Data set: "North Atlantic cooling is slowing down mass loss of Icelandic glaciers"

This data set includes the materials required to reproduce the figures and tables presented in the study: "North Atlantic cooling is slowing down mass loss of Icelandic glaciers". The data consist of:

1. Maps of annual surface mass balance (SMB) of Icelandic glaciers and ice caps (ICL) from RACMO2.3 at 500 m spatial resolution in NetCDF format.

• smb_rec.1958-2019.RACMO2.3-ERA.ICL-0.5km.YY.nc: annual cumulative SMB of Icelandic glaciers and ice caps (kg m^-2 or mm w.e. per year) from RACMO2.3 forced by ERA reanalyses for the period 1958-2019, and further statistically downscaled to 500 m spatial resolution. Forcing includes ERA-40 (1958-1978), ERA-Interim (1979-2018) and ERA5 (2019) reanalyses.
• smb_rec.1958-2099.RACMO2.3-CESM2-SSP85.ICL-0.5km.YY.nc: annual cumulative SMB of Icelandic glaciers and ice caps (kg m^-2 or mm w.e. per year) from RACMO2.3 forced by CESM2 for the historical period 1958-2014 and by CESM2 under a high-end warming scenario SSP5-8.5 for the period 2015-2099, further statistically downscaled to 500 m spatial resolution.
• Topo_icemask_lsm_lon_lat_ICL-0.5km.nc: mask file including an ice mask, land/sea mask and surface topography derived from the ArcticDEM, and longitude/latitude coordinates on the 500 m grid.

NB: the NetCDF files above use a Polar Stereographic North (EPSG:3413) projection with a horizontal resolution of 500 m x 500 m. The reference point is located at 45ºW longitude and 70ºN latitude.

2. Time series of annual ICL-integrated SMB components (Gigatons or Gt per year), annual mean 2 m air temperature above Icelandic glaciers and ice caps (T2m; K), annual mean sea surface temperature (SST) in the Northern Blue Blob. These time series are available in ASCII format for the RACMO2.3 simulation forced by ERA reanalyses (1958-2019) and the RACMO2.3 projection forced by CESM2 under a high-end warming scenario SSP5-8.5 (1958-2099).

RACMO2.3-ERA

• SMB-components-RACMO2.3-ERA-1958-2019.txt: time series of annual integrated SMB, snowfall, rainfall, runoff, total melt, refreezing and retention (Gt per year) from the ERA-forced RACMO2.3 simulation (1958-2019).
• T2m-glacier-RACMO2.3-ERA-1958-2019.txt: time series of annual mean glacier T2m and anomalies relative to the period 1958-1994 (K) from the ERA-forced RACMO2.3 simulation (1958-2019).
• SST-Northern-Blue-Blob-RACMO2.3-ERA-1958-2019.txt: time series of annual mean Northern Blue Blob SST and anomalies relative to the period 1958-1994 (K) derived from the ERA reanalyses (1958-2019).The reanalyses include ERA-40 (1958-1978), ERA-Interim (1979-2018) and ERA5 (2019).

RACMO2.3-CESM2

• SMB-components-RACMO2.3-CESM2-SSP85-1958-2099.txt: time series of annual integrated SMB, snowfall, rainfall, runoff, total melt, refreezing and retention (Gt per year) from the CESM2-forced RACMO2.3 projection under a SSP5-8.5 scenario (1958-2099).
• T2m-glacier-RACMO2.3-CESM2-SSP85-1958-2099.txt: time series of annual mean glacier T2m and anomalies relative to the period 1958-1994 (K) from the CESM2-forced RACMO2.3 projection under a SSP5-8.5 scenario (1958-2099).
• SST-Northern-Blue-Blob-RACMO2.3-CESM2-SSP85-1958-2099.txt: time series of annual mean Northern Blue Blob SST and anomalies relative to the period 1958-1994 (K) derived from the CESM2 projection under a SSP5-8.5 scenario (1958-2099).

3. Time series of monthly ICL-integrated SMB (Gt per month) for the period 1958-2099. 

• SMB-monthly-RACMO2.3-1958-2099.txt: time series of monthly integrated SMB (Gt per month) combining RACMO2.3-ERA (January 1958 - December 2019) with RACMO2.3-CESM2 under a SSP5-8.5 scenario (January 2020 - December 2099) at 500 m horizontal resolution.

The daily downscaled SMB data sets from the ERA-forced RACMO2.3 simulation and the CESM2-forced RACMO2.3 projection under a SSP5-8.5 scenario are freely available from the authors upon request and without conditions (contact: b.p.y.noel@uu.nl). Besides SMB, the data sets include daily total precipitation (snow and rain), snowfall, total melt (snow and ice), runoff, refreezing and retention, total sublimation (surface and drifting snow), snow drift erosion, as well as 2 m air temperature at 500 m horizontal resolution. 

Abstract: Icelandic glaciers have been losing mass since the Little Ice Age in the mid-to-late 1800s, with higher mass loss rates in the early 21^st century, followed by a slowdown since 2011. As of yet, it remains unclear whether this mass loss slowdown will persist in the future. By reconstructing the contemporary (1958-2019) surface mass balance of Icelandic glaciers, we show that the post-2011 mass loss slowdown coincides with the development of the Blue Blob, an area of regional cooling in the North Atlantic Ocean to the south of Greenland. This regional cooling signal mitigates atmospheric warming in Iceland since 2011, in turn decreasing glacier mass loss through reduced meltwater runoff. In a future high-end warming scenario, North Atlantic cooling is projected to mitigate mass loss of Icelandic glaciers until the mid-2050s. High mass loss rates resume thereafter as the regional cooling signal weakens.