Weird as it may seem, the Tambora explosion, unnoticed outside Java, not only unleashed devastating weather, destroying crops and communities around the globe. As you discover in gory detail in Gillen D’Arcy Wood’s 2014 book Tambora, it also transformed cholera from a local nuisance in Bengal into one of the world’s most virulent and feared diseases.

Wood writes: “Tambora’s Frankenstein weather, wild and weird, created a microbial time bomb in the waters of the estuarine Bengal delta. Once exploded, life on Earth, at least for human beings, became a far more dangerous proposition.” In 1817, a global cholera pandemic suddenly erupted, a “phantom agent of death that was brutal, unknowable, and potentially limitless in its reach”.

From India, where in weeks it consumed 10,000 followers of Indian governor Lord Hastings’ British army, a newly virulent strain of cholera spread to Myanmar and Thailand in 1819 and 1820 and Iran in 1822 before reaching France in 1830 and eventually the United States in 1832.

Recent work by microbiologists – in particular, the sequencing of the cholera genome in 2000 – clearly reveals that cholera had been around for aeons, never pestering humans, but instead subsisting on plants and algal blooms in brackish water across the world. It took the climatic upheaval triggered by Tambora to mutate the bacterium Vibrio cholerae into the 19th century’s most virulent killer.

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In Wood’s telling, microbiologists like Rita Colwell have discovered that extreme weather events are “capable of both amplifying transmission of cholera and producing the non-linear transformation of organic pathogens into new and potentially deadly forms”.

Tambora’s disruption of the monsoon over the Bay of Bengal “stimulated an unprecedented event of genetic mutation in the ancient career of the cholera bacterium … cholera outbreaks are climate driven, and cholera is a climate change disease”.

The article was based on research published two weeks ago in Nature Medicine by an international team drawn from the Scripps Research Institute in California, the University of Edinburgh, Columbia University in New York, the University of Sydney and Tulane University in New Orleans.

If I understand the science right, the novel coronavirus, Sars-CoV-2, is indeed related to a bat virus, but has only a 96 per cent match to the bat virus – rather than a higher match if the virus had jumped directly from a bat to a human eating it. The virus might have made the jump decades ago, and been mutating in human beings since then.

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The researchers also found that the virus’ structure was too convoluted to have been man-made, quashing accusations that the coronavirus had been synthetically manufactured.

The Nature Medicine article does not say if a specific weather event – or climate change in general – triggered the transformation of the coronavirus causing Covid-19. But many kinds of change might trigger a dangerous mutation.

The story of Tambora and cholera is a reminder of how new and dangerous threats to human health can come from traumatic climate events, not just poor hygiene or unfamiliar culinary exotica.

Important lessons can be learned by comparing these two serendipitous events. Viruses can stick around for a very long time, simmering gently, awaiting that one random transformative event that enables them to mutate and scourge an unprepared world. If extreme weather events are potential triggers, that surely gives us yet more reasons to be anxious about global warming.

Today, the vectors include urbanisation and refugees from conflict areas, and pandemics now move at warp speed. As we bring the present pandemic under control, serious thought will need to be given to how we put brakes on the spread, without destroying the global benefits of international trade and travel.

Thank goodness that the novel coronavirus is not the scourge cholera was in the 19th century. But if, like cholera, it was born out of climate change, then there will for sure be more to come. Life on Earth has indeed become a far more dangerous proposition.

David Dodwell researches and writes about global, regional and Hong Kong challenges from a Hong Kong point of view