Poles apart: why has Antarctic sea ice increased, and why can't coupled climate models reproduce observations?

由于其苍白的颜色，海冰将大部分入射的太阳辐射反射回太空，使当地温度相对较低。然而，如果变暖发生，海冰融化，取而代之的是颜色更深的海洋。这吸收了更多的太阳能，导致变暖，因此循环，即所谓的“冰反照率反馈”循环，继续下去。海冰还通过覆盖海洋上层，减少海洋向大气散失的热量，改变了区域表面能量平衡。此外，海冰很重要，因为它在大气和海洋之间的二氧化碳交换中起着重要作用，从而影响到大气中这种温室气体的含量，并导致全球变暖。此外，海冰的形成是推动全球海洋热盐热盐环流的一个重要因素。这种环流的一个组成部分是北大西洋暖流，它将温暖的热带水带过大西洋，使英国的冬季温度比其他情况下高得多。政府间气候变化专门委员会（IPCC）的评估报告是推动世界各国政府政策的重要工具。然而，用于预测这些报告中所描述的未来气候情景的当前一代气候模式，无法一贯地再现最近南极海冰的增加。因此，他们对未来气候的预测必然带有相当大的不确定性。这一建议旨在提高我们对地球气候的认识，并促进对其未来变化的更好预测，以帮助决策者。这将通过以下目标来实现：解释最近南极海冰增加所涉及的关键气候过程。我们从观测中知道，南极周围近地表风的变化是观测到的海冰增加的主要原因，但我们并不确切知道风和冰是如何相互作用的。使用最先进的海冰和海洋的计算机模型，根据最新的大气数据，我们将建立关键的过程，通过这些过程，风的变化导致了冰的增加。以确定海冰增加的最终驱动因素。决策者需要知道我们是否可以将观测到的南极海冰变化归因于人类活动。这可能是由于“臭氧空洞”或温室气体增加引起的南极洲近地表风的变化而发生的。或者，它可能仅仅是由于南极气候系统的自然变化。如果前者是正确的，我们必须确定哪些人类活动应对此负责。如果后者是正确的，我们必须努力理解关键过程与气候系统更广泛方面之间的联系。为了理解为什么目前的气候模型无法模拟南极海冰的增长。我们将详细检查当前的英国气候模型，以诊断出哪些因素是罪魁祸首，并与我们的气象局合作伙伴一起，我们将设计一个发展计划，以确保我们的发现及时转化为未来模型的改进，以便在下一份IPCC报告中使用。为了帮助世界各地的其他气候模型开发者，我们还将分析IPCC报告中使用的其他模型是否也存在这些缺陷。

Due to its pale colour, sea ice reflects much of the incoming solar radiation back into space, keeping local temperatures relatively cold. However, if warming occurs and sea ice melts, it is replaced by darker ocean. This absorbs more solar energy, causing warming, and so the cycle, the so-called 'ice-albedo feedback' loop, continues. Sea ice also modifies the regional surface energy balance by capping the upper layer of the ocean, reducing its loss of heat to the atmosphere. In addition, sea ice is important because it plays a role in the exchange of carbon dioxide between the atmosphere and ocean, thereby affecting how much of this greenhouse gas is in the atmosphere and contributing to global warming. Moreover, sea ice formation is an important element in driving the global thermohaline circulation of heat and salt through the world's oceans. One component of this circulation is the North Atlantic Drift current that carries warm tropical water across the Atlantic and keeps the UK's winter temperatures much warmer than they would be otherwise.The Intergovernmental Panel on Climate Change (IPCC) assessment reports are an important tool in drivng government policy around the world. However, the present generation of climate models, which are used to predict the future climate scenarios described in these reports, are unable to consistently reproduce the recent increase in Antarctic sea ice. As a result considerable uncertainty must be attached to their predictions of future climate.This proposal aims to both advance our understanding of the Earth's climate and facilitate improved predictions of its future change to aid policy makers. This will be achieved through the following objectives: 1. To explain the key climate processes involved in the recent Antarctic sea ice increase. We know from observations that changes in the near-surface wind around Antarctica are predominantly responsible for the observed increase in sea ice but we don't know exactly how the wind and the ice interact. Using a state-of-the-art computer model of sea ice and the ocean forced by the latest atmospheric data we will establish the key processes through which changes in the wind are causing the ice to increase.2. To establish the ultimate driver of the sea ice increase. Policymakers need to know whether we can attribute the observed changes in Antarctic sea ice to human activity. This might happen through changes in the near-surface winds around Antarctica caused by the 'ozone hole' or greenhouse gas increases for example. Alternatively, it may be simply due to natural variations in the Antarctic climate system. If the former is true, we must determine which human activities are responsible. If the latter is correct, we must try to understand connections between the key processes and wider aspects of the climate system.3. To understand why current climate models fail to simulate the growth in Antarctic sea ice. We will examine the current UK climate model in detail to diagnose which components are to blame and, with our Met Office partner, we will design a development programme to ensure that our findings are transferred into future model improvements in time for the next IPCC report. To help other climate model developers around the world, we will also analyse whether the failings are common to the other models used in the IPCC reports.