Research ArticleMETEOROLOGY

Decreasing cloud cover drives the recent mass loss on the Greenland Ice Sheet

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Science Advances  28 Jun 2017:
Vol. 3, no. 6, e1700584
DOI: 10.1126/sciadv.1700584
  • Fig. 1 Total change in summer (JJA) cloud cover from satellites and a regional climate model.

    (A) Comparison between AVHRR (12) (left, top) and MAR (right, top) total JJA cloud cover change (%) during the full available data period of AVHRR between 1982 and 2009. Bottom: Trend of JJA 500-hPa geopotential height (Z500) in meters per year. The arrows show the wind trend in meters per second per year and highlight the circulation anomalies induced by the JJA Z500 changes. The arrow length of a change of 0.2 m/s per year is given in the legend for indication. (B) Comparison is the same as in (A) but for MODIS (11) (left; full observation period, 2002–2015) and MAR (right; 2002–2015). Values inside the black line have a significance level of P < 0.10, and the dotted areas indicate statistical significance at P < 0.05. All cloud cover trends are individually based on a linear regression analysis for every pixel.

  • Fig. 2 Summer (JJA) cloud cover time series, trends, and impacts of clouds on melt and radiation.

    (A) Time series of average Greenland cloud cover from AVHRR sensor (orange; 1982–2009) and MAR (blue; 1982–2015). Linear fit (dark gray): AVHRR (1994–2009): R2 = 0.76, P < 0.001; MAR (1994–2015): R2 = 0.46, P < 0.001. Length of one average spatial SD is shown in the legend. (B) Correlation between MAR JJA cloud cover anomalies and JJA SWD anomalies (R2 = 0.58, P < 0.001). A similar scatterplot showing the correlation between cloud cover and LWD anomalies can be found in fig. S3. (C) Correlation between JJA cloud cover anomalies and JJA melt anomalies (R2 = 0.32, P < 0.001). All anomalies in (B) and (C) are calculated on the basis of the 1970–1995 average.

  • Fig. 3 Accumulated melt anomalies and contributing factors.

    (A) Accumulated annual melt anomalies (in Gt) and JJA SWD, SWnet, LWD, and LWnet (net longwave radiation) anomalies. Radiation anomalies converted from joules to “melt potential” (in Gt) (see Materials and Methods). Anomalies are based on the 1970–1995 average of MAR (Eq. 2), and the accumulation of anomalies starts in 1979. (B) Description the same as in (A) but showing JJA latent heat flux (LHF) and sensible heat flux (SHF). (C) Accumulated annual precipitation anomalies (MAR and NCEP version 1 reanalysis) and annual melt anomalies. NCAR, National Center for Atmospheric Research. (D) Correlation between annual melt anomalies and annual SMB anomalies (R2 = 0.77, P < 0.001). (E) Correlation between JJA SWD anomalies and melt anomalies (R2 = 0.26, P < 0.001). (F) Correlation between JJA SWnet anomalies and melt anomalies (R2 = 0.75, P < 0.001). (G) Correlation between JJA LWD anomalies and melt anomalies (R2 = 0.63, P < 0.001).

  • Fig. 4 Correlation between cloud cover (model) and measured NAO/GBI index during summer (JJA).

    (A) Five-year running average of MAR JJA cloud cover (green; %), JJA NAO index (blue), and JJA GBI (orange). (B) The scatterplot (purple) shows the correlation (R2 = 0.75, P < 0.001) between observed NAO index and MAR cloud cover (both for JJA). (C) The scatterplot (red) shows the correlation (R2 = 0.74, P < 0.001) between GBI and MAR cloud cover (both for JJA).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/6/e1700584/DC1

    fig. S1. Long-term NAO index from observations on Iceland and the Azores (1950–2016) (19).

    fig. S2. Extended GBI (1850–2016) (14).

    fig. S3. Correlation between JJA cloud cover and LWD anomalies.

    fig. S4. Correlation between summer radiation anomalies and albedo.

    fig. S5. Correlation between annual melt and runoff anomalies.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Long-term NAO index from observations on Iceland and the Azores (1950–2016) (19).
    • fig. S2. Extended GBI (1850–2016) (14).
    • fig. S3. Correlation between JJA cloud cover and LWD anomalies.
    • fig. S4. Correlation between summer radiation anomalies and albedo.
    • fig. S5. Correlation between annual melt and runoff anomalies.

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