Banner by Khusbu Patel

The Sixth Mass Extinction

by Emily Forsyth

The history of Earth is a story, and each species is like a well-known and beloved character. At the moment, we are in the midst of a massive character genocide, with species dying off on every page. There have been five known mass extinctions since complex life formed on Earth. Thanks to rapidly decreasing biodiversity, alarming extinction rates and concerning threats to the environment, scientists now speculate that we may soon fall subject to a sixth. But how did we get to this point? And what does this sixth mass extinction mean for the Earth and for humans?

Scientists characterize a mass extinction as a time when Earth loses more than 75% of its species in a relatively short interval of around two million years. Extinction is common and actually relatively healthy for Earth’s ecosystems; nearly 99 percent of species that have existed over the past 3.5 billion years are now extinct. However, like most things in life, extinction is only healthy in moderation or at a sensible background rate that can be balanced out by the evolution and formation of new species. The more extinction rates climb away from background rates, the greater the risk of Earth falling prey to another mass extinction. Now, the extreme of a mass extinction could be reached within a few short centuries, no longer than the blink of an eye in the context of the vast expanse of Earth’s lifespan.

Currently, scientists worldwide are recognizing a disturbing decrease in biodiversity at a rate greater than that of the last mass extinction 65 million years ago. This was the extinction of the Cretaceous period, correlated with the infamous asteroid impacts that killed off the dinosaurs. We are witnessing a devastating time period illustrated by rapid decreases in numbers of vertebrate species, growing “dead zones” at the mouths of major rivers, monoculture crops replacing forests rich with biodiversity and graveyards where breathtaking coral reefs once stood. 

However, it is difficult to tell just how close we are to the brink of another mass extinction, as serious roadblocks stand in the way of observing the data necessary to tell us just how many species have gone extinct recently. Species counts are constantly changing, and the number of species being assessed or having enough observable members to be assessed, is regrettably low. There is also the debate as to whether “threatened” species should count for or against extinction rates. Due to these difficulties, scientists tend to make their observations on the conservative side. They set strict guidelines to consider a species “extinct” and opt for the numbers that minimize the peril our environment potentially could face. However, even with these careful estimates, the conclusions are frightening. In the last 500 years, up to 43 percent of amphibian species, 29 percent of reptile species and 27 percent of coral species have gone extinct or become seriously threatened. Even species not yet facing extinction are experiencing severe population declines. In a study analyzing data from 1900 to 2015, 40 percent of a sample of 177 mammalian species faced significant population declines, as did 32 percent out of a sample of 27,600 vertebrate species. 

Yet to truly understand how close our Earth is to another mass extinction, current overarching extinction rates need to be compared to standard background rates. In the name of caution, scientists have set background rates at two mammal extinctions out of 10,000 species per 100 years, despite healthy background rates used in the past ranging from 0.1 to one. Of vertebrate species evaluated by the International Union of Conservation of Nature (IUCN), 617 have been declared extinct or probably extinct since 1500. This sets current extinction rates at a frightening 100 times the background rate. On top of this, most of the listed extinctions occurred over the past 114 years, showing that extinction rates are increasing rapidly. Scientists suggest that current extinction rates in tropical rainforests alone could reach up to 100 species a day. The extinctions over the past 100 years should have taken 800 to 10,000 years to occur, so why are these species dying out so fast?

The cause of the impending mass extinction is not surprising: us. Over the past century the human population has increased by over 300 percent and the global economy by no less than 1500 percent. Ocean life is no more than our food and sport. We raze rainforests of anything valuable, with between twenty-five to forty percent of the Amazon Rainforest lost in the last fifty years. We flatten forests for their wood and have deforested a total area greater than South Africa since 1990. In fact, the five greatest causes of biodiversity loss today are all chiefly driven by human society: habitat loss, impacts of alien species, over-exploitation, pollution and climate change. Even ignoring the infamous events of the past five mass extinctions, such as asteroid collisions and volcanic eruptions, the extinctions all existed primarily due to drastic climate changes and ecological stressors. Temperatures on Earth have risen 1.2 degrees Celsius since 1911 and carbon dioxide levels are higher than they’ve been in the past 800,000 years. High levels of CO2 have caused up to a 30 percent increase of acidity in oceans. These factors, along with the previously listed anthropogenic ecological stressors, set the stage for another mass extinction. 

Well, so what? To put it bluntly, plants and animals are going extinct, but humans are not, so why be concerned? Biodiversity is responsible for the ecosystems that provide for human survival, and biodiversity is exactly what’s at stake. It provides our food, fiber, medicine, fresh water, pollination, pollutant filtration, protection from natural disasters and the potential for knowledge and medical advancements. But not only does this impending extinction risk human resources, it risks human morality. We are blatantly ignoring the rights of other species to a continued existence. As humans, we are gifted with rational thinking and morality, setting us apart from other animals, yet that morality seems to be lost when we continue to treat other animals as disposable. Humans are not the authors of Earth’s story, but rather characters that take up a very short chapter.

What can be done? Although much of the damage humans have done to earth and its ecosystems is irreversible, there are solutions. With the percentage of species extinct over the past 500 years, the rates of modern extinctions are noticeably slower than those of the past five major extinctions. However, if we consider critically threatened species over the past 500 years as inevitably extinct, current extinction rates practically match those of the past five mass extinctions. This points to a critical observation: if we can revive currently threatened species and reverse much of our damage on biodiversity over the past 500 years we could delay or even prevent a sixth mass extinction. We need to stop committing crimes against Mother Nature so we can continue to watch the story of Earth and all of its inhabitants unfold.