Greenland Ice Sheet and sea-level response under climate change from AD 1600 to 2100

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The Greenland Ice Sheet contains enough mass to raise global sea-level by seven metres. Greenland Ice Sheet mass loss arising from global warming is currently the main icy contributor to global sea-level rise and could contribute several tens of centimetres to global sea level by the year 2100, although this prediction is highly uncertain. Most recent studies show that surface mass balance (defined as net solid precipitation minus surface meltwater that runs off from the ice sheet) is the main part of 21st century Greenland Ice Sheet mass change; yet key gaps remain in our knowledge and understanding of Greenland Ice Sheet change at the multi-century timescale. Improved information on surface mass balance changes over space and time is needed to improve the reliability of computer models of ice-sheet flow and loss of ice via calving of icebergs (called ice dynamics). The present limited understanding of recent surface mass balance change resulting from the lack of constrained computer simulations, especially for time periods before the last 50 years or so, propagates through to unreliable estimates of future total mass balance (i.e. the sum of surface mass balance and ice dynamical changes) and therefore projections of sea level rise. Most current Greenland Ice Sheet surface mass balance datasets do not extend back before around 1900, while the more sophisticated surface mass balance models tend to focus on relatively short periods since 1960 due to unavoidable requirements of large amounts of reliable, complex input data (for example those relating to surface heat and energy flows between the ice sheet's surface and the atmosphere) which are typically unavailable before the 1960s. Also, estimates of the ice dynamic portion of ice-sheet mass change are based on statistical relationships of ice output with recent climatology, which is unlikely to be representative of the pre-instrumental period or the future. Therefore, bridging the major gap in the understanding of Greenland Ice Sheet-climate interactions and effect on sea-level during the large climate shifts between Little Ice Age (around 1600 to 1850) and the 20th/21st Century is urgently needed to reduce the significant uncertainty propagating through to the global sea-level contribution of Greenland Ice Sheet changes during the rest of the Twenty First Century. Our proposal combines a wide range of models, observations and scientific expertise to address this key knowledge gap.This project will produce estimates of past and future Greenland Ice Sheet surface mass balance and dynamic ice changes using cutting-edge climate and ice sheet models and datasets and mathematical evaluation of the uncertainties in these. The main aim of the proposed work is to produce a novel constrained surface and full mass balance history of the Greenland Ice Sheet from 1600 to 2021 and Greenland Ice Sheet mass balance projections to 2100, and to assess the resulting contribution to historical and future global sea-level. The reconstruction of the Greenland Ice Sheet surface mass balance back to 1600, for a period where such records are largely lacking, will quadruple the length of the existing published surface mass balance record, and form the basis of an improved understanding of the ice sheet's history and sensitivity to climate change. Our approach offers several key methodological improvements - most notably its inclusion of all the main outlet glaciers and determination of a range of most likely results - over previous attempts to forecast future changes in the Greenland Ice Sheet. We will combine our Greenland Ice Sheet surface mass balance projections with the total mass balance projections from our ice-sheet modelling work to calculate the relative contributions of surface mass balance and ice dynamics in space and time to total mass changes, and to determine their sensitivity to ongoing human-driven climate change during 1600-2100.