Extinction is a word that usually evokes images of tyrannosaurs, velociraptors or beaked and wide-winged pterosaurs . We all have some notions about the time when these gigantic reptiles roamed the planet and, in general, we feel an almost morbid fascination for their teeth and claws. Obviously, we all also know that they no longer exist. They became extinct 65 million years ago, in the Cretaceous, when a fireball crossed the skies and hit the planet’s surface violently.
This was the last but not the worst of the great extinctions. That dubious honor belongs to the one that occurred 250 million years ago, in the Permian, so massive that it is known as the Great Dying . Three others occurred at different times, since 3.8 billion years ago life first emerged. Now, everything indicates that we are witnessing the sixth great extinction in the first row.
It was 1998 when a survey by the American Museum of Natural History in New York sounded the alarms for the first time. “Most of the biologists in the country are convinced that a mass extinction of animals and plants is underway,” could be read in early April of that year in the pages of The Washington Post . According to the museum, seven out of ten biologists claimed that a fifth of all living species could disappear in less than three decades and that the rate of disappearance was higher than at any other time in history.
Anyone would imagine that, faced with such dramatic predictions, political and social decisions would be made, but it was not. The survey only had the opinion of four hundred experts and there were not a few who questioned the conclusions. Without solid data to back up the extinction argument, the matter fell into oblivion, until things took on a rather more serious tint .
Have alarmist estimates been made?
Today, the scientific program of the Millennium Ecosystem Assessment, sponsored by the United Nations, estimates that between 150 and 200 species are extinct every day. And the International Union for Conservation of Nature (IUCN) affirms that they are in danger 41 % of amphibians, 33 % of corals, 34 % of conifers, 25 % of mammals and 13 % of the birds. Despite this, articles are still being written, such as one published in the journal Science in 2013, in which it is stated that these data are nothing more than “alarmist estimates”. Rigorously evaluating this issue is not easy.
To begin with, we are not even sure how many species there are. The United Nations Environment Program (UNEP) considers that the most reliable data are those of a study published in the journal PLOS Biology , in 2011, which states that there are 8,700,000 species. An immense amount if we take into account that only a million and a half have been cataloged. In addition, to know their rate of disappearance, it is necessary to know the current rate of extinction and the speed at which they were extinguished in the past. Information that is very difficult to obtain.
To declare an extinction without a shadow of a doubt is a challenge. There are examples of species that, despite being considered extinct, returned from the dead . There are also cases such as the Tasmanian tiger, whose loss is well documented, but which, even so, is supposedly sighted from time to time. In addition, to determine the average rate of disappearance of species in the past, known as the background extinction rate, it is necessary to resort to fossils, with all the difficulties that this entails.
In order to settle this issue, at the beginning of 2015 a group of experts from Stanford, Princeton and Berkeley universities, led by Gerardo Ceballos, from the Institute of Ecology of the Autonomous University of Mexico, decided to get to work to get there to a more or less definitive conclusion. Is it true that the rate of extinction has increased in recent decades ? Based on your results, yes.
To eliminate any possibility that their estimates were considered exaggerated, the experts limited the analysis to the best-studied group of organisms, vertebrates . In addition, “we use very high background extinction rates, which minimize the difference with the current ones,” explains Ceballos. “And we only took into account – he continues – species whose extinction was assured, not including others that are likely to have also been lost, although we are still not sure.”
Until today, no study has followed such conservative patterns, or yielded such disappointing results. “We did not expect them to be so bad,” confesses Ceballos. According to the article published in Science Advances , it would be normal for nine species of vertebrates to have disappeared since 1900. However, we lost 468 among mammals, birds, reptiles, amphibians and fish .
“It is a number that in other circumstances would have taken between 800 and 10,000 years to disappear,” he says. We are facing an extinction rate one hundred times higher than normal and “if we obtain such a high value using a conservative approach, which undoubtedly minimizes the problem, then the situation is really serious”, clarifies Ceballos. In this sense, Anthony Barnosky, a professor at the University of California at Berkeley and another of the study’s authors, proposes a simple exercise: “Look around you and kill half of everything you see.”
Man invades every corner of the planet
This is the true dimension of the problem and, for the first time in Earth’s history, the forces behind this disaster are not weather, volcanoes or a meteorite . The person responsible is Homo sapiens . An article published in mid-June 2015, in which Barnosky also participated, details why and how we have managed to destabilize the biosphere in such an incredible way. It is easy to summarize: “There is no place on Earth that has not been altered by human beings.”
