by Gillen D’Arcy Wood

(Princeton University Press 2014)

In my last year at Harvard, before I decided to drop out of the PhD program and pursue other things, I took a graduate meteorology class. The class teacher, Brian Farrell, was doing what other professors did and quietly sounded students out about taking him on as their thesis advisor. Farrell’s work was so interesting that I seriously considered the idea.

He was a pioneer of something called paleometeorology, the study of ancient weather patterns. He was motivated by fossil evidence showing that around 50-70 million years ago, dinosaurs, mammals related to hippos and the plants they fed on thrived at latitudes as high as 80 degrees north, equivalent to living on Spitzbergen or northern Greenland. And these dinosaurs were not furry, warm-blooded creatures like polar bears. How could they survive up there?

A clue came from fossil plankton. Their skeletons contain trapped atmospheric oxygen, whose isotopic mix records a faint memory of ancient sea temperature. Study of high-latitude plankton fossils revealed that temperatures were temperate even close to the North Pole, allowing cold-blooded dinosaurs to roam. This condition became known as the ‘equable climate’. Farrell and other paleometeorologists sought to reconstruct the weather patterns that allowed the equable climate to persist ““ a challenge because the polar regions are plunged in darkness for months every winter.

I remembered Farrell’s research when reading Gillen D’Arcy Wood’s Tambora. In April 1815, a volcano in an obscure corner of what is now Indonesia erupted in a colossal explosion, one of the largest in recorded human history. Tambora hurled so much ash and sulphur dioxide into the stratosphere that the Earth’s weather changed for two years, part of which was known as ‘the year without a summer’.

As D’Arcy Wood documents, the destructive effect of Tambora was far wider than in its immediate environment. The weather changes caused famines in Europe and China, and devastating epidemics of cholera and typhus that killed millions. A professor of English literature, D’Arcy Wood does a clever job bringing together the scientific record with the references to Tambora’s impact that he spots in the literature of the time, from Romantic Poets to Imperial China.

I wasn’t convinced by everything D’Arcy Wood says. Via its impact on Swiss weather, the Indonesian volcano may have influenced Mary Shelley’s writing of Frankenstein but surely the book would have been written anyway. And the book’s subtitle ““ ‘the eruption that changed the world’ also seems like over-egging the pudding. Yes, millions died and painters like Constable might have depicted more storms and clouds than normal. But by 1818 things largely had returned to normal and the effect was soon forgotten. The world did not change, or at least carried on changing in the way it was doing before the eruption.

D’Arcy Wood seems to acknowledge this in his chapter called ‘The Polar Garden’. In contrast with temperate climes, the effect of Tambora in the Arctic was to temporarily warm things up, raising the tantalising prospect that a Northwest Passage was opening from Europe to the Pacific. Civil servants in Britain’s Admiralty seized upon reports of open water west of Greenland, and sent off expeditions that would perish miserably in the polar ice once the transient impact of Tambora passed.

This takes me back to the equable climate. D’Arcy Wood quotes a passage from Percy Shelley’s poem Queen Mab (written before Tambora) which speaks of polar ice melting while ‘fragrant zephyrs there from spicy isles ruffle the placid ocean deep’. For D’Arcy Wood this is part of the hype that led the Admiralty astray. But looking at Shelley’s words today, could they be in fact, a prophecy?

The University of Colorado’s National Snow & Ice Data Center has compiled polar satellite images dating back to 1979. Looking at the extent of polar sea ice at the warmest point of the summer 35 years ago reveals that the Northwest Passage was still very firmly frozen solid, with ice extending from the pole to the north coasts of Alaska and Siberia. Contrast that with the image from September 2015, in which the seas off the north coasts of Alaska, mainland Canada and Russia are completely ice-free for hundreds of miles.

While this is by no means an equable climate, it is valid to ask whether ‘dinosaur weather’ might return and vindicate Shelley’s prophecy.

Returning once again to paleometeorology, since my encounter with Farrell, the field has progressed. There are now multiple theories that overcome the main obstacle to the equable climate ““ the long polar night that normally freezes the ocean. The best explanations involve polar clouds that trap heat and prevent it from escaping into space during the winter darkness, an effect that would be reinforced by increases in carbon dioxide and methane. And as the polar ice retreats it no longer reflects sunlight when winter ends, further accelerating the warming effect.

If all this happened, the Earth would in effect be jumping to a new state, one that would be irreversible on the scale of millions of years. At the very least, the melting of polar ice caps and rise in sea level would have a devastating effect on humans, although the uncertain linkages between physics, chemistry and biology make the impact hard to predict. Here I agree with D’Arcy Wood when he concludes his book with the warning that Tambora’s transient destruction serves as a cautionary tale about what is likely to be coming.