With the aim of studying the recent Greenland Ice Sheet (GrIS) Surface Mass Balance (SMB) decrease with respect to the last century, we have forced the regional climate MAR model (version 3.5.2) with the ERA-Interim (1979–2015), ERA-40 (1958–2001), NCEP-NCARv1 (1948–2015), NCEP-NCARv2 (1979–2015), JRA-55 (1958–2014), 20CRv2(c) (1900–2014) and ERA-20C (1900–2010) reanalysis. While all of these forcing products are reanalyses

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... sumed to represent the same climate, they produce significant differences in the MAR simulated SMB over their common period. A temperature adjustment of +1&amp;thinsp;&amp;deg;C (respectively &amp;minus;1&amp;thinsp;&amp;deg;C) improved the accuracy of MAR boundary conditions from both ERA-20C and 20CRv2 reanalyses given that ERA-20C (resp. 20CRv2) is 1&amp;thinsp;&amp;deg;C colder (resp. warmer) over Greenland than ERA-Interim over 1980&amp;ndash;2010. Comparisons with daily PROMICE near-surface observations validated these adjustments. Comparisons with SMB measurements from PROMICE, ice cores and satellite derived melt extent reveal the most accurate forcing data sets for simulating the GrIS SMB to be ERA-Interim and NCEP-NCARv1. However, some biases remain in MAR suggesting that some improvements need still to be done in its cloudiness and radiative scheme as well as in the representation of the bare ice albedo. <br><br> Results from all forcing simulations indicate: (i) the period 1961&amp;ndash;1990 commonly chosen as a stable reference period for Greenland SMB and ice dynamics is actually a period when the SMB was anomalously positive (~&amp;thinsp;+10&amp;thinsp;%) compared to the last 120 years; (ii) SMB has decreased significantly after this reference period due to increasing and unprecedented melt reaching the highest rates in the 120 year common period; (iii) before 1960, both ERA-20C and 20CRv2 forced MAR simulations suggest a significant precipitation increase over 1900&amp;ndash;1950 although this increase could be the result of an artefact in reanalysis not enough constrained by observations during this period. These MAR-based SMB and accumulation reconstructions are however quite similar to those from Box (2013) after 1930, which confirms the Box (2013)'s stationarity assumption of SMB over the last century. Finally, the ERA-20C forced simulation only suggests that SMB during the 1920&amp;ndash;1930 warm period over Greenland was comparable to the SMB of the 2000's due to both higher melt and lower precipitation than normal.