During the last 100 years, human civilization has faced a few pandemics (Asian flu, Cholera, AIDS, Swine flu). COVID-19 might be the most severe pandemic that strikes the world since the pandemic of “Spanish flu” back in 1918 as it pauses a significant threat to the health systems all over the globe. Next to climate change, COVID-19 is a major current threat to large parts of the world’s population. This should ring the bell and bring into our attention two key questions: Will climate change contribute to new pandemics in the future? And does the current lack of political will to address climate change put humanity in a potential risk of new pandemics?
Climate change and human health are interconnected in many complex ways. The impacts of climate change include warming temperatures, changes in precipitation, an increase in the frequency or intensity of some extreme weather events, changes in the distribution of wildlife, and rising sea levels. These impacts threaten our health by affecting the food we eat, the water we drink, the air we breathe, and the weather we experience.
Climate change may especially affect people who live in areas that are vulnerable to coastal storms, drought and sea-level rise, or people who live in poverty, older adults, and immigrant communities. People in developing countries may be the most vulnerable to health risks globally, but climate change poses significant threats to health even in wealthy nations.
Climate change scenarios include a change in the distribution of infectious diseases with warming and changes in outbreaks associated with weather extremes. The ranges of several vector-borne diseases are already changing in altitude due to warming. The incidence of mosquito-borne parasitic and viral diseases is among those diseases most sensitive to climate (e.g. West Nile Virus, malaria, Dengue fever, etc.). Climate change affects disease transmission by shifting the vectors’ geographic range and by shortening the pathogens’ incubation period. The temperature may modify the growth of disease-carrying vectors by altering their biting rates, as well as affecting vector population dynamics and altering the rate at which they come into contact with humans. A shift in temperature regime can alter the length of the transmission season. Disease carrying vectors may adapt to changes in temperature by changing geographical distribution.
Possibly one of the most dangerous consequences of climate change is the potential for emergence or re-emergence of novel pathogenic bacteria, viruses, and parasites. Heat stress may elevate the potential for animal-to-animal transmission of zoonotic pathogens. Moreover, it may provide possibilities for pathogens to cross between species. For many pathogens, the environment plays an important role in the transmission, and hence changing environmental conditions (e.g. temperature) may alter the geographical distribution, diversity, levels and seasonality of the pathogen in nature, which could lead to emerging outbreaks (e.g. Ebola, SARS, MERS).
Infectious disease transmission should be viewed within an ecological framework. In this era of global development and land-use changes, it is unlikely that climatic changes exert an isolated effect on the disease. Changes in mean climatic conditions and climate variability also can affect human health via indirect pathways, particularly via changes in biological and ecological processes that influence infectious disease transmission. In the Amazon, for example, an increase in deforestation by some 4% increased the incidence of Malaria by nearly 50%, because mosquitoes, which transmit the disease, thrive in the right mix of sunlight and water in recently deforested areas.
Diseases have always come out from ecological habitats and wildlife and found their way into human populations, as 75 per cent of all infectious diseases come from the zoonotic origin. But emerging disease numbers are rising evidently in the last decades, largely because of increasing human encroachment into habitats, e.g. through deforestation. Virus spillover risk from wildlife to people rises as contact increases between them. In diverse ecosystems well separated from human settlements, viruses ebb, and flow without ever having a chance to cause an outbreak. Disrupted ecosystems tend to lose their biggest predators first, and what they leave behind are smaller creatures that live fast, reproduce in large numbers, and have immune systems more capable of carrying the disease without dying to it, and they thrive near people!
And with a robust market in wildlife trafficking, the potential for a serious outbreak in large population centers is enormous. When wildlife is stressed, farmed in small cages, and kept in close contact with humans, the risk of disease transmission rises. Poorly treated animals are stressed, and they are more likely to harbor new diseases because their immune systems are compromised. Wet markets, where there are stressed animals in close contact with humans, are the perfect breeding ground for new diseases.
The key to forecasting and preventing the next pandemic is understanding of “protective measures” to keep nature intact. Biodiversity protection in one part of the world can prevent novel diseases from emerging and leaping into another.
Another serious development due to climate change is the frozen emerging danger that lies currently unexposed. Back in 2015, a group of scientists has worked on samples of ice from the Tibetan Plateau of China to study ice core microbiological communities and how to use them to understand past climatic and environmental conditions archived in the glaciers. They found out that for the past 15,000 years, the glacier has hosted an ensemble of frozen viruses, many of them unknown to modern science. The experiment revealed 33 groups of virus genera in the ice cores, 28 of these, never-before-seen virus groups without knowledge or experience of their potential threat.
Due to climate change and the anthropogenic-enhanced warming of Earth’s ocean-atmosphere system, glaciers around the world are rapidly shrinking and this will lead to the release of glacial microbes and viruses. Scientists have not yet identified all the potential risks associated with the newly registered viruses which make preventive measures hard to plan. Future studies will provide a better understanding of microbial and viral evolution and interactions and will contribute to establishing predictive ecological models of past climate changes from such “frozen archive” environments. The most proactive and effective solution remains to be the need to protect the integrity of the glaciers and snow cover.
Emerging infections have resulted in the most devastating infectious diseases that humanity has ever faced (e.g. Measles), history has taught us that emerging infections can be major threats. COVID19 has taken the world by surprise and we should be prepared to face further possible pandemics in the future that can be triggered by climate change. Unlike our complete surprise by COVID19, we already have an important level of knowledge about the health impacts of climate change and we still have the “luxury” of being able to plan proactively for global mitigation measures.
Seham Momaneh is an environmental health researcher from Jordan.