DEFIANT: Drivers and Effects of Fluctuations in sea Ice in the ANTarctic

自工业革命开始以来，大气中的二氧化碳浓度一直在稳步上升。科学家们已经证实，最近北极海冰在夏季的损失直接伴随着人类引起的二氧化碳排放量的增加，从20世纪70年代末的约700万平方公里北极海冰减少到2010年代的约350万平方公里。卫星观测显示，在1979-2015年期间，事实恰恰相反。南极海冰范围的趋势是每十年小幅增加约1.5%。然而，在2016年，这种增加突然被海冰范围的急剧减少所打断，这远远超出了先前观察到的范围。自2016年极端事件以来，南极海冰范围几乎恢复到2016年前的值，凸显了南极海冰条件在一年到下一年之间可能发生的显著变化。海冰的这些变化对整个地球的气候都很重要，因为它们影响到南极冰盖的融化，以及南大洋对大气热量和二氧化碳的捕获。最近南极海冰范围的极端波动，以及准确预测、理解和建模的挑战，强调了需要：（i）增加我们对驱动南极海冰变化的过程的了解，包括极端事件，（ii）了解不同时间尺度（从数周到数十年）南极海冰损失的驱动因素和气候影响。为了弥补这一知识差距，需要开展一项重要的研究计划，该计划需要进行全年观测，包括南极严酷的冬季，并有效地改善最新计算机气候模型中的基本过程。南极海冰波动的驱动因素和影响，将开始一项最雄心勃勃的观测活动，旨在了解南极海冰的变化。来自德国研究船Polarstern，英国新的极地研究船大卫阿滕伯勒爵士，英国南极调查局的罗瑟拉研究站，飞机飞越和卫星的科学测量将与尖端机器人技术（包括水下航行器Boaty McBoatface和一套冰上浮标）无缝合作，为我们提供全面的全年测量大气，海冰和海洋。从这些观测中获得的知识将使我们的团队能够开发新的海洋和气候模型，以便更准确地表示南极海冰过程。对这些改进模型的分析将使我们能够更好地了解南极海冰突然减少的潜在驱动因素，确定这些极端事件对全球海洋环流的影响，并预测热量和二氧化碳在整个气候系统中的运动。通过开发新的观测、新的卫星记录和新的模型，DEFIANT将在我们对南极海冰系统及其对全球气候的更广泛影响的理解方面取得重大进展。

Since the start of the industrial revolution the CO2 concentration in the atmosphere has steadily risen. Scientists have confirmed that the recent loss of Arctic sea ice in summer directly follows this rise in human-induced CO2 emissions, reducing from about 7 million km2 of Arctic sea ice in the late 1970s to around 3.5 million km2 in the 2010s.While climate models suggest Antarctic sea ice extent should also reduce in response to rising CO2, satellite observations reveal that during 1979-2015 the opposite was in fact true. The trend in Antarctic sea ice extent has been a small increase of approximately 1.5% per decade. In 2016, however, this increase was abruptly interrupted by a dramatic reduction in sea ice extent that was far outside the previously observed range. Since the extreme event in 2016, Antarctic sea ice extent has almost returned to its pre-2016 values, highlighting the significant variability in Antarctic sea ice conditions that can occur from one year to the next. These variations in sea ice are important to the whole Earth's climate, because they affect the melting of the glacial Antarctic Ice Sheet, and the capture of atmospheric heat and CO2 by the Southern Ocean.The recent extreme swings in Antarctic sea ice extent, and the challenge of accurately predicting, understanding and modelling them, emphasise the need to: (i) increase our knowledge of the processes that drive Antarctic sea ice variations, including extreme events, and (ii) understand the drivers and climate implications of Antarctic sea ice loss over different time-scales, from weeks to decades. To address this knowledge gap requires a significant research programme, one that takes year-round observations, including throughout the harsh Antarctic winter, and is effective in improving the underlying processes in the latest computer climate models.Our project, known as DEFIANT (Drivers and Effects of Fluctuations in sea Ice in the ANTarctic), will embark on one of the most ambitious observational campaigns aimed at understanding Antarctic sea ice variability. Scientific measurements from the German research ship Polarstern, the UK's new polar research ship Sir David Attenborough, the British Antarctic Survey's Rothera research station, aircraft overflights and satellites will work seamlessly together with cutting-edge robotic technologies (including the underwater vehicle Boaty McBoatface and a suite of on-ice buoys) to provide us with comprehensive, year-round measurements of atmosphere, sea ice and ocean. The knowledge gained from these observations will enable our team to develop new ocean and climate models in order to more accurately represent Antarctic sea ice processes.The analysis of these improved models will allow us to better understand the underlying drivers of the sudden decrease in Antarctic sea ice, determine the impact of these extreme events on the global ocean circulation, and forecast the implications for the movements of heat and CO2 through the climate system. By developing new observations, new satellite records, and new models, DEFIANT will deliver a major advance in our understanding of the Antarctic sea ice system and its wider impacts on global climate.