Health on a Heating Planet

The impact of climate change on human health is clear and evident across countries around the world. Some of the obvious ways in which this happens are extreme heat, floods, and droughts directly affecting people, and the respiratory and cardiac diseases occurring as a result of air pollution. There are indirect effects of climate change too: the rise in the frequency and intensity of infectious diseases (both vector-borne and water-borne), as well as a fall in crop yields. In this article, we will discuss these direct and indirect effects of climate change on human health.

Direct and Indirect Effects of Climate Change on Human Health

Many countries have carried out detailed vulnerability and adaptability assessments in the context of climate change. Such assessments map the impact of climate change on people, identify vulnerable populations, and then suggest adaptation policies. Here, we will broadly examine the direct and indirect effects of climate change on human health.

Direct Effects

Among the direct effects of climate change are those that impact the biological aspects of human health. Some of these are:

• Extreme Heat: The effects include heat strokes and acute dehydration. Extreme heat days were once limited to Asia and Africa, but are now common in Europe and North America as well. The heat wave in Europe in 2023 was well documented, leading to the deaths of more than fifty thousand people.
• Extreme Weather Events: Storms and cyclones have become more frequent and carry very high moisture, leading to widespread flooding. These are now common in coastal areas, including the USA, the Philippines, and the Caribbean.
• Forest Fires: In dry weather conditions, forest fires are increasingly frequent. The fires in Canada in 2023 and in California in 2024 were devastating, leading to injuries and deaths.
• Air Pollution: The rise in greenhouse gas emissions due to increased fossil fuel use has worsened air pollution, primarily in developing-country cities such as Delhi, Cairo, Hanoi, and Dhaka.

Indirect Effects

The indirect effects of climate change on human health include:

• Vector-Borne Diseases: Longer warm periods, increased temperatures, and higher humidity create perfect breeding grounds for mosquitoes (Anopheles, which causes malaria, and Aedes aegypti, which causes dengue), as well as other insects and ticks. These conditions lengthen transmission periods for diseases.
• Waterborne Diseases: Erratic and skewed rainfall often leads to water contamination, causing outbreaks of cholera, typhoid, and diarrhoea.
• Food Security: Flooding and droughts have disrupted the flowering season of many cereals and plants, reducing agricultural productivity. Livestock deaths and a decline in fish populations in coastal areas add to the challenge.

Unequal Burden

The direct and indirect effects are felt most acutely in poor and developing countries, which have far fewer resources to adapt to these challenges. Vector-borne diseases, for instance, are most common in South America, Asia, and Africa. Widespread outbreaks of cholera and typhoid follow a similar pattern. The rising disease load in these countries also puts immense pressure on fragile health systems, which already face financial and infrastructural challenges even in normal times.

In short, extreme and severe weather—high heat, erratic rainfall, floods, and droughts—affects water quality and triggers vector-borne and water-borne diseases, lowers agricultural productivity, and strains food supply. Pollution, forest fires, and extreme heat also drive an increase in heart and lung diseases.

Conclusion

Climate change and global warming adversely affect human health, with impacts felt across the economy and society in the form of reduced human and agricultural productivity. To use the term coined by U.S. security expert Sherri Goodman during the Clinton administration, climate change and global warming act as a “threat multiplier”, compounding existing challenges in critical sectors such as agriculture, health, and infrastructure.