The Sixth Mass Extinction


The fossil record tells us that our planet has faced five mass extinctions in the past. The first, at the Cambrian-Ordovician transition around 480 million years ago was significant in extinguishing many species of trilobite. The second, at the Ordovician-Silurian transition around 440 million years ago, was perhaps two extinction events and was even more significant than the one that preceded it. Around 360 million years ago at the Devonian-Carboniferous transition roughly 70% of all species became extinct. The largest extinction ever – around 520 million years ago and the Permian-Triassic transition, killed around 96% of all marine life and perhaps 70% of land life. Around 200 million years ago at the Triassic-Jurassic transition, the extinction event was much smaller but still significant, and the final extinction, around 65 million years ago at the Cretaceous-Paleogene transition is the one most widely-known, for this extinction wiped out the dinosaurs, as well as half of all other species.

It is now very widely (although not universally) accepted that we are currently in the Earth’s sixth mass extinction, even though it may not seem dramatic to us in our daily lives. This mass extinction is quite unique, though, in that it has been driven by human beings, in particular by overexploiting species, pollution, transforming the landscape, and introducing what are known as “alien” species (i.e. species that don’t belong in a particular area). E. O. Wilson suggests the problem is particularly bad, indicating that each year 27,000 species are doomed to extinction, which means 74 a day, or 3 every hour. He notes that the normal rate of extinction for species is around one species per million every year, and explains how, as the result of human actions, this rate is now somewhere between 1000 and 10 000 times greater in some areas of the world, such as the rainforests.

It may be true that nature recovers from extinction events, although recovery in this sense is purely in terms of number of species – extinct species can never, ever be enjoyed again. Yet the length of time taken to restore the balance is mind-boggling – somewhere between 20 and 100 million years! This would mean that human beings are unlikely ever to see a world as full of life as we do today.

“We are now at the point where we have lost half of the world’s forests, half of the world’s wetlands, half of the world’s grasslands.” Flora across the world are dying out - Brazil’s Cerrado savannah, for example, is now so fragmented that “it is unlikely that its 10,000 plant species will all be able to disperse to climactically suitable areas.” European funghi are experiencing a 40-50% decline in species in some areas during the last 60 years, mainly because of air pollution. When we look at Amazonian rainforest cover, and compare it with prehistoric cover, we find that it is now half what it once was, and rapidly decreasing – nearly 2% every year (often better expressed as the area of a football field every second. Of course, climate change also brings with it the threat of invasive species, some of which we have already mentioned (the spruce bark beetle). One invasive species of great concern in southeastern America is the red fire ant, which is expected to start destroying more flora and fauna.

The statistics for extinction are really staggering - “We used to have 1000 species go extinct every year. Now we are maybe losing between 15,000 and 60,000 species a year.” What is important for human beings is that it is the larger animals that are going extinct, not just small insects. That has massive implications on the human food chain. Not only is the human food chain threatened, but the extinction of species and habitats also affects living conditions. For example, because their fruit trees were washed away, the 2000 people who lived on Carteret Island in Papua, New Guinea had to move to an adjoining island. As the two uninhabited Kiribati Islands were taken by the sea in 1999, it has become clear that the other 33 islands in the region, home to over 100 000 people, will all be taken by the sea.

In 2004, Chris Thomas of Leeds University published his study of extinction rates in Nature magazine. He showed how 15-37% of plant and animal species across the areas that he studied could face extinction by the year 2050, although that figure jumped to 21-52% should human emissions continue to increase. His survey showed that more than 30% of amphibians were found to be vulnerable, frogs particularly.

These figures were confirmed in October 2007 by the United Nations Environment Programme, who discovered that 30% of amphibians, 23% of mammals and 12% of birds are under threat of extinction. A smaller, connected report discovered that nearly 30% of all primate species are facing extinction. In fact, “you could fit all the surviving members of these 25 [most-at-risk primate] species in a single football stadium; that’s how few of them remain on Earth today.”

The IUCN Red List shows how many species are facing extinction, or are believed to have become extinct. From their website, the annual increase in threatened species across the global is plain to see. From a total of 1,589,361 species counted, the number of species deemed to be threatened in the years 2000-2007 were 10 533, 11 046, 11 167, 12 259, 15 503, 16 116, 16 306.

2007 was a very important year in terms of extinction because in that year, after extensive searching, the Yangtse River Dolphin was declared extinct – the first large animals to be declared extinct in 50 years and, more importantly, only the fourth mammal to be declared extinct in the last 500 years. The causes of this extinction were, without question, increased river traffic in the Yangtse and human pollution. “80 per cent of the rivers in China are now so polluted that they are unable to support any fish of any kind, and that indicates a probably horrendous amount of extinction species in the river systems of China”

Causes of the Sixth Mass Extinction

Given the almost-universal recognition that we are in a human-induced mass extinction, it is important for us to recognise more clearly what the causes of that extinction are.

