On the robustness of predictions of sea level fingerprints

Abstract

S U M M A R YThe rapid melting of the Earth's ice reservoirs will produce geographically distinct patterns of sea level change that have come to be known as sea level fingerprints. A basic, gravitationally self-consistent theory for computing these patterns appeared in the 1970s; however, recent, highly discrepant fingerprint calculations have led to suggestions that the algorithms and/or theoretical implementation adopted in many previous predictions is not robust. We present a suite of numerical predictions, including benchmark comparisons with analytic results, that counter this argument and demonstrate the accuracy of most published predictions. Moreover, we show that small differences apparent in calculations published by some groups can be accounted for by subtle differences in the underlying physics. The paper concludes with two sensitivity analyses: (1) we present the first-ever calculation of sea level fingerprints on earth models with 3-D variations in elastic structure and density, and conclude that this added complexity has a negligible effect on the predictions; (2) we compare fingerprints of polar ice sheet mass flux computed under the (very common) assumption of a uniform melt distribution to fingerprints calculated using melt geometries constrained by analysing recent trends in GRACE gravity data. Predictions in the near field of the ice sheets are sensitive to the assumed melt geometry; however, this sensitivity also extends to the far field, particularly in the case of Antarctic mass changes, because of the strong dependence of the rotational feedback signal on the melt geometry. We conclude that inferences of ice sheet mass flux based on modern sea level constraints should consider these more realistic melt geometries.

The multimillennial sea-level commitment of global warming

“…Information about the spatial distribution of mass loss from within each ice sheet is not known, and so the model runs assumed a uniform thinning of ice over a 2,000-y period with no margin retreat. Although this simplification will affect the accuracy of the results (68,69), the general characteristics of the pattern will not be affected. Over millennial time scales, the dominant component of solid Earth deformation is nonelastic, and so we used a viscoelastic Maxwell rheology (70).…”

Estimates of twenty-first century sea-level changes for Norway

“…Gomez et al 2010;Mitrovica et al 2011;Tamisiea and Mitrovica 2011). The results of these studies suggest that, as Norway sits in the near field of Greenland, sea-level changes along the Norwegian coast will be highly sensitive to the pattern of ice sheet change.…”

“…We do not show these individual patterns here but refer the reader to the existing literature (e.g. Gomez et al 2010;Mitrovica et al 2011;Tamisiea and Mitrovica 2011) which show sea level projections generated from changes in Greenland and Antarctica, and details of how they deviate from the global mean. These studies also show that the sea level response is highly sensitive to the assumed pattern of ice mass change and the underlying physics of the sea level model applied (see also the Discussion in Sect.…”

Increased threat of tropical cyclones and coastal flooding to New York City during the anthropogenic era

“…The two reconstructions were combined to produce a single, regional relative sea level record, which is what an observer at the coast would have experienced, and is the net outcome of multiple and simultaneous processes including GIA. A caveat of using this data set is that relative sea level differences between southern New Jersey and NYC may arise over decades to centuries because of spatial differences in the rate of GIA (35), the fingerprint of ice sheet melt (36), and the role of ocean currents, including the strength and position of the Gulf Stream (24,37).…”