Badgeley Jessica A, Morlighem Mathieu, Seroussi Hélène
Department of Earth Sciences, Dartmouth College, Hanover, NH 03755.
Thayer School of Engineering, Dartmouth College, Hanover, NH 03755.
Proc Natl Acad Sci U S A. 2025 Jun 24;122(25):e2411904122. doi: 10.1073/pnas.2411904122. Epub 2025 Jun 16.
State-of-the-art ice sheet model simulations used in the Ice Sheet Model Intercomparison Project (ISMIP) that informs the Intergovernmental Panel on Climate Change tend to underestimate observed mass loss from the Greenland Ice Sheet, leading to the question of whether future sea-level rise may be larger than projected. We use one of these models, the Ice-sheet and Sea-level System Model, to investigate how transient calibration impacts historical and projection simulations. Transient calibration is an emerging capability in ice flow models; it uses time series of surface observations and time-dependent physics to constrain uncertain model parameters-in this case, the basal friction coefficient in the sliding law. With more constraints than the common snapshot inversion method, transient calibration has been shown to better capture trends in ice dynamics. Here, we apply both methods to northwestern Greenland, a region undergoing rapid changes. For simulations initialized with the snapshot inversion, we find that subsequent modeled velocities are generally too slow, leading to an underestimation of the mass loss. With transient calibration, however, our simulation better matches a time series of observed velocities, bringing it within observational error for mass loss; however, the fit to observed surface elevation is slightly reduced. Together with the ISMIP results, our simulations show that reproducing the high rates of historical mass loss leads to greater projected sea-level contribution from this region over the coming century. Finally, we suggest a path forward for making transient calibration scalable to the entire Greenland Ice Sheet.
用于为政府间气候变化专门委员会提供信息的冰盖模型相互比较项目（ISMIP）中的先进冰盖模型模拟往往低估了格陵兰冰盖观测到的质量损失，这引发了未来海平面上升是否可能大于预测值的问题。我们使用其中一个模型，即冰盖与海平面系统模型，来研究瞬态校准如何影响历史和预测模拟。瞬态校准是冰流模型中一种新兴的能力；它使用地表观测的时间序列和随时间变化的物理过程来约束不确定的模型参数——在这种情况下，是滑动定律中的基底摩擦系数。与常见的快照反演方法相比，由于有更多的约束条件，瞬态校准已被证明能更好地捕捉冰动力学中的趋势。在这里，我们将这两种方法应用于格陵兰西北部，这是一个正在经历快速变化的地区。对于用快照反演初始化的模拟，我们发现随后模拟的速度通常过慢，导致质量损失被低估。然而，通过瞬态校准，我们的模拟更好地匹配了观测速度的时间序列，使其在质量损失的观测误差范围内；不过，与观测到的地表高度的拟合度略有降低。与ISMIP的结果一起，我们的模拟表明，再现历史上的高速度质量损失会导致该地区在未来一个世纪对海平面上升的贡献更大。最后，我们提出了一条使瞬态校准能够扩展到整个格陵兰冰盖的前进道路。
