溫室氣體造成發生在上次冰河期的冰河後退現象

原文網址：www.sciencedaily.com/releases/2015/08/150821082727.htm

Greenhouse gases caused glacial retreat during last Ice Age

溫室氣體造成發生在上次冰河期的冰河後退現象

A recalculation of the dates at which boulders were uncovered by melting glaciers at the end of the last Ice Age has conclusively shown that the glacial retreat was due to rising levels of carbon dioxide and other greenhouse gases, as opposed to other types of forces.

重新計算上次冰河期末時因為冰河融化而露出來的礫石年代，確認了冰河後退的主因為二氧化碳以及其他溫室氣體的濃度上升，而非其他作用力。

Carbon dioxide levels are now significantly higher than they were at that time, as a result of the Industrial Revolution and other human activities since then. Because of that, the study confirms predictions of future glacial retreat, and that most of the world's glaciers may disappear in the next few centuries.

工業革命以及之後的其他人類活動，造成現今的二氧化碳濃度遠比上次冰河期末高上許多。這使得此篇研究也證實了未來冰河將會繼續後退，而世界上大多數的冰河也許在不久之後的數個世紀內就會融化殆盡。

The findings were published today in Nature Communications by researchers from Oregon State University, Boston College and other institutions. They erase some of the uncertainties about glacial melting that had been due to a misinterpretation of data from some of these boulders, which were exposed to the atmosphere more than 11,500 years ago.

此篇刊登在今日《自然通訊》(Nature Communications )的研究的作者來自於奧勒岡州立大學、波士頓學院以及其他機構。之前利用這些暴露在空氣中的時間已超過11,500年的礫石，來預估冰河融化的時間時，有可能會因為判讀錯誤而產生誤差。而這群科學家在這篇論文中成功降低了這些誤差。

"This shows that at the end of the last Ice Age, it was only the increase in carbon dioxide and other greenhouse gases that could have caused the loss of glaciers around the world at the same time," said Peter Clark, a professor in the OSU College of Earth, Ocean and Atmospheric Sciences, and co-author on the study.

「在上次冰河期末時，唯有二氧化碳以及其他溫室氣體的濃度上升，才能造成世界各地的冰河在同一時間開始融化。」本研究的共同作者，奧勒岡州立大學地球、海洋與大氣科學系的教授Peter Clark說。

"This study validates predictions that future glacial loss will occur due to the ongoing increase in greenhouse gas levels from human activities," Clark said. "We could lose 80-90 percent of the world's glaciers in the next several centuries if greenhouse gases continue to rise at the current rate."

「此研究證實了未來冰河將會因為人類活動造成的溫室氣體濃度持續上升而消失。」Clark說。「若溫室氣體的濃度繼續以現在的速率攀升，在未來的數世紀內我們可能就會失去世界上百分之80至90的冰河。」

Glacial loss in the future will contribute to rising sea levels and, in some cases, have impacts on local water supplies.

冰河的消失在未來將會造成全球海平面上升，而在某些地區當地的水源供應可能也會受到相當大的影響。

As the last Ice Age ended during a period of about 7,000 years, starting around 19,000 years ago, the levels of carbon dioxide in the atmosphere increased from 180 parts per million to 280 parts per million. But just in the past 150 years, they have surged from 280 to about 400 parts per million, far higher than what was required to put an end to the last Ice Age.

從19,000年前起，上次冰河期末的7,000年間，大氣中二氧化碳的濃度從百萬分之180(180 p.p.m.)升高至280 p.p.m.。但僅僅在過去的150年間，二氧化碳已從280 p.p.m.飆升至400 p.p.m.，遠比終結上次冰河期所需的濃度還要高上許多。

The new findings, Clark said, were based on a recalculation of the ages at which more than 1,100 glacial boulders from 159 glacial moraines around the world were exposed to the atmosphere after being buried for thousands of years under ice.

Clark說這項新發現建立於重新測量159層世界各地冰磧(glacial moraine)中的1100顆冰河礫石的年代。這些冰磧曾被深埋在冰層底下數千年，直到冰河融化後才重見天日。

The exposure of the boulders to cosmic rays produced cosmogenic nuclides, which had been previously measured and used to date the event. But advances have been made in how to calibrate ages based on that data. Based on the new calculations, the rise in carbon dioxide levels -- determined from ancient ice cores -matches up nicely with the time at which glacial retreat took place.

冰河融化後露出的礫石會暴露在宇宙射線的照射之下，而產生宇生核種(cosmogenic nuclide)，在先前的研究中可以測量其濃度來定年事件發生的年代。本研究改良之處在於如何以測量到的數據來換算成更精確的年代。根據他們新的計算方式而得出的冰河後退年代，與顯示在古老冰芯中的二氧化碳濃度上升時刻，兩者之間相當符合。

"There had been a long-standing mystery about why these boulders were uncovered at the time they were, because it didn't properly match the increase in greenhouse gases," said Jeremy Shakun, a professor at Boston College and lead author on the study. "We found that the previous ages assigned to this event were inaccurate. The data now show that as soon as the greenhouse gas levels began to rise, the glaciers began to melt and retreat."

「長久以來的疑惑在於為何這些礫石會在這個時間點開始暴露在地表，因為這與溫室氣體開始升高的時刻並不太符合。」本研究的第一作者，波士頓學院的Jeremy Shakun教授說。「我們發現之前對這起事件的年代的推估並不準確。現在的數據顯示溫室氣體的濃度一開始上升，冰河便會開始融化並後退。」

There are other forces that can also cause glacial melting on a local or regional scale, the researchers noted, such as changes in the Earth's orbit around the sun, or shifts in ocean heat distribution. These factors probably did have localized effects. But the scientists determined that only the change in greenhouse gas levels could have explained the broader global retreat of glaciers all at the same time.

研究人員注意到尚有其他因素會造成局部或區域性的冰河融化，像是地球繞日軌道的變化，或者海洋熱能分佈的改變。這些因素或多或少會造成區域性效應，然而科學家斷定唯有溫室氣體濃度的改變，才能在同一時間造成範圍廣至全球的冰河後退。

In the study of climate change, glaciers have always been of considerable interest, because their long-term behavior is a more reliable barometer that helps sort out the ups-and-downs caused by year-to-year weather variability, including short-term shifts in temperature and precipitation.

在氣候變遷的研究當中，冰河總是佔有一席之地，這是由於它們的長期變化並不會被年際氣候變化影響，包括溫度以及降雨的短週期變化，使得它們可以做為較可靠的長時間尺度氣壓計。

Other collaborators on this research were from the University of Wisconsin, Purdue University, and the National Center for Atmospheric Research. The work was supported by the National Oceanic and Atmospheric Administration and the National Science Foundation.

其他的協同研究人員來自威斯康辛大學、普渡大學以及美國國家大氣研究中心。本研究由美國國家海洋和大氣管理局及美國國家科學基金會所資助。

引用自：Oregon State University. "Greenhouse gases caused glacial retreat during last Ice Age." ScienceDaily. ScienceDaily, 21 August 2015.