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Global heating has spurred some peculiar changes in plants and animals from the Caribbean to the Rockies
In June 1802, the German naturalist Alexander von Humboldt ascended the inactive volcano Mount Chimborazo in Ecuador. As he climbed from tropical rainforest towards the snow-covered peak almost 21,000ft above sea level, he acquired a new vision of nature, interwoven with "a thousand threads". It was like taking a journey from the equator to the poles: an entire world of diversity collapsed on to this single mountain, a "microcosm on one page". Here Humboldt began to develop the notion he called Naturgemälde, a scarcely translatable word that implies a unity or wholeness in nature.
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Humboldt is often credited with the idea of an ecosystem as a web of interdependent living species, each playing a part in supporting the whole. But as conservation biologist Thor Hanson says in Hurricane Lizards and Plastic Squid, Chimborazo also opened the intrepid German naturalist's eyes to another profound realisation: climate, not mere geographical location, "dictated what grew where, and similar vegetation should occur in any place where temperature, humidity and other conditions were the same, regardless of geography".
The corollary - when climate changes, ecosystems must change too - is the topic of Hanson's book. The simplest outcome is a shifting of boundaries separating different climatic zones: as temperatures rise, temperate flora and fauna will move poleward. If that were all there was to it, climate change would rearrange but not otherwise perturb the mosaic of life that Humboldt identified. But it isn't so straightforward. The responses of the natural world to the changes that human activities have induced in our climate range from the alarming, such as species extinctions, to the creative. The natural world is resilient, but to different degrees in different places and among different organisms. What's more, timescales matter: adaptations feasible over the slow climate shifts that have happened naturally in the distant past might not be managed in the face of today's rapid warming. Nature is doing what it can, but it is confused and often imperilled.
It's a somewhat guilty pleasure, then, to revel in Hanson's globetrotting exploits, some of them conducted under the constraints of the pandemic. We are taken from the rainforests of Costa Rica to the Arctic ice of Franz Josef Land and the coral reefs of Indonesia. The range of species he investigates and the climate responses they exhibit are sometimes dizzying, but some general features emerge.
When confronted with a climate shift - warmer ocean or air temperatures, say, or altered patterns of rainfall or melting ice - organisms have several options. They can migrate to where the original conditions still prevail, or they can try to adapt their behaviour to the new. In some cases they can evolve: Darwinian natural selection is often imagined to happen slowly over millennia, but it can take place much more quickly (as the coronavirus reminds us). As they decimate populations, sudden and extreme changes in climate are a brutally selective filter. The "hurricane lizards" of the title are those individuals in a species of Caribbean lizard whose stronger grip, thanks to larger toe pads, allowed them to survive more frequent hurricanes by clinging to trees and shrubs.
Another option is that organisms find niches in their existing habitat where the original conditions persist: so-called refugia, such as slopes sheltered from the sun. Whether this is a viable long-term solution is not clear - but it has so far sustained populations of rabbit-like American pikas in the western Rockies, which find their preferred cooler conditions preserved in the cold air that gathers over scree slopes, even while the snowpack elsewhere retreats.
But amid these diverse strategies, the ecosystem as a whole may still be disrupted. It's no good one species adapting to stay put if its main food source has migrated elsewhere. And as climate change moves the boundaries of the seasons, the delicate interlocking of growth patterns may be thrown out of kilter. "Timing is everything in ecosystems," Hanson writes. "If plants at the foot of trees have not finished their bloom and growth before the trees overhead come into leaf and block much of the sunlight, they're in trouble."
Hanson supplies abundant reason to marvel at nature's ingenuity, but also to fear for it in the face of the drastic changes we are generating. He reminds us that our own responses, as we try to adjust to wildfires, heatwaves and sea level rise, are a part of that story too. "It's now a running joke that every biologist in the world is studying the effects of climate change," he writes. "Some of them just don't know it yet." It's a good joke, but nothing to laugh about.
