The World Health Organization estimates that approximately 40 new infectious diseases have been discovered since the 1970s. Although most of them emerged due to the natural evolution of microorganisms, human behaviours and practices promote the appearance of new pathogens. The environmental effects of climate change are one of the main causes of the spread of emerging infectious diseases.
Microorganisms are sensitive to the smallest alterations around them, rapidly adapting to the new conditions and challenges of their surroundings. Through mechanisms of natural selection, every generation is more resistant to the environment than the previous. As a consequence, organisms that succeed in surviving have better chances of becoming pathogens, especially if they proliferate close to human activities.
But how does climate change directly influence the increase of pathogenic microorganisms? Human emissions have led to an increase in temperature globally, causing a shift in weather patterns and producing extreme phenomena, such as the wildfires that plagued Australia, California, and Siberia in 2020. Not only do increases in temperature endanger the wildlife, but they also promote the migration of species. Mosquitos are known to be the vector of Plasmodium, a parasite that causes malaria. Heatwaves around the globe prompted mosquitos to move from the tropics towards areas where malaria was not endemic, producing an increase in patients with the disease. Similarly, West Nile fever is now seen in colder climates due to the rise in temperatures. Although these pathogens are not new to humans per se, they have appeared in countries which were not used to dealing with the disease, causing spikes of infection.
Plant diseases are also on the rise. Late and sheath blight, two conditions attacking potatoes and rice cultivars, have decreased the production of the two goods for centuries. Even though they are not nearly as rampant as in the past, late and sheath blight cost the agricultural industry millions of pounds. Xylella fastidiosa, an anaerobic bacterium, attacking a wide range of plants, including grapevines, olives, and peach trees. While human pathogens may arise from new species of microorganisms, plant pathogens are often already present in the environment. However, slight changes in temperature, humidity or nutrients stimulate the reproduction of pathogens, originating in waves of infections. Plant diseases indirectly affect humans. When plant epidemics strike, those populations that mainly rely on cultivation are more exposed to impoverishment and deteriorating sanitary conditions, which in turn are fertile grounds for human diseases.
Glaciers in the Arctic and Antarctic are melting due to heatwaves. What worries scientists are the potential amounts of pathogens embedded in the ice that have been inactive due to freezing temperatures. Anthrax, a bacterium causing multi-system organ failure, has been found in Siberian ice, along with smallpox and hundreds of other pathogens. The major risk, however, comes from those microorganisms that have been quiescent in permafrost for thousands of years and are only now seeing the light again. Microorganisms that have not yet been in contact with humans, so they have not been studied and understood. How many of them could cause the next pandemic?
It is apparent how climate change is damaging the environment, both directly and indirectly. If we want to prevent a new COVID-19, we must minimise our contribution to global warming.