How well can we predict future sea level rise?
As ice sheets melt, global mean sea level rises. However, the rate at which ice sheets will melt in the future is uncertain, due to our poor understanding of ice sheet processes, but also the unknown future trajectory of local climate in the vicinity of ice sheets and individual glaciers. To estimating the range of possible future sea level rise, we can use a variety of approaches from computer science, applied mathematics, and physics. In our group, we are working on projects that span the very theoretical: which processes drive the range and spread of uncertainty in future sea level projections (Robel et al. 2019, figure below), to more applied: how can we make the best estimates of sea level rise uncertainty using computationally expensive models and how do we bridge the gap between global scale sea level rise projections and community- or building-scale flooding estimates. To do so we work with computer scientists, physicists, and engineers to understand what sea level information is needed by decision-makers and how we can provide the most robust estimates.
How do ice sheets respond to environmental changes?
In the Greenland and Antarctic ice sheets, ice primarily moves by flow in individual glaciers or “ice streams”. We want to understand how and why the flow in these glaciers changes over time. We do so by examining the processes which mediate flow in glaciers occurring, and how they respond to different types of environmental changes, including climate (Robel & Tziperman 2016, Robel et al. 2018), melt and friction beneath glaciers (Robel et al. 2013, 2014), ice fabric and temperature (Minchew et al. 2018), or ocean tides (Robel et al. 2017). By explaining the causes and rates of glacier changes, we can improve our understanding past ice sheet deglaciations, distinguish natural from human-caused changes in the present, and more accurately predict future ice sheet melt.
Under the right conditions, ice sheets can become unstable, leading to their irreversible and rapid decline. We are examining which climatic and geological conditions may lead to these instabilities and how fast ice sheets melt when they become unstable. We have shown the critical role of ice sheet shape in causing “meltwater pulses”, the most rapid periods of sea level rise in recent Earth history (Robel & Tsai 2018). We have also explored how changing friction at the bottom of ice sheets on ice sheet stability (Robel et al. 2016) and the multiple time scales and mechanisms of marine ice sheet collapse (Robel et al. 2018). We have recently used tools from statistical physics to explore the collective dynamics of draining melt ponds on ice shelves (Robel & Banwell, 2019, animation right). Dr. Samantha Buzzard, a postdoctoral fellow in the Ice & Climate group, is currently examining how the flow of water over ice shelves affects their propensity to rapidly disintegrate.
What controls iceberg calving and melting?
Ice sheets that end in water lose ice through the process of iceberg calving (ice fracture and detachment). Calving is likely influenced by many factors within and outside of ice sheets, including the presence of sea ice within densely packed icebergs floating in the ocean, known as “mélange”. We have adapted a discrete element model (see animation above), a tool more commonly used in condensed matter physics, to explore the role of sea ice and calving in the aggregate properties of iceberg mélange (Robel 2017). Graduate student Ziad Rashed is currently exploring how to simulate the two-way interactions between mélange and glacier calving. We also use laboratory experiments (see video below of small wave flume built in our lab) to explore the processes through which ocean waves melt icy surfaces.