April 06, 2017

Greenland's coastal ice is losing mass -- which is projected to raise global sea levels by a whole 1.5 inches by 2100

1). How can "coastal meltwater be filled to its capacity"?  Greenland is surrounded by ocean.  Any water added to that ocean will simply pass into the ocean as a whole.  It is not as if there is a bathtub waiting to be filled up.  The world's oceans as a whole are the only bathtub.

2). Most of the Greenland icecap is in an interior basin and has remained unmelted in past warming events.  There are however isolated blobs of ice along the coast -- and it is they that are being referred to below.  The main Greenland icecap is not affected.

3). The data is arrived at via modelling and estimation so should be taken seriously only if you believe that Greenies are honest.  Their chronic secrecy about their data and calculations make that an heroic assumption.

4). The future extension of processes in the coastal ice to Greenland ice as a whole is just a bit of speculation.  The only measurements mentioned below refer to the coastal ice

Journal Abstract and Introduction included below


Greenland's glaciers and ice caps have passed a 'tipping point' and are no longer able to regrow lost ice, experts have warned in a new study. The proverbial 'tipping point' was passed in 1997, when coastal meltwater was filled to its capacity.

Researchers predict that the subsequent melting of Greenland's coastal ice will raise global sea levels by about 1.5 inches by 2100.

Greenland's glaciers and ice caps have passed a 'tipping point' and are no longer able to regrow lost ice, experts have warned in a new study. The proverbial 'tipping point' was passed in 1997, when coastal melt water was filled to its capacity

The problem lies in a layer of snow called the firn, which lies between fresh surface snow and the ice. Normally, meltwater drains through gaps in the firn down to the ice surface. But when the firn became saturated in 1997, it froze through.

Since then, there haven't been any gaps to capture meltwater, and the ice hasn't been able to grow.

They found that, for the last 20 years, mass loss has been exactly equal to the amount of meltwater runoff lost to sea, with a frozen firn the most likely cause.

The study was conducted by researchers at Ohio State University, who looked at the glaciers and ice caps that dot the edges of the Greenland coast.

Twenty years ago, the island passed a tipping point, meaning the smallest glaciers and ice caps on the coast are no longer able to regrow lost ice.

The findings reveal exactly why the most vulnerable parts of Greenland ice are melting so quickly – the deep snow layer that normally captures coastal melt-water was filled to capacity in 1997.

That layer of snow and melt-water has since frozen solid, meaning all new melt-water flows over it and out to sea.

Fortunately, the findings only apply to a fairly small amount of ice along the coast, and not the Greenland Ice Sheet – the second biggest ice cache in the world.

Dr Ian Howat, who led the study, said: 'These peripheral glaciers and ice caps can be thought of as colonies of ice that are in rapid decline, many of which will likely disappear in the near future. 'In that sense, you could say that they're "doomed."

'However, the ice sheet itself is still not "doomed" in the same way. The vast interior ice sheet is more climatologically isolated than the surrounding glaciers and ice caps.

SOURCE

A tipping point in refreezing accelerates mass loss of Greenland’s glaciers and ice caps

B. Noël et al.

Abstract

Melting of the Greenland ice sheet (GrIS) and its peripheral glaciers and ice caps (GICs) contributes about 43% to contemporary sea level rise. While patterns of GrIS mass loss are well studied, the spatial and temporal evolution of GICs mass loss and the acting processes have remained unclear. Here we use a novel, 1 km surface mass balance product, evaluated against in situ and remote sensing data, to identify 1997 (±5 years) as a tipping point for GICs mass balance. That year marks the onset of a rapid deterioration in the capacity of the GICs firn to refreeze meltwater. Consequently, GICs runoff increases 65% faster than meltwater production, tripling the post-1997 mass loss to 36±16 Gt−1, or ∼14% of the Greenland total. In sharp contrast, the extensive inland firn of the GrIS retains most of its refreezing capacity for now, buffering 22% of the increased meltwater production. This underlines the very different response of the GICs and GrIS to atmospheric warming.

Introduction

Covering a total area of ∼90,000 km2, Greenland’s peripheral glaciers and ice caps (GICs) represent ∼12% of the world’s glacierized area outside of the Antarctic and Greenland ice sheets1. Greenland’s GICs account for 14 to 20% of total current Greenland glacial mass loss2, although they only represent ∼5% of the area and ∼0.5% (∼39 mm SLE) of the volume of the Greenland ice sheet (GrIS). In a scenario of continued global warming, Greenland’s GICs may lose 19–28% (7.5–11 mm) of their volume by 2100 (ref. 3). Despite multiple in situ observational campaigns since the early 1950s (ref. 4), glacier modelling5 and satellite-based2,6 estimates, large uncertainties remain in the spatial and temporal distribution of Greenland’s GICs mass loss. To fill these gaps, regional climate models (RCMs) are often used7,8,9,10,11,12,13,14,15, but their horizontal resolution (typically 5–20 km) fails to resolve the steep surface mass balance (SMB) gradients in the topographically complex regions in which GICs are often situated16.

To address this issue, we created a 1 km data set, statistically downscaled from output of the regional atmospheric climate model RACMO2.3 using regressions of SMB components against elevation estimated at the model resolution of 11 km. These regressions are then applied to a downsampled 1 km version of the topography and ice mask of the Greenland Ice Mapping Project (GIMP) Digital Elevation Model (DEM)17. The downscaling procedure also includes a bare ice albedo correction based on a 1 km MODIS albedo product to avoid underestimation of melt and runoff, especially on dark, low-lying glacier tongues. Earlier, the downscaling method was successfully applied to the GrIS16.

Here we use the novel SMB product at 1 km resolution to quantify Greenland’s GICs mass loss, assuming changes in solid ice discharge to be negligible18,19,20. The data set includes individual SMB components (precipitation, sublimation, melt, refreezing and runoff) for all GICs on a daily time scale (1958–2015), which is crucial for evaluation using irregular (in time and space) observations and to understand the drivers of mass loss. Using this product, we identify 1997 (±5 years) as a tipping point for the mass balance of Greenland’s GICs, which marks the onset of a rapid deterioration of inland firn capacity to refreeze meltwater, causing long-term mass loss

Nature Communications 8, Article number: 14730 (2017)    doi:10.1038/ncomms14730





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