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In the Great Lakes overfishing has caused whitefish, walleye, and sturgeon populations to decline. Beyond their role in the food supply, freshwater and marine fish are also trapped for the aquarium trade and fished for sport.

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Phase two of the Sixth Extinction began around 10,000 years ago with the invention of agriculture-perhaps first in the Natufian culture of the Middle East. Agriculture appears to have been invented several different times in various different places, and has, in the intervening years, spread around the entire globe. Agriculture represents the single most profound ecological change in the entire 3.5 billion-year history of life. With its invention:

-humans did not have to interact with other species for survival, and so could manipulate other species for their own use

-humans did not have to adhere to the ecosystem’s carrying capacity, and so could overpopulate
Humans do not live with nature but outside it.

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Overexploitation of plants.

Plants are vital to our survival and are the foundation of most of the Earth’s ecosystems. People harvest plants for food, medicine, building materials, and as raw materials for making other products.  But we are taking too many plants from the wild. Some plants, such as orchids, are so prized by collectors that they are now endangered and  legally protected from poaching by international law. Some medicinal plants, such as American ginseng, have also been so enthusiastically collected that it is now very hard to find them in the wild. A number of tree species that are prized for their wood, such as mahogany, are under threat because of overharvesting.

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Until mankind's big expansion some 500 years ago, mammal extinctions were very rare: on average, just two species died out every million years.

But in the last five centuries, at least 80 out of 5,570 mammal species have bitten the dust, providing a clear warning of the peril to biodiversity.

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Overexploitation of mammals

Reptiles are harvested and traded around the world for their skins or shells, their eggs, meat, and for the pet trade. Overharvesting of the Kemp’s ridley sea turtle’s eggs nearly led to its extinction, and today it is still an endangered species. In the U.S., box turtles are being collected at unsustainable levels for the overseas pet trade. Some reptile skins—such as crocodile, python and monitor lizard—are highly prized as exotic leathers.

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The first phase began shortly after Homo sapiens evolved in Africa and the anatomically modern humans began migrating out of Africa and spreading throughout the world. Humans reached the middle east 90,000 years ago. They were in Europe starting around 40,000 years ago. Neanderthals, who had long lived in Europe, survived our arrival for less than 10,000 years, but then abruptly disappeared — victims, according to many paleoanthropologists, of our arrival through outright warfare or the more subtle, though potentially no less devastating effects, of being on the losing side of ecological competition.Everywhere, shortly after modern humans arrived, many (especially, though by no means exclusively, the larger) native species typically became extinct. Humans were like bulls in a China shop:

They disrupted ecosystems by overhunting game species, which never experienced contact with humans before.

And perhaps they spread microbial disease-causing organisms as well.

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This shows how marine species, terrestrial species, and fresh water species have declined over the years.

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Birds are collected or hunted for sport,  food and the cage-bird pet trade (parrots and songbirds are prized as pets). Millions of birds are traded internationally each year. Close to 30% of globally threatened birds are threatened by overexploitation, particularly parrots, pigeons and pheasants. The Carolina parakeet was once the only species of parrot in the U.S., but it was hunted to extinction early in the last century for food, to protect crops and for its feathers (which adorned ladies’ hats).

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Alaska's dynamic, often ice-covered seas are home to a remarkable diversity of life-crustaceans, fish, seals, sea lions, porpoises, whales, and more. Few places in the world offer such beauty and bounty. This region of nearly 1.5 million square miles includes waters in the Gulf of Alaska, Bering Sea, Aleutian Islands, Chukchi Sea, and Beaufort Sea.

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Animals are mostly dying out because of habitat destruction done by humans, hunting, and species introductions/invasions.

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A majority of the nation's biologists are convinced that a "mass extinction" of plants and animals is underway that poses a major threat to humans in the next century, yet most Americans are only dimly aware of the problem, a poll says.

The rapid disappearance of species was ranked as one of the planet's gravest environmental worries, surpassing pollution, global warming and the thinning of the ozone layer, according to the survey of 400 scientists commissioned by New York's American Museum of Natural History.

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When the population of a species grows beyond the capacity of its environment to sustain it, it reduces that capacity below the original level, ensuring an eventual population crash.

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- Noise Pollution Sound waves from ships, sonar devices and oil rigs can travel for miles disrupting migration, communication, hunting and reproduction patterns of many marine animals. The deafening noise of gas and oil explorations are so loud that they are causing devastating effects to the sea life residing in our world’s oceans such as mass strandings, reckless diving, the inability to find food and chronic stress. Extreme noise pollution has been known to kill hundreds of dolphins and whales at a time, many of which are already on the brink of extinction.

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Species are going extinct because of deforestation. Deforestation includes fires, clear-cutting for agriculture, ranching and development, unsustainable logging for timber, and degradation due to climate change. Forests play a critical role in mitigating climate change because they act as a carbon sink—soaking up carbon dioxide that would otherwise be free in the atmosphere and contribute to ongoing changes in climate patterns.

