The Causes n o i t c n i t x E of

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The Causes of Extinction Every species on Earth has a natural life span, and sooner or later will disappear. In recent decades, however, the rate of extinction, at least on continental mainlands and in sea freshwater ecosystems, has increased dramatically. Currently species are dying out at a rate between a hundred and a thousand times faster than in previous geological eras.

Some estimates predict that by 2100, 12% of birds, 25% of mammals, 30% of fish and 32% of amphibians will be definitively gone from our planet. According to renowned entomologist and botanist Edward O. Wilson, species—plants and animals, but also fungi, bacteria and other microbes—are disappearing at the rate of around 27,000 a year. That’s three every hour. The Red List produced by the International Union for Conservation of Nature (IUCN) tells us that over a third of all known species of flora and fauna in the world are at risk: one out of every eight birds, one out of every four conifers, one out of every three amphibians. A 2011 study by researchers at the University of Exeter in the UK calculated that the current loss of biodiversity could lead to the extinction of one in ten species by the end of this century. According to these experts, we are currently experiencing the sixth mass extinction. The fifth, 65 million years ago, brought about the end of the dinosaurs. But there is a major difference between this extinction and those of the past: the cause. The responsibility no longer lies with natural events. Instead, the leading role in this global ecological crisis is being played by humans.

32% 25%

30% 12%

There are five main reasons behind this dramatic and on-going loss of biodiversity:

1 Reduction of habitats Over half of all known plant and animal species are found in rainforests (in Borneo, in the Amazon, in Africa), but every year 10 million hectares (38,610 square miles) of rainforest are cut down or degraded, to make space for oil palm or soya plantations, to create new grazing land for extensive livestock farms, to obtain timber or to facilitate urbanization. This means an area the size of a football field is being cleared every two seconds. In one century, we have lost a billion hectares of forest. Between 1970 and 2000, the species living in temperate grasslands have been reduced by 10%, but during the same period tropical areas have lost 80% of their species.

2 Spread of invasive species The impact of invasive foreign species is immense, insidious and often irreversible. Plants and animals colonizing a new area is nothing new—it’s a part of evolution—but it used to happen slowly, restricted by ecological barriers like oceans, mountains, rivers and deserts. Over the past few centuries, however, the actions and trading of humans, facilitated by increasingly rapid means of transport, have allowed foreign species—mammals, plants, fish and fungi, but also bacteria and viruses—to rapidly travel over long distances, reaching new habitats and decimating local populations. One of the most tragic cases has been in Lake Victoria in East Africa. Nile perch was introduced to the lake in the 1960s. One of the 100 most invasive species in the world, it multiplied rapidly and, in just a few years, caused the extinction of over 200 native species, impoverishing the lake and worsening the local food situation. Insects, viruses and bacteria can also travel around the world. One of the most devastating examples has been the Citrus tristeza virus, which attacks citrus trees. Originally from Southeast Asia, it has spread quickly, causing epidemics in Florida, Argentina, Brazil, Venezuela and the Mediterranean basin. The affected trees wither away as their leaves fall, their branches dry out and their roots die. Already 70 million citrus plants have had to be cut down, including 40 million in Cyprus, Israel and Spain, the three worst-hit countries. No effective treatment has yet been developed.

3 Chemical pollution The success of industrial agriculture in terms of productivity is linked to the growing application of chemical fertilizers, herbicides, pesticides and fungicides, plus the use of hybrid seeds and selected animal breeds. Wheat yields have tripled, corn yields have quadrupled, potato yields have almost doubled, but these numbers are the result of the massive transfer of inorganic, non-renewable substances mined around the world, processed using energy from oil and showered on the countryside, often in exorbitant quantities. The excessive use of nitrogenous fertilizers has contaminated waterways with nitrates, which are very harmful to both humans and other animals. Atrazine, a herbicide used a few decades ago, is now emerging in aquifers and contaminating cities’ drinking water. Year after year, soil is being mineralized and its organic life jeopardized. Along with constant mechanized tilling, chemical compounds have made the soil less fertile and more compact, reducing its ability to absorb water and so threatening the hydrogeological equilibrium of specific areas. Yields have reached their maximum, often the soil can no longer absorb more fertilizer and herbicides are increasingly ineffective. The same pesticides have become less effective as parasites have developed resistance. According to the FAO, in 1957, there were 25 arthropods (insects, spiders, mites, millipedes and so on) showing resistance to at least one pesticide, while now there are 430. The consequences are also worrying for human health. Chemical compounds accumulate in the soil and in the fat tissue of animals that have drunk contaminated water and eaten contaminated fodder, hay and grains, and they can pass into milk and meat. The people who work and live in areas where pesticides are sprayed are more prone to degenerative diseases (particularly Parkinson’s and Alzheimer’s) and various types of cancer. The gravity of these impacts is underestimated and their incidence is growing in both western countries and in the global south. Environmental disasters in ocean ecosystems have increased due to the considerable presence of microplastics, as well as dioxins and PCBs, long-lasting contaminants identified by scientists as endocrine-disrupting chemicals, which threaten the reproductive systems of many fish species and the polar bears that feed on them.

4 World population growth It took humans 48,000 years to reach a population of one billion, a milestone which was passed in the early 1800s, when the majority of people on the planet lived in rural areas. By 1900, the population had reached 1.7 billion (with one-tenth concentrated in large cities in Europe and North America). Between 1950 and 1986, the population grew from 2.5 to 5 billion. In 2011, the world population reached 7 billion, and according to UN predictions, will stand at 11 billion by the end of 2100. In 1950, New York and Tokyo were the only cities with a population of over 10 million. Now there are more than 30. This growth has a devastating impact. According to some experts, from an ecological perspective humanity has been living on credit since 1987, meaning that since then, resources are being consumed faster than the planet can replenish them. At the same time, the amount of waste and pollution we produce far exceeds the planet’s ability to absorb it.

5 Overexploitation of biological resources Poaching and fishing represent a threat to many animal species. Poaching, for example, is putting at risk of extinction the African elephant, due to the illegal ivory trade; as well as the rhinoceros, whose horn is sought after for its supposed medicinal and aphrodisiac properties; various species of tiger, hunted for their skin and their bones and flesh, used in Chinese medicines; many species of lemurs in Madagascar and no shortage of other animals. But an even more serious situation is facing the oceans. Between 1950 and 1990, the quantity of fish caught in the world quintupled, from 17 million to 84 million tons, thanks to increasingly efficient technology. In the 1940s, California’s sardine fishery collapsed, in the 1970s the Peruvian anchoveta, while in 1993 cod disappeared from Canadian waters. In recent years, the stocks of sole in the Irish Sea, Atlantic salmon, bluefin tuna, swordfish, sharks and rays have all fallen dramatically. Humans are also exploiting inland waterways and groundwater. One of the most chilling examples is the Aral Sea, on the border between Uzbekistan and Kazakhstan. Before 1960, it covered 68,000 square kilometers (26,255 square miles), but then the Soviet government diverted its rivers to irrigate cotton and to fill reservoirs, reducing the lake to 10% of its original size. The water level has fallen by 16 meters (52 feet), 20 out of its 24 species have disappeared, and the local fishing industry, which employed 60,000 people, has been wiped out. The chemical products used in cotton cultivation contaminated the remaining water, leaving it undrinkable.

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