and disease, which are affected by drought and heat.

Rising sea levels caused by warming temperatures are imposing significant health risks for people living in low-lying areas. Coastal flooding can both directly accelerate the spread of disease associated with contaminated water, and lead to population displacement with many consequences for health.

Climate change can affect mental health through many different pathways. Among them, climate-related extreme weather events can increase psychological trauma as a reaction to impacts on physical health, to damage to homes and landscapes, and to loss of livestock and disruption to food supply. Being displaced by flooding can increase the likelihood of conflict and violence, which can make anxiety conditions and post-trauma mental disorders more likely.

How can the negative health impacts of climate change be reduced? Selected adaptation strategies

Adaptation strategies seek to reduce the risks posed by climate change and can reduce people’s vulnerability to its impacts, including impacts on health. For example:

  • Early warning systems are a cost-effective way to monitor and forecast anticipated health risks related to climate and to provide effective and timely public health recommendations. However, hard-to-reach and disadvantaged populations may not be able to access or act on these warnings or recommendations.
  • Investment in energy-efficient cooling infrastructure and green spaces, and increased access to drinking water, along with accessible and affordable healthcare facilities, can reduce the heat effects of climate change.
  • Post-disaster social adaptation interventions linked to wellbeing can be effective in reducing mental health impacts caused by extreme weather events. These interventions include strengthening health surveillance and monitoring psychological impacts from disasters through health screening, while expanding access to mental health care through primary health care facilities; and incorporating psychological preparedness into community-level responses to better understand the perceived risks and to cope with climate-related disasters.
  • The many different adaptation measures to reduce flooding risk, from engineered defences to planting trees, and measures to improve people’s capacity to cope with flooding, such as affordable insurance, can reduce the impact of flooding on physical and mental health.
  • Ecosystem-based adaptation (EbA) measures, such as the restoration of mangrove forests and water and forest management, can reduce flooding, improve water quality and quantity, and enhance food production, with associated positive impacts for health.

This Explainer was written by Alice Bian with input from Elizabeth Robinson.

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