No turning point, the slowdown of current!? 洋流減緩流動！？

 

【縛雞之見】英文拷到 G / D 找中文翻譯
“Major Atlantic ocean current system might be approaching critical threshold”? 
Really?

That is a disastrous phenomenon if not doomsday.  I keep thinking that almost all countries encourage and invest in the so-called Green energy; however, Green energy is not completely clean. 
According to the law of conservation of energy, it needs resources to transform static or dynamic energy into electricity. 
For example, utilizing the wind and current energy arise the friction of the earth surface through countless high towers and maritime devices, which slow down the speed of the natural flow and may cause consequences we are yet to know.  Solar energy needs land, which may produce crops, or helps environmental protection. 
It is not science fiction.  The shutdown or slowdown of the thermohaline circulation might cause hypothesized effect of global warming on the major ocean circulations.

大西洋環流「千年來最弱」 停擺恐使北美歐洲「陷入極寒」    自由20210807

德國柏林自由大學發表在《自然氣候變化》（ Nature Climate Change）期刊的新研究發現，大西洋經向翻轉環流（AMOC）瀕臨崩潰邊緣，歐洲、北美洲恐因此陷入極度寒冷的狀態。

綜合外媒報導，大西洋經向翻轉環流是1條洋流，從熱帶地區出發，把溫暖、鹽分濃度較高的海水送往寒帶地區，再循環將較冷、鹽分較低的海水沿著海床送往熱帶地區。

過去有研究表示，古代氣候劇烈變遷，原因之一是這道洋流當時突然停止運作，造成沿岸地區天氣系統完全改變，進而引發災難。

德國柏林自由大學氣候科學家博爾斯（Niklas Boers）領導的研究，透過地球的古氣候記錄與電腦模擬運算得知，大西洋經向翻轉環流有著「強模式」與「弱模式」，兩者之間是可能突然轉換的，而目前此環流正處於1000年來最弱的狀態，瀕臨崩潰邊緣。

模式顯示，一旦完全停擺，北美洲、歐洲將陷入極寒；導致這種狀況的因素中，全球暖化使淡水流入海洋的影響最大。

博爾斯強調，格陵蘭冰蓋融化的淡水流入、海冰融化、降雨量與河流流量增加，是導致環流減弱的主要因素之一，由於淡水稀釋了從熱帶地區北上的環流密度，若繼續下去，將導致環流無法繼續推動，因而停擺。

博爾斯說，若此環流真的崩潰，需要更劇烈的氣候變遷才能使它重新運作，眼下當務之急是減少排放溫室氣體，延緩全球暖化。

  

Major Atlantic ocean current system might be approaching critical threshold   

A major Atlantic ocean current -- the Atlantic Meridional Overturning Circulation, or AMOC -- may have been losing stability in the course of the last century, according to new research. A potential collapse of this ocean current system could have severe consequences.

The major Atlantic Ocean current, to which also the Gulf stream belongs, may have been losing stability in the course of the last century. This is shown in a new study published in Nature Climate Change.  The Atlantic Meridional Overturning Circulation, or AMOC, transports warm water masses from the tropics northward at the ocean surface and cold water southward at the ocean bottom, which is most relevant for the relatively mild temperatures in Europe.  Further, it influences weather systems worldwide.  A potential collapse of this ocean current system could therefore have severe consequences.

"The Atlantic Meridional Overturning really is one of our planet's key circulation systems," says the author of the study, Niklas Boers from the Potsdam Institute for Climate Impact Research, Freie Universität Berlin and Exeter University.  "We already know from some computer simulations and from data from Earth's past, so-called paleoclimate proxy records, that the AMOC can exhibit -- in addition to the currently attained strong mode -- an alternative, substantially weaker mode of operation.  This bi-stability implies that abrupt transitions between the two circulation modes are in principle possible."

Loss of dynamical stability could ultimately lead to collapse

It has been shown previously that the AMOC is currently at its weakest in more than a 1000 years.  However, so far it has remained an open question whether the observed weakening corresponds to a change in the mean circulation state, or whether it is associated with an actual loss of dynamical stability.  "The difference is crucial," says Niklas Boers, "because the loss of dynamical stability would imply that the AMOC has approached its critical threshold, beyond which a substantial and in practice likely irreversible transition to the weak mode could occur."

Long-term observational data of the strength of the AMOC does unfortunately not exist, but the AMOC leaves so-called fingerprints in sea-surface temperature and salinity patterns of the Atlantic ocean.  "A detailed analysis of these fingerprints in eight independent indices now suggests that the AMOC weakening during the last century is indeed likely to be associated with a loss of stability," says Boers.  "The findings support the assessment that the AMOC decline is not just a fluctuation or a linear response to increasing temperatures but likely means the approaching of a critical threshold beyond which the circulation system could collapse."

In addition to global warming, freshwater inflow is a factor -- which is also linked to climate change

A number of factors are likely important for the phenomenon -- factors that add to the direct effect that the warming of the Atlantic ocean has on its circulation.  These include freshwater inflow from the melting of the Greenland ice sheet, melting sea-ice, increasing precipitation and river run-off.  Freshwater is lighter than saltwater and reduces the tendency of the water to sink from the surface to greater depths, which is one of the drivers of the overturning.

"I wouldn't have expected that the excessive amounts of freshwater added in the course of the last century would already produce such a response in the overturning circulation," says Boers.  "We urgently need to reconcile our models with the presented observational evidence to assess how far from or how close to its critical threshold the AMOC really is."  While the respective relevance of the different factors has to be further investigated, they're all linked to human-caused climate change.