The Arctic Ocean began warming decades earlier than previously thought, new research shows
(CNN)The Arctic Ocean has been warming since the onset of the 20th century, decades earlier than instrument observations would suggest, according to new research.
The study, published Wednesday in the journal Science Advances, found that the expansion of warm Atlantic Ocean water flowing into the Arctic, a phenomenon known as "Atlantification," has caused Arctic water temperature in the region studied to increase by around 2 degrees Celsius since 1900.
Francesco Muschitiello, an author on the study and assistant professor of geography at the University of Cambridge, said the findings were worrisome because the early warming suggests there might be a flaw in the models scientists use to predict how the climate will change.
"The Arctic Ocean has been warming up for much longer than we previously thought," Muschitiello told CNN. "And this is something that's a bit unsettling for many reasons, especially because the climate models that we use to cast projections of future climate change do not really simulate these type of changes."
The researchers used marine sediments in the Fram Straight, where the Atlantic meets the Arctic east of Greenland, to reconstruct 800 years of data that paint a longer historical picture of how Atlantic water has flowed into the Arctic. The marine sediments are "natural archives," the researchers wrote, which record data on past climate conditions.
Researchers found temperature and salinity, the saltiness of ocean water, remained fairly constant up until the 20th century -- then they suddenly increased.
"The reconstructions suggest a substantial increase in the Atlantic Ocean heat and salt transport into the Nordic Sea at the beginning of the 20th century, which is not well simulated by (climate models)," Rong Zhang, a senior scientist at NOAA's Geophysical Fluid Dynamics Laboratory, who was not involved with the study, told CNN. "It's important to understand the cause of this rapid Atlantification, as well as the discrepancies between the model simulations and the reconstructions."
Muschitiello said it's not clear how much of a role, if any, human-caused climate change played in the early Arctic warming, and more research is needed.
"We're talking about the early 1900s, and by then we've already been supercharging the atmosphere with carbon dioxide," he said. "It is possible that the Arctic Ocean is more sensitive to greenhouse gases than previously thought. This will require more research, of course, because we don't have a solid grip on the actual mechanisms behind this early Atlantification."
The study notes that changes in the Atlantic Meridional Overturning Circulation (AMOC) — a system of currents that moderates temperatures in the Northern Hemisphere — could have played a role in the Arctic warming. Notably, the AMOC weakened after a period of cooling ended in the mid-1800s in the North Atlantic region, which researchers suggest could have led to rapid Atlantification along the east Fram Strait.
A recent study found that the AMOC, often described as a "conveyor belt" that transports warm water from the tropics and redistributes it northward, is now showing signs of further instability due to human-caused climate change. Scientists have warned that a collapse of the circulation could lead to an abrupt shift in weather patterns across the globe — colder winters in Europe, changes to monsoons and potentially permanent drought in West Africa.
The rapidly warming temperatures in the Arctic have caused sea ice to melt, which in turn causes more warming -- while bright white sea ice reflects the sun's energy, dark ocean absorbs the energy as heat.
James E. Overland, NOAA Arctic scientist based at NOAA Pacific Marine Environmental Lab in Seattle, said such long-term changes in the North Atlantic, coupled with recent loss of sea ice in the Arctic, threatens marine ecosystems.
"Loss of sea ice and ocean currents has shifted the buffer region between the Atlantic and Arctic Ocean to something closer to an arm of the central Atlantic," Overland, who was not involved with the study, told CNN. "Important fisheries and marine mammals are vulnerable to ecosystem reorganization from such Atlantification."
A recent UN state-of-the-science report on the climate crisis found the Arctic will continue to warm faster than the rest of the planet as long as humans continue to burn fossil fuels and release greenhouse gases into the atmosphere. On top of that, Muschitiello said the Arctic Ocean may experience further warming due to Atlantification.
"When I talk to my students I always try to make them aware that the Arctic is warming very, very quickly, and much faster than any other area on the planet," Muschitiello said. "It's very unsettling and very troubling, especially because we still don't have a full understanding of feedbacks at play."
"We're still slowly getting to know how the whole system works," he said. "And my fear is that by the time that we do crack the problem, it's going to be too late."
