Sunday 21 June 2015

Scientists warn of the Sixth Great Extinction

What was amazing that this actually made it onto the midday news on Radio New Zealand. Will wonders never cease!

Stanford researcher warns sixth mass extinction is here

There is no longer any doubt: We are entering a mass extinction that threatens humanity's existence. That is the bad news at the center of a new study by a group of scientists including Paul Ehrlich, the Bing Professor of Population Studies in biology and a senior fellow at the Stanford Woods Institute for the Environment. Ehrlich and his co-authors call for fast action to conserve threatened species, populations and habitat, but warn that the window of opportunity is rapidly closing. 

The Earth stands on the brink of its sixth mass extinction and the fault is ours
The rate at which vertebrate species are now dying far exceeds the norm

21 June, 2015

Life on Earth is in trouble. That much we know. But how bad have things become – and how fast are events moving? How soon, indeed, before the Earth’s biological treasures are trashed, in what will be the sixth great mass extinction event? This is what Gerardo Caballos of the National Autonomous University of Mexico and his colleagues have assessed, in a paper that came out on Friday.

These are extraordinarily difficult questions. There are many millions of species, many elusive and rare, and inhabiting remote and dangerous places. There are too few skilled biologists in the field to keep track of them all. Demonstrating beyond reasonable doubt that any single species is extinct is arduous and painstaking (think how long it took to show – to most people, at least – that Loch Ness probably does not harbour a large monster).

And it’s not just a case of making a head-count of modern extinctions. This needs to be compared with a long-term “baseline” rate of extinctions in our planet’s long geological history. This can only be extracted via the equally painstaking and difficult work of excavating and identifying millions of fossils from the almost endless rock strata. Not surprisingly, different studies made so far on different fossils have yielded different baseline rates.

Caballos and colleagues have thought through these difficulties, and come up with probably the most robust estimate yet of how severe the modern crisis is.
They have been deliberately conservative – they’re well aware of the dangers of crying wolf on a topic of such importance, and where passions run so high. For a start, they limit themselves to the best-studied group of organisms, the vertebrates. Then, they take a high estimate of background extinctions to compare with, to make the modern figures as undramatic as possible. And then, they either consider only those animals known to be extinct (the “highly conservative” scenario), or they add in those extinctions in the wild that are likely to have happened, but are not yet verified.

Even with this caution, the figures are still shocking. Rather than the nine extinctions among vertebrates that would be expected to have occurred in normal geological circumstances since 1900, their conservative estimate adds in another 468 extinctions, spread among mammals, birds, reptiles, amphibians and fish. 

Examples of lost species would include the Yangtze dolphin and the Costa Rica golden toad. Depending on the group, extinction rates are 10 times to more than 100 times higher than normal. A sixth mass extinction, therefore, is beginning. They estimate that it would grow to rival the last great catastrophe of the past, when the dinosaurs and much else died out 65m years ago, in as little as three human lifetimes.

Once more, this is a conservative estimate. It simply considers the kill mechanisms operating today, of habitat loss, predation, pollution and so on. The Caballos projection does not try to factor in, for instance, the effects of global warming, or of ocean acidification. Once these kick in in earnest, they will sweep many species out of their habitability zones, and ratchet up the extinction rate still further.

In terms of scale, we are now living through one of those brief, rare episodes in Earth history when the biological framework of life is dismantled. It is in every sense a tragedy – but, in itself, it might be viewed as just one more episode of biological destruction in our planet’s history. The Earth has been here before – and will be here again, before its life is completely extinguished a billion or so years into the future.

This particular perturbation to the biosphere, though, has some very special features. Indeed, there has been nothing remotely like it in our planet’s history. By coincidence, one of the authors of the Caballos study, Anthony Barnosky of the University of California at Berkeley, was involved in another study published the same week, a study that sought to put its finger on exactly what is so different – and so weird, in planetary terms, not to put too fine a point on it – about what is happening to the biosphere right now.

This second study, led by Mark Williams, a palaeontologist at the University of Leicester, identified some quite extraordinary novelties at the heart of current events. First, past extinctions have been driven by what are now becoming very familiar horsemen of a planetary apocalypse: massive volcanic outbursts to choke the atmosphere and poison the seas; the mayhem caused by major asteroid impact; and the wrenching effects of rapid climate change. None of these has really figured in the current biological crisis – not even climate change, which is still only in its early stages.

