A century of variability in Greenland melting and iceberg calving

关于气候变化和海平面上升的一些最具标志性的图像，包括一大块冰从冰川末端断裂的戏剧性时刻，以及冰山融化的场景。在大众的想象中，冰山还与近100年前泰坦尼克号的沉没联系在一起。导致泰坦尼克号沉没的冰山很可能是在几个月前，也就是1911/ 1912年的冬天，从西格陵兰冰川的末端开始的。总的来说，这些冰和冰山的印象传达了这项拟议研究的核心要素，即冰山从北半球主要冰盖格陵兰岛“崩解”的方式，以及北大西洋这些冰山的命运。尽管冰山在大众的想象中很突出，但令人惊讶的是，它们被气候科学家忽视了，而且在用于预测气候变化和海平面上升的模型中几乎被忽略了。我们对冰山崩解的速度所知甚少，对于冰山在何处融化，我们也只有一个大致的概念。随着科学家们越来越确信格陵兰冰盖正在以惊人的速度融化和分裂，这种忽视正变得越来越成问题。自从能够远程测量冰盖厚度的专门卫星系统发射以来，已经确定，在过去几年中，这种破裂已经加速，没有迹象表明冰盖将重新稳定下来。据估计，格陵兰岛大约一半的“消失”是由于冰山崩解造成的。我们计划使用现有的海洋和冰山的详细模型，该模型应该可以重现20世纪在纽芬兰附近观测到的冰山变化。为了检验模型的可重复性，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NEMO海洋模型中。这些模型将用于格陵兰岛的高分辨率、长达一个世纪的地表质量平衡模型。通过用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，而在其他年份没有。我们的模型将帮助我们区分这种变化的两种原因：由于产犊率的变化（产生更多或更少的冰山）或洋流的变化（将冰山向北或向南移动）。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冰山崩解在20世纪是如何变化的，以及这与过去几千年的自然变化相比是如何变化的，这将有助于我们理解为什么格陵兰岛在过去10-15年里开始如此迅速地分裂。

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.