New threats on the horizon from climate–health interactions

Key messages

  • Compounding and cascading risks due to climate change are adversely impacting human, animal and environmental health.
  • Climate change is already responsible for close to 40% of heat-related deaths and every inhabited continent is experiencing increased heat-related mortality.
  • Wildfires are increasing in frequency due to the combination of higher temperatures and drought, bringing short- and long-term physical and mental health impacts.
  • Outbreaks of infectious diseases are likely to increase due to climate change.

Insight explained

Climate change has been described by the World Health Organization (WHO) as the single biggest health threat facing humanity. Research consistently reveals compounding and cascading risks of climate change on human, animal and environmental health. These risks have the potential to slow advances made in population health over the last decades and disrupt functioning health systems.

Climate change is already responsible for 37% of heat-related deaths globally (measured timeframe: 1991–2018) – with the burden likely exacerbated by recent 2022 heatwaves that exceeded temperature records. In the meantime, every inhabited continent is experiencing increased heat-related mortality. Most attribution studies likely underestimate the numbers of deaths, illnesses, hours of lost productivity, and adverse economic consequences. Some regions, such as mountainous areas, are newly experiencing heatwaves, with dire implications for their populations. The observed increase in “tropical nights” exposes more people to heat stress because of the reduction in cooling respite. Heat exposure also results in adverse reproductive outcomes such as preterm birth, low birthweight, stillbirth and lower sperm production.

Infectious diseases are likely to increase due to climate change, especially waterborne and vector-borne diseases, as evidenced by increased childhood diarrhoeal disease being observed in some regions during extreme weather events. In addition to temperature-related changes in geographic range, large-scale outbreaks of infectious disease can affect local and global health from cascading pathways involving weather and climate events, population movement, land-use changes, urbanisation, global trade and other drivers. Increasing impacts are also observed among plants and animals, with attribution of climate change effects at national and local levels. For example, wildfires, extreme heat, drought and flooding events impact livestock health and production, fisheries and populations of wild animals. Increases in the spread and severity of animal and plant diseases can then affect food security and ecosystem functions. This risk has resulted in the increased use of pesticides and antimicrobials. Climate change brings an increase in cross-species viral transmission risk, and zoonotic virus spillover and spread in humans is more likely, especially at high elevations, in biodiversity hotspots, and in areas of high human population density in Asia and Africa.

Significant numbers of lives can be protected by investing in early warning systems (relevant to extreme weather events, microbial transmission, and disease outbreaks and other health risks such as respiratory distress or toxicity), which should include monitoring and evaluation. To address the growing climate challenge, health systems need to become more resilient, addressing inequities to better manage complex and compounding hazards in a systems-based manner.


Extreme heat and wildfires, a cascading hazard

Extreme record-breaking temperatures in Europe in July 2022 led to wildfires raging throughout Spain, Portugal, France and the United Kingdom. Worldwide, the combination of higher temperatures and drought is increasing the number of wildfires with short- and long-term physical and mental health impacts. Wildfires contain ambient air pollution in the form of fine particulate matter, which is more toxic, and brings greater health impacts, than exposure to comparable concentrations of other conventional air pollution particulates.

Implications & Recommendations

At a global level, it is suggested that parties at COP27:

  • Improve understanding of how climate change is causing injuries, illnesses and deaths today to ensure mitigation and adaptation strategies take a multisectoral approach with health as a central motivation.
  • Expand statistical monitoring related to health to help countries sufficiently track impacts on human, animal and environmental health (one health approach) and document progress towards health protection and resilience.
  • Advocate improved microbial and disease surveillance, including from known, novel and antimicrobial-resistant pathogens.

At a national and local level, policymakers must:

  • Build climate resilience and environmental sustainability into healthcare systems, and design broader policy tools that reflect the uncertainties of climate change impacts and development choices, and their varied effects on humans, animals, plants and ecosystems.
  • Consider the current cost of climate inaction on human, animal and environmental health systems and re-examine budgets and financial incentives to ensure adequate investment in prevention and addressing vulnerabilities.
  • Invest in early warning systems to save lives (see Insight 4 discussion on anticipatory humanitarian actions) and optimise information sharing from early warning systems across sectors so that threats can be detected early and sufficient action can be taken rapidly.
  • Improve knowledge about the benefits of disaster preparedness and adaptation options that address inequities.
  • Align sectoral action plans for shared interventions towards improved climate change mitigation and adaptation, health security, antimicrobial resistance, universal health coverage, biodiversity protection and wider sustainable development.
  • Tackle inequities and increase resilience across population groups (See Insight 2) to be better prepared for complex and compounding hazards in a holistic manner, to effectively protect health and wellbeing.
Figure 3. Urgent policy needs on selected risks and potential downstream consequences of climate change on health.

Where do we stand?

Earth system


Why care?


What to do?

Solutions and Barriers





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Private sustainable finance practices are failing to catalyse deep transitions

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Loss and Damage: the urgent planetary imperative

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Inclusive decision-making for climate-resilient development

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Breaking down structural barriers and unsustainable lock-ins

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