Greenland is losing ice at fastest rate in 350 years (?)

Is anybody bothered that the researchers examined meltwater that did NOT run off into the sea to estimate how much meltwater DID run off into the sea?  A large question about the validity of their measuring instrument there, I think. That one type of melting estimates the other is just an assumption and not a terribly plausible one.  Processes in the two areas are known to be different in one way so why are there not differences in other ways?

And they used results from a few icecores in one part of Greenland to estimate what has happened in the whole of Greenland.  How did they accomplish that vast feat of overgeneralization?  By running models.  But you can get whatever you want out of models.  I am betting that there were a few "adjustments" before a final model run was accepted

Too many assumptions there for any firm conclusions.  Different methods could yield different conclusions

Vast ice sheet's dramatic transformation revealed by ice cores, satellite data and climate models.

Ice melt across Greenland is accelerating, and the volume of meltwater running into the ocean has reached levels that are probably unprecedented in seven or eight millennia. The findings, drawn from ice cores stretching back almost 350 years, show a sharp spike in melting over the past two decades.

Previous studies have shown record melting on parts of Greenland's ice, but the latest analysis includes the first estimate of historical runoff across the entire ice sheet. The results, published on 5 December in Nature, show that the runoff rate over the past two decades was 33% higher than the twentieth-century average, and 50% higher than in the pre-industrial era.

“The melting is not just increasing — it’s accelerating,” says lead author Luke Trusel, a glaciologist at Rowan University in Glassboro, New Jersey. “And that’s a key concern for the future.”

Centuries of ice

A team led by Trusel drilled a series of ice cores, the biggest 140 metres long, in central West Greenland in 2014 and 2015. There, snow that melts in the summer later refreezes, rather than running off into the ocean — creating an annual record of ice melt. The researchers compared data from these ice cores, and an older core from the same area, with satellite observations of melting across Greenland, and estimates of melt and runoff from a regional climate model.

The team’s analysis suggested that the rate of melting at its drilling sites is representative of trends across Greenland. Armed with this knowledge, the researchers used the ice-core data as a proxy to estimate runoff rates going back centuries — before satellites and climate models existed.

The findings bolster a study published in March that found that West Greenland is melting faster than it has in at least 450 years2. “What this paper does nicely is expand that record to the whole ice sheet,” says Erich Osterberg, a climatologist at Dartmouth College in Hanover, New Hampshire, and a co-author of the March study.


Journal Abstract:

Nonlinear rise in Greenland runoff in response to post-industrial Arctic warming

Luke D. Trusel et al.


The Greenland ice sheet (GrIS) is a growing contributor to global sea-level rise1, with recent ice mass loss dominated by surface meltwater runoff2,3. Satellite observations reveal positive trends in GrIS surface melt extent4, but melt variability, intensity and runoff remain uncertain before the satellite era. Here we present the first continuous, multi-century and observationally constrained record of GrIS surface melt intensity and runoff, revealing that the magnitude of recent GrIS melting is exceptional over at least the last 350 years. We develop this record through stratigraphic analysis of central west Greenland ice cores, and demonstrate that measurements of refrozen melt layers in percolation zone ice cores can be used to quantifiably, and reproducibly, reconstruct past melt rates. We show significant (P < 0.01) and spatially extensive correlations between these ice-core-derived melt records and modelled melt rates5,6 and satellite-derived melt duration4 across Greenland more broadly, enabling the reconstruction of past ice-sheet-scale surface melt intensity and runoff. We find that the initiation of increases in GrIS melting closely follow the onset of industrial-era Arctic warming in the mid-1800s, but that the magnitude of GrIS melting has only recently emerged beyond the range of natural variability. Owing to a nonlinear response of surface melting to increasing summer air temperatures, continued atmospheric warming will lead to rapid increases in GrIS runoff and sea-level contributions.

Nature volume 564, pages104–108 (2018)

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