Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)
Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)
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DOI：
10.5194/esd-11-35-2020
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发表时间：
2020-02-14
影响因子：
7.3
通讯作者：
van de Wal, Roderik S. W.
中科院分区：
文献类型：
--
作者：
Levermann, Anders;Winkelmann, Ricarda;van de Wal, Roderik S. W.
南极冰盖对海平面的贡献是未来海平面预测的一个很大的不确定性。在这里，我们应用线性响应理论的方法，以16个国家的最先进的冰盖模型，估计南极冰盖的贡献，从基础冰架融化在21世纪。这种计算的目的是估计南极洲未来对全球海平面上升的贡献的不确定性，这种不确定性来自海洋强迫和相关的冰架融化的巨大不确定性。冰架融化被认为是一个主要的，如果不是最大的扰动冰盖流入海洋。然而，通过仅计算海平面对冰架融化的贡献，我们的研究忽略了一些过程，如表面质量平衡相关的贡献。在假设线性响应理论，我们能够捕捉到复杂的时间响应的冰盖，但我们忽略了任何自阻尼或自放大过程。这在不稳定性主导冰损失的情况下特别相关。因此，这里获得的结果是相关的，特别是在冰损失是由强迫，而不是内部不稳定，例如在强烈的海洋变暖的情况下占主导地位。为了进行比较，选择与早期研究完全相同的方法（Levermann等人，2014年），但有16个而不是5个冰盖模型。我们包括大气变暖对碳排放的响应的不确定性（CMIP 5气候模型的全方位敏感性），海洋向南大洋输送的不确定性（从CMIP 5模型中与全球平均表面变暖相关的延迟和缩放的海洋次表层变暖中获得），以及观测到的冰架腔外基底冰架融化对海洋变暖的响应范围。然后将基底冰架融化的不确定性与16个冰盖模型中每个模型的线性响应函数进行卷积，以获得对单个全球变暖路径的冰流响应。1992年至2017年观测期间由于基底冰架融化造成的冰损失的模型中位数为10.2 mm，范围可能在5.2和21.3毫米之间。在同一时期，南极冰盖的质量损失相当于全球海平面上升7.4毫米，标准偏差为3.7毫米（Shepherd等人，2018年），包括所有过程，特别是表面质量平衡的变化。对于有增无减的变暖路径，代表性浓度路径8.5（RCP 8.5），我们得到了南极冰盖对全球平均海平面上升的贡献中位数为17厘米，在21世纪世纪内，可能的范围（平均值的第66百分位数）在9和36 cm之间，非常可能的范围（平均值的第90百分位数）在6和58 cm之间。对于RCP 2.6变暖路径，这将使全球平均温度保持在全球变暖2摄氏度以下，因此符合巴黎气候协定，该程序产生的全球平均海平面贡献的中位数为13厘米。RCP2.6情景的可能范围在7和24 cm之间，非常可能的范围在4和37 cm之间。该方法中的结构不确定性不允许解释任何更高的不确定性。我们提供了预测的五个南极地区和每个模型和每个场景分别。在RCP8.5情景下，海平面的贡献率最高，21世纪世纪的最大中值为每十年4厘米，可能范围为每十年2至9厘米，非常可能范围为每十年1至14厘米。
The sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty of Antarctica's future contribution to global sea level rise that arises from large uncertainty in the oceanic forcing and the associated ice shelf melting. Ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean. However, by computing only the sea level contribution in response to ice shelf melting, our study is neglecting a number of processes such as surface-mass-balance-related contributions. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any self-dampening or self-amplifying processes. This is particularly relevant in situations in which an instability is dominating the ice loss. The results obtained here are thus relevant, in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong ocean warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014) but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP5 models in relation to the global mean surface warming), and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 of the ice loss due to basal ice shelf melting is 10.2 mm, with a likely range between 5.2 and 21.3 mm For the same period the Antarctic ice sheet lost mass equivalent to 7.4 mm of global sea level rise, with a standard deviation of 3.7 mm (Shepherd et al., 2018) including all processes, especially surface-mass-balance changes. For the unabated warming path, Representative Concentration Pathway 8.5 (RCP8.5), we obtain a median contribution of the Antarctic ice sheet to global mean sea level rise from basal ice shelf melting within the 21st century of 17 cm, with a likely range (66th percentile around the mean) between 9 and 36 cm and a very likely range (90th percentile around the mean) between 6 and 58 cm. For the RCP2.6 warming path, which will keep the global mean temperature below 2 degrees C of global warming and is thus consistent with the Paris Climate Agreement, the procedure yields a median of 13 cm of global mean sea level contribution. The likely range for the RCP2.6 scenario is between 7 and 24 cm, and the very likely range is between 4 and 37 cm. The structural uncertainties in the method do not allow for an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario separately. The rate of sea level contribution is highest under the RCP8.5 scenario.The maximum within the 21st century of the median value is 4 cm per decade, with a likely range between 2 and 9 cm per decade and a very likely range between 1 and 14 cm per decade.