Assessing simulations of Southern Hemisphere tropospheric jet, meridional overturning circulation of the Southern Ocean and carbon uptake

在人类活动每年产生的二氧化碳排放量中，只有大约一半留在大气中。其余的则被陆地和海洋所占据，数量大致相等。目前，环绕南极洲的南大洋占海洋总摄入量的不到一半。如果不这样做，大气中二氧化碳水平的增加速度将比我们目前观察到的要快得多。世界上的海洋由一个巨大而缓慢的循环系统连接在一起，水在北大西洋下沉，向南移动，然后在南大洋上升到表面。当它到达表面时，这些水能够与大气交换二氧化碳，然后环流再次下降到表面以下，锁定海洋中的二氧化碳，并返回北方。如果这种环流发生变化，南大洋的碳吸收也会发生变化。因此，科学家们需要回答的一个关键问题是，气候变化是否会导致南大洋颠覆的环流发生变化？如果答案是肯定的，那么这可能会改变大气中的二氧化碳含量，并对气候变化起到强烈的反馈作用。最近引起了关注，因为一些观测表明，考虑到目前大气中二氧化碳的浓度，南大洋吸收的二氧化碳确实比我们历史上预期的要少。那么，气候变化可能会如何影响南大洋颠覆环流？南冰洋上空刮起了强风。风直接驱动环流向北移动到地表。它们还通过对海洋风暴的产生产生影响，间接推动环流向相反方向流动，即在表面向南移动，即所谓的“涡流”。由此产生的环流向北指向地表，是这些相反的环流的微妙平衡。据观察，近几十年来，风力一直在增加。大气层的两个变化被认为引发了风的变化，这两个变化都有人为原因：大气中温室气体的增加和平流层臭氧的减少。因此，有理由问一问，未来南大洋的碳吸收是否会受到大气温室气体浓度变化和臭氧层恢复的影响。用于预测未来气候的计算机模型只有在能够恰当地表示大气和海洋中将大气组成与通过南大洋风吸收海洋碳的不同物理过程联系起来的情况下，才能解决这个问题。该项目旨在评价将作为气专委下一份报告基础的最新一代模型中这些进程的表现。

Of the carbon dioxide emissions human activities generate each year, only about half stay in the atmosphere. The rest are taken up by the land and the oceans, in approximately equal measure. At present the Southern Ocean that encircles Antarctica accounts for just under half of the total ocean uptake. Were it not to do so, carbon dioxide levels in the atmosphere would increase at a significantly faster rate than we currently observe. The world's oceans are connected by a vast, slow circulation system with water sinking in the North Atlantic, travelling southward, and then rising to the surface in the Southern Ocean. When it reaches the surface, this water is able to exchange carbon dioxide with the atmosphere, before the circulation dips below the surface again, locking the carbon dioxide in the ocean, and returns north. If that circulation were to change, the carbon uptake of the Southern Ocean would change. So a key question to scientists to answer is, will climate change invoke changes to the overturning circulation of the Southern Ocean? If the answer is yes, then this could change the amount of carbon dioxide in the atmosphere and act as a strong feedback on climate change. Concern has been raised recently because some observations have indicated that indeed the Southern Ocean is taking up less carbon dioxide than we would have historically expected given the current atmospheric carbon dioxide concentrations.So how might climate change be impacting the Southern Ocean overturning circulation? Strong winds blow around Antarctic over the Southern Ocean. The winds directly drive a circulation that is directed northward at the surface. They also indirectly drive a circulation in the opposite direction, i.e. southward at the surface, via their influence on the generation of ocean storms, known as "eddies". The resultant circulation, which is directed northward at the surface, is a subtle balance of these opposing circulations. The winds have been observed to increase in recent decades. Two changes to the atmosphere are thought to have instigated the change in the winds, both of which have human cause: the increase in greenhouse gases in the atmosphere and the decrease in ozone in the stratosphere. It is reasonable to ask therefore whether the carbon uptake of the Southern Ocean might be influenced in the future by changes to the atmospheric concentration of greenhouse gases and by the recovery of the ozone layer. Computer models used to project future climate can only address this question if they are able to properly represent the different physical processes in the atmosphere and ocean that link the atmospheric composition to ocean carbon uptake via the Southern Ocean winds. This project aims to evaluate the representation of these processes in the latest generation of models that will be used as a basis for the next IPCC report.