A century of variability in Greenland melting and iceberg calving

一些最具标志性的气候变化和海平面上升的图像包括一个戏剧性的时刻，当一大块冰从冰川的末端断裂和冰山融化的场景镜头。在大众的想象中，冰山也与近100年前泰坦尼克号的沉没有关。沉没泰坦尼克号的冰山可能是在几个月前，即1911/12年冬天，从西格陵兰冰川的终点开始的。总的来说，这些冰和冰山的印象传达了这项研究的核心内容，即冰山从北方主要冰盖格陵兰岛“崩解”的方式，以及这些冰山在北大西洋的命运。尽管冰山在大众的想象中占有重要地位，但令人惊讶的是，它们被气候科学家所忽视，并且在用于预测气候变化和海平面上升的模型中几乎被忽视。我们对冰山崩解的速度知之甚少，对它们在哪里融化也只有一个粗略的概念。随着科学家越来越确定格陵兰冰盖正在以惊人的速度融化和破裂，这种忽视正变得越来越成问题。自从发射了一个可以远程测量冰盖厚度的专门卫星系统以来，已经确定，过去几年中这种破裂加速了，没有迹象表明冰盖将重新稳定。据估计，格陵兰岛大约一半的“消失”是由于冰山崩解造成的。我们计划使用一个现有的海洋和冰山的详细模型，该模型应再现世纪期间在纽芬兰附近观察到的冰山变化。为了检查该模型的可重复性，并使这项技术能够转移到哈德利中心的气候模型中，冰山模块将被添加到气象局哈德利中心使用的海洋模型NEMO中。这些模式将使用格陵兰岛的高分辨率、长达一个世纪的表面质量平衡模式作为强迫。通过对我们的模型进行一系列仔细的实验，我们将能够更清楚地解释这些巨大的变化，在某些年份看到数千座冰山，而在其他年份则没有。我们的模型将帮助我们区分这种变化的两个原因：由于产犊率的变化（产生更多或更少的冰山）或洋流的变化（携带冰山进一步向北或向南）。如果我们能够准确地重现观测到的冰山数量，我们的模型将能够告诉我们在20世纪世纪冰山崩解是如何变化的，以及与过去几千年的自然变化相比，这一改进的知识应该有助于我们理解为什么格陵兰岛在过去10-15年中如此迅速地开始分裂。

Some of the most iconic images of climate change and sea level rise include footage of the dramatic moment when a large fragment of ice breaks off from the terminus of a glacier and scenes of melting icebergs. In the popular imagination, icebergs are also associated with the sinking of the RMS Titanic nearly 100 years ago. The iceberg that sank the Titanic likely started out at the terminus of a west Greenland glacier a few months earlier, in winter 1911/12. Taken together, these impressions of ice and icebergs convey the central elements of this proposed study, namely the ways in which icebergs are 'calved' from the principal ice sheet of the northern hemisphere, Greenland, and the fate of those icebergs in the North Atlantic Ocean. Despite the prominence of icebergs in the popular imagination, they are surprisingly overlooked by climate scientists, and are practically ignored in the models that are used to predict climate change and sea level rise. Very little is known about the rate at which icebergs calve, and we have only a rough idea of where they melt. This neglect is becoming problematic as scientists grow more certain that the Greenland ice sheet is melting and breaking apart at an alarming rate. Since the launch of a specialized satellite system that can remotely measure the ice sheet thickness, it has been established that this break-up has accelerated over the last few years, with no indication that the ice sheet will re-stabilize. Around a half of the 'disappearance' of Greenland is estimated to occur through iceberg calving. We plan to use an existing detailed model of the ocean and icebergs that should reproduce variations in icebergs observed off Newfoundland during the 20th century. To examine the reproducibility of the model, and to enable transfer of this technology to the Hadley Centre's climate model, the iceberg module will be added to NEMO, the ocean model used by the Hadley Centre of the Meteorological Office. These models will use as forcing a high resolution, century-long surface mass balance model for Greenland. Through a careful set of experiments with our models, we will be able to more clearly explain these large variations, with thousands of icebergs seen in some years and none in other years. Our models will help us to distinguish between the two causes of such variations: due to changes in calving rate (producing more or less icebergs) or changes in ocean currents (carrying the icebergs further north or south). If we can accurately reproduce the observed iceberg count, our models will be able to tell us how iceberg calving varied during the 20th century, and how this compared to natural variability during the last few thousand years, an improved knowledge that should help us to understand why Greenland has started breaking up so rapidly in the last 10-15 years.