Climate change causes innumerable changes to the planet’s ecosystems, one of which is the melting of the cryosphere. Scientists have found that melting ice in the Arctic is releasing microbes that have previously been frozen for decades to millennia. While some of these microbes could present serious threats to humanity and other organisms, warming temperatures are having a more immediate effect on disease transmission. The topic is especially relevant with the COVID-19 pandemic, which has caused a global catastrophe within a mere few months. No causal link between SARS-CoV-2 and climate change has been established; however, the possibility of more (and worse) disease outbreaks occurring due to climate change is real and a number of studies over the past decade have illustrated the various mechanisms that could contribute to them.
Weakened Immune Response
Warmer temperatures could weaken the immune system’s ability to fight off infection. A study published in the Proceedings of the National Academy of Sciences showed that mice exposed to a high ambient temperature had less effective immune responses against influenza and Zika viruses. For influenza specifically, the researchers found that mice exposed to high heat conditions experienced reduced food intake, which resulted in autophagy, or the body’s own metabolic breakdown of tissues. This in turn prompted a weaker immune response.
“Because half of the world’s population could face a severe food crisis as a result of global warming by the end of this century, our results imply possible public health problems and concerns that outside temperature and host nutritional status may be critical determinants of live attenuated influenza vaccine efficacy in tropical or developing countries,” the researchers concluded.
Loss of Biodiversity Increases Disease Transmission
Loss of biodiversity is driven by a number of anthropogenic causes, and the disruptions to the balance of ecosystems caused by climate change in particular is driving many species to extinction and eliminating natural habitats. A study in Nature suggests that this loss of biodiversity increases disease transmission, although pathogens may originate in areas with high biodiversity. The study found that biodiversity loss tends to increase both pathogen transmission and disease incidence for a broad range of pathogens, hosts, ecosystems and modes of transmission.
For example, a strong correlation was detected between low avian diversity and an increased risk for humans to contract the West Nile virus from mosquitos. Also, areas with lower diversity of small mammals have an increased prevalence of the hantavirus in animals, which increases potential exposure for humans. The study also found that the findings hold true for plants. Lower biodiversity increases the prevalence of two fungal pathogens that infect grasses and other plants.
More Severe Flu Seasons
Research published in PLOS indicates that warmer winters are followed by severe epidemics with earlier onset for both influenza A and B. This is because fewer people are infected with the flu during warm weather, leaving an unusually large fraction of the population more susceptible to infection early on in the subsequent season.
“The severity of the next season could potentially be exacerbated by the early onset, if the onset occurs before most of the population has had the opportunity to be vaccinated,” the study authors concluded.” Our observation that climate patterns can have a profound impact on influenza epidemics beyond just the time frame of the current season will likely open up interesting avenues of further research.”