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Spix's macaw (or little blue macaw; Cyanopsitta spixii)

What: Bright blue birds with long tails and grey/white heads

Domain: Brazil

Population: The last known wild bird disappeared in 2000; there are 78 in captivity

Main threats: Destruction of the birds' favoured Tabebuia caraiba trees for nesting, and trapping

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Another animal that is on the verge of extinction is the Mountain Gorriilla. As humans have moved into areas near mountain gorillas, they have cleared land for agriculture and livestock. Even land within protected areas is not safe from clearing—in 2004, for example, illegal settlers cleared 3,700 acres of gorilla forest in Virunga National Park.

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Because of human over population the Atlantic bluefin tuna is going extinct. Marine fish provide 15 percent of all animal protein consumed by human beings. Fisheries management, however, has been outpaced by our population growth, causing global fisheries to collapse under the unsustainable pressure. A 2009 assessment found that 80 percent of global fish stocks are either overly and fully exploited or have collapsed. Though a catch reduction of 20-50 percent is needed to make global fisheries sustainable, the demand for fish is expected to increase by 35 million tons by 2030.
Of greatest concern is the western Atlantic bluefin tuna that spawns in the Gulf of Mexico and has declined by more than 80 percent since 1970 due to overharvesting. Prized as a sushi fish around the world, it has become more valuable as it has become rare. One fish in 2011 sold for $396,000. The large, warm-blooded bluefin tuna is a common, upscale sushi menu item and has been severely overfished. The Atlantic bluefin, like so many other ocean species, is threatened by humans’ ravenous appetites: Demand far exceeds sustainable fishing levels.

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Black Carbon

According to Science Daily, scientists estimate that 25 to 35 of black carbon in the global atmosphere was emitted by China and India from the burning of wood and cow dung in household cooking and coal to heat homes (see an earlier post). Nations that rely heavily on diesel fuel for transportation also contribute large amounts.

Wired Science reported that over the last century, Arctic temperatures have risen by an estimated 3.4-degree-Fahrenheit, and scientists estimate that half of this rise can be attributed to black-carbon pollution. It’s likely that black carbon has altered weather patterns in a way that’s reduced rainfall over South Asia and West Africa.  Also, scientists believe that black carbon has played a role in causing Himalayan glaciers to melt, threatening water supplies for hundreds of millions of people

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Some fish are migrating to cooler waters already. Black sea bass, once most common off the coast of Virginia, have moved up to New Jersey. Less fortunate species may not be able to find new ranges. At the same time, carbon emissions are altering the chemistry of seawater, making it more acidic.

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The current mass extinction is different from past events in several ways. First, it is happening much more quickly: each of the "Big Five" played out over thousands of years, but the current mass extinction is likely to be concentrated within 200 years. By the end of the 21st century, we may have lost two-thirds of the species on Earth (footnote 16). Second, past mass extinctions are thought to have been caused by natural phenomena such as the shifting of continents, comet or meteoroid impacts, or climate change independent of human influence, or some combination of these factors. In contrast, as we will see below, humans are causing the current mass extinction.

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- Ingestion of Plastic Around 100 million tons of plastic is produced every year, of which 1 percent ends up in the sea. Ocean litter comes from many sources, including trash that washes off city streets, waste blown in from landfills and containers that fall off ships during heavy storms. Once in the water, the debris accumulates in large patches, travels with currents and washes up onshore. This litter is frequently consumed, often with fatal effects, by marine mammals, fish and birds who mistake it for food.

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Unlike past mass extinctions, caused by events like asteroid strikes, volcanic eruptions, and natural climate shifts, the current crisis is almost entirely caused by us — humans.

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In the past 500 years, we know of approximately 1,000 species that have gone extinct, from the woodland bison of West Virginia and Arizona’s Merriam’s elk to the Rocky Mountain grasshopper, passenger pigeon and Puerto Rico’s Culebra parrot — but this doesn’t account for thousands of species that disappeared before scientists had a chance to describe them [4]. Nobody really knows how many species are in danger of becoming extinct. Noted conservation scientist David Wilcove estimates that there are 14,000 to 35,000 endangered species in the United States, which is 7 to 18 percent of U.S. flora and fauna. The IUCN has assessed roughly 3 percent of described species and identified 16,928 species worldwide as being threatened with extinction, or roughly 38 percent of those assessed.

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In addition to tracking extinction rates, scientists can look at population decline and habitat loss trends to estimate how quickly Earth's biodiversity levels are changing. To date, about 50 percent of the planet's natural habitats have been cleared for human use, and another 0.5 to 1.5 percent of nature is lost each year. Ongoing and current mass extinctions have been documented for many groups of organisms, including marine and freshwater fish, amphibians, and European farmland birds and macrofungi.

