Sensitivity of sea level rise (SLR) along U.S./Canadian coastlines to Greenland Ice Sheet (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 (23) 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 (29) 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) (28), hence representing a truly global “ice” fingerprint. Graphic: Larour, et al., 2017 / Science Advances

By Chris Mooney
15 November 2017

(The Washington Post) – New York City has plenty to worry about from sea level rise. But according to a new study by NASA researchers, it should worry specifically about two major glacier systems in Greenland’s northeast and northwest — but not so much about other parts of the vast northern ice sheet.

The research draws on a curious and counterintuitive insight that sea level researchers have emphasized in recent years: As ocean levels rise around the globe, they will not do so evenly. Rather, because of the enormous scale of the ice masses that are melting and feeding the oceans, there will be gravitational effects and even subtle effects on the crust and rotation of the Earth. This, in turn, will leave behind a particular “fingerprint” of sea level rise, depending on when and precisely which parts of Greenland or Antarctica collapse.

Now, Eric Larour, Erik Ivins and Surendra Adhikari of NASA’s Jet Propulsion Laboratory have teased out one fascinating implication of this finding: Different cities should fear the collapse of different large glaciers.

“It tells you what is the rate of increase of sea level in that city with respect to the rate of change of ice masses everywhere in the world,” Larour said of the new tool his team created.

The research was published in Science Advances, accompanied by an online feature that allows you to choose from among 293 coastal cities and see how certain ice masses could affect them if the ice enters the ocean. The scientists also released a video that captures some of how it works.

The upshot is that New York needs to worry about certain parts of Greenland collapsing, but not so much others. Sydney, however, needs to worry about the loss of particular sectors of Antarctica — the ones farther away from it — and not so much about the ones nearer. And so on.

This is the case because sea level actually decreases near a large ice body that loses mass, because that mass no longer exerts the same gravitational pull on the ocean, which accordingly shifts farther away. This means that from a sea level rise perspective, one of the safest things is to live close to a large ice mass that is melting.

“If you are close enough, then the effect of ice loss will be a sea level drop, not sea level rise,” said Adhikari. The effect is immediate across the globe. [more]

These are the melting glaciers that might someday drown your city, according to NASA


ABSTRACT: 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.

Should coastal planners have concern over where land ice is melting?

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