Climate change – CryoSat-2 confirms exponential ice melt

Data from CryoSat-2 are consistent with an average yearly Greenland ice-melt for the ten years to 2021 more than double that of the previous decade.

In addition, ice loss from western Antarctica is accelerating even more quickly: by a factor of about three.

The two ice sheets combined are thinning at a rate of 500 cubic kilometres a year, the highest rate observed since altimetry satellite records began about 20 years ago.

Moreover, common sense suggests that, with global warming not only continuing but accelerating, this rate is likely to increase.

To the informed layman that I am it seems that we must therefore expect a sea level rise of about 2m by the middle of the century.* Clearly, if this is the case, we can’t afford to wait until 2020 for the next IPCC report to confirm it.

I’m also thinking of the first studies of Arctic sea ice which indicated there would be no summer summer ice at all — in about 150 years. A few years later another study brought that down to 50 years. It was only when sufficient data became available that scientists realised the graph was not linear but exponential and the estimate came down to 15 years. That was… what, 10 years ago? — and it was right on the nail.

Arctic sea ice melt

The authority of the IPCC’s numbers, based on 10-year averages, stems from their resistance to year-by-year anomalies, and this is invaluable. However, in the presence of a phenomenon which is both extremely important and rapidly evolving, 10-year averages struggle to provide timely information.

As things stand today there are only two points on the IPCC graph of Greenland ice-melt: 34 Gt/yr and 210 Gt/yr, yearly averages for the two decades to 2011. That is to say, the data from 20 years of observations are presented in such a way that nothing can be extrapolated from them. But the Paris conference in December 2015 will need to be provided with starkly unambiguous evidence if it is to take the appropriately radical decisions.

That being the case, I would suggest that  the IPCC should urgently consider recalculating 10-year averages on a sliding year-to-year basis. This would provide 25 points on the graph by December 2015 while preserving the current method’s built-in resistance to anomalies.

The ice at both poles seems to be melting much faster than the models suggested. If this is so, it needs to be said loud and clear and the sooner the better.

*If not worse. See here for the Excel spreadsheet. CryoSat ice melt for blog – Copie3

NB – This Excel file was amended on 30 August at 13:20 CEST. I corrected a mistake in cell G6 which now reads “=100*$A$6”. This pushes the 2m sea level rise back three or four years, but it doesn’t change the fact that, after that point, the graph goes absolutely fucking ballistic. If anyone can find other mistakes, please — I’d be delighted!

I further amended this article on 1 September to include reference to Arctic sea ice melt.

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