With climate change influencing more than 1,000 transmission pathways like those and climate hazards increasingly globally, we concluded that expecting societies to successfully adapt to all of them isn’t a realistic option. The world will need to reduce the greenhouse gas emissions that are driving climate change to reduce these risks.
MAPPING CLIMATE HEALTH HAZARDS
To be able to prevent global health crises, humanity needs a comprehensive understanding of the pathways and the magnitude with which climate change might affect pathogenic diseases.
We focused on 10 climate-related hazards linked to rising greenhouse gas emissions: atmospheric warming, heat waves, drought, wildfires, heavy precipitation, flooding, storms, sea-level rise, ocean warming and land cover change. Then we looked for studies discussing specific and quantifiable observations of human disease occurrences linked to those hazards.
In total, we reviewed over 77,000 scientific papers. Of those, 830 papers had a climatic hazard affecting a specific disease in an explicit place and/or time, allowing us to create a database of climatic hazards, transmission pathways, pathogens and diseases. An interactive map of every pathway between hazard and pathogen is available online.
The largest number of diseases aggravated by climate change involved vector-borne transmission, such as those spread by mosquitoes, bats or rodents. Looking at the type of climate hazard, the majority were associated with atmospheric warming (160 diseases), heavy precipitation (122) and flooding (121).
HOW CLIMATE INFLUENCES PATHOGEN RISK
We found four key ways climatic hazards interact with pathogens and humans:
1) Climate-related hazards bring pathogens closer to people.
In some cases, climate-related hazards are shifting the ranges of animals and organisms that can act as vectors for dangerous pathogenic diseases.
2) Climate-related hazards bring people closer to pathogens.
Climate disasters can also alter human behavior patterns in ways that increase their chances of being exposed to pathogens. For example, during heat waves, people often spend more time in water, which can lead to an increase in waterborne disease outbreaks.
In some cases, climate-related hazards have led to either environmental conditions that can increase opportunities for pathogens to interact with vectors or increase the ability of pathogens to cause severe illness in humans.
Studies have shown that rising temperatures may also help viruses become more resistant to heat, resulting in increased disease severity as pathogens become better able to adapt to fever in the human body.
4) Climate-related hazards weaken the body’s ability to cope with pathogens.Climate-related hazards can affect the human body’s ability to cope with pathogens in two key ways. They can force people into hazardous conditions, such as when disaster damage leads to people living in crowded conditions that might lack good sanitation or increase their exposure to pathogens.
Hazards can also reduce the body’s capacity to fight off pathogens, through malnutrition, for example. Living through climatic hazards may also induce increased cortisol production from stress, leading to a reduction in the human body’s immune response.
WHAT TO DO ABOUT IT
Climate change presents a significant threat to human lives, health and socioeconomic well-being. Our map shows just how extensive that threat can be. In our view, to dial back the risk, humanity will have to put the brakes on the human-caused greenhouse gas emissions fueling global warming.