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Pesticides & Fertilizers:

Pesticides and fertilizers on farms has increased by 26-fold over the past 50 years, fueling increases in crop production globally. Indiscriminate pesticide and fertilizer application may pollute nearby land and water, and chemicals may wash into nearby streams, waterways and groundwater when it rains. Pesticides can kill non-target organisms, including beneficial insects, soil bacteria and fish. Fertilizers are not directly toxic, but their presence can alter the nutrient system in freshwater and marine areas. This alteration can result in an explosive growth of algae due to excess nutrients. As a result, the water is depleted of dissolved oxygen, and fish and other aquatic life may be killed

Noise & Light Pollution:

Artificial light/noise drown out natural landscapes. In the Arctic, the sounds of oil and gas explorations are so loud that belugas, bowhead whales and other sea life have had difficulty feeding and breeding. Light pollution disrupts circadian rhythms for both humans and animals alike and may even contribute to the development of cancer. Light pollution also can impact sea turtles. Adult and hatchling sea turtles are drawn toward lights along the beach, thinking they are heading toward the moon. Coastal developments, therefore, are encouraged to turn

Algal Blooms/Dead Zones:

Human activities, especially agriculture, have led to large increases in the levels of nitrogen and phosphorus in the environment. In water, this overabundance of nutrients, a process called eutrophication, can fuel the excessive growth of phytoplankton and algae, which can sometimes have devastating consequences. Harmful algal blooms—blooms of species that produce deadly toxins and sometimes known as “red tides” or “brown tides” for their appearance in the water—can kill fish, marine mammals and seabirds and harm humans. And when the algae and other organisms that had been allowed to bloom because of the nutrient excess eventually die off, bacteria may suck up all the oxygen from the water as the algae decompose. This hypoxia creates a “dead zone” where fish cannot live. More than 400 areas around the

Acid Rain:

When water in the atmosphere mixes with certain chemicals—particularly sulfur dioxide and nitrogen oxides emitted during the burning of fossil fuels—mild acidic compounds are formed. This acid rain can leach toxic aluminum from the soil, which at low levels can stress fish in lakes and streams or, at higher concentrations, kill them outright. Acid rain also weakens trees in forests and contributes to air pollution that can harm humans.

Ocean Garbage Patches:

Plastics and other marine debris that can float may persist in the oceans for years, traveling the currents. Some of this material accumulates in the centers of ocean gyres, creating great garbage patches. ¨Garbage patch” brings to mind floating islands of trash, but little of the debris can be seen on the surface. Garbage patches, instead, are areas where concentrations of flotsam and jetsam, mostly small pieces of plastic, are particularly high. Litter can distribute toxic chemicals throughout the oceans, snag/ tear corals, and harm animals if they eat pieces of plastic or become entangled in the debris.

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Several lines of evidence suggest that Earth is experiencing a sixth mass extinction today. Estimates of extinction rates are imprecise for many reasons. In particular, they are extrapolated from a few well-known groups with relatively few species, such as birds and large mammals, to other groups for which there is little data—for example, fungi. However, there is wide agreement that current rates of extinction are at least several hundred times greater than historical background levels. Most scientific studies estimate that in the near term, extinction rates could rise by three to four orders of magnitude above past averages (footnote 15).

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the meat industry causes 18% of our greenhouse emissions

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extinction by humans today is becoming much more rapid.

The rapid loss of species today is estimated by some experts to be between 100 and 1,000 times higher than the natural extinction rate, while others estimate rates as high as 1,000-11,000 times higher.

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Ecologists, zoologists and other scientists believe that, without urgent steps to stem the losses, we are facing global scale tipping points from which we may never look back or recover. Many animals are threatened with human-caused extinction now, with researchers expressing particular concern over amphibian and invertebrate (creatures without a backbone) losses.

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Golden coqui frog (Eleutherodactylus jasperi)

What: Small orange frog living in forest or open rocky areas

Domain: Sierra de Cayey, Puerto Rico

Population: No sightings since 1981
Main threats: Unknown but suspected habitat destruction, climate change, disease (chytridiomycosis) and invasive predators

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Wetlands are dredged and filled in to accommodate urban, industrial, and agricultural development. Cities, factories, and farms create waste, pollution, and chemical effluent and runoff that can wreak havoc on reefs, sea grasses, birds, and fish.

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Unlike past mass extinctions, caused by events like asteroid strikes, volcanic eruptions, and natural climate shifts, the current crisis is almost entirely caused by us — humans. In fact, 99 percent of currently threatened species are at risk from human activities, primarily those driving habitat loss, introduction of exotic species, and global warming [3]. Because the rate of change in our biosphere is increasing, and because every species’ extinction potentially leads to the extinction of others bound to that species in a complex ecological web, numbers of extinctions are likely to snowball in the coming decades as ecosystems unravel.

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In the jargon it's an "Anthropocene defaunation," or sixth mass extinction, and one caused by humans. Scientists can't be sure of the current die-off rate, perhaps because much of it is happening to beetles and other insects that are notoriously overlooked. But according to that new study in Science, the total number of such invertebrates fell by half over the past 35 years while the human population doubled. Other recent studies suggest that the current extinction rate is roughly 1,000 times faster than the average pace in Earth's history. That makes this the fastest extinction event on record, even if it is not yet a mass die-off.