E. O. Wilson explains the five main causes using the acronym HIPPO. The first letter is the most important factor in causing extinction of species, the last being the least important (but nonetheless clearly significant). The H stands Habitat Destruction, I for Invasive species (which push out niche species or bring diseases), P is Pollution and the overPopulation, and the O is Overexploitation of species. He cites the example of 1033 species of fish in the waters of the United States, Canada and Mexico, and shows that the causes that pushed them into decline were destruction of habitat (73% of species), displacement by an introduced species (68%), chemical pollutants (38%), hybridization with other species (38%) and overharvesting (15%). It should be noted that these percentages go beyond 100 because some species were subjected to more than one factor. It is well recognised that species around the world are experiencing stress caused by many factors, so simply reducing one is not enough.

Wilson states that considering our species appropriates 20-40% of the Sun’s energy captured in organic material, we are bound to drastically reduce the state of most other species, simply because of our abnormal use of global resources.

Rainforest destruction reached serious proportions over twenty years ago, and yet it gets worse with the recent rise in palm oil production. Palm oil can be found in approximately 1 in every 10 items bought in a supermarket, and is usually grown from unsustainable sources. This means that forests around the world, particularly in Borneo and Sumatra are being cut down to grow palm oil. While the carbon emissions from this endeavour are catastrophic, it is the plight of the orang-utan, whose last habitat is seriously threatened by palm oil plantations, that seems to have recently captured the public’s eye, numbers having dropped from 300 000 to around 25 000. Unfortunately, the new market in biofuels started by George W. Bush has increased the demand for crops that cause massive deforestation. In October 2007, MPs voted in favour of the Renewable Transport Fuel Obligation which will require all petrol and diesel sold to come from renewable source by 2010. Some supermarkets, such as Tesco and Morrisons, already blend 5 per cent ethanol in their supplies. Not all biofuels do damage the rainforests, it should be noted – in November the UK’s first bioethanol plant was opened in Norfolk.

Biofuels have become a human rights issue too, since families are being forcibly removed from their land in order to grow crops, and there have been cases of murder in order to force eviction of families. Vicente Castaño, leader of Colombia’s Jiguamiandó and Curvaradó paramilitaries said that he was responsible for bringing African oil palm to the area and that “he and his paramilitary group had become the legal owners of African oil palm plantations. Meanwhile, the people of Jiguamiandó and Curvaradó have suffered more than 110 assassinations and disappearances since 1996, as well as forced displacement and constant threats. The paramilitaries’ arrival in the region in May 1997 is scarred deep in people’s memories. They decapitated the local pastor, then forced members of the community to watch as they played football with his head. They then advised the community to leave the area. Nearly six thousand people fled.”

Yet the greatest cause of deforestation is legal and black-market logging. In 2005, the BBC reported that the amount of deforestation that had been estimated was 60% lower than predicted. NASA imagery helped the US team produce their results, which were published in the magazine Nature, although the results were held to be exaggerated by the Brazilian government. The team also discovered that carbon emissions from Amazonian deforestation were 25% higher than predicted. This is disturbing since “Brazil’s National Institute for Amazon Research estimates that deforestation puts four times more carbon into the atmosphere than the nation’s fossil-fuel burning does.” “Africa, which accounts for about 16 per cent of the world’s forests, lost more than 9 per cent of its trees between 1990 and 2005. In Latin America and the Caribbean, home to nearly half of the world’s forests, 0.5 per cent of the forests were lost every year between 200 and 2005, up from an annual net rate of 0.46 per cent in the 1990s.” In total, deforestation accounts for approximately 20 per cent of global carbon emissions.

If there were any doubt as to the atmospheric impacts of the clearing of the Amazonian forest, one need only look at South America in October of 2007, when thick layers of smoke covered vast areas of Brazil, Paraguay and Bolivia due to fires. The rains were weaker than usual at that time, and more than 10,000 fires started by ranchers on grazing land taken from rainforest caused such pollution that flights had to be cancelled.

It should be noted that deforestation is not just an environmental-emissions issue, but also a human-rights issue. The Toba tribe in Argentina are dying from malnourishment, tuberculosis and the Chagas virus brought about by indiscriminate deforestation to make way for soya plantations. The Toba tribe have always relied on algarrobo trees which gave them the highly nutritious algarroba bean. Because the tribe are too weak physically and politically, they are unable to protest, and the logging continues. In Congo, the World Bank has been accused of encouraging foreign companies to destructively log the forest, endangering the lives of the Congolese Pygmies, who number between 250,000 and 600,000, and who were apparently not considered when the World Bank encouraged logging in the area to help with development.