Climate change and the anthropocene extinction
The Anthropocene extinction rate has swept far above the natural momentum of evolution.
Extreme weather has become a global feature, like the floods in California last winter and the punishing summer now visiting South Asian and some Chinese cities. Climate change and its follow-on effects have often been precursors to the extinction of species and human habitats, especially cities (Mohenjo-Daro, for instance). There were five great extinctions before humans evolved. Of them, the Permian-Triassic extinction of about 250 million years ago, which marked the boundary between the Paleozoic and Mesozoic eras, was the most catastrophic event in the history of life, wiping out nine out of 10 species and clearing the board for the age of the dinosaurs. More knowledge about its development may help us survive the sixth wave, the Holocene or Anthropocene extinction, which we are living through.
Of course, the current wave of extinctions has a novel feature: humans have accelerated it. Megafauna extinctions ― even recent events like the dwindling of the North American bison ― are associated with the spread of humans, who have hunted recklessly. Species which had developed in isolation, like the dodo and the moa, began to disappear during the age of exploration, when development chipped away at habitats, and new diseases, vectors, invasive species and crop plants travelled from continent to continent on board trading ships, changing economies and cultures. But now, the climate crisis is more urgently visible than extinctions, especially in big cities, where modern design and construction materials have turned into heat traps. Their ambient temperatures are rising much faster than the rates negotiated at climate talks. Cities are the most visible works of human civilisation ― the very word is related to civitas, Latin for ‘city’ ― and the establishment of early urban centres in a belt across the Old World, from Egypt and Turkey to the Indian subcontinent, marked the beginning of modern culture. Ironically, the city is now signalling the ecological crisis that urbanised civilisation created. And a sharper irony could lie in the Holocene extinction.
Large apex predators are canaries in the coal mine for mass extinction events triggered by ecosystem destabilisation, suggests a recent paper in Current Biology by Christian F Kammerer, Pia A Viglietti, Elize Butler and Jennifer Botha. They base their finding on the discovery of the sabre-toothed mammal-like predator Inostrancevia in South Africa just before the devastating Permian-Triassic extinction. Earlier, Inostrancevia had been found only in the region now called Russia, and it was traditionally believed that northern and southern species of Pangea kept to their sectors of the ancient supercontinent. However, it now appears that after the southern areas ― including present-day South Africa ― lost their apex predators early in the extinction event, Inostrancevia migrated thousands of kilometres south to fill the ecological niche. But despite the lack of competition for its ecological niche, the new apex predator died out soon after that.
The Permian-Triassic extinction, which made Inostrancevia adventurous and then put away in the fossil record after a brief success, is a useful point of comparison for the extinction event now in progress. But the irony is that while Inostrancevia could be used as a barometer because it was the apex predator of the time, Homo sapiens could have taken its role, though it is only the top hunter. The apex predator is the species which can prey on others, but no other species can prey on it. That roughly describes humanity, but it’s in a league of its own. We are the first species to farm other species to eat them at a larger scale than would be possible in the wild.
The Anthropocene extinction rate has swept far above the natural momentum of evolution. It is 100-1,000 times the background extinction rate (from before human activity pressed the accelerator) and proceeds about 100 times faster than the ‘Great Dying’ of the Permian-Triassic. Life scientists acknowledged a crisis in the 1990s, and it is accepted that half of the higher life forms could be rendered extinct by human intervention by the end of this century. That is not too far away: many people born this year will see the day, assuming that sapiens can escape the fate of apex predators ― which it is, in terms of scale. Archaeologists gloomily joke that our civilisation will be identified by their future peers by a thick stratum of chicken bones where towns and cities used to stand. We eat enough chicken to create a defining urban horizon of their mortal remains like a meteorite strike leaves a layer of ash with unusual concentrations of minerals across the globe.
Extinction events doom apex predators because it’s lonely at the top ― they depend on access to specific species of large herbivores for survival. This has been a feature of their lives from the Permian-Triassic to the present. Their prey is, in turn, dependent on specific kinds of vegetation, which are quickly affected by climate change. Since every link in the food chain is vulnerable to change, the carnivore at the top suffers a multiplier effect and is especially vulnerable. The fate of Inostrancevia could have been the product of inflexibility.
Omnivorous, humanity has the elbow room that true apex predators don’t. Our chances of surviving the developing climate crisis are probably higher than we anticipate because we are flexible in terms of both food and habitat. By developing industrial civilisation, we have painted ourselves into an inhospitable corner, but we can also step away from it. But whether we have the sense to do so is another matter.
Editor of The India Cable