The rapidly melting Greenland Ice Sheet (GrIS) has been one of the most visible changes in the climate system during the current era of global warming. An extensive body of work links the abrupt increase in meltwater runoff to a shift in summer atmospheric circulation, characterized by more frequent and intense bouts of Greenland blocking. While these stalled circulation patterns and the persistent, anomalous weather conditions that follow have clearly played a leading role in driving recent GrIS surface mass balance trends, the precise mechanisms by which blocking encourages melt are still an active area of research. Moreover, there is no consensus on why summer Greenland blocking has increased in recent decades. The timing of the change, set against a backdrop of amplified Arctic warming, has naturally sparked questions regarding whether it may be a dynamical response to anthropogenic climate change that should be expected to continue.
This dissertation investigates the drivers of GrIS surface mass loss within the context of amplified Arctic warming. First, this research provides a more comprehensive look at the mechanisms by which blocking promotes GrIS melt by identifying common Greenland blocking patterns and considering spatiotemporal differences in the synoptic-scale forcing of GrIS surface conditions between them. This analysis demonstrates that more frequent high-amplitude Omega blocking patterns have promoted melt of the northern GrIS by generating above-normal downwelling longwave radiation and enhanced sensible heat flux in the region. Next, this work investigates remote forcing of summer atmospheric circulation over Greenland, revealing two potentially synergistic mechanisms by which amplified Arctic warming favors Greenland blocking: (1) Disproportionate high-latitude warming promotes wavier atmospheric circulation over the North Atlantic—conditions that are conducive to the formation of blocking anticyclones. (2) Low spring North American snow cover generates a stationary Rossby wave response that favors anticyclonic conditions over Greenland. Through regional climate modeling, this work then estimates the contribution of the change in local thermodynamic background conditions to observed GrIS surface mass loss. The results demonstrate that surface mass loss would have been reduced by ~62% had the recent dynamical forcing of the GrIS occurred in a preindustrial climate.
This dissertation investigates the drivers of GrIS surface mass loss within the context of amplified Arctic warming. First, this research provides a more comprehensive look at the mechanisms by which blocking promotes GrIS melt by identifying common Greenland blocking patterns and considering spatiotemporal differences in the synoptic-scale forcing of GrIS surface conditions between them. This analysis demonstrates that more frequent high-amplitude Omega blocking patterns have promoted melt of the northern GrIS by generating above-normal downwelling longwave radiation and enhanced sensible heat flux in the region. Next, this work investigates remote forcing of summer atmospheric circulation over Greenland, revealing two potentially synergistic mechanisms by which amplified Arctic warming favors Greenland blocking: (1) Disproportionate high-latitude warming promotes wavier atmospheric circulation over the North Atlantic—conditions that are conducive to the formation of blocking anticyclones. (2) Low spring North American snow cover generates a stationary Rossby wave response that favors anticyclonic conditions over Greenland. Through regional climate modeling, this work then estimates the contribution of the change in local thermodynamic background conditions to observed GrIS surface mass loss. The results demonstrate that surface mass loss would have been reduced by ~62% had the recent dynamical forcing of the GrIS occurred in a preindustrial climate.