Humans on Verge of Causing 6th Great Mass Extinction

Stephanie Pappas, LiveScience 2 Mar 11;

Are humans causing a mass extinction on the magnitude of the one that killed the dinosaurs?

The answer is yes, according to a new analysis — but we still have some time to stop it.

Mass extinctions include events in which 75 percent of the species on Earth disappear within a geologically short time period, usually on the order of a few hundred thousand to a couple million years. It's happened only five times before in the past 540 million years of multicellular life on Earth. (The last great extinction occurred 65 million years ago, when the dinosaurs were wiped out.) At current rates of extinction, the study found, Earth will enter its sixth mass extinction within the next 300 to 2,000 years.

"It's bittersweet, because we're showing that we have this crisis," study co-author Elizabeth Ferrer, a graduate student in biology at the University of California, Berkeley, told LiveScience. "But we still have time to fix this."

Others aren't so optimistic that humans will actually do anything to stop the looming disaster, saying that politics is successfully working against saving species and the planet.

The 6th extinction

Species go extinct all the time, said Anthony Barnosky, the curator of the Museum of Paleontology at UC Berkeley and another co-author of the paper, which appears in today’s (March 2) issue of the journal Nature. But new species also evolve constantly, meaning that biodiversity usually stays constant. Mass extinctions happen when that balance goes out of whack. Suddenly, extinctions far outpace the genesis of new species, and the old rules for species survival go out the window. [Read: Mass Extinction Threat: Earth on Verge of Huge Reset Button?]

"If the fossil record tells us one thing, it's that when we kick over into a mass extinction regime, results are extreme, they're irreversible and they're unpredictable," David Jablonski, a paleontologist at the University of Chicago who was not involved in the study, told LiveScience. "Factors that promote success and survival during normal times seem to melt away."

Everyone knows that we now lose many species a year, Barnosky said. "The question is, 'Is the pace of extinction we're seeing today over these short time intervals usual or unusual?'"

Answering the question requires stitching together two types of data: that from the fossil record and that collected by conservation biologists in the modern era. They don't always match up well. For example, Barnosky said, fossils tell us lots about the history of clams, snails and other invertebrates. But in the modern world, biologists have only assessed the extinction risk for 3 percent of known species of such invertebrates. That makes comparisons tough.

The fossil record also presents a blurrier history than today's yearly records of species counts. Sparse examples of a species may be distributed across millions of years of fossil history, the researchers wrote, while modern surveys provide dense samples over short periods of time. And even the best source of modern data — the International Union for the Conservation of Nature Red List of threatened and endangered species — has catalogued the conservation status of less than 2.7 percent of the 1.9 million named species out there.

Coming crisis

The researchers worked to combine these two sources of data, Ferrer said, taking a conservative approach to filling in gaps and estimating future directions. They found that the overall rate of extinction is, in fact, between three to 80 times higher than non-mass extinction rates. Most likely, species are going extinct three to 12 times faster than would be expected if there were no crisis, Ferrer said.

That gives Earth between three and 22 centuries to reach the point of mass extinction if nothing is done to stop the problem. (The wide range is a factor of the uncertainty in the data and different rates of extinction found in various species.) The good news, Barnosky said, is that the total loss so far is not devastating. In the last 200 years, the researchers found, only 1 to 2 percent of all species have gone extinct.

The strongest evidence for comparison between modern and ancient times comes from vertebrate animals, Barnosky said, which means there is still work to do collecting better data for more robust comparisons with better invertebrate data. But, he said, the research "shows absolutely without a doubt that we do have this major problem."

Back from the brink?

The culprits for the biodiversity loss include climate change, habitat loss, pollution and overfishing, the researchers wrote.

"Most of the mechanisms that are occurring today, most of them are caused by us," Ferrer said.

So can we fix it? Yes, there's time to cut dependence on fossil fuels, alleviate climate change and commit to conservation of habitat, the study scientists say. The more pressing question is, will we?

Barnosky and Ferrer both say they're optimistic that people will pull together to solve the problem once they understand the magnitude of the looming disaster. Jablonski puts himself into the "guardedly optimistic category."

"I think a lot of the problems probably have a lot more to do with politics than with science," Jablonski said.

That's where Paul Ehrlich, the president of the Center for Conservation Biology at Stanford University and author of "The Population Bomb" (Sierra Club-Ballantine, 1968), sees little hope.

"Everything we're doing in Washington [D.C.] today is working in the wrong direction," Ehrlich, who was not involved in the research, told LiveScience. "There isn't a single powerful person in the world who is really talking about what the situation is … It's hard to be cheery when you don't see the slightest sign of any real attention being paid."

Other researchers take an upbeat view.

"If we have a business-as-usual scenario, it is pretty grim, but it isn't yet written," Stuart Pimm, a professor of conservation ecology at Duke University who was not involved in the research, told LiveScience in a phone interview from Chile, where he was doing fieldwork.

In 2010, Pimm said, the United Nations declared the International Year of Biodiversity. According to a UN statement, the 193 countries involved agreed to protect 17 percent of Earth's terrestrial ecosystems and 10 percent of marine and coastal areas. Some types of ecosystems still lag behind, Pimm said, but there is reason for hope.

"I hope that this will alert people to the fact that we are living in geologically unprecedented times," Pimm said. "Only five times in Earth's history has life been as threatened as it is now."

Are We in the Middle of a Sixth Mass Extinction?
Ann Gibbons Science Now 2 Mar 11;

Earth's creatures are on the brink of a sixth mass extinction, comparable to the one that wiped out the dinosaurs. That's the conclusion of a new study, which calculates that three-quarters of today's animal species could vanish within 300 years. "This is really gloom-and-doom stuff," says the study's lead author, paleobiologist Anthony Barnosky of the University of California, Berkeley. "But the good news is we haven't come so far down the road that it's inevitable."