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hunting endangered species for consumer products

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Carbon Dioxide - High levels of atmospheric carbon dioxide, caused mainly by the burning of fossil fuels, are absorbed by the oceans, where the gas dissolves into carbonic acid. This elevated acidity inhibits the ability of marine animals, including many plankton organisms, to create shells, disrupting life within the very foundation of the ocean's food web.

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In around 300 years time, 75% of all mammal species will have disappeared from this planet. That's the startling prediction from Anthony Barnosky, a palaeobiologist at the University of California, Berkeley – that’s if the current rates of extinction continue and the animals already threatened or endangered are wiped out this century.

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Draining Rivers

The Aral Sea, located on the Uzbekistan-Kazakhstan border, was once the fourth largest lake, but has now shrunk by 75 percent.  The Aral Sea was once fed by two major rivers which now, due to human activity, run dry before they reach the lake. In the early 1960’s. The reduced water flow caused salt concentrations to increase, making it inhabitable for the fish species that once lived there.  The Aral Sea used to absorb heat during the summer and keep the temperature mild during the winters, but now that it is drying up, the local climate is changing.  The summers are now longer and hotter and the winters are colder. Scientists believe that the northwest Mediterranean once supported a vibrant array of plant and animal species.  Today, however, the stripped-down ecosystem is dominated by bacteria and jellyfish, which exhibit a reduced capacity to regulate flows of nutrients and energy.

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Habitat Destruction - Humans destroy wild land to build homes, factories, shopping malls, amusement parks, garbage dumps, even to build a visitor center, store and restaurant in a park, the land is changed. The animals that once lived there, from the bugs that lived in the ground to the birds that ate them, all are disappearing.

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only 2-4% of the species that have ever lived on Earth are thought to be alive today.

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Habitat loss

Proximate causes

The chief proximate causes of habitat destruction are:

Conversion of natural habitat for agricultural use including crops and grazing activity

Pollution, especially chemical herbicide and pesticide use, water pollution, air pollution and acid rain

Urban development and infrastructure, including roads, power plants, desert solar arrays, pipelines and transmission lines

Timber harvesting and slash-and-burn practices leading to deforestation

Introduction of alien species

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The invertebrate population has decreased by half in the last 35 years, while the human population has doubled.

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Burning of fossil fuels and toxic gases produced in factories causes pollution. Air pollution infects the environment and threatens the health of all who inhabit the earth. According to the United Nations, "The estimations we have now tell us there are 3.5 million premature deaths every year caused by household air pollution, and 3.3 million deaths every year caused by outdoor air pollution."

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Of about 6 to 10 million currently existing species, we have still only identified 1 million; we know more about vertebrate species than we do about plants and insects. But for groups that we know well, knowledge of very recent species extinctions -- and for current species, their ranges and the threats to them -- allows us to be certain that extinction rates are comparable to those of the great past extinctions. For example, for birds, of about 10,000 species worldwide, at least 128 have disappeared in the last 500 years, about 1,200 are currently seriously threatened with extinction (all but three from human activities); there is a real prospect of the loss of 500 bird species within this century

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Frogs are on the verge of extinction because of the artificial environment that we've created. This extinction is unlike the five that came before it, according to the paper's authors from UC Berkeley, because it has nothing to do with any asteroid impact, or volcanic surge, or great sea cooling. Instead, it may have almost everything to do with us. Amphibians made it through last time, when the dinosaurs disappeared. But with new, people-driven pressures on biodiversity, the survivors are now some of the most vulnerable.

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Unlike past mass extinctions, caused by events like asteroid strikes, volcanic eruptions, and natural climate shifts, the current crisis is almost entirely caused by us — humans. In fact, 99 percent of currently threatened species are at risk from human activities, primarily those driving habitat loss, introduction of exotic species, and global warming [3]. Because the rate of change in our biosphere is increasing, and because every species’ extinction potentially leads to the extinction of others bound to that species in a complex ecological web, numbers of extinctions are likely to snowball in the coming decades as ecosystems unravel. In the past 500 years, we know of approximately 1,000 species that have gone extinct,

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The Holocene extinction, sometimes called the Sixth Extinction, is a name proposed to describe the currently ongoing extinction event of species during the present Holocene epoch (since around 10,000 BCE) mainly due to human activity. The large number of extinctions span numerous families of plants and animals including mammals, birds, amphibians, reptiles and arthropods. Although 875 extinctions occurring between 1500 and 2009 have been documented by the International Union for Conservation of Nature and Natural Resources,[1] the vast majority are undocumented. According to the species-area theory and based on upper-bound estimating, the present rate of extinction may be up to 140,000 species per year.[2]

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Globally, 21 percent of the total evaluated reptiles in the world are deemed endangered or vulnerable to extinction by the IUCN — 594 species — while in the United States, 32 reptile species are at risk, about 9 percent of the total.

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Farming

As the world’s population continues to grow exponentially, so does the amount of farmland needed to provide sufficient food.  According to the UN Food and Agriculture Organization (FAO), over 40 percent of Earth’s surface is now comprised of agricultural lands, and a large portion of these lands were once covered by forests.  Much of Europe, for example, was once covered with dense temperate forests, but over time population growth-driven deforestation has led to more farm land.

