Busy day at the ISMASS Workshop here at SCAR 2012 (see here: ISMASS website). There were invited lectures from a number of prominent scientists, including Erik Ivins, Pippa Whitehouse, Jay Zwally, Catherine Ritz, Slawek Tulaczyk, Catia Domingues, and Robert Nicholls. For me, two talks stood out as exceptional.
Pippa Whitehouse (Durham University) gave a talk on Glacial Isostatic Adjustment (GIA) modelling. Some people may know this as Post Glacial Rebound, or PGR. Understanding GIA is important, because it affects modern estimates of ice loss from the Greenland and Antarctic ice sheets. During glaciations, the mass of ice depresses the earth’s crust, and there is solid earth subsidence. Mantle flows away from the ice sheet. Following deglaciation, solid earth deformation results in rebound of the crust.The redistribution of water across the Earth (i.e., transfer of water from ice sheets to the oceans) results in solid earth deformation beneath the oceans.GIA (or PGR) is different to elastic rebound, which happens more quickly following deglaciation. By modelling GIA, and understanding the rate at which the earth is deforming, we can correct satellite measurements of ice sheet mass balance and rates of ice sheet melting (e.g., correct GRACE data). We can better understand rates of modern sea level change and rates of solid earth deformation.
I also really enjoyed the talk by Robert Nicholls from Southampton University on the global impacts of sea level rise. I learned that 1.2 billion people live within 100 km and 100 m of the coast and sea level respectively. There are 136 port cities within this region, and large assets within the 1000 year flood plain. High-end sea level rise threatens all these people; not just from direct sea level rise and inundation, but also from flood and storm damage, wetland loss, erosion, saltwater intrusion, higher water tables and impeded drainage (which indirectly leads to more flooding). Deltas are also under threat, especially in the Nile and south, south-east and east Asia: mitigation will be challenging in these areas and is an important topic for research and cooperation. The impacts of sea level rise are highest in SE Asia, the Nile and Africa, where poverty limits mitigation. Pacific ocean islands also have a limited capacity to respond, and are at a high risk.
What can be done about sea level rise? There are two responses: source control and avoidance (stop the ice caps melting!), and adaptation. Adaptation includes planned retreat, accommodation (building houses on stilts?), and protection (build a new Thames Barrier).Current scenarios suggest that mitigation will only slow and reduce sea level rise – it will not stop it. Climate-induced sea-level rise is inevitable; the uncertainty is the magnitude. What will you do to avoid sea level rise, and to adapt to it when it comes?
Uncertainty in sea level projections arise because:
- Current mitigation and avoidance strategies are unclear (reducing fossil fuel emissions;)
- The dynamic response of ice caps and glaciers to environmental change is uncertain; see Ice Shelves, the Marine Instability Hypothesis, and Ice Streams.