Species naturally come and go over long periods of time. But what sets a mass extinction apart is that three-quarters of all species vanish quickly. Earth has already endured five mass extinctions, including the asteroid that wiped out dinosaurs and other creatures 65 million years ago. Conservationists have warned for years that we are in the midst of a sixth, human-caused extinction, with species from frogs to birds to tigers threatened by climate change, disease, loss of habitat, and competition for resources with nonnative species. But how does this new mass extinction compare with the other five?

Barnosky and colleagues took on this challenge by looking to the past. First, they calculated the rate at which mammals, which are well represented in the fossil record, died off in the past 65 million years, finding an average extinction rate of less than two species per million years. But in the past 500 years, a minimum of 80 of 5570 species of mammals have gone extinct, according to biologists' conservative estimates—an extinction rate that is actually above documented rates for past mass extinctions, says Barnosky. All of this means that we're at the beginning of a mass extinction that will play out over hundreds or thousands of years, his team concludes online today in Nature.

The picture gets even grimmer when all mammals currently endangered or threatened are added to the count. If those all disappear within a century, then by 334 years from now, 75% of all mammal species will be gone, says Barnosky. "Look outside of your window. Imagine taking away three-quarters of the living things you see and ask yourself if you want to live in that world."

The team extended the same methods of analysis to amphibians, reptiles, birds, plants, mollusks, and other forms of life. They found fairly consistent patterns: From amphibians to birds to mammals, about 1% to 2% of species already are extinct today, and 20% to 50% are threatened—numbers that approach those of the great mass extinctions of the past. "Our best guess is that the current extinction rate is between three to 80 times too high" even without counting all threatened species, says Barnosky. "Assuming threatened species would actually go extinct—which is not inevitable—puts the extinction rate off the charts."

"There's been a lot of general talk on this issue, but attempts to draw more rigorously on the lessons of the fossil record have been rare," says paleobiologist David Jablonski of the University of Chicago in Illinois, who was not involved in the study. "It's really valuable to look at how current losses stack up against the past extinction events."

The silver lining in this dark cloud is that if humans work quickly to protect endangered and threatened species and their habitats now, the mass extinction can be prevented or at least delayed by thousands of years, says Barnosky. Adds Jablonski, "This approach provides a way to gauge progress in walking the world back from that brink [of a mass extinction]."

World's sixth mass extinction may be underway -- study
Richard Ingham And Laurent Banguet Yahoo News 3 May 11;

PARIS (AFP) – Mankind may have unleashed the sixth known mass extinction in Earth's history, according to a paper released on Wednesday by the science journal Nature.

Over the past 540 million years, five mega-wipeouts of species have occurred through naturally-induced events.

But the new threat is man-made, inflicted by habitation loss, over-hunting, over-fishing, the spread of germs and viruses and introduced species, and by climate change caused by fossil-fuel greenhouse gases, says the study.

Evidence from fossils suggests that in the "Big Five" extinctions, at least 75 percent of all animal species were destroyed.

Palaeobiologists at the University of California at Berkeley looked at the state of biodiversity today, using the world's mammal species as a barometer.

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.

"It looks like modern extinction rates resemble mass extinction rates, even after setting a high bar for defining 'mass extinction," said researcher Anthony Barnosky.

This picture is supported by the outlook for mammals in the "critically endangered" and "currently threatened" categories of the Red List of biodiversity compiled by the International Union for Conservation of Nature (IUCN).

On the assumption that these species are wiped out and biodiversity loss continues unchecked, "the sixth mass extinction could arrive within as little as three to 22 centuries," said Barnosky.

Compared with nearly all the previous extinctions this would be fast-track.

Four of the "Big Five" events unfolded on scales estimated at hundreds of thousands to millions of years, inflicted in the main by naturally-caused global warming or cooling.

The most abrupt extinction came at the end of the Cretaceous, some 65 million years ago when a comet or asteroid slammed into the Yucatan peninsula, in modern-day Mexico, causing firestorms whose dust cooled the planet.

An estimated 76 percent of species were killed, including the dinosaurs.

The authors admitted to weaknesses in the study. They acknowledged that the fossil record is far from complete, that mammals provide an imperfect benchmark of Earth's biodiversity and further work is needed to confirm their suspicions.

But they described their estimates as conservative and warned a large-scale extinction would have an impact on a timescale beyond human imagining.

"Recovery of biodiversity will not occur on any timeframe meaningful to people," said the study.

"Evolution of new species typically takes at least hundreds of thousands of years, and recovery from mass extinction episodes probably occurs on timescales encompassing millions of years."

Even so, they stressed, there is room for hope.

"So far, only one to two percent of all species have gone gone extinct in the groups we can look at clearly, so by those numbers, it looks like we are not far down the road to extinction. We still have a lot of Earth's biota to save," Barnosky said.

Even so, "it's very important to devote resources and legislation toward species conservation if we don't want to be the species whose activity caused a mass extinction."

Asked for an independent comment, French biologist Gilles Boeuf, president of the Museum of Natural History in Paris, said the question of a new extinction was first raised in 2002.

So far, scientists have identified 1.9 million species, and between 16,000 and 18,000 new ones, essentially microscopic, are documented each year.

"At this rate, it will take us a thousand years to record all of Earth's biodiversity, which is probably between 15 and 30 million species" said Boeuf.

"But at the rate things are going, by the end of this century, we may well have wiped out half of them, especially in tropical forests and coral reefs."