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Zoonotic diseases already comprise roughly 70 percent of all human infections, but experts fear the climate crisis will accelerate their transmission by changing the boundaries and characteristics of existing animal habitats. Weather pattern changes and global warming are predicted to cause many wildlife species to migrate poleward(away from the equator) and toward higher altitudes, potentially putting animals in contact with new diseases to which they haven’t evolved resistance. In addition, as animals experience increased stress from these migratory changes, their immune systems may become weakened, thereby increasing both the risk of infection and amount of viral replication once infected. Decreased species diversity, an inevitable consequence of pollution and deforestation, has also been associated with more zoonotic infections within host animal populations. In summary, the climate crisis will lower host animals’ immune responses to zoonotic diseases, increase the rate of zoonotic infection by crippling biodiversity, and push animals into new migration routes that will bring them into greater contact with humans — all ultimately increasing the frequency and associated risks of infectious disease outbreaks.

https://blogs.ei.columbia.edu/2020/02/24/coronavirus-climate-induced-pandemics/