Climate change is the greatest challenge of the 21st century, threatening human health and development. The longer we delay action, the greater the risks to human lives and health. Climate changes threaten access to clean air, safe drinking water, nutritious food supply, and safe shelter. It is already causing rising sea levels, more frequent and extreme weather events, heat waves and droughts, forest fires and increased spread of mosquito-borne diseases like malaria.
A highly conservative estimate of 250 000 additional deaths each year because of climate change has been projected between 2030 and 2050: of these, 38 000 from heat exposure among the elderly; 48 000 from diarrhoea; 60 000 from malaria; and 95 000 from childhood undernutrition.
What is the impact of climate change on health?
Although global warming may bring some localised benefits, such as fewer winter deaths in temperate climates and increased food production in certain areas, the overall health effects of a changing climate are likely to be overwhelmingly negative. Climate change affects social and environmental determinants of health–clean air, safe drinking water, sufficient food, and secure shelter.
Health and Climate Change, What the Future?
Climate change poses an enormous risk to the health of all living things. With a changing climate, we may face threats to food production and more extreme weather. These risks can have devastating consequences on human health and wellbeing.
Effect on nutrition
Climate variability and extremes are among the leading causes of severe food crises and affect the nutrient quality of crops, dietary diversity of food produced and consumed, water and sanitation, patterns of health risks and disease, as well as changes in maternal care, childcare, and breastfeeding. On the other end of the scale, the meat and dairy industries contribute to approximately 15% of greenhouse gas emissions and diets that are high in meat and dairy increase risks of cancer and cardiovascular disease.
Rising sea level
Rising sea levels are already causing population displacement, particularly in island states. More than half of the world’s population now lives within 60 km of coastlines. Floods can directly cause injury and death and increase the risks of diseases. Population displacement can increase tensions and potentially the risks of conflict. In 2017 WHO launched a Special Initiative on Climate Change and Health in Small Island Developing States. While these countries contribute very little to the causes of climate change, they are among the most vulnerable to climate change effects.
More variable rainfall patterns are likely to compromise the supply of safe drinking water. Globally, water scarcity already affects 4 out of 10 people. A lack of safe drinking water increases the risk of diarrhoea (which kills approximately 2.2 million people every year), trachoma (an eye infection that can lead to blindness) and other illnesses. Water scarcity also means people are forced to transport water long distances and store supplies in their homes. This can increase the risk of household water contamination.
The most direct link between the drivers of climate change, and of poor health, is air pollution. Burning fossil fuels–for power, transportation and industry–is the primary source of the carbon emissions driving climate change, and also a major contributor to air pollution, which kills 7 million people every year. Black carbon, produced by inefficient combustion in sources such as cookstoves and diesel engines, is the second greatest contributor to global warming. Over 90% of the urban population of the world breathes air that exceeds WHO’s guideline levels for outdoor air pollution.
Heat stress can lead to increased death rates from heart and respiratory diseases, particularly in elderly or vulnerable populations. With 1.5°C warming, 350 million more people could be exposed to deadly heat stress by 2050. Pollen and other aeroallergen levels are also higher in extreme heat. These can trigger asthma, which affects around 300 million people. Warmer climatic conditions also increase the risk of deadly water-borne and mosquito-borne diseases.
What are the health impacts of the heatwave?
- Kidney diseases
- Respiratory diseases
- Heat cramps
Cities at high risk
Many of the actions to reduce carbon emissions, improve health and increase resilience occur at the subnational level, particularly in cities. Local authorities are often wholly or partly responsible for services, including energy provision, transport, and water and sanitation and health. Cities, in particular, are important drivers for climate and health action.
From the tropics to the arctic, climate and weather have powerful direct and indirect effects on human life. The most disadvantaged, vulnerable and poor populations are expected to be disproportionately affected by climate change, with rising food and water insecurity, higher food prices, loss of income and livelihood opportunities, negative health effects, and population displacement (including forced migration).
Patterns of infection
Climatic conditions increases water-borne diseases and diseases transmitted through insects, snails or other cold-blooded animals. Changes in climate are likely to lengthen the transmission seasons of important vector-borne diseases and to alter their geographic range.
For example, climate change is projected to widen significantly the area of China where the snail-borne disease schistosomiasis occurs. Malaria is strongly influenced by climate. Transmitted by Anopheles mosquitoes, malaria kills over 400 000 people every year–mainly African children under 5 years old. The Aedes mosquito vector of dengue is also highly sensitive to climate conditions, and studies suggest that climate change is likely to continue to increase exposure to dengue.
Natural disasters and variable rainfall patterns
Globally, the number of reported weather-related natural disasters has more than tripled since the 1960s. Every year, these disasters result in over 60 000 deaths, mainly in developing countries. Rising sea levels and increasingly extreme weather events will destroy homes, medical facilities, and other essential services. More than half of the world’s population lives within 60 km from the sea. People may be forced to move, which cause heightens the risk of a range of health effects, from mental disorders to communicable diseases. Increasingly variable rainfall patterns are likely to affect the supply of freshwater.
A lack of safe water can compromise hygiene and increase the risk of diarrhoeal disease, which kills over 500 000 children aged under 5 years, every year. In extreme cases, water scarcity leads to drought and famine. By the late 21st century, climate change is likely to increase the frequency and intensity of drought at the regional and global scale. Floods are also increasing in frequency and intensity, and the frequency and intensity of extreme precipitation are expected to continue to increase throughout the current century.
Floods contaminate freshwater supplies, heighten the risk of water-borne diseases, and create breeding grounds for disease-carrying insects such as mosquitoes. They also cause drownings and physical injuries, damage homes and disrupt the supply of medical and health services. Rising temperatures and variable precipitation are likely to decrease the production of staple foods in many of the poorest regions. This will increase the prevalence of malnutrition and undernutrition, which currently cause 3.1 million deaths every year.
Who is at risk by climate change?
All populations will be affected by climate change, but some are more vulnerable than others. People living in small island developing states and other coastal regions, megacities, and mountainous and polar regions are vulnerable. Children–in particular, children living in poor countries–are among the most vulnerable to the resulting health risks and will be exposed longer to the health consequences. The health effects are also expected to be more severe for elderly people and people with infirmities or pre-existing medical conditions. Areas with weak health infrastructure–mostly in developing countries–will be the least able to cope without help to prepare and respond.
The positive note on climate change on health
Steps to reduce greenhouse gas emissions can have more immediate positive health effects. For example, promoting the safe use of public transportation and active movement – such as biking or walking as alternatives to using private vehicles – reduces carbon dioxide emissions and air pollution. It can also reduce traffic injuries and increase levels of physical activity, which helps prevent diseases like diabetes, heart disease, and cancer.
The negative note on climate change on health
Meeting the goals of the Paris Agreement could save about a million lives a year worldwide by 2050 through reductions in air pollution alone. The health benefits far outweigh the costs of meeting climate change goals, and the benefit-to-cost ratio is even higher in countries such as China and India. The same human activities that are destabilising the Earth’s climate also contribute directly to poor health. The key driver of climate change is fossil fuel combustion–also a major contributor to air pollution, which causes 7 million premature deaths worldwide every year.
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