Fertilizers, Their use has injected vast amounts of nitrogen and phosphorous into regional ecosystems.These practices add a tremendous amount of nitrogen and phosphorus to the biosphere than would occur naturally.  Runoff from farmland often carries large amounts of fertilizer into rivers and streams which eventually drain into the sea.  The increase of these elements to ocean ecosystems has been detrimental and is fueling rapidly growing marine dead zones.

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Deforestation is clearing Earth's forests on a massive scale, often resulting in damage to the quality of the land. Forests still cover about 30 percent of the world’s land area, but swaths the size of Panama are lost each and every year.The world’s rain forests could completely vanish in a hundred years at the current rate of deforestation.Forests are cut down for many reasons, but most of them are related to money or to people’s need to provide for their families.The biggest driver of deforestation is agriculture. Farmers cut forests to provide more room for planting crops or grazing livestock. Often many small farmers will each clear a few acres to feed their families by cutting down trees and burning them in a process known as “slash and burn” agriculture.

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Deforestation is clearing Earth's forests on a massive scale, often resulting in damage to the quality of the land. Forests still cover about 30 percent of the world’s land area, but swaths the size of Panama are lost each and every year.The world’s rain forests could completely vanish in a hundred years at the current rate of deforestation.Forests are cut down for many reasons, but most of them are related to money or to people’s need to provide for their families.The biggest driver of deforestation is agriculture. Farmers cut forests to provide more room for planting crops or grazing livestock. Often many small farmers will each clear a few acres to feed their families by cutting down trees and burning them in a process known as “slash and burn” agriculture.

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Birds

Birds occur in nearly every habitat on the planet and are often the most visible and familiar wildlife to people across the globe. As such, they provide an important bellwether for tracking changes to the biosphere. Declining bird populations across most to all habitats confirm that profound changes are occurring on our planet in response to human activities.

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Carbon Dioxide Emissions

The human activity most widely viewed as changing the planet is the burning of fossil fuels.  In order to produce the energy that drives the world’s economy, countries rely on carbon-rich energy sources like coal, oil, and gas.  By burning these materials, 40 billion tons of carbon dioxide are added into the atmosphere each year.  Right now, atmospheric levels of carbon dioxide are higher than any time in the last 15 million years. Carbon dioxide is a heat-trapping gas, and as a result of these atmospheric changes, average temperatures on the planet are rising and global weather patterns are changing.  Some of the carbon dioxide in the atmosphere is absorbed into the oceans, and has altered the acidity of the water.  This change has had far reaching affects on oceanic ecosystems and the food chains that support underwater plant and animal life.

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Causes of Ocean Habitat Loss

Natural causes followed with human destruction:

Wetlands are dredged and filled in to accommodate urban, industrial, and agricultural development. Cities, factories, and farms create waste, pollution, and chemical effluent and runoff that can wreak havoc on reefs, sea grasses, birds, and fish.

Inland dams decrease natural nutrient-rich runoff, cut off fish migration routes, and curb freshwater flow, increasing the salinity of coastal waters. Deforestation far from shore creates erosion, sending silt into shallow waters that can block the sunlight coral reefs need to thrive.

Destructive fishing techniques like bottom trawling, dynamiting, and poisoning destroy habitats near shore as well as in the deep sea.

Tourism is another cause since boats go out into ocean very often for viewing purposes.

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Meanwhile, we've been artificially boosting the populations of certain select species, such as cows, dogs, rice, maize and chickens – most of which have been bred to create new varieties radically different from their wild ancestors.

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Climate Change

Perhaps the most devastating of all habitat-altering agents, however, is climate change. Scientists are still coming to grips with the consequences that excessive atmospheric carbon dioxide and Earth's rapid warming are having on ecosystems. But there is ample evidence indicating that the oceans are bearing the brunt of these changes.

As Earth's temperature rises, it is primarily the oceans that absorb the extra heat. Even small temperature changes can have far-reaching effects on the life cycles of marine animals from corals to whales.

In addition, warmer temperatures cause excess melting of ice caps and glaciers, raising sea levels and flooding estuaries.

High levels of atmospheric carbon dioxide, caused mainly by the burning of fossil fuels, are absorbed by the oceans, where the gas dissolves into carbonic acid. This elevated acidity inhibits the ability of marine animals, including many plankton organisms, to create shells, disrupting life within the very foundation of the ocean's food web.

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We've also been spreading pests and diseases from place to place, often causing local extinctions

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Since we have become such a dominant force on our planet, we have to decide how best to manage the situation we're creating. Many are calling for a change in the way that conservation has traditionally been practiced. Instead of battling to return ecosystems to a pre-human state, as previous efforts have tried to do, some conservationists say we should be realistic and recognise that humans are an integral part of many ecosystems now. In many cases, they argue, we should accept ecosystems that incorporate non-native species, value them and try to conserve them as “novel ecosystems” that are worth protecting.

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Today, there is widespread concern that the ozone layer is deteriorating due to the release of pollution containing the chemicals chlorine and bromine. Such deterioration allows large amounts of ultraviolet B rays to reach Earth, which can cause skin cancer and cataracts in humans and harm animals as well.

