the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Aug 2024
Projecting the Response of Greenland's Peripheral Glaciers to Future Climate Change: Glacier Losses, Sea Level Impact, Freshwater Contributions, and Peak Water Timing
Abstract. Greenland's peripheral glaciers are significant contributors to sea level rise and freshwater fluxes, yet their future evolution remains poorly constrained. This study projects the response of these glaciers to future climate change using the Open Global Glacier Model (OGGM) forced by CMIP6 climate data under four emission scenarios. By 2100, the glaciers are projected to lose 19–44 % of their area and 29–52 % of their volume, contributing 10–19 mm to sea level rise. Solid ice discharge is projected to decrease, while freshwater runoff will peak within the 21st century. The runoff composition is projected to change drastically, with shares of glacier ablation decreasing from 92 % in 2021–2030 to 72 % by 2091–2100 and shares of rainfall and snowmelt increasing 8-fold and 15-fold, respectively, suggesting a shift in the hydrological regime. Timing of the maximum runoff varies across scenarios (2050 ± 21 for SSP126; 2082 ± 9 for SSP585) and subregions, with the projected maximum runoff reaching 214–293 Gt/yr, implying significantly increased future freshwater fluxes. These changes will impact fjord water characteristics and coastal hydrography, and potentially influence larger ocean circulation patterns.
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RC1: 'Comment on egusphere-2024-2184', Anonymous Referee #1, 11 Nov 2024
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PAPER SUMMARY AND RECOMMENDATION
This study looks at how Greenland's peripheral glaciers may change in the future due to climate change. It emphasizes the distinction between solid ice discharge (calving of icebergs) and liquid freshwater runoff (melting and rain). The study employs the Open Global Glacier Model (OGGM), which simulates the evolution of glaciers using climate data from the Coupled Model Intercomparison Project Phase 6 (CMIP6) under four emission scenarios. Key findings include:
- Projected declines in area and volume: By 2100, the glaciers are projected to lose 19-44% of their area and 29-52% of their volume, contributing 10-19 mm to sea level rise.
- Shifting freshwater contributions: Projections show solid ice discharge decreasing over the century, especially after 2050, as marine-terminating glaciers retreat inland
- Peak water timing: Peak water, the time of maximum annual freshwater release, is projected to occur around 2050 under low emissions (SSP126) and shift to around 2082 under high emissions (SSP585)
The article explores an innovative and relevant topic for The Cryosphere and is well-written and easy to follow. The approach is sound, and the study’s core findings offer insights that will be beneficial for future research efforts. To further strengthen the manuscript, I recommend that the authors incorporate some additional analyses and provide further clarifications. These improvements will help make the article ready for publication.
MAJOR COMMENTS
- Despite the improved modeling of marine-terminating glaciers, it would be useful to include a comparison with outputs from multiple global models (e.g., PyGEM, GloGEM, OGGM v1.6). Although these model results are briefly discussed, I suggest including a summary table with results (e.g., volume and area) and comparing them statistically (methods in Section 2.5). This comparison is valuable given the similarity of the GCMs (L114).
- Section 2 could benefit from a clearer separation of data, models, and calibration methods. For instance, the climate section mentions a precipitation factor without explaining its calibration. The OGGM model section includes all data related to glaciers, so model calibration could be placed in its own subsection under modeling.
- Reproducibility: There is no mention of the version of OGGM used in this study. According to the documentation, the most recent version was not used due to issues with the proposed frontier ablation (https://tutorials.oggm.org/stable/notebooks/tutorials/kcalving_parameterization.html). It would be helpful to specify the version used.
- Oceanic Forcing: The study frequently notes the lack of oceanic forcing in the OGGM model, but the potential implications of this limitation are not discussed. I recommend that the authors explore how incorporating oceanic forcing might affect their projections, particularly for solid ice discharge and regional variability. Could the current projections underestimate or overestimate the actual contribution?
- Regional Variability: The study mentions significant regional variability in projected glacier loss, sea level rise contributions, and freshwater runoff. I encourage the authors to expand their analysis of these regional differences, examining how factors such as glacier size, geometry, elevation, and local climate contribute to the observed variability.
- Figures Quality: Please check the quality of the figures, particularly Figures 3 and 4. It is unclear whether the glaciers are represented as points, polygons, or grid interpolations. Additionally, several panels show mismatched axis ranges, which makes the analysis difficult to interpret. Consider using color palettes that are more accessible for colorblind readers (e.g., ColorBrewer palettes: https://www.datanovia.com/en/blog/the-a-z-of-rcolorbrewer-palette).
- Precipitation Factor Calibration: The manuscript does not explain how the precipitation factor is calibrated, which is important for analyzing freshwater contributions. Please consider adding a table listing all parameters, their values, and any calibrations involved (Section 2.4).
MINOR COMMENTS
- Abstract: Clarify how the values (e.g., 19-44%) were calculated—are they multi-model means or medians for extreme scenarios?
- Fig 1: Define "MT glaciers" and consider adjusting the size or transparency of the triangles for better clarity.
- Fig 1c: Change "Numbers" to "Number of glaciers" and verify the caption.
- L125: Please elaborate on the delta method and explain how anomalies are calculated.
- L234: Could one variable be analyzed using different methods? Please clarify.
- Fig 3: Was smoothing applied to the confidence intervals? Consider sharing the vertical axis across subplots to increase the size of the lower subplots. This applies to subsequent figures as well.
- Section 3.2: The section heading suggests a comparison, but there is little temporal and spatial comparison between variables. Please expand this comparison.
- References: Some references are listed with full journal titles, while others use abbreviations. Please ensure consistency throughout the reference list.
- Data: Clarify whether the data on Zenodo is available at the subregional scale or glacier-ID scale.
Citation: https://doi.org/10.5194/egusphere-2024-2184-RC1
Data sets
Data: Projecting the Response of Greenland's Peripheral Glaciers to Future Climate Change: Glacier Losses, Sea Level Impact, Freshwater Contributions, and Peak Water Timing Muhammad Shafeeque and Ben Marzeion https://doi.org/10.5281/zenodo.12737991
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