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標題: [生物多樣性] 研究:地球現第6次大滅絕
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發表於 2015-6-21 12:35  資料 文集 短消息 
研究:地球現第6次大滅絕

「脊椎動物快正常百倍消失」

【明報專訊】美國3所著名大學專家領導研究小組發表報告,指近百年來脊椎動物消失的速度是正常逾100倍,顯示地球可能已進入「第6次物種大滅絕」。不過,亦有專家質疑報告言過其實,指地球可能要再過數百年才會出現第6次大滅絕。

3大名校分析 「採保守計算」

最新報告由美國史丹福、普林斯頓和加州大學柏克萊分校的專家領導撰寫,前日(19日)於《科學進展》期刊刊登。報告指出,現時是繼恐龍在6500萬年前滅絕後,地球經歷的最快物種滅絕期。研究員主要透過分析化石紀錄及有紀錄的動物滅絕事件得出結論。

報告說,自1900年以來,有約400種脊椎動物絕種,在正常情况下這要1萬年才發生。由於過往不少物種滅絕的評估被指「太悲觀」,高估了當今物種滅絕的嚴重程度,因此這次研究人員採用更保守計算,把估計的「背景滅絕率」(無人為干擾下的自然滅絕)較廣泛研究採用的提高一倍。

按此推算,自然情况下,過往的物種滅絕速度為每100年每1萬物種中有2種哺乳類動物絕種。研究人員發現,即使在這最保守估計下,過去一世紀的脊椎動物平均滅絕率也比沒人類活動下的快114倍。

每年最少50動物瀕絕種

報告強調,所用計算方法極可能低估了危機,因為研究旨在反映人類對生態多樣性的真實「下限」(lower bound)影響。

一如過往報告,最新研究把物種滅絕歸因於氣候轉變、污染及伐林等因素。這些人類行為破壞環境,自1500年以來已導致77種哺乳類、140種雀鳥,以及34種兩棲類動物消失,包括渡渡鳥(dodo)、大海牛、福克蘭狼、台灣雲豹、阿特拉斯棕熊和裏海虎等,人類也須為過往2000年間大洋洲熱帶島嶼上的1800種鳥類絕種負責。根據國際自然保護聯盟(IUCN)估算,現有41%兩棲類動物以及26%哺乳類動物有絕種危機,每年有最少50種動物接近絕種。

「人類或首當其衝消失」

身為主筆的墨西哥州自治大學專家賽瓦略斯(Gerardo Ceballos)警告,如果情况持續,地球物種或須數百萬年才可恢復,而且人類可能首當其衝而消失。報告敦促人類及時透過大力保育行動改變命運。

全球生物多樣性觀測網絡(GEO BON)主席佩雷拉(Henrique Miguel Pereira)則認為,新報告並無新意。他認為,地球確有生物多樣性危機,不過可能要再過數百年才會到達第6次大滅絕階段。

(綜合報道)

http://news.mingpao.com/pns/%E7% ... 00014/1434822720636


圖片: 明報.jpg (2015-6-21 12:35, 161.24 K)

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發表於 2015-6-21 12:37  資料 文集 短消息 
Humans creating sixth great extinction of animal species, say scientists

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

The modern world is experiencing a “sixth great extinction” of animal species even when the lowest estimates of extinction rates are considered, scientists have warned.

The rate of extinction for species in the 20th century was up to 100 times higher than it would have been without man’s impact, they said.

Many conservationists have been warning for years that a mass extinction event akin to the one that wiped out the dinosaurs is occurring as humans degrade and destroy habitats.

But the authors of a study published on Friday said that even when they analysed the most conservative extinction rates, the rate at which vertebrates were being lost forever was far higher than in the last five mass extinctions.

“We were very surprised to see how bad it is,” said Dr Gerardo Ceballos of the National Autonomous University of Mexico. “This is very depressing because we used the most conservative rates, and even then they are much higher than the normal extinction rate, really indicating we are having a massive loss of the species.”