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Today, there is widespread concern that the ozone layer is deteriorating due to the release of pollution containing the chemicals chlorine and bromine. Such deterioration allows large amounts of ultraviolet B rays to reach Earth, which can cause skin cancer and cataracts in humans and harm animals as well.

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Deforestation is also one of the leading causes of habitat loss. For centuries, humans have altered landscapes, through deforestation, fire and over-use.

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Urbanization has dramatically increased the rate of habitat loss and change.

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Unlike past mass extinctions, caused by events like asteroid strikes, volcanic eruptions, and natural climate shifts, the current crisis is almost entirely caused by us — humans.

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The population of any given animal among the five million or so species on the planet is, on average, 28 percent smaller, thanks to humans. And as many as one third of all animals are either threatened or endangered

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Barnosky calculates that humans are now creating a mass extinction on the same scale – the planet's sixth one – through a combination of habitat encroachment and fragmentation, hunting, climate change, pollution, and the spread of disease and introduced species. As many as 30% of all species may be lost over the next four decades, conservationists estimate.

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Extinction is actually a natural and common phenomenon – of the roughly 4 billion species estimated to have evolved on Earth, some 99% are gone. In the past, the extinction rate has been balanced by the evolution of new species, but the current, human-caused extinction is happening so fast that evolution cannot keep pace. Barnosky estimates that the current rate is 1,000 times the natural rate, putting it easily on a par with the so-called “big 5” mass extinction events.

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Our species caused 322 animal extinctions over the past 500 years, with two-thirds of those occurring in the last two centuries, Many animals are threatened with human-caused extinction now, with researchers expressing particular concern over amphibian and invertebrate (creatures without a backbone) losses. Numbers of the latter group have nearly halved as our population doubled in size over the past 35 years.

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Frogs, toads, and salamanders are disappearing because of habitat loss, water and air pollution, climate change, ultraviolet light exposure, introduced exotic species, and disease.

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Humans annually absorb 42 percent of the Earth’s terrestrial net primary productivity, 30 percent of its marine net primary productivity, and 50 percent of its fresh water.

Forty percent of the planet’s land is devoted to human food production, up from 7 percent in 1700 .

Fifty percent of the planet’s land mass has been transformed for human use .

More atmospheric nitrogen is now fixed by humans that all other natural processes combined

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The Holocene extinction, sometimes called the Sixth Extinction, is a name proposed to describe the currently ongoing extinction event of species during the present Holocene epoch (since around 10,000 BCE) mainly due to human activity. Only during these most recent parts of the extinction have plants also suffered large losses. Overall, the Holocene extinction can be characterized by the human impact on the environment.

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As the population of humans increases, the extinctions of organisms also increases.

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We're in the midst of the Earth's sixth mass extinction crisis. Harvard biologist E. O. Wilson estimates that 30,000 species per year (or three species per hour) are being driven to extinction. Compare this to the natural background rate of one extinction per million species per year, and you can see why scientists refer to it as a crisis unparalleled in human history.

The current mass extinction differs from all others in being driven by a single species rather than a planetary or galactic physical process. When the human race - Homo sapiens sapiens - migrated out of Africa to the Middle East 90,000 years ago, to Europe and Australia 40,000 years ago, to North America 12,500 years ago, and to the Caribbean 8,000 years ago, waves of extinction soon followed. The colonization-followed-by-extinction pattern can be seen as recently as 2,000 years ago, when humans colonized Madagascar and quickly drove elephant birds, hippos, and large lemurs extinct [1].

Lange's metalmark butterfly from Amy Harwood.

The first wave of extinctions targeted large vertebrates hunted by hunter-gatherers. The second, larger wave began 10,000 years ago as the discovery of agriculture caused a population boom and a need to plow wildlife habitats, divert streams, and maintain large herds of domestic cattle. The third and largest wave began in 1800 with the harnessing of fossil fuels. With enormous, cheap energy at its disposal, the human population grew rapidly from 1 billion in 1800 to 2 billion in 1930, 4 billion in 1975, and over 7.5 billion today. If the current course is not altered, we'll reach 8 billion by 2020 and 9 to 15 billion (likely the former) by 2050.

No population of a large vertebrate animal in the history of the planet has grown that much, that fast, or with such devastating consequences to its fellow earthlings. Humans' impact has been so profound that scientists have proposed that the Holocene era be declared over and the current epoch (beginning in about 1900) be called the Anthropocene: the age when the "global environmental effects of increased human population and economic development" dominate planetary physical, chemical, and biological conditions [2].

Humans annually absorb 42 percent of the Earth's terrestrial net primary productivity,30 percent of its marine net primary productivity, and 50 percent of its fresh water [3].

Forty percent of the planet's land is devoted to human food production, up from 7 percent in 1700 [3].

Fifty percent of the planet's land mass has been transformed for human use [3].

More atmospheric nitrogen is now fixed by humans that all other natural processes combined [3].

