OCE-RIG: Identifying the role of ocean circulation in polar climate change

近几十年来，高纬度地区发生了很大的变化：北极变暖的速度比地球上任何其他地方都快，与此同时，它的海冰覆盖面积迅速减少，而南大洋则大幅降温，海冰覆盖面积适度扩大。引起这些观测到的变化的动力尚不清楚，这一点在我们最先进的全球气候模式模拟的过去和未来极地气候变化的大范围蔓延中得到了证明。然而，提高对极地海洋变化的了解对极地和全球气候的可预测性都至关重要。本研究旨在建立海洋、大气和冰冻圈在极地气候变化中的相对作用和相互作用，并确定起作用的关键过程。该项目的另一个目标是向代表性不足的高中生介绍海洋在气候变化中的关键作用。研究高纬度气候变化的一个主要挑战是控制系统动力学的固有耦合性质。例如，南极洲周围的海洋变化是由多种因素共同驱动的，例如温室气体强迫、淡水输入增加以及平流层臭氧消耗导致的地面风的变化；每一种驱动因素的影响都受到它们所作用的背景海洋环流的进一步影响，这使得很难确定观测到的——甚至是模拟的——极地气候变化的主要原因，也妨碍了对未来一个世纪的极地气候进行可靠的预测。本研究试图通过数值模拟的海洋环流模式来克服这些挑战，该模式是由这些不同的气候强迫分别或共同施加的海洋表面驱动的。这种方法使我们能够确定极地海洋环流在设定对温室气体强迫的响应方面的关键作用，并揭示了极地海洋的不同环流在最近几十年中引起了它们的对比变化——由于经向海洋热输送变化的差异，北极变暖的速度远远大于南大洋。该研究进一步检查了对各种气候强迫的响应——包括淡水通量变化和大尺度和区域地面风的变化——使我们能够确定背景海洋环流在调节对每种强迫的响应中的作用。此外，通过用不同综合耦合全球气候模式特有的气候表面边界条件驱动海洋模式，我们评估了不同背景海洋条件对这些耦合模式模拟的大范围极地气候预估的影响。研究高纬度气候变化的一个主要挑战是控制系统动力学的固有耦合性质。例如，南极洲周围的海洋变化是由多种因素共同驱动的，例如温室气体强迫、淡水输入增加以及平流层臭氧消耗导致的地面风的变化；每一种驱动因素的影响都受到它们所作用的背景海洋环流的进一步影响，这使得很难确定观测到的——甚至是模拟的——极地气候变化的主要原因，也妨碍了对未来一个世纪的极地气候进行可靠的预测。本研究试图通过数值模拟的海洋环流模式来克服这些挑战，该模式是由这些不同的气候强迫分别或共同施加的海洋表面驱动的。这种方法使我们能够确定极地海洋环流在设定对温室气体强迫的响应方面的关键作用，并揭示了极地海洋的不同环流在最近几十年中引起了它们的对比变化——由于经向海洋热输送变化的差异，北极变暖的速度远远大于南大洋。该研究进一步检查了对各种气候强迫的响应——包括淡水通量变化和大尺度和区域地面风的变化——使我们能够确定背景海洋环流在调节对每种强迫的响应中的作用。此外，通过用不同综合耦合全球气候模式特有的气候表面边界条件驱动海洋模式，我们评估了不同背景海洋条件对这些耦合模式模拟的大范围极地气候预估的影响。

The high-latitudes have changed substantially over recent decades: the Arctic has warmed faster than anywhere else on Earth, concurrent with a rapid decline of its sea-ice cover, while the Southern Ocean has largely cooled and its sea-ice cover has modestly expanded. The dynamics giving rise to these observed changes are not yet understood - as evidenced in the large spread of past and future polar climate changes simulated by our state-of-the-art global climate models. Yet, improved understanding of the changing polar oceans is critical to both polar and global climate predictability. This study aims to establish the relative roles of, and interactions between, the oceans, atmosphere and cryosphere in polar climate change and identify the key processes at work. A further goal of the project is to introduce an audience of under-represented high-school students to the key role of the ocean in our changing climate.A major challenge to studying high-latitude climate change is the inherently coupled nature of the governing system dynamics. For instance, oceanic changes around Antarctica have been driven by a combination of factors, such as greenhouse gas forcing, increased freshwater input, and changes in surface winds due to stratospheric ozone depletion; the effects of each of these drivers have been further shaped by the background ocean circulation on which they act, making it difficult to attribute the primary causes of observed - or even simulated - polar climate changes, and precluding confident polar climate prediction over the coming century. This study seeks overcomes these challenges through numerical simulation with an oceanic general circulation model driven at the ocean surface by these distinct climate forcings - applied separately and together. This approach allows us to identify the key role of polar ocean circulation in setting the response to greenhouse gas forcing, and reveals that distinct circulations of the polar oceans have given rise to their contrasting changes over recent decades - with the Arctic warming at a far greater pace than the Southern Ocean due to differences in meridional ocean heat transport changes. The study further examines the response to the full range of climate forcings - including fresh water flux changes and variations in both large-scale and regional surface winds - allowing us to identify the role of the background ocean circulation in mediating the response to each. Furthermore, by driving the ocean model with climatological surface boundary conditions unique to different comprehensive coupled global climate models, we assess the influence of distinct background ocean conditions in the large spread of polar climate projections simulated across those coupled models.A major challenge to studying high-latitude climate change is the inherently coupled nature of the governing system dynamics. For instance, oceanic changes around Antarctica have been driven by a combination of factors, such as greenhouse gas forcing, increased freshwater input, and changes in surface winds due to stratospheric ozone depletion; the effects of each of these drivers have been further shaped by the background ocean circulation on which they act, making it difficult to attribute the primary causes of observed - or even simulated - polar climate changes, and precluding confident polar climate prediction over the coming century. This study seeks overcomes these challenges through numerical simulation with an oceanic general circulation model driven at the ocean surface by these distinct climate forcings - applied separately and together. This approach allows us to identify the key role of polar ocean circulation in setting the response to greenhouse gas forcing, and reveals that distinct circulations of the polar oceans have given rise to their contrasting changes over recent decades - with the Arctic warming at a far greater pace than the Southern Ocean due to differences in meridional ocean heat transport changes. The study further examines the response to the full range of climate forcings - including fresh water flux changes and variations in both large-scale and regional surface winds - allowing us to identify the role of the background ocean circulation in mediating the response to each. Furthermore, by driving the ocean model with climatological surface boundary conditions unique to different comprehensive coupled global climate models, we assess the influence of distinct background ocean conditions in the large spread of polar climate projections simulated across those coupled models.