greenland

Melting of Greenland ice is ‘off the charts,’ study shows

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greenlandA new study that has just been published in Nature reveals that something dramatic is happening in Greenland.

The title of the study is “Nonlinear rise in Greenland runoff in response to post-industrial Arctic warming“.

When you are talking about a measurement of meltwater from a body of ice that by itself contains enough water to lift sea level by 20 feet, then the one word that you really really don’t want to see is the word “nonlinear”.

Study Details

We have very precise and accurate measurements of the extent of the melt in Greenland via satellite technology. One problem with that is the lack of any measurements over a longer period. This study now resolves that and places it all in a far bigger context …

Here we present the first continuous, multi-century and observationally constrained record of Greenland ice sheet surface melt intensity and runoff, revealing that the magnitude of recent Greenland ice sheet melting is exceptional over at least the last 350 years.

How exactly did they do this?

They have managed to achieve this by conducting a very careful study of ice cores taken from central west Greenland. The term they use is “stratigraphic analysis”. Basically this means looking at the seasonal layering (stratification) contained within the cores and determining the degree of historical melt by measuring the refrozen melt layers. This approach has enabled them to reconstruct past melt rates.

Below are some illustrations of this taken from the study.

On the left you have an illustration of the simulation of positive trends in annual surface meltwater production over 1958–2016.

On the right it shows the locations of where their ice cores are situated within the Jakobshavn drainage basin (blue outline; basin 7.1) of central west Greenland and on the Nuussuaq Peninsula, as well as air-temperature observations integrated into a composite Ilulissat air-temperature record. The satellite image in b was obtained with the NASA MODIS instrument.

Just how reliable are their measurements?

There are independent models that predict what the melt rate would have been – they match.

We know what the melt rate was during the satellite era – once again we have a match.

Thus we can have confidence that the numbers derived by looking back over the last 350 years are realistic.

So what exactly have they got?

This …

We find that the initiation of increases in Greenland ice sheet melting closely follow the onset of industrial-era Arctic warming in the mid-1800s, but that the magnitude of Greenland ice sheet melting has only recently emerged beyond the range of natural variability.

… and so that then naturally leads to this …

Owing to a nonlinear response of surface melting to increasing summer air temperatures, continued atmospheric warming will lead to rapid increases in Greenland ice sheet runoff and sea-level contributions.

Here is a graphical illustration from the study. It reveals a pronounced 250% to 575% increase in melt intensity over the last 20 years, relative to a pre-industrial baseline period (eighteenth century) for cores from the Nuussuaq Peninsula (orange) and central west Greenland (red), respectively

They sum it all up as follows …

Today, surface melting and melt-induced runoff in Greenland occur at magnitudes not previously experienced over at least the last several centuries, if not millennia. Melt–temperature nonlinearity and general circulation changes mean that further twenty-first-century warming has important implications for the ice-sheet mass balance, by accelerating the intensity of surface melting and amplifying Greenland ice sheet contributions to global sea-level rise.

Permit me to put this another way by deploying a one word non-scientific summary … yikes!.

Does this matter?

Chris Mooney, a science writer for the Washington Post, tweets about the serious implications of this …

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