Committed retreat of Smith, Pope, and Kohler Glaciers over the next 30 years inferred by transient model calibration
Committed retreat of Smith, Pope, and Kohler Glaciers over the next 30 years inferred by transient model calibration
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DOI：
10.5194/tc-9-2429-2015
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发表时间：
2015-01-01
期刊：
影响因子：
5.2
通讯作者：
Smith, B.
中科院分区：
文献类型：
--
作者：
Goldberg, D. N.;Heimbach, P.;Smith, B.
Smith、Pope和Kohler冰川的冰川流动模型是根据2002年至2011年期间冰高和冰速度随时间变化的年度分辨率观测数据，通过控制方法进行校准的。这种反演——被称为“瞬态校准”——产生一组最佳的时间均值、空间变化参数，以及一个随时间变化的状态，该状态解释了观测的瞬态性质和模型动力学。作为最优初始条件，在没有额外强迫的情况下，使用2011年的估计状态来预测未来30年的接地冰体积损失和接地线退缩。瞬态校准模型预测，在此期间，地面冰体积的损失接近稳定，约为21 km(3) a(-1)，地面面积的损失为33 km(2) a（-1）。我们将这种预测与常用的“快照”或稳态反演所获得的预测进行对比，后者不考虑时间依赖性，并假设所有观测都是同期的。瞬态校准可以更好地与变薄和接地线后退历史的观测结果相吻合，并产生关于冰体积损失和非接地的定量不同的投影。敏感性研究表明，在对未知参数的不确定性作出合理假设的情况下，这些冰流在不久的将来会对海平面产生很大的非受迫性贡献。
A glacial flow model of Smith, Pope and Kohler Glaciers is calibrated by means of control methods against time varying, annually resolved observations of ice height and velocities, covering the period 2002 to 2011. The inversion - termed "transient calibration" - produces an optimal set of time-mean, spatially varying parameters together with a time-evolving state that accounts for the transient nature of observations and the model dynamics. Serving as an optimal initial condition, the estimated state for 2011 is used, with no additional forcing, for predicting grounded ice volume loss and grounding line retreat over the ensuing 30 years. The transiently calibrated model predicts a near-steady loss of grounded ice volume of approximately 21 km(3) a(-1) over this period, as well as loss of 33 km(2) a(-1) grounded area. We contrast this prediction with one obtained following a commonly used "snapshot" or steady-state inversion, which does not consider time dependence and assumes all observations to be contemporaneous. Transient calibration is shown to achieve a better fit with observations of thinning and grounding line retreat histories, and yields a quantitatively different projection with respect to ice volume loss and ungrounding. Sensitivity studies suggest large near-future levels of unforced, i.e., committed sea level contribution from these ice streams under reasonable assumptions regarding uncertainties of the unknown parameters.