The American Geological Society points out that we have transformed half of the available soil and there is little more than that of the deserts, the tundra, the great mountains and the odd patch of forest. Also, never so much carbon dioxide was released into the atmosphere. It is unprecedented and so geologically unusual that, as several experts recently explained in Oceanography magazine, it is likely to make this period “one of the most remarkable, if not cataclysmic, in the history of the planet.”
Perhaps we have become numb to a problem that we only see in the long term. But we must begin to worry, because we already live with “extinction rates comparable to those that existed when the dinosaurs disappeared ,” says Barnosky. And such a dramatic loss of biodiversity will endanger our very survival.
The vast majority of today’s species, ourselves included, evolved to cope with the climatic conditions that have existed for the past two million years. However, from now on, they will have to face very different scenarios. “The average temperature will perhaps be higher in 2070 than at any other time in human evolution,” adds the expert. If warming continues, the year 2100 will reach the highest temperatures in the last fourteen million years . The adaptations and survival strategies that favored the current species are unlikely to be of much help to them.
According to an article published in the journal Nature , if measures are not taken to mitigate climate change, between 38 % and 52 % of species will disappear . In fact, we have come so far that some changes are already inevitable, and will likely condemn between 22 % and 31 % of living beings. The current warming is so fast that no species will have time to adapt.
The only possibility, according to studies by Ken Caldeira, an ecologist at Stanford University, is that plants and animals move, to accompany their ideal temperature range. Some are already doing it: in the Andes, data collected by Kenneth Feeley, a tropical biologist at Florida International University in Miami, reveals that plants of the genus Schefflera are moving through the mountains at a rate of 100 feet a year .
Unfortunately, according to Caldeira, to keep up with the accelerating pace of climate change they would have to climb ten meters a day. Maybe some living being will do it, but the odds are slim. Even animals that move easily face cities, roads, dams or deforested areas , barriers that fragment the habitat and impede their progress.
A mass extinction means, in technical terms, the disappearance of 75 % or more of the planet’s species in a period of less than a million years. From a geological point of view, it is undoubtedly too much in too little time. But, for us, with a reduced life expectancy, it is neither a monumental nor a notorious event. “Most people have no idea that there is a problem, ” Barnosky laments.
The cycle of life at stake
Even those who are aware of it are not too scared. What does it matter if there are lions in Africa or frogs in Panama? But the truth, the expert points out, is that “for an ecosystem to be able to maintain balance, it needs species, because diversity ensures resilience (the ability of the ecosystem to overcome difficulties)”. When one species goes extinct, this delicate balance disappears, causing a cascading effect that threatens many others.
“Although we tend to forget it, our survival depends largely on the biological and geochemical systems that regulate the planet,” says Barnosky. All species play an important role. Biodiversity is one of the factors that sustains an infinity of resources that man needs to survive. Food, drinking water, wood, fibers, fuels and medicines are just a few examples of so-called ecosystem services. And any change that affects biodiversity can put access to these resources at risk .
An example: what would happen in Africa if there were no lions? Without a large predator lurking, the number of herbivores would most likely increase out of control. More mouths eating plants would give rise to important changes in the landscape, a gradual degradation of the vegetation cover, soil erosion and an increase in diseases related to parasites such as ticks, very common in these animals.
It would not be the first time that something like this has happened. Towards the end of the last Ice Age, almost all regions of the world were inhabited by animals that, to this day, we would consider gigantic. Mammoths , saber teeth or huge sloths disappeared , gradually, in a series of extinction pulses that some scientists associate with the arrival of human beings in their territories.
In Australia, the large herbivores became extinct 41,000 years ago . Without large animals to consume the vegetation, the forests grew and accumulated organic matter. The fires were more frequent and, according to the sediments of that time, caused drastic alterations in the landscape. Where once leafy species, typical of tropical forests, thrived, plants adapted to drier climates and with greater tolerance to fires, such as acacias, began to predominate.
“Two hundred years from now,” argues primatologist Jane Goodall in the newly released documentary Racing Extinction , “people are going to look back at this particular period in history and ask themselves: ‘How is it possible that did the people of that time allow all these wonderful creatures to disappear? For most scientists, “the enormous environmental problem we are facing derives from the excessive growth of the human population, ” explains Ceballos. And he adds: “It is imperative to stop it. If not, we may be lost ”.
Ceballos estimates that, in less than three generations, we will not have access to many ecosystem services. But avoiding a massive loss of biodiversity is “still possible if conservation efforts are intensified … We are the last generation with the power to make decisions, ” he argues. But whatever we do will establish the world we will live in for decades and centuries to come. There will be no turning back.
