Surface mass-balance changes of the Greenland ice sheet since 1866

Mass loss from the Greenland ice sheet over the past decade has caused the impression that the ice sheet has been behaving anomalously to the warming of the 1990s. We have reconstructed the recent (1866-2005) surface mass-balance (SMB) history of the Greenland ice sheet on a 5 � 5 km grid using a runoff-retention model based on the positive degree-day method. The model is forced with new datasets of temperature and precipitation patterns dating back to 1866. We use an innovative method to account for the influence of year-on-year surface elevation changes on SMB estimates and have found this effect to be minor. All SMB estimates are made relative to the 1961-90 average SMB and we compare annual SMB estimates from the period 1995-2005 to a similar period in the past (1923-33) where SMB was comparable, and conclude that the present-day changes are not exceptional within the last 140 years. Peripheral thinning has dominated the SMB response during the past decade, as in 1923-33, but we also show that thinning was not restricted to the margins during this earlier period.