研究：大西洋洋流遭氣候嚴重削弱後仍可恢復

作者：阿格涅什卡・奧倫斯卡與路易絲・拉斯穆森By Agnieszka Olenska and Louise Rasmussen

哥本哈根，10月14日（路透社）——丹麥氣象研究所週三公布的一項研究顯示，因全球暖化而減弱的大西洋洋流系統，若氣候降溫，可能會隨著時間恢復。COPENHAGEN, Oct 14 (Reuters) - An Atlantic Ocean current system weakened by global warming could recover over time if the climate cools, a study by the Danish Meteorological Institute showed on Wednesday.

大西洋經向翻轉環流（AMOC）會把來自熱帶的溫暖海水向北帶往北極，而暖流有助於維持歐洲冬季的溫和氣候。The Atlantic Meridional Overturning Circulation brings warm water from the tropics northward toward the Arctic, and the flow of warm water helps keep Europe's winters mild.

這項發表於《科學進展》（Science Advances）期刊的研究指出，並未發現AMOC存在不可逆轉的臨界點跡象，這與部分先前研究的說法不同；不過，這些變化的影響可能持續數百年。Published in the journal Science Advances, the study found no sign there was an irreversible tipping point for AMOC, as suggested by some previous studies, although the effects of the changes could last for centuries.

然而，研究也指出，格陵蘭冰蓋會將冰冷淡水注入海洋，導致AMOC減弱；一旦融化，即使暖化趨勢逆轉，也無法復原。However, it also said that the Greenland ice sheet that contributes to weakening the AMOC as it pours cold freshwater into the ocean could not be restored once it had melted — even if the warming trend was reversed.

AMOC若受到擾動，仍可能使全球降雨模式失去穩定，並加速沿海海平面上升。A disrupted AMOC could still destabilise global rainfall patterns and accelerate coastal sea-level rise.

模型未顯示會導致崩潰的臨界點NO TIPPING POINT LEADING TO COLLAPSE SEEN IN MODEL

研究指出，在全球升溫約攝氏7度時，AMOC每秒輸送水量可能從約1,700萬立方公尺，減緩至約600萬立方公尺。The study said the AMOC could slow to about 6 million cubic metres of water per second from around 17 million at around 7 degrees Celsius of global warming.

主要作者郭春成（Chuncheng Guo）表示：「在我們的模型中，我們沒有看到會導致崩潰的臨界點。AMOC會逐漸減弱，但我們發現，如果全球暖化逆轉，它也會立即恢復強度。」"In our model, we do not see a tipping point leading to a collapse. The AMOC gradually weakens, but we find that it also immediately regains its strength if global warming is reversed," lead author Chuncheng Guo said.

不過他警告，即使氣溫一下降，復原就會開始，但整個過程可能需要數百年才能完成；在此期間，洋流減弱造成的影響仍會持續存在。However, he warned that even though recovery starts as soon as temperatures fall, it could take several centuries to finish, all while the effects of a weakened current would persist.

模型中為科學研究目的所採用的升溫攝氏7度，遠高於目前對暖化趨勢的預測。The 7 C rise used in the modelling used for scientific interest is far beyond the current projections for the warming trend.

聯合國環境機構9月表示，全球升溫將在「幾年內」超過攝氏1.5度這個關鍵門檻。各國政府已在2015年《巴黎協定》下承諾，將升溫控制在攝氏1.5度以內，以限制極端天氣造成的衝擊。The UN's environmental body said in September global temperature rises are set to exceed the key threshold of 1.5 C "within a few years". Governments committed to keeping temperature rises within 1.5 C to limit the impacts of extreme weather under the 2015 Paris Agreement.

郭春成補充說，要讓AMOC逆轉所需的降溫速度，也超過目前技術被認為可實現的範圍；他指出，這是這項單一模型研究的限制。研究也表示，還需要以其他模型進一步檢驗。The cooling rate required to reverse the AMOC also exceeds what is considered realistic with current technology, Guo added, pointing to a limitation of the single-model study. Further testing against other models was also needed, the study said.

未參與這項研究的波茨坦氣候影響研究所（Potsdam Institute for Climate Impact Research）威廉・豪伊斯坎普（Willem Huiskamp）表示，若AMOC較為穩定會是好消息，但他說，他懷疑現實世界中的洋流是否如部分模型所顯示的那樣穩定。Willem Huiskamp at the Potsdam Institute for Climate Impact Research, who was not involved in the study, said a more stable AMOC would be good news, but said he doubted the real-world current was as stable as some models suggested.

研究人員估計，在升溫攝氏1.5度後，格陵蘭冰蓋融化將導致長期海平面上升約20公分，並呼籲更快採取行動控制排放。The researchers estimated a long-term sea-level rise of around 20 cm from the melting of the Greenland ice sheet following a 1.5 C rise, and urged faster action to rein in emissions.

郭春成表示：「與其仰賴全球降溫會發生，一開始就避免暖化，是安全得多、也穩妥得多的策略。」"Instead of relying on the global cooling to happen, it's a much, much safer strategy to not have warming in the first place," Guo said.

（阿格涅什卡・奧倫斯卡與路易絲・拉斯穆森報導；特耶・索爾斯維克與艾莉森・威廉斯編輯）(Reporting by Agnieszka Olenska and Louise Rasmussen; Editing by Terje Solsvik and Alison Williams)