How well can we predict future sea level rise and attribute past ice sheet changes?
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 unpredictable fluctuations in the climate. 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-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.
Funded: The Antarctic Ice Sheet Large Ensemble (AISLENS) Project
AISLENS (pronounced like “islands”) is an NSF-funded project within the GT Ice & Climate group to simulate many possible scenarios (i.e. a large ensemble, analogous to large climate simulation ensembles) of historical and future evolution of the Antarctic Ice Sheet under realistic variability in oceanic and atmospheric processes. To do so, we are developing novel statistical and machine learning tools to emulate output from state-of-the-art global climate models (working together with the Department of Energy E3SM team at Los Alamos National Laboratory) including high-resolution forcing of the Antarctic Ice Sheet from both the ocean and atmosphere. The purpose of this project is to understand the role of climate variability in the uncertainty of future sea level projections, and also to disentangle the role of internal vs. anthropogenic climate change in the observed rapid ice loss from Antarctica over the past several decades.
How fast can ice sheets change?
When climate changes, the response of ice sheets and glaciers is complex and mediated by a variety of processes beyond simple melting. The Ice & Climate group has investigated such glacier responses to environmental changes, including the mechanisms which determine the magnitude and speed of glacier change in response to: climate change (Robel & Tziperman 2016, Robel et al. 2018), melt and friction beneath glaciers (Robel et al. 2013, 2014, 2016), ice fabric and temperature (Minchew et al. 2018), or ocean tides (Robel et al. 2017).
Under the right conditions, ice sheets can become unstable, leading to their irreversible and rapid decline. However, the climatic and geological conditions which initiate and control the rate of this ice sheet decline are not well understood. Work from the Ice & Climate group has 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), the many time scales of marine ice sheets collapse (Robel et al. 2018), and the collective behavior of draining melt ponds on ice shelves (Robel & Banwell, 2019, animation right).
Funded: Model of Antarctic Ice Shelf Hydrology and Stability (MONARCHS)
MONARCHS is a NASA-funded project, led by Ice & Climate Group postdoctoral fellow, Dr. Samantha Buzzard, and including collaboration with with Professors Yi Deng and Jingfeng Wang at Georgia Tech. We seek to understand how the complex interactions of melt water with ice shelves may (or may not) destabilize them under future climate change. The primary project goal is to build a numerical model which simulates surface melting on ice sheets, and the vertical and horizontal melt water flow over and interaction with the ice sheet surface. This model is an open-source, python-native, standalone model, which is built with extensive community input and a plan to be coupled with state-of-the-art ice sheet and climate models. It will include many new processes and schema including a maximum entropy production (MEP) scheme for calculating surface melt, re-freezing of water within snow, formation of melt lakes, erosion of ice by water flow, and flexure of ice under loading by water.
What controls iceberg calving and melting?
Ice sheets in contact with 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.