Previous studies have warned that the impact of humans taking land for buildings, farming and timber has been to make species extinct at speeds unprecedented in Earth’s 4.5bn-year history.

Ceballos said that his study, co-authored by Paul R Ehrlich who famously warned of the impact of humanity’s “population bomb”, employed better knowledge of natural or so-called background extinction rates. He said it was conservative because it looked only at species that had been declared extinct, which due to stringent rules can sometimes take many years after a species has actually gone extinct.

Under a “natural” rate of extinction, the study said that two species go extinct per 10,000 species per 100 years, rather than the one species that previous work has assumed.

Modern rates of extinction were eight to 100 times higher , the authors found. For example, 477 vertebrates have gone extinct since 1900, rather than the nine that would be expected at natural rates.

“It’s really signalling we’ve entered a sixth extinction and it’s driven by man,” said Ceballos.

However, Prof Henrique Miguel Pereira, the chair of the Group on Earth Observations Biodiversity Observation Network, said that the new paper did not add anything revolutionarily new.

“They argue that recent extinction rates are up to 100 times higher than in the past. I think it improves our documentation of the process but it does not yet confirm a sixth mass extinction. I tend to think we have a major biodiversity crisis, but it would take either a fast acceleration of current extinction rates or a couple of centuries at current extinction rates, for the current process to become a sixth mass extinction.”

The team behind the new analysis said “rapid, greatly intensified efforts” would be needed to stop or slow the extinctions currently underway.

Ceballos pointed to the Pope Francis’s encyclical on the environment, which was published on Thursday and lamented the loss of the world’s biodiversity, and interventions by Barack Obama, as signs of hope. “These important figures are starting to really grasp the problem,” he said.

On why people should be worried about the rate of extinctions, he said: “People say that’s really sad, but why does it affect me? There are many reasons we should care. We are the species that are causing the loss of all these other species.”

But the most important reason, he said, was that by losing species humanity was losing what enabled us to have a “good standard of living”.

The paper, Accelerated modern human–induced species losses: Entering the sixth mass extinction, was published in the journal Science Advances.

http://www.theguardian.com/envir ... cies-say-scientists
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發表於 2015-6-21 12:41  資料 文集 短消息 
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 study] shows without any significant doubt that we are now entering the sixth great mass extinction event," Ehrlich said.

Although most well known for his positions on human population, Ehrlich has done extensive work on extinctions going back to his 1981 book, Extinction: The Causes and Consequences of the Disappearance of Species. He has long tied his work on coevolution, on racial, gender and economic justice, and on nuclear winter with the issue of wildlife populations and species loss.

There is general agreement among scientists that extinction rates have reached levels unparalleled since the dinosaurs died out 66 million years ago. However, some have challenged the theory, believing earlier estimates rested on assumptions that overestimated the crisis.

The new study, published in the journal Science Advances, shows that even with extremely conservative estimates, species are disappearing up to about 100 times faster than the normal rate between mass extinctions, known as the background rate.

"If it is allowed to continue, life would take many millions of years to recover, and our species itself would likely disappear early on," said lead author Gerardo Ceballos of the Universidad Autónoma de México.

Conservative approach

Using fossil records and extinction counts from a range of records, the researchers compared a highly conservative estimate of current extinctions with a background rate estimate twice as high as those widely used in previous analyses. This way, they brought the two estimates -- current extinction rate and average background or going-on-all-the-time extinction rate -- as close to each other as possible.

Focusing on vertebrates, the group for which the most reliable modern and fossil data exist, the researchers asked whether even the lowest estimates of the difference between background and contemporary extinction rates still justify the conclusion that people are precipitating "a global spasm of biodiversity loss." The answer: a definitive yes.

"We emphasize that our calculations very likely underestimate the severity of the extinction crisis, because our aim was to place a realistic lower bound on humanity's impact on biodiversity," the researchers write.

