Climate Change and Health

Climate change affects human health through many pathways - more frequent extreme heat and weather events, shifting patterns of infectious disease, threats to food and water security, and worsening air quality. Because its drivers and impacts cross every border and sector, the relationship between climate change and health has become one of the defining cross-cutting challenges of contemporary global health.

Definition

Climate change and health is the study of how long-term changes in temperature, precipitation, and weather extremes - driven largely by greenhouse-gas emissions - affect human health directly and indirectly, and of how those effects can be reduced through mitigation and adaptation.

Scope

This entry covers the principal pathways through which a changing climate affects health, the populations most exposed, and the concepts of mitigation and adaptation as they apply to health protection. It treats climate and health as a population-health and global-health topic, framed for understanding rather than as clinical or environmental-management guidance.

Core questions

• Through what pathways does climate change affect human health?
• Which populations and regions are most vulnerable to climate-related health risks?
• How do mitigation and adaptation differ as responses to protect health?
• Why is climate change framed as a defining global health challenge of the century?

Key concepts

• Direct pathways (extreme heat, floods, storms)
• Indirect pathways (vector-borne and water-borne disease, food and water insecurity)
• Air pollution and shared fossil-fuel drivers
• Vulnerability and adaptive capacity
• Mitigation and adaptation
• Health co-benefits of emissions reduction
• Planetary health

Mechanisms

Climate change influences health through direct and indirect pathways. Directly, rising temperatures and more frequent extreme events increase heat-related illness, injury, and death. Indirectly, shifts in temperature and rainfall alter the geographic range and seasonality of vector-borne and water-borne diseases, undermine crop yields and water supplies, and worsen air quality; the same fossil-fuel combustion that drives warming also produces air pollution, so emissions reduction can yield health co-benefits. The size of these effects depends on a population's exposure and its adaptive capacity.

Clinical relevance

Recognising climate-sensitive health risks helps professionals and students anticipate changing disease patterns and the needs of vulnerable populations. The entry describes population-level pathways and determinants and is not a basis for individual diagnostic or treatment decisions.

Epidemiology

Assessments such as the Lancet Countdown track indicators linking climate change to health, including heat exposure among vulnerable groups, the changing suitability for transmission of infectious diseases, and impacts on food security and air quality, documenting widening health risks tied to continued fossil-fuel dependence.

Evidence & guidelines

The health-and-climate literature emphasises both mitigation (reducing greenhouse-gas emissions, with co-benefits for health) and adaptation (strengthening health systems and protection against climate hazards) as complementary strategies. This entry summarises that framing and does not provide operational or clinical protocols.

History

The framing of climate change as a major determinant of human health gained prominence with the 2009 Lancet and University College London Institute for Global Health Commission, which described climate change as the biggest global health threat of the twenty-first century. Subsequent annual Lancet Countdown reports, beginning later in the 2010s, established systematic indicator-based tracking of the climate-health relationship.

Debates

Mitigation versus adaptation as the priority for protecting health.

Analyses weigh investment in reducing emissions - which addresses root causes and yields air-quality co-benefits - against adaptation that protects populations from impacts already underway; most frameworks argue both are needed, but emphasis and resourcing remain contested.

Key figures

• Anthony Costello
• Marina Romanello

Seminal works

• costello-2009
• romanello-2022

Frequently asked questions

What are the main ways climate change harms health?

Directly through extreme heat and weather events, and indirectly through shifting infectious-disease patterns, food and water insecurity, and worsened air quality.

What is the difference between mitigation and adaptation?

Mitigation reduces the greenhouse-gas emissions that drive climate change, while adaptation strengthens systems and protections to cope with impacts that are already occurring; both are considered necessary to protect health.