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都是我們的錯:科學家:全球暖化 人類是罪魁禍首

立報/本報訊 2013.10.02 00:00
策劃、編譯■劉耘

IPCC公布最新報告,確信人類是暖化罪魁禍首之外,

也企圖為過去15年間暖化趨緩現象釋疑。

當暖化論和懷疑論的爭辯再次興起時,

是否有觀看暖化懷疑論的不同角度?

頂尖氣候專家27日表示,他們比以往更加確信人類是造成全球暖化的元凶,並預測溫室氣體排放造成的衝擊將持續數世紀之久。

(上圖)擅長在公共場所裸拍群眾的美國攝影師杜尼克(Spencer Tunick)號召志願者裸身站在瑞士阿雷奇冰川前拍照,圖攝於2007年8月18日。(圖/路透)

聯合國政府間氣候變遷問題小組(IPCC)在報告中表示,這個世紀發生暖化趨緩的現象,也就是溫室氣體排放量雖增加、暖化速度卻趨緩的情形,只是短暫的自然氣候變化,不會持續下去。

報告指出,大氣中逐漸累積的溫室氣體,讓地球面臨更多的熱浪、水災、乾旱,極地冰層融解造成海平面上升,也將淹沒海岸及較低的島嶼。

發展綠能不能再拖

這份研究旨在引導各國政府轉而發展更環保的綠能,並表示人類活動至少有95%的「極大可能性」是20世紀中期以來造成暖化的主因。

比起2001年報告中66%的「可能」和上一次2007年報告中90%的「非常可能」,人為影響的可能性提高了。

聯合國秘書長潘基文表示,這份研究是對各國政府的呼籲;目前許多國家只關心如何刺激疲弱的經濟,而非努力對抗氣候變遷,努力在2015年擬訂對抗全球暖化的聯合國協議。

美國國務卿凱瑞說,這份報告有如一記警鐘:「那些否認科學研究或寧願找藉口也不願行動的人,無異是在玩火。」他指的是那些質疑是否需要採取立即行動的暖化懷疑論者。

這些暖化懷疑論者之所以如此肯定是根據一項事實:過去15年來,儘管溫室氣體排放量增加,氣溫增加的速度卻趨緩,而這是幾乎所有氣候模型都未能預測到的。

歐洲氣候與能源部長海德嘉說,是時候好好治療地球的健康狀況:「如果你的醫生95%確定你罹患了重症,你一定會立刻開始尋找解藥。」她說。

這份報告匯集了數百位科學家的努力成果,不過在2007年的氣候報告被指出有誤、報告誇大喜馬拉雅冰川消融速度的事件後,這次這份報告面臨了格外嚴格的檢驗。當時一份外部評論稍晚發現,這個錯誤並未影響到其主要結論。

排碳影響逾千年

聯合國政府間氣候變遷問題小組表示,暖化造成的部分影響將遠超過現今這些世代。

報告指出,某些情況下,冰層消融加上深海海水因溫度升高而膨脹,可能使海平面在2300年前上升最多3公尺。人類排放的二氧化碳,則約有15%到40%會停留在大氣層中逾1千年。

「根據我們過去與現在的數據,以及對未來二氧化碳排放量的預測來看,我們勢必會面臨氣候變遷,而衝擊也將遺留數個世代,即便二氧化碳排放停止了也一樣。」大會聯合主席斯托克說。

聯合國政府間氣候變遷問題小組表示,人類的碳排量達5,300億公噸,超過預估人類尚能控制暖化上限的1兆公噸的半數;如今排放量將近每年1百億公噸,且還在持續增加。

暖化趨緩只是一時

這份報告解釋,近年暖化速度放緩的現象,是受到1998年聖嬰現象的紀錄所扭曲;當年太平洋表面海水暖化,使得這年成為史上最熱年份。

報告說,暖化趨緩也肇因於其他「程度相當」的因素,例如氣候中的隨機變動及其它因素的影響,像是火山爆發產生的塵埃遮蔽陽光、以及太陽週期造成的熱度降低。

聯合國政府間氣候變遷問題小組主席帕卓里說,暖化速度趨緩的現象至少要持續長達「30或40年」,才能被視為新趨勢的徵兆。

報告預測,暖化速度趨緩的現象不會持續下去,並表示2016年至2035年間的氣溫,很可能比1986年至2005年間高上攝氏0.3度到0.7度。

不過報告也表示,二氧化碳對氣候造成的暖化影響並不如過去預測的那麼大。

報告表示,大氣中二氧化碳含量若加倍,將使氣溫上升攝氏1.5度至4.5度;此數據低於2007年預估的攝氏2度至4.5度。新溫度上升幅度與聯合國政府間氣候變遷問題小組在2007年之前的研究結果相同。

