Q&A: Could climate change and biodiversity loss raise the risk of pandemics?

Across the world, millions of people have tested positive for Covid-19 – and countless more have seen their lifestyles completely transformed as a result of the virus.

It is not yet known exactly what triggered the current outbreak, but researchers suspect that the virus passed from bats to humans through an unknown intermediary animal, possibly a pangolin.

Politicians in the UK have called this pandemic a “ once-in-a-century ” crisis. But scientists have warned that the ongoing disturbance of species through human activities and climate change could be raising the risk of potentially pandemic-causing diseases passing from animals to humans.

The study of the “spillover” of disease from animals to humans has received renewed focus in light of the pandemic. The Intergovernmental Panel on Climate Change ( IPCC ) – a major international collaboration of climate scientists – is now looking into how the influence of warming on such events could be included in its next major climate report due next year.

In this explainer, Carbon Brief examines what is known about how climate change and biodiversity disturbance, including habitat loss and human-animal conflict, could influence the risk of diseases being transmitted from animals to humans.

How does an animal-to-human disease spillover turn to a pandemic?
Could climate change and biodiversity disturbance affect the risk of spillover?
Will the risk of animal-borne disease pandemics increase in the future?

How does an animal-to-human disease spillover turn to a pandemic?

When humans come into contact with other animals, they can pass harmful pathogens between one another. The passing of an infection or disease from a vertebrate animal to a human is known as a “ zoonosis ”, according to the World Health Organisation (WHO). (Vertebrate animals include mammals, birds and reptiles, but not insects, such as mosquitoes.)

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Such diseases have a major impact on health, accounting for two-thirds of all human infectious diseases and three out of four newly emerging diseases.

Serious diseases that have spilled over from animals to humans include Ebola in Africa, Marburg in Europe (and subsequently in Africa), Hendra virus in Australia and severe...