Global warming may have caused all major mass extinction events, including this one
It all comes down the oceans
Recently, 23 species were removed from the endangered species list, not because they are now flourishing, no, because they are extinct.
Life is a rough business. Countless species have gone extinct without humans being around. And many of those extinctions have been caused by another species. In the past three billion years, life has seen not only a regular march of extinctions but five mass extinction events where a majority of species have gone extinct.
The sixth, known as the Holocene or Anthropocene event, is currently underway, and we’ve seen nothing yet. According to Wagner, et al. publishing on insect declines in the Proceedings of the National Academy of Sciences, one of the world’s most prestigious academic journals,
[M]ost biologists agree that the world has entered its sixth mass extinction event, the first since the end of the Cretaceous Period 66 million y ago, when more than 80% of all species, including the nonavian dinosaurs, perished.
They go on to list some of the losses:
Terrestrial vertebrate population sizes and ranges have contracted by one-third, and many mammals have experienced range declines of at least 80% over the last century (5). A 2019 assessment suggests that half of all amphibians are imperiled (2.5% of which have recently gone extinct) (6). Bird numbers across North America have fallen by 2.9 billion since 1970 (7). Prospects for the world’s coral reefs, beyond the middle of this century, could scarcely be more dire (8). A 2020 United Nations report estimated that more than a million species are in danger of extinction over the next few decades
About 8.7 million species are estimated to exist on Earth today and, if nothing changes, the million species of the next few decades could easily become several million extinctions in the next century or two.
As in most extinction events, there are winners and losers. Mammals “won” the last extinction event of the Cretaceous period, becoming the dominant class on Earth.
Losers greatly outnumber winners in a mass extinction, e.g., “64% losers (declining populations), 14% winners and 22% stable or neutral populations” in a study by McKinney and Lockwood in 1999. The Earth is undergoing a process of defaunation, in which large numbers of animal species, both vertebrates and invertebrates, vanish.
The result is that a few winners replace a large number of losers and biodiversity declines. This has been observed in previous mass extinctions as well.
Winners tend to be species that are both resistant to destruction of their habitats or other adverse circumstances as well as able to move into new habitats. We often call these species “invasive” for thriving in new habitats, but they are also successful at avoiding destruction. Many bird and insect species, as well as plants, have been successful while related species decline because of their ability to thrive in urban and suburban regions, for example, but also just being more hardy in general.
Bond and Grasby suggest that, based on a review of existing literature, in the past “large scale volcanism is the main driver of mass extinction.” The outcome of volcanism is excess carbon dioxide and hence “[m]ost extinctions are associated with global warming and marine anoxia” (anoxia being a deprivation of oxygen) as well as “ocean acidification”. There was also a rash of toxic metal poisoning in many events such as airborne mercury poisoning in the Cretaceous (which had a meteorite as its cause).
Surprisingly, global cooling, while often a direct consequence of volcanism, has not typically led to mass extinction events but followed them. And all five mass extinctions are linked with a global warming trend that preceded global cooling. The reason is because global warming invariably reduces the ocean’s ability to hold oxygen, suffocating marine life. It goes to show how dependent our planet’s life is on the oceans.
While the finger is often pointed at habitat destruction and pesticides from agriculture and certainly many species are extinct from these causes, this primarily affect land animals, particularly forest and grassland dwellers. Global warming will, it seems, be the ultimate driver of the Holocene extinction event. After all, despite toxic runoff, algae blooms, industrial waste, and overfishing, industry and agriculture generally cannot affect ocean life nearly as much as global warming.
Studies have found that protecting species does result in increases in population. Rare European bird species, for example, have been generally increasing in population while common bird species decline. Yet, this may be too little too late given the global catastrophe unfolding.
While human beings will likely continue past this event in some form, our planet will never be the same. Surrounded by those species that manage to figure out how to survive us, things we consider weeds and invasive irritants, we will continue in a world that is nothing like the beautiful garden we were given. Instead, we will live in a menagerie containing those few examples of once wild species we managed to save, ourselves among them.
All the more reason why human beings must learn to terraform this planet before we even think about trying to terraform another, dead world like Mars. We have already managed to do it by accident with fossil fuels, now it is time to learn to do it on purpose.
Despite the sadness of what is happening around us, we have to remind ourselves that we never asked to live in such times. We are paying for the sins of our ancestors, the sins of the rich and powerful, and the rest of the Earth’s species are paying along with us.
Yet, we are not powerless. We have ability to take back the power we have lost. We as a species can repent. We can demand an immediate end to fossil fuel use. We can ensure that we do whatever we can to reduce our own dependence on it. We can hold those who are leading us down the path of destruction, those who lied to us when they knew the truth decades ago, accountable. We can recognize that our relentless consumption is a disease that is killing us, not making us happier.
Humanity is on trial right now, and we are guilty, but we can still be forgiven. It is not too late.
Wagner, David L., et al. “Insect decline in the Anthropocene: Death by a thousand cuts.” Proceedings of the National Academy of Sciences 118.2 (2021).
McKinney, Michael L., and Julie L. Lockwood. “Biotic homogenization: a few winners replacing many losers in the next mass extinction.” Trends in ecology & evolution 14.11 (1999): 450–453.
Bond, David PG, and Stephen E. Grasby. “On the causes of mass extinctions.” Palaeogeography, Palaeoclimatology, Palaeoecology 478 (2017): 3–29.
Banerjee, Neela, Lisa Song, and David Hasemyer. “Exxon’s own research confirmed fossil fuels’ role in global warming decades ago.” Inside Climate News 16 (2015).