The authors of Human Domination of Earth's Ecosystems, including the current director of the National Oceanic and Atmospheric Administration, concluded:

"[A]ll of these seemingly disparate phenomena trace to a single cause: the growing scale of the human enterprise. The rates, scales, kinds, and combinations of changes occurring now are fundamentally different from those at any other time in history. . . . We live on a human-dominated planet and the momentum of human population growth, together with the imperative for further economic development in most
of the world, ensures that our dominance will increase."

Predicting local extinction rates is complex due to differences in biological diversity, species distribution, climate, vegetation, habitat threats, invasive species, consumption patterns, and enacted conservation measures. One constant, however, is human population pressure. A study of 114 nations found that human population density predicted with 88-percent accuracy the number of endangered birds and mammals as identified by the International Union for the Conservation of Nature [4]. Current population growth trends indicate that the number of threatened species will increase by 7 percent over the next 20 years and 14 percent by 2050. And that's without the addition of global warming impacts.
When the population of a species grows beyond the capacity of its environment to sustain it, it reduces that capacity below the original level, ensuring an eventual population crash.
"The density of people is a key factor in species threats," said Jeffrey McKee, one of the study's authors. "If other species follow the same pattern as the mammals and birds... we are facing a serious threat to global biodiversity associated with our growing human population." [5].

So where does wildlife stand today in relation to 7.5 billion people? Worldwide, 12 percent of mammals, 12 percent of birds, 31 percent of reptiles, 30 percent of amphibians, and 37 percent of fish are threatened with extinction [6]. Not enough plants and invertebrates have been assessed to determine their global threat level, but it is severe.

Extinction is the most serious, utterly irreversible effect of unsustainable human population. But unfortunately, many analyses of what a sustainable human population level would look like presume that the goal is simply to keep the human race at a level where it has enough food and clean water to survive. Our notion of sustainability and ecological footprint - indeed, our notion of world worth living in - presumes that humans will allow for, and themselves enjoy, enough room and resources for all species to live.

REFERENCES CITED

1. Eldridge, N. 2005. The Sixth Extinction. ActionBioscience.org.

2. Crutzen, P. J. and E. F. Stoermer. 2000. The 'Anthropocene'. Global Change Newsletter 41:17-18, 2000; Zalasiewicz, J. et al. 2008. Are We Now Living in the Anthropocene?. GSA Today (Geological Society of America) 18 (2): 4-8.

3. Vitousek, P. M., H. A. Mooney, J. Lubchenco, and J. M. Melillo. 1997. Human Domination of Earth's Ecosystems. Science 277 (5325): 494-499; Pimm, S. L. 2001. The World According to Pimm: a Scientist Audits the Earth. McGraw-Hill, NY; The Guardian. 2005. Earth is All Out of New Farmland. December 7, 2005.

4. McKee, J. K., P. W. Sciulli, C. D. Fooce, and T. A. Waite. 2004. Forecasting Biodiversity Threats Due to Human Population Growth. Biological Conservation 115(1): 161-164.

5. Ohio State University. 2003. Anthropologist Predicts Major Threat To Species Within 50 Years. ScienceDaily, June 10, 2003.

6. International Union for the Conservation of Nature. 2009. Red List.

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We're in the midst of the Earth's sixth mass extinction crisis. Harvard biologist E. O. Wilson estimates that 30,000 species per year (or three species per hour) are being driven to extinction. Compare this to the natural background rate of one extinction per million species per year, and you can see why scientists refer to it as a crisis unparalleled in human history.

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Life depends heavily on the supply of fresh water that exists in rivers, lakes, and aquifers. It’s estimated that one fourth of Earth’s river basins run dry before ever reaching the ocean. This is the result of reduced rainfall caused by deforestation and the construction of man-made dams.  Less water flowing through river basins has also altered local weather patterns.

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we've been artificially boosting the populations of certain select species, such as cows, dogs, rice, maize and chickens – most of which have been bred to create new varieties radically different from their wild ancestors.

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It’s frightening but true: Our planet is now in the midst of its sixth mass extinction of plants and animals — the sixth wave of extinctions in the past half-billion years. We’re currently experiencing the worst spate of species die-offs since the loss of the dinosaurs 65 million years ago. Scientists estimate we’re now losing species at 1,000 to 10,000 times the background rate, with literally dozens going extinct every day [1].

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An alarmingly large hole in the Earth’s protective covering of atmospheric ozone appears over the Antarctic. Toxic hazes settle over major cities. Once fertile areas of the planet become desert, never to be green again within our lifetimes.

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An alarmingly large hole in the Earth’s protective covering of atmospheric ozone appears over the Antarctic. Toxic hazes settle over major cities. Once fertile areas of the planet become desert, never to be green again within our lifetimes.

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Plastic Production

Technological development has led to the invention of new materials, such as plastics, that were previously unknown to the planet.  Many of these new materials are made up of chemical compounds that can remain active in the environment for thousands of years and have lasting impacts on the delicate regulatory cycles and ecosystems.  Today, the world produces approximately 60 billion tons of plastics each year, and traces of their existence can be found around the globe, even in areas with no human activity.  The United Nations estimates that for every square mile of ocean, there are approximately 47,000 pieces of plastic.

