Committed retreat: controls on glacier disequilibrium in a warming climate
Committed retreat: controls on glacier disequilibrium in a warming climate
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DOI：
10.1017/jog.2018.57
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发表时间：
2018-08-01
影响因子：
3.4
通讯作者：
Roe, Gerard
中科院分区：
文献类型：
--
作者：
Christian, John Erich;Koutnik, Michelle;Roe, Gerard
山地冰川的广泛退缩是最近气候变化的一个显著标志。然而，质量平衡观测表明，许多冰川与当前气候不平衡，这意味着观测到的退缩并未显示出对变暖的完全响应。这是冰川动力学的一个基本结果：山地冰川通常具有几十年的响应时间尺度，因此它们的响应滞后于百年尺度的气候趋势。瞬态冰川长度和平衡冰川长度之间的巨大差异在整个增暖期持续存在；我们把这种长度差异称为“不平衡”。强迫理想的冰川几何形状与逐渐变暖表明，冰川响应的时间尺度从根本上控制着不平衡的演变。比较不同冰川模型的层次结构表明，对控制时间尺度的冰厚和气候学的准确估计比捕捉不平衡的高阶冰动力学更重要。目前的冰川不平衡以前已经对个别冰川的选择进行了估计；我们的理想模型表明，持续的不平衡是冰川动力学的基本响应，并且在一系列冰川几何形状中都是稳健的。这意味着，即使没有进一步变暖，许多山地冰川也会进一步退缩，退缩规模达到千米。在校准用于气候重建和预测未来变暖后退缩的冰川模型时，也必须解决不平衡问题。
The widespread retreat of mountain glaciers is a striking emblem of recent climate change. Yet mass-balance observations indicate that many glaciers are out of equilibrium with current climate, meaning that observed retreats do not show the full response to warming. This is a fundamental consequence of glacier dynamics: mountain glaciers typically have multidecadal response timescales, and so their response lags centennial-scale climate trends. A substantial difference between transient and equilibrium glacier length persists throughout the warming period; we refer to this length difference as 'disequilibrium'. Forcing idealized glacier geometries with gradual warming shows that the glacier response timescale fundamentally governs the evolution of disequilibrium. Comparing a hierarchy of different glacier models suggests that accurate estimates of ice thickness and climatology, which control the timescale, are more important than higher order ice dynamics for capturing disequilibrium. Current glacier disequilibrium has previously been estimated for a selection of individual glaciers; our idealized modeling shows that sustained disequilibrium is a fundamental response of glacier dynamics, and is robust across a range of glacier geometries. This implies that many mountain glaciers are committed to additional, kilometer-scale retreats, even without further warming. Disequilibrium must also be addressed when calibrating glacier models used for climate reconstructions and projections of retreat in response to future warming.