| 30 Jan 2026
The Anomalously Warm Summer of 2023 Over Greenland as Compared to Previous Record Melt Summers of 2012 and 2019
Abstract. Atmospheric circulation anomalies have increasingly contributed to extreme summer melt events over the Greenland ice sheet (GrIS). Based on our analysis of the visible and near-infrared top-of-atmosphere reflectance (RTOA), we identified the summer of 2023 as another such instance comparable to the anomalously warm conditions observed in 2012 and 2019. Individual summer month and summer-wide RTOA averages reveal that in 2023 the largest fraction of the GrIS experienced negative anomalies exceeding one standard deviation below the 2007–2024 mean, including the high-albedo central ice sheet. By incorporating higher-level satellite retrievals, in situ automatic weather station data, reanalysis, and regional climate model output, we disentangle the RTOA signal to better assess the processes that preconditioned and led to the observed negative anomalies. We compare the extreme melt summers of 2012 and 2019 with 2023, to identify distinct pathways through which anticyclonic conditions contribute to GrIS surface melt. Our findings reveal that both dry (clear-sky) conditions, observed in 2019, and wet (cloudy) conditions, observed in 2012 and 2023, can trigger anomalous melting of the GrIS, with the primary difference being whether it is the margins or the central ice sheet that is most affected. Moreover, we find that both types of conditions are driven by atmospheric circulation patterns, shaped by the position, intensity, and persistence of anticyclones and the atmospheric rivers they help steer.
General Comments
This paper analyzes spectrometer data from GOME-2, ERA5 reanalysis fields, and 10 km MAR meltwater output to evaluate the role of clouds atop the Greenland Ice Sheet (GrIS) in shaping the three most anomalous melt summers since 1979, which were 2012, 2019, and 2023 with the latter receiving the least attention to date. The authors find comparisons between these cases in terms of elevated two-metre air temperatures, melt area, and meltwater production over the ice sheet. They also find similarities between 2012 and 2023 in terms of July cloudiness linked to anomalous accumulation zone melt, though 2023 cloudiness was relatively more widespread across the ice sheet. The authors note that a colder-than-average June 2023 precluded that summer melt season from competing with 2012 for the largest melt summer on record.
Overall, the paper provides a timely comparison of monthly atmospheric circulation, clouds, and GrIS surface conditions through the progression of summers that experience notable melt. Pending some additional details about data products and considerations regarding methods (e.g., base period calculation), the paper could be a good fit for the journal and contribution to the literature on cloud-radiative effects on extreme monthly and seasonal GrIS melt. Comments are provided below by line number (L) of the submitted manuscript.
Specific Comments
L5 and L8: Negative anomalies in what?
L35: Is this role of clouds dependent on their type and occurrence within the summer season?
L50: “higher-level” data products and model results such as?
L78-80: What is the accuracy of GOME-2 retrievals? Have these measurements been validated by surface observations, especially over the GrIS?
L103-107: Why use ERA5 versus another global reanalysis? Specifically, how does ERA5 two-meter temperature compare versus other global atmospheric reanalyses over the ice sheet?
L137: Are 2012, 2019, and 2023 included in the 2007-2024 mean? If so, how do anomalies compare in Fig 2 if those years are removed? Are results impacted?
L143: The Geological Survey of Denmark and Greenland (GEUS), which manages the PROMICE weather station network, took over operations of GC-Net weather stations ~2020 (see https://promice.org/about/). It would be a good idea to confirm that more recent ERA5 datasets (2021-2024) do or do not assimilate data from one or both of these networks.
L237: “coming in second” since when and second to which year?
L284: What type(s) of clouds enhance meltwater run-off?
L295: A note here is warranted whereabouts on the GrIS this fixed elevation threshold may not accurately estimate the ELA.
Technical Corrections
L132: …and daily data forced by ERA5 reanalysis. Also, is this daily-averaged or sub-daily? Please clarify.
L272: “and go in opposite directions” – this portion of the sentence could be re-written to improve clarity.
L155: Should “all three months” be “all three weeks”?
Figure 9: The top portions of panels (a) and (b) are illegible due to the placement of the legends overlaid on the data.
L312: Would suggest adding “regional” before “model” for clarity.