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In This Issue

Heinrich Events, in which large masses of icebergs rapidly break free from ice sheets, are thought to influence global climate by altering ocean circulation patterns with a large influx of freshwater. To investigate whether the changing height of the ice sheet may also influence global climate by altering atmospheric circulation, William Roberts et al. (pp. 16688–16693) simulated Heinrich Events in climate models, adjusting the models to consider freshwater influx only, changing ice sheet height only, or both factors together. The simulations, reconstructing Heinrich Events in Hudson Bay, resulted in widespread climate change. The authors found that the climate effects in the simulations that considered both freshwater influx and changing topography were not simply the sum of the climate effects of each component considered separately. In a simulation of changing ice sheet height only, warming was observed in the North Atlantic and in southeastern North America; both effects have been observed in the paleoclimate record and cannot be accounted for with freshwater influx models alone. The results suggest that altered atmospheric circulation due to changing ice sheet thickness is likely not the sole driver of climate change in Heinrich Events but may need to be considered in future climate models. — P.G.