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No group of animals has a higher rate of endangerment than amphibians. Scientists estimate that a third or more of all the roughly 6,300 known species of amphibians are at risk of extinction [6]. The current amphibian extinction rate may range from 25,039 to 45,474 times the background extinction rate

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Reef Destruction

Ocean reefs make up the foundation of many marine ecosystems, and their demise is disturbing the flow of nutrients and energy that support animal and plant life in our oceans.  As a result of water pollution, ocean acidification, overfishing, and climate change, experts estimate that one-quarter of global reef cover has been lost in the last 50 years and one-third of reef species are endangered.  Scientists believe that massive ocean extinction events in the past caused fluctuations in the Earth’s carbon cycle that led to changes in climate and weather.  The continued destruction of reefs and disruption of ocean food chains jeopardizes the stability of Earth’s critical regulatory systems.

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The first wave of extinctions targeted large vertebrates hunted by hunter-gatherers. The second, larger wave began 10,000 years ago as the discovery of agriculture caused a population boom and a need to plow wildlife habitats, divert streams, and maintain large herds of domestic cattle. The third and largest wave began in 1800 with the harnessing of fossil fuels. With enormous, cheap energy at its disposal, the human population grew rapidly from 1 billion in 1800 to 2 billion in 1930, 4 billion in 1975, and over 7 billion today. If the current course is not altered, we’ll reach 8 billion by 2020 and 9 to 15 billion (likely the former) by 2050.

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Introduced species -- those who migrate to a new area -- are the second leading cause of endangerment and extinction. Information on the rate of species introduction and the nature of the impacts of introduced species on native species and ecosystems allows inferences about extinction rates. The evidence all points to a global tragedy with a profound loss of biodiversity.

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Humans annually absorb 42 percent of the Earth’s terrestrial net primary productivity, 30 percent of its marine net primary productivity, and 50 percent of its fresh water [3].

Forty percent of the planet’s land is devoted to human food production, up from 7 percent in 1700 [3].

Fifty percent of the planet’s land mass has been transformed for human use [3].

More atmospheric nitrogen is now fixed by humans that all other natural processes combined [3].

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Barnosky studies biodiversity changes and extinction rates that occurred in the deep past, and compares them to trends happening now. Since life first evolved billions of years ago and flourished, diversified, and made our planet what it is, there have been five mass extinctions. Each was triggered by a cataclysmic event and resulted in at least 75% of all species going extinct. The last of these events occurred 65 million years ago, when a meteorite slammed into Earth, throwing up persistent clouds of debris that darkened the sky for years. The resulting change in climate led to a mass extinction that included the dinosaurs. Barnosky calculates that humans are now creating a mass extinction on the same scale – the planet's sixth one – through a combination of habitat encroachment and fragmentation, hunting, climate change, pollution, and the spread of disease and introduced species. As many as 30% of all species may be lost over the next four decades, conservationists estimate.

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Black Carbon

For centuries, humans have been engaging in activities that produce black carbon particles.  Black carbon particles are released into the atmosphere in the form of smoke that is produced by cooking with solid fuels, biomass burning, and diesel exhaust.  When the black carbon particles reach the atmosphere, they form a heat-absorbing layer that causes temperatures to rise.  Raindrops tend to form around black carbon particles in the atmosphere, and when they fall to the ground, they absorb heat on the ground too, thus magnifying the warming effect.

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Warmer temperatures cause mass bleaching of corals. However, even in a warmer world, deep ocean temperatures would still remain well below surface temperatures and there would be safe havens where cooler water upwells from the deep ocean.

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Oil destroys the insulating ability of fur-bearing mammals, such as sea otters, and the water repellency of a bird's feathers, thus exposing these creatures to the harsh elements. Without the ability to repel water and insulate from the cold water, birds and mammals will die from hypothermia.

Many birds and animals also ingest oil when they try to clean themselves, which can poison them.

Fish and shellfish may not be exposed immediately, but can come into contact with oil if it is mixed into the water column. When exposed to oil, adult fish may experience reduced growth, enlarged livers, changes in heart and respiration rates, fin erosion, and reproduction impairment. Oil also adversely affects eggs and larval survival.

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Fish

Increasing demand for water, the damming of rivers throughout the world, the dumping and accumulation of various pollutants, and invasive species make aquatic ecosystems some of the most threatened on the planet;

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Global climate change will affect people and the environment in many ways. Some of these impacts, like stronger hurricanes and severe heat waves, could be life threatening. Others, like spreading weeds, will be less serious. And some effects, like longer growing seasons for crops, might even be good! However, as the Earth keeps getting warmer, the negative effects are expected to outweigh the positive ones.

The more we learn about how climate change will affect people and the environment, the more we can see why people need to take action to reduce the greenhouse gas emissions that are causing climate change. We can also take steps to prepare for the changes we know are coming.

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Biologists and paleoecologists estimate that humans have driven roughly 1,000 species extinct in our 200,000 years on the planet