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Climate change could worsen a whopping 58% of the infectious diseases humans come into contact with worldwide, from common waterborne viruses to deadly diseases like the plague, our new research shows.
Our team of environmental and health scientists has reviewed decades of scientific papers on all known pathogenic disease pathogens to create a map of human risks exacerbated by climate-related hazards.
The numbers were terrifying. Out of 375 human diseases, we found that 218 of them, well over half, can be affected by climate change.
For example, flooding can spread hepatitis. Rising temperatures could extend the lifespan of malaria-carrying mosquitoes. Drought can bring rodents infected with hantavirus into communities as they forage for food.
With climate change affecting more than 1,000 transmission pathways like these and climate risks increasingly global, we concluded that expecting societies to successfully adapt to all of them is not a realistic option. The world will need to reduce the greenhouse gas emissions that drive climate change to reduce these risks.
Mapping climate health risks
In order to prevent global health crises, humanity needs a comprehensive understanding of the pathways and extent to which climate change can affect pathogenic diseases.
We focused on 10 climate-related hazards linked to increasing greenhouse gas emissions: atmospheric warming, heat waves, droughts, wildfires, heavy rainfall, floods, storms, sea level rise, ocean warming and land cover change. We then looked for studies that discussed specific and quantifiable observations of human disease linked to these hazards.
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In total, we have reviewed over 77,000 scientific articles. Of these, 830 papers had a climate risk affecting a specific disease at an explicit location and/or time, allowing us to create a database of climate risks, transmission pathways, pathogens and diseases. An interactive map of each hazard-pathogen pathway available online.
The largest number of diseases exacerbated 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 rainfall (122) and floods (121).
How the climate affects pathogen risk
We found four key ways that climate risks interact with pathogens and humans:
1) Climate-related hazards for pathogens closer to humans.
In some cases, climate-related hazards are changing the supply of animals and organisms that can act as vectors for dangerous pathogenic diseases.
For example, warming or changes in precipitation patterns may alter the distribution of mosquitoes, which are vectors of many human pathogenic diseases. In recent decades, geographic changes in outbreaks of mosquito-borne diseases such as malaria and dengue fever have been linked to these climate risks.
2) Climate-related hazards bring humans closer to pathogens.
Climate disasters can also change human behavior patterns in ways that increase their chances of exposure to pathogens. For example, during heat waves, people often spend more time in water, which can lead to an increase in waterborne disease outbreaks.
Notably, Vibrio-related infections increased significantly in Sweden and Finland after a heat wave in northern Scandinavia in 2014.
3) Climate-related hazards enhance pathogens.
In some cases, climate-related hazards have led to either environmental conditions that may increase the opportunities for pathogens to interact with vectors or increase the ability of pathogens to cause serious disease in humans.
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For example, standing water left by heavy rainfall and flooding can provide breeding grounds for mosquitoes, leading to increased transmission of diseases such as yellow fever, dengue fever, malaria, West Nile fever and leishmaniasis.
Studies have shown that rising temperatures can also help viruses become more resistant to heat, resulting in increased disease rates as pathogens become better at adapting to fever in the human body.
For example, studies have suggested that rising global temperatures lead to increased heat tolerance of fungal pathogens. The sudden emergence on several continents of treatment-resistant human infections of Candida auris, a fungus that was previously non-pathogenic to humans, has been associated with increasing global temperatures.
Similarly, fungi in urban environments have been shown to be more heat tolerant than those in rural areas, which tend to be cooler.
4) Climate-related hazards weaken the body’s ability to deal with pathogens.
Climate-related hazards can affect the human body’s ability to deal with pathogens in two important ways. They can force people into dangerous conditions, such as when disaster damage causes people to live in cramped conditions that may lack good sanitation or increase their exposure to pathogens.
Hazards can also reduce the body’s ability to fight pathogens, for example through malnutrition. Living through climate risks can also induce an increase in cortisol production from stress, leading to a decrease in the human body’s immune response.
What to do about it
Climate change poses a significant threat to human life, health and socio-economic well-being. Our map shows how extensive the threat can be. In our view, humanity must curb the human-caused emissions of greenhouse gases that drive global warming to reduce the risk.
This article was written by Tristan McKenzie, postdoctoral researcher in marine science at the University of Gothenburg; Camilo Mora, associate professor of biology at the University of Hawaii; and Hannah von Hammerstein, a Ph.D. candidate in geography and environmental science at the University of Hawaii. It is republished from The Conversation under a Creative Commons license. Read the original article.
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