To history's steady drumbeat, a human population growing in numbers, per capita consumption and economic inequity has altered or destroyed natural habitats. The long list of impacts includes:

Land clearing for farming, logging and settlement
Introduction of invasive species
Carbon emissions that drive climate change and ocean acidification
Toxins that alter and poison ecosystems
Now, the specter of extinction hangs over about 41 percent of all amphibian species and 26 percent of all mammals, according to the International Union for Conservation of Nature, which maintains an authoritative list of threatened and extinct species.

"There are examples of species all over the world that are essentially the walking dead," Ehrlich said.

As species disappear, so do crucial ecosystem services such as honeybees' crop pollination and wetlands' water purification. At the current rate of species loss, people will lose many biodiversity benefits within three generations, the study's authors write. "We are sawing off the limb that we are sitting on," Ehrlich said.

Hope for the future

Despite the gloomy outlook, there is a meaningful way forward, according to Ehrlich and his colleagues. "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 study's authors write.

In the meantime, the researchers hope their work will inform conservation efforts, the maintenance of ecosystem services and public policy.

Co-authors on the paper include Anthony D. Barnosky of the University of California at Berkeley, Andrés García of Universidad Autónoma de México, Robert M. Pringle of Princeton University and Todd M. Palmer of the University of Florida.

Video: https://www.youtube.com/watch?v=cmb5hn2X2ok

Story Source:
The above post is reprinted from materials provided by Stanford University. The original item was written by Rob Jordan. Note: Materials may be edited for content and length.

Journal Reference:
Gerardo Ceballos, Paul R. Ehrlich, Anthony D. Barnosky, Andrés García, Robert M. Pringle and Todd M. Palmer. Accelerated modern human–induced species losses: Entering the sixth mass extinction. Science Advances, 2015 DOI: 10.1126/sciadv.1400253

Stanford University. "Sixth mass extinction is here: Humanity's existence threatened." ScienceDaily. ScienceDaily, 19 June 2015. <www.sciencedaily.com/releases/2015/06/150619152142.htm>.
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pyling (快樂的小魚兒)
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發表於 2015-7-16 00:01  資料 短消息 
回覆 #1 Xoni 的帖子

"不過,亦有專家質疑報告言過其實,指地球可能要再過數百年才會出現第6次大滅絕。"-->This is an example of the problem of "balanced journalism". Not to mentioned that the translation of Prof. Pereira's quote from the Guardian newspaper is misleading, he is not doubting that we are in a serious problem.

Prof. Pereira:
“They argue that recent extinction rates are up to 100 times higher than in the past. I think it improves our documentation of the process but it does not yet confirm a sixth mass extinction. I tend to think we have a major biodiversity crisis, but it would take either a fast acceleration of current extinction rates or a couple of centuries at current extinction rates, for the current process to become a sixth mass extinction.”

1. He thinks that a "mass extinction event" happens in a much shorter time.
2. He thinks that the study should have compared the extinction rate of the current time and of the extinction events in the past in order to confirm that this 100-times higher rate is comparable to any of the 5 mass extinction events happened in the past.

All he pointed out are very scientific challenges, but the news report interpreted what he said as a disagreement of the study. What a shame.

本帖最近評分記錄
Xoni   2015-7-21 01:39  種子  +26   感謝分享 Thanks for sharing !
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kingarthur
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發表於 2015-7-16 23:23  資料 文集 短消息 
地球環境惡化速度愈來愈快, 若能捱過21世紀人類可能還能有希望, 但個人地我是悲觀的.
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發表於 2015-7-21 01:41  資料 文集 短消息 


QUOTE:
原帖由 pyling 於 2015-7-16 00:01 發表
"不過,亦有專家質疑報告言過其實,指地球可能要再過數百年才會出現第6次大滅絕。"-->This is an example of the problem of "balanced journalism". Not to mentioned that the translation of  ...

無錯, 所以最好都係睇多幾份報導, 特別係外國新聞最好睇返英文原文.
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