新研究表明，北冰洋开始变暖的时间比以前认为的早了几十年
（美国有线电视新闻网）根据一项新的研究，自 20 世纪初以来，北冰洋一直在变暖，比仪器观测所表明的要早几十年。
周三发表在《科学进展》杂志上的这项研究发现，流入北极的大西洋暖水膨胀，这种现象被称为“大西洋化”，自那时以来，该地区的北极水温升高了约 2 摄氏度。 1900。
该研究的作者、剑桥大学地理学助理教授 Francesco Muschitiello 表示，这些发现令人担忧，因为早期变暖表明科学家用来预测气候变化的模型可能存在缺陷。
“北冰洋变暖的时间比我们之前想象的要长得多，”Muschitiello 告诉 CNN。 “出于多种原因，这有点令人不安，特别是因为我们用来预测未来气候变化的气候模型并没有真正模拟这些类型的变化。”
研究人员利用弗拉姆海峡的海洋沉积物，在那里大西洋与格陵兰以东的北极相遇，重建了 800 年的数据，描绘了大西洋水如何流入北极的更长历史画面。研究人员写道，海洋沉积物是“自然档案”，它记录了过去气候条件的数据。
研究人员发现温度和盐度，即海水的咸度，直到 20 世纪都保持相当稳定——然后它们突然增加。
美国国家海洋和大气管理局地球物理流体动力学高级科学家张荣说：“重建表明，在 20 世纪初，进入北欧海的大西洋热量和盐分大量增加，而（气候模型）并没有很好地模拟这种情况。”没有参与这项研究的实验室告诉 CNN。 “了解这种快速大西洋化的原因以及模型模拟与重建之间的差异非常重要。”
Muschitiello 说，目前尚不清楚人为气候变化在北极早期变暖中的作用有多大，需要更多的研究。
“我们谈论的是 1900 年代初期，到那时我们已经用二氧化碳给大气增压了，”他说。 “北冰洋对温室气体的敏感性可能比以前想象的要高。当然，这需要更多的研究，因为我们对这种早期大西洋化背后的实际机制没有把握。”
该研究指出，大西洋经向翻转环流 (AMOC)——一种调节北半球温度的洋流系统——的变化可能在北极变暖中发挥了作用。值得注意的是，在 1800 年代中期北大西洋地区的冷却期结束后，AMOC 减弱，研究人员认为这可能导致沿东弗拉姆海峡快速大西洋化。
最近的一项研究发现，AMOC，通常被描述为“传送带”，从热带输送温水并向北重新分配，现在由于人为引起的气候变化显示出进一步不稳定的迹象。科学家警告说，环流的崩溃可能会导致全球天气模式的突然转变——欧洲的冬季更冷、季风的变化以及西非可能的永久性干旱。
北极迅速升温的温度导致海冰融化，从而导致更多的变暖——而明亮的白色海冰反射太阳的能量，而黑暗的海洋则以热量的形式吸收能量。
位于西雅图的 NOAA 太平洋海洋环境实验室的 NOAA 北极科学家 James E. Overland 表示，北大西洋的这种长期变化，加上最近北极海冰的消失，威胁着海洋生态系统。
“海冰和洋流的消失已经将大西洋和北冰洋之间的缓冲区转移到了更接近大西洋中部的一部分，”没有参与这项研究的欧弗兰告诉美国有线电视新闻网。 “重要的渔业和海洋哺乳动物很容易受到这种大西洋化带来的生态系统重组的影响。”
联合国最近一份关于气候危机的最新科学报告发现，只要人类继续燃烧化石燃料并将温室气体排放到大气中，北极将继续比地球其他地区变暖得更快。最重要的是，Muschitiello 表示，由于大西洋化，北冰洋可能会进一步变暖。
“当我和我的学生交谈时，我总是试图让他们意识到北极变暖的速度非常非常快，而且比地球上任何其他地区都快得多，”Muschitiello 说。 “这非常令人不安，也非常令人不安，尤其是因为我们仍然没有完全了解正在发挥作用的反馈。”
“我们仍在慢慢了解整个系统的运作方式，”他说。 “而我担心的是，当我们真正解决问题时，为时已晚。”