Instead, the extinctions are being driven by the effects of just one single species,Homo sapiens. Such a mass extinction has not occurred before (with the possible exception, 2.5bn years ago, when a type of microbe evolved photosynthesis to spew out oxygen, a gas that would have been highly toxic to the other microbes living then, and these would have been pushed to the fringes of life on Earth – where they still remain). Even more extraordinarily, this single species is land-living, but has managed to become the top predator in the oceans too, causing populations of whales and fish to collapse.

In all, our single species now commandeers somewhere between 25% and 40% of primary productivity on Earth. It is a productivity, that over large areas of land, is “hyper-fertilised” by the extraction of millions of tons of nitrogen from the air, in the Haber-Bosch process, and by digging comparable amounts of phosphate from the ground.

These super-fed crops are fed, highly efficiently, to farm animals, that we eat in turn. The scale of this operation is a large reason for the scale of the ongoing mass extinction of other organisms.

The scientist Vaclav Smil, of the University of Manitoba, has calculated that simply measured by mass, humans now make up a third of land vertebrates, and the animals that we keep to eat – cows, pigs, sheep and so on – make up most of the other two thirds. All the wild animals – elephants, giraffes, tigers and so on – are now less than 5% by mass. It’s a measure of how they have been pushed to the fringes by humans.

Humans change things in other ways – they now direct the evolution of the animals that are useful to them, by breeding and by genetic engineering: again, it’s a planetary novelty. The energy our species obtains from photosynthesis is not enough, and so we mine stored photosynthetic energy from the ground, as hydrocarbons, in enormous amounts, and use that to power our machines.

These machines – cars, planes, computers and much else – have, together with their human software, been termed the technosphere by the geologist Peter Haff of Duke University. He views it as an emergent system with its own internal dynamics (and which humans currently drive but don’t really control) – in effect an offshoot of the biosphere. Whatever it is, it is evolving at lightning speed by comparison with biological evolution.

The changes to the Earth’s biology do, therefore, include a rapidly developing mass extinction event, as charted by Gerardo Caballos and his colleagues.
But this may be seen as part of a much more thoroughgoing transformation. Fundamental new patterns are emerging that may be compared, say, with the change, half a billion years ago, when a biosphere consisting only of microbes gave way to one dominated by multicellular animals.

Could this new planetary pattern develop – perhaps well enough to help prevent a mass extinction? Currently, the technosphere is more a parasite than a partner of the biosphere – it is terrible at recycling, for instance.

But some aspects might help alleviate the worst effects of global warming. For instance, humans have caused the greatest trans-migration of species in history. Some of these invasive species may be well adapted to new higher temperatures. 

And better use of energy and materials can reduce pressure on remaining natural ecosystems.

Averting a mass extinction is still possible – but we don’t have much time.
The author is professor of palaeobiology at Leicester University


Previous mass extinctions

Geological history includes many periods when species have died in large numbers. In each of the following, more than half the Earth’s species disappeared:

1 End-Ordovician, 443 million years ago.

This coincides with very rapid glaciation; sea level fell by more than 100 metres, devastating shallow marine ecosystems; less than a million years later, there was a second wave of extinctions as ice melted, sea level rose rapidly, and oceans became oxygen-depleted.

2 Late Devonian, c 360 million years ago.

A messy prolonged event, again hitting life in shallow seas very hard, and an extinction that was probably due to climate change.

3 Permian-Triassic mass extinction, c 250 million years ago.

The greatest of all, ‘The Great Dying’ of more than 95% of species, is strongly linked with massive volcanic eruptions in Siberia that caused, among other effects, a brief savage episode of global warming.

Triassic-Jurassic mass extinction, c 200 million years ago.

This has been linked with another huge outburst of volcanism.

Cretaceous-Tertiary mass extinction 65 million years ago.

This killed off the dinosaurs and much else; an asteroid impact on Mexico probably did the damage, but the world’s ecosystem may have been weakened by volcanic outbursts in what is now India.

Study reveals rate of extinction for species in the 20th century has been up to 100 times higher than would have been normal without human impact

Here's More Proof Earth Is in Its 6th Mass Extinction

Mei Xiang, a giant panda (Ailuropoda melanoleuca) at the Smithsonian's National Zoo in Washington, D.C. There are fewer than 2,500 mature giant pandas left in the wild, according to the IUCN. Credit: Abby Wood, Smithsonian's National Zoo

19 June, 2015

Diverse animals across the globe are slipping away and dying as Earth enters its sixth mass extinction, a new study finds.

Over the last century, species of vertebrates are dying out up to 114 times faster than they would have without human activity, said the researchers, who used the most conservative estimates to assess extinction rates. That means the number of species that went extinct in the past 100 years would have taken 11,400 years to go extinct under natural extinction rates, the researchers said.

