“Our study is dense and technical, but the results are appalling and urgent.” On Twitter, the words of biologist Colin J. Carlson, research professor at the Center for Global Health Science and Security at Georgetown University, are chilling for the future of the planet.
Many scientists have already warned that pandemics may become more frequent with climate change, but team work for several years by this young American biologist leaves no doubt. “We provide evidence that in the decades to come, the world will not only be warmer, but also sicker,” warns disease ecologist Gregory Albery, one of the co-authors of the study published Thursday in the magazine “Nature”.
Threat to human health
According to these researchers, over the next fifty years, global warming will cause thousands of viruses to pass from one species of mammal to another. The study speaks of a future “network” of viruses that will expand as the Earth warms. At least 15,000 viral transmissions between species could take place by 2070.
This accelerated mixing between animals will promote the emergence of new diseases that could potentially be transmitted to humans. “As climate change reshapes life on Earth, it may also become the primary driver of pandemic risk,” writes Colin J.Carlson .
We know Zika, dengue fever, malaria, chikungunya, which are transmitted by mosquitoes. But today, at least 10,000 species of virus, the vast majority of which currently circulate “silently” in mammals, are able to infect humans, the authors fear. Indeed, by pushing more and more animals to flee their ecosystem to find a more livable habitat, climate change and land use are changing the situation. They “will create new opportunities for viral sharing between previously geographically isolated wild species,” the researchers explain.
The study modeled how more than 3,000 mammalian species share viruses and reveals a potentially devastating “mechanism” between the changing environment on Earth and the emergence of disease. Scientists estimate that their future movements could lead to more than 300,000 “first encounters” of species, twice the current potential… even if warming remains below 2°C, which is an optimistic scenario.
These dreaded “spillovers” are obviously not all likely to trigger a global pandemic like that of Covid-19, but the picture is worrying. Bats play a central role, say the researchers “because of their unique ability to disperse” around the world. It is first through these small mammals, carriers of pathogens such as coronaviruses, that the latter could infect humans via a host animal. The researchers indicate that bats in Southeast Asia will be particularly prone to these transmissions.
If the threat is global, this region is with tropical Africa one of the “hot spots” where these mixings are likely to concentrate, according to the researchers, because the population density will be strong there around 2070. The Sahel, the highlands plateaus of Ethiopia and the Great Rift Valley, India, eastern China, Indonesia and the Philippines are among the most exposed areas.
Colin Carlson judges that it is too late to reverse the trend, the simulation made by the researchers shows that the viruses have already started to be brewed. There is an “urgent need to combine surveillance and viral discovery efforts with biodiversity surveys,” write the study authors. But we must also “prepare our health systems” for the emergence of diseases.
At least six global pandemics have occurred since the 1918 influenza pandemic, including those of HIV/AIDS, SARS and COVID-19, as well as three caused by influenza viruses (IPBES, 2020).