報告表示,全球溫度很可能在本世紀末前上升攝氏0.3度至4.8度;其中,最低數字僅有在各國政府溫室氣體排放量銳減的情況下才有可能達到。

報告也表示,海平面可能在本世紀末前上升26公分至82公分,威脅如上海及舊金山等沿岸城市。這個上升幅度比2007年預估的數字18公分到59公分要來的高,因為當年並未完全意識到南極洲和格陵蘭冰原消融的影響。

對此,著有《持疑的環保論者》一書的隆伯格表示,聯合國政府間氣候變遷問題小組「溫和的預測結果」,很顯然與某些行動者對於全球溫度及海平面上升「危言聳聽的警告」剛好相反。

(路透)

Leading climate scientists said on Friday they were more convinced than ever that humans are the main culprits for global warming, and predicted the impact from greenhouse gas emissions could linger for centuries.

The Intergovernmental Panel on Climate Change (IPCC) said in a report that a hiatus in warming this century, when temperatures have risen more slowly despite growing emissions, was a natural variation that would not last.

It said the Earth was set for more heatwaves, floods, droughts(1) and rising sea levels from melting ice sheets that could swamp coasts and low-lying islands as greenhouse gases built up in the atmosphere.

The study, meant to guide governments in shifting towards greener energies, said it was "extremely likely", with a probability of at least 95 percent, that human activities were the dominant cause of warming since the mid-20th century.

That was an increase from "very likely", or 90 percent, in the last report in 2007 and "likely", 66 percent, in 2001.

U.N. Secretary-General Ban Ki-moon said the study was a call for governments, many of which have been focused on spurring weak economies rather than fighting climate change, to work to reach a planned U.N. accord(2) in 2015 to combat global warming.

U.S. Secretary of State John Kerry said the report was a wake-up call. "Those who deny the science or choose excuses over action are playing with fire," he said, referring to skeptics(3) who question the need for urgent action.

They have become emboldened by the fact that temperatures rose more slowly over the last 15 years despite increasing greenhouse gas emissions. Almost all climate models failed to predict the slowing.

European Climate Commissioner Connie Hedegaard said it was time to treat the Earth's health. "If your doctor was 95 percent sure you had a serious disease, you would immediately start looking for the cure," she said.

Compiled from the work of hundreds of scientists, the report faces extra scrutiny this year after its 2007 edition included an error that exaggerated the rate of melting of Himalayan glaciers. An outside review later found that the mistake did not affect its main conclusions.

The IPCC said some effects of warming would last far beyond current lifetimes.

Sea levels could rise by 3 metres under some scenarios by 2300 as ice melted and heat made water in the deep oceans expand, it said. About 15 to 40 percent of emitted carbon dioxide would stay in the atmosphere for more than 1,000 years.

"As a result of our past, present and expected future emissions of carbon dioxide, we are committed to climate change and effects will persist for many centuries even if emissions of carbon dioxide stop," said Thomas Stocker, co-chair of the talks.

The IPCC said humanity had emitted about 530 billion tonnes of carbon, more than half the 1 trillion tonne budget it estimated as a maximum to keep warming to manageable limits. Annual emissions are now almost 10 billion tonnes and rising.

Explaining a recent slower pace of warming, the report said the past 15-year period was skewed by the fact that 1998 was an extremely warm year with an El Nino event - a warming of the ocean surface - in the Pacific.

It said warming had slowed "in roughly equal measure" because of random variations in the climate and the impact of factors such as volcanic eruptions, when ash dims sunshine, and a cyclical(4) decline in the sun's output.

Rajendra Pachauri, chair of the IPCC, said the reduction in warming would have to last far longer - "three or four decades" - to be a sign of a new trend.

And the report predicted that the reduction in warming would not last, saying temperatures from 2016-35 were likely to be 0.3-0.7 degree Celsius warmer than in 1986-2005.

Still, the report said the climate was slightly less sensitive than estimated to warming from carbon dioxide.

A doubling of carbon in the atmosphere would raise temperatures by between 1.5 and 4.5 degrees Celsius, it said, below the 2-4.5 range in the 2007 report. The new range is identical to the ranges in IPCC studies before 2007.

The report said temperatures were likely to rise by between 0.3 and 4.8 degrees Celsius by the late 21st century. The low end of the range would only be achieved if governments sharply cut greenhouse gas emissions(5).

And it said world sea levels could rise by between 26 and 82cm by the late 21st century, in a threat to coastal cities from Shanghai to San Francisco. That range is above the 18-59 cm estimated in 2007, which did not take full account of Antarctica and Greenland.

Bjorn Lomborg, author of "The Skeptical Environmentalist" said "the IPCC's moderate projections clearly contradict alarmist rhetoric" of higher temperature and sea level rises by some activists.(Reuters)

關鍵字詞

1.drought(n.)乾旱

2.accord(n)協議

3.skeptic(n.)懷疑論者

4.cyclical(a.)週期性的

5.emission(n.)排放

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