Horizon 2070: how climate change will increase the risk of cross-species viral transmission
Global warming
Horizon 2070: how climate change will increase the risk of cross-species viral transmission
Even under the most optimistic climate scenario, the displacement of mammals driven by global warming will result in at least 15,000 new cross-species viral transmissions by 2070. The emergence of the Covid-19 virus will probably not be an isolated incident, warn American researchers. According to their calculations published in Nature, at least 15,000 new viral transmissions between mammalian species will take place by 2070, mainly in Southeast Asia. In question, climate change leads to a displacement of animal species and therefore new opportunities for contagion.
Climate change forces species to move
This analysis was carried out “just a few weeks” before the Covid-19 pandemic, revealing the authors of the study. An almost divinatory temporality, while their work precisely alerts to the impact of climate change on the increase in viral transmissions. This is important data because the more numerous they are and the closest to us, the higher the risk that a virus will be transmitted to humans - thus becoming a zoonosis - is high. “Even in the best-case scenario, the geographic range of many species is expected to shift a hundred kilometers or more over the next century,” bringing with them their parasites, viruses, and bacteria, the researchers explain.
In these new environments, species that have never interacted could come into contact. The transmission of their pathogens from one to the other will then depend on two parameters. On the one hand the opportunity - they must be close enough to each other -, and on the other hand the compatibility - that they are genetically similar enough for the pathogen to infect the one like the other. Conditions are much less frequently met than one might think. “Most hosts do not have the possibility of exchanging pathogens”, point out the scientists. Thus, of the 21 million pairs of potential mammals, only 7% share the same geographical area (and therefore have the opportunity to meet), and 6% harbor one or more identical virus species (signifying sufficient compatibility for transmission ).
A predictive model of mammal migrations by 2070
Armed with these data, but also with the potential habitats towards which the 3,870 mammalian species examined can migrate, the researchers predict “how and where global change could potentially create new opportunities for viral sharing”. They work for this according to an optimistic hypothesis, in which global warming would remain at 2°C thanks to rapid and effective human interventions. And a pessimistic one, in which warming would exceed 4°C, with continued reliance on fossil fuels and rapid land degradation and change.
At least 15,000 new cases of transmission, especially by bats
The models are formal: whatever the climate scenario, the movement of species will lead to a doubling of potential contacts. "These 'first encounters' between mammalian species will occur all over the world, but are concentrated in tropical Africa and Southeast Asia," the researchers reveal, not at higher latitudes, contradicting some assumptions according to which the animals would go there to seek a little freshness. On the other hand, they could well meet at altitude, according to their cartography. As a result, even in the most optimistic scenario of +2°C, the researchers predict at least 15,000 cases of inter-species transmission of at least one new virus.
A family of mammals with significant migratory capacities stands out. Bats represent almost 90% of these first inter-species contacts, whatever the climate scenario, mainly in Southeast Asia. “Even non-migratory bats can regularly cover hundreds of kilometers in a lifetime, far exceeding what small mammals can cover in 50 years,” the researchers explain.
Areas densely populated by humans are more at risk
These inter-species transmissions "are disproportionately likely to occur in areas that are predicted to be inhabited by humans or used as cropland, and less likely to occur in forests", yet rich in high biodiversity, say the scientists. The new hotspots of the next 50 years should thus notably concern the Sahel, the Ethiopian highlands, the Rift Valley in East Africa, India, eastern China, Indonesia, and the Philippines.
Limiting climate change will not prevent the process
Unfortunately, according to the researchers' calculations, no amount of climate change mitigation will halt the process. On the contrary, the most optimistic scenarios even seem likely to produce greater inter-species viral transmission than more violent climate change! Because slower warming also gives species time to move little by little following their evolution, leading to greater geographical expansion and therefore more contact with other species.
“We caution that these results should not be interpreted as a justification for inaction, or as a possible benefit of unmitigated warming” with devastating consequences, but rather as an urgent call to “improve wildlife disease surveillance systems and public health infrastructure as a form of adaptation to climate change,” the authors conclude.
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