Sci. Adv. paper on Gradient Fingerprint Mapping

We use ISSM to map sea level rise for major cities depending on which parts of the Earth's ice sheets melt, and by how much. We share the results in a new online tool, the Virtual Earth System Laboratory - Gradient Fingerprint Mapping.

There is a general consensus among Earth scientists that melting of land ice greatly contributes to sea-level rise (SLR) and that future warming will exacerbate the risks posed to human civilization. As land ice is lost to the oceans, both the Earth’s gravitational and rotational potentials are perturbed, resulting in strong spatial patterns in SLR, termed sea-level fingerprints. We lack robust forecasting models for future ice changes, which diminishes our ability to use these fingerprints to accurately predict local sea-level (LSL) changes. We exploit an advanced mathematical property of adjoint systems and determine the exact gradient of sea-level fingerprints with respect to local variations in the ice thickness of all of the world’s ice drainage systems. By exhaustively mapping these fingerprint gradients, we form a new diagnosis tool, henceforth referred to as gradient fingerprint mapping (GFM), that readily allows for improved assessments of future coastal inundation or emergence. We demonstrate that for Antarctica and Greenland, changes in the predictions of inundation at major port cities depend on the location of the drainage system. For example, in London, GFM shows LSL that is significantly affected by changes on the western part of the Greenland Ice Sheet (GrIS), whereas in New York, LSL change predictions are greatly sensitive to changes in the northeastern portions of the GrIS. We apply GFM to 293 major port cities to allow coastal planners to readily calculate LSL change as more reliable predictions of cryospheric mass changes become available.

E. Larour, E. Ivins, S. Adhikari, Should coastal planners have concern over where land ice is melting?, Sci. Adv., 3(11), doi:10.1126/sciadv.1700537.

Sensitivity of SLR along U.S./Canadian coastlines to GrIS thickness variations.
Gradient −dS/dH (in 10−3 μm/m per km2) at U.S. and Canadian coastal cities. Maps 1 to 9 correspond, respectively, to gradients computed for each of the named ports numbered clockwise from Halifax. −dS/dH is computed using the ISSM-AD gradient solver. The forward SLR run used to support the derivation of –dS/dH is shown in the center Earth map (in mm/year). It is computed using the ISSM-SESAW solver with model inputs (ice thickness change) inferred from GRACE for the period 2003–2016. This forward model therefore captures the response to thickness changes in all of the main glaciated areas of the world (including, among others, Alaskan and Canadian Arctic Glaciers, Himalayan Glaciers, Patagonia Glaciers, and the Greenland and Antarctica Ice Sheets), hence representing a truly global “ice” fingerprint.