It has been well documented that climate change is the single biggest health threat facing humanity. Every year, environmental factors take the lives of more than 13 million people, according to the World Health Organization. As stated by the same agency, between 2030 and 2050, climate change is expected to cause approximately 250,000 additional deaths per year — whether caused by extreme weather events, heat-related illnesses, air quality deterioration, food insecurity, or forced displacements.
Less discussed though has been how the same causes will additionally create the conditions for new epidemics and pandemics to erupt, as evidenced by a prevalence of emerging infections that has already drastically increased in the past decade. According to epidemiology and predictive modeling experts, there is a 47%-57% chance the world will experience another pandemic or epidemic that kills at least as many people as COVID-19 in the next 25 years, with a 22-28% chance within the next 10 years.
There are six main reasons why their prediction might turn into reality:
1. Warmer temperatures can increase the range of disease-carrying insects and other pests. This can, in turn, increase the likelihood of disease outbreaks. For vector-borne diseases such as malaria, dengue, and now Zika, climate change affects insect vectors or animal reservoir habitats significantly, which modifies disease transmission and increases severity. This phenomenon is further amplified by the effects of deforestation. According to a study conducted by researchers from the University of Florida, almost 57% of mosquito species in deforested areas were confirmed carriers of human disease, compared with about 28% of mosquito species in forested areas.
2. Climate change can cause large displacement of populations. Extreme weather events, such as floods and hurricanes, can cause large numbers of people to leave their rural homes to regroup in cities or refugee camps. This may create overcrowded and unsanitary living conditions, which can increase the risk of infectious diseases. According to ProMED reports, the mean incidence of outbreak events involving forcibly displaced populations increased by 404% when comparing the first period of the study — 1996 to 2002 — to the last — 2010 to 2016, this in a context where displaced population numbers tripled.
3. Air pollution can catalyze the emergence of new infectious diseases, influence their spread, and reduce our ability to combat them. Air pollution weakens immune systems, making people more susceptible to infectious diseases. According to a recent Nature publication, inhaled particulates from environmental pollutants accumulate in macrophages — a specialized type of white blood cell that detects and destroys harmful organisms — in lung-associated lymph nodes over years, compromising immune surveillance. In addition, air pollution can also increase the risk of respiratory infections, such as pneumonia, by damaging the lungs and making it more difficult for the body to fight off infections. Finally, air pollution can also affect the environment in ways that can increase the spread of infectious diseases, for example by providing favorable conditions for the growth of bacteria and other pathogens.
4. Changes in climate and water cycles will challenge water availability and increase exposure to unsafe water. This will cause the conditions for water-related pathogens to reproduce or replicate faster. Waterborne pathogens cause diseases in humans through two major exposure pathways: drinking water and recreational waters. And the poorest populations are the first ones exposed to so-called diseases of the past such as the recent re-emergence of cholera in Haiti, a dramatic event clearly aggravated by a lack of access to clean water.
5. As the Earth's climate continues to warm, infectious diseases may migrate to areas that were previously too cold for them to survive. According to the U.S. Centers for Disease Control, Lyme disease, West Nile virus disease, and Valley fever are just some of the infectious diseases that are on the rise and spreading to new areas of the United States. Due to increased temperature and changes in rainfall trends, mosquito larvae that transmit a range of parasites can now survive in settings that were once inhospitable to these species, increasing their range and impact on the human population. This means diseases expand into new geographic areas and infect more vulnerable people, with immune systems that have never been exposed to the migrating pathogens.
6. The melting of permafrost or glaciers could potentially lead to the release of pathogens into the environment. Frozen for centuries, the release of bacteria and viruses could also lead to the spread of infectious diseases, some of which recent generations have never encountered, and certainly not the victims of anthrax in the melting Siberia permafrost back in 2017.
All of us would rather see a way to turn the climate change tide as the way to save millions of lives in decades to come. Unfortunately, we have already passed that tipping point, and the only viable path forward will be to adapt to a new normal for epidemics and pandemics. The strengthening of outbreak monitoring with increased local genome sequencing capacity, the deployment of epidemics surveillance cockpits able to link early outbreak signals with travelers’ migration maps, the innovation of research and development pathways for equitable distribution of vaccines and treatments in the first one hundred days of an epidemics — will all be necessary tools as part of this adaptation arsenal. In the true spirit of the new “One Health” approach, let us as global citizens initiate a new advocacy movement to build and nurture our new surveillance and response tools, and let us make sure every United Nations Climate Change Conference of the Parties in the future will have pandemic preparedness on its agenda.
Visit the Pandemic Preparedness series for details on how we can implement health security solutions for a safer planet. Join the conversation by using the hashtag #PandemicPreparedness.