Much of the extinction is due to human activities that lead to pollution, habitat loss, the introduction of invasive species and increased carbon emissions that drive climate change and ocean acidification, the researchers said. [7 Iconic Animals Humans Are Driving to Extinction]

"Our activities are causing a massive loss of species that has no precedent in the history of humanity and few precedents in the history of life on Earth," said lead researcher Gerardo Ceballos, a professor of conservation ecology at the National Autonomous University of Mexico and a visiting professor at Stanford University.
Ceballos said that, ever since he was a child, he struggled to understand why certain animals went extinct. In the new study, he and his colleagues focused on the extinction rates of vertebrates, which include mammals, birds, reptiles, amphibians and fishes.

Chart of extinction events that wiped out most life on Earth.
Scientists found that species are dying off more than 100 times faster than they would without human activity.
Credit: By Karl Tate, Infographics Artist

First, they needed to establish how many species go extinct naturally over time. They used data from a 2011 study in the journal 
Nature showing that typically, the world has two extinctions per 10,000 vertebrate species every 100 years. That study based its estimate on fossil and historical records.

Moreover, that background extinction rate, the researchers found, was higher than that found in other studies, which tend to report half that rate, the researchers said.

Then, Ceballos and his colleagues calculated the modern extinction rate. They used data from the International Union for Conservation of Nature (IUCN), an international organization that tracks threatened and endangered species. The 2014 IUCN Red List gave them the number of extinct and possibly extinct vertebrate species since 1500.

These lists allowed them to calculate two extinction rates: a highly conservative rate based solely on extinct vertebrates, and a conservative rate based on both extinct and possibly extinct vertebrates, the researchers said.

According to the natural background rate, just nine vertebrate species should have gone extinct since 1900, the researchers found. But, using the conservative, modern rate, 468 more vertebrates have gone extinct during that period, including 69 mammal species, 80 bird species, 24 reptile species, 146 amphibian species and 158 fish species, they said.

Each of these lost species played a role in its ecosystem, whether it was at the top or bottom of the food chain.

"Every time we lose a species, we're eroding the possibilities of Earth to provide us with environmental services," Ceballos told Live Science.

Researchers typically label an event a mass extinction when more than 5 percent of Earth's species goes extinct in a short period of time, geologically speaking. Based on the fossil record, researchers know about five mass extinctions, the last of which happened 65 million years ago, when an asteroid wiped out the nonavian dinosaurs. [Wipe Out: History's Most Mysterious Extinctions]

"[The study] shows without any significant doubt that we are now entering the sixth great mass extinction event," study researcher Paul Ehrlich, a professor of population studies in biology at Stanford University, said in a statement.

Bye-bye, birdie

At this rate, a huge amount of biodiversity will be lost in as little as two to three human lifetimes, Ceballos said. And it can take millions of years for life to recover and repopulate the Earth, he said.

Species make up distinct populations that can spread over a continent. But some vertebrate populations have so few individuals left that they cannot efficiently play their role in the ecosystem, Ceballos said.

snow leopard
The snow leopard (Panthera uncial) is endangered; its numbers have declined by at least 20 percent over the past 16 years, mainly due to poaching and loss of habitat and prey, according to the IUCN.
Credit: Dennis W. Donohue |

For instance, elephant populations are now far and few between. "The same [goes for] lions, cheetah, rhinos, jaguars — you name it," Ceballos said.

"Basically, focusing on a species is good because those are the units of evolution and ecosystem function, but populations are in even worse shape than species," he dded.

However, there is still time to save wildlife by working with conservationists and creating animal-friendly public policy, he said.

"Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species, and to alleviate pressures on their populations — notably, habitat loss, over-exploitation for economic gain and climate change," the researchers wrote in the study, published online today (June 19) in the journal Science Advances.

The study supports other findings on Earth's high extinction rate, said Clinton Jenkins, a visiting professor at the Institute of Ecological Research in Brazil, who was not involved with the study.

In 2014, Jenkins and his colleagues published a study in the journal Science that came to the same broad conclusions detailed in the new study, but in last year's study, they also included flowering and cone plants. That study found that current extinction rates are about 1,000 times higher than they would be without human activities.

"This latest study is further evidence of a human-induced mass extinction now underway," Jenkins told Live Science. "Much like the situation with human-caused climate change, years of research have built an enormous scientific case that humanity is driving a mass extinction. What the world’s many species now need are actions to reverse the problem."

No comments:

Post a Comment

Note: only a member of this blog may post a comment.