Greenland ice sheet surface air temperature and accumulation rate reconstruction (1840- 2007) from in-situ data records

Meteorological station and ice core records are combined with regional climate model output to develop a continuous 168-year (1840-2007) spatial reconstruction of seasonal mean Greenland ice sheet near-surface air temperatures and ice sheet snow accumulation rates. Independent observations are used to assess and compensate systematic errors. Uncertainty is quantified using residual non-systematic error. Spatial and temporal temperature variability is investigated on seasonal and annual time scales. We find that volcanic cooling episodes are concentrated in winter and around western Greenland. Warming trends coincide with an absence of major volcanic eruptions. Year 2003 was the only year 1840-2007 with a warm anomaly that exceeds three standard deviations from the 1951-1980 base period. The annual whole ice sheet 1919-1932 warming trend is 33% greater in magnitude than the 1994-2007 warming. The recent warming was, however, stronger along western Greenland in autumn and southern Greenland in winter. Spring trends marked the 1920s warming onset while autumn lead the 1994-2007 warming. In contrast to the 1920s warming, the 1994- 2007 warming has not surpassed the northern hemisphere anomaly. An additional 1.0-1.5°C of annual mean warming would be needed for Greenland to be in phase with the Northern Hemispheric pattern. We thus predict that the ice sheet melt rates and recent mass deficit will continue to grow in the early 21st century as Greenland climate catches up with the Northern Hemispheric warming trend and Arctic climate warms according with climate forecasts. Reconstructed accumulation rates exhibit significant inter-decadal trends. Spatial and temporal surface mass balance is reconstructed from melt intensity derived from the air temperature and accumulation reconstructions. The effect of recent and past century warming on surface mass balance is presented.