Attributing observed Greenland responses to natural and anthropogenic climate forcings

We attribute climate variability in four independent reconstructions of Greenland-average temperature and precipitation over the twentieth century. The reconstructions exhibit substantial differences in the timing and amplitudes of climate variations. Linear, empirical models of Greenland-average temperature and precipitation variations on multi-decadal timescales are established from a suite of Community Climate System Model 3 simulations of the preindustrial millennium. They are compared against observational reconstructions after being tested against simulations of the industrial and future periods. Empirical estimates of variations over the industrial and future periods are correlated at greater than 0.95 with simulated values. Greenhouse gas increases account for the majority of the temperature and precipitation increases after the mid-1900s. In contrast to the simulations, observed temperatures and precipitation do not increase until the mid-1990s. Thus, the empirical models over-predict the response to greenhouse gases over the twentieth century. We conclude that CCSM3 is not capturing processes that are proving important to Greenland surface conditions. Furthermore, modes of North Atlantic variability exhibit opposite relationships with some observations compared with the simulations. In those cases, reversing the sign of this component of variability yields significant correlations between the estimated and observed accumulation values.