- Bishop Hill blog

There is much excitement among the green fraternity this morning over a new paper that claims to have found an acceleration in sea-level rise that is even more dramatic than previously thought.

Stop yawning at the back there.

As usual, a brief perusal beyond the headlines reveals a considerably more nuanced story. The paper is based on tide gauge records and finds a slow increase over the 20th century of just over 1mm/year. This is rather less than some previous estimates.

However, the authors go on to say that:

Our analysis, which combines tide gauge records with physics-based and model-derived geometries of the various contributing signals, also indicates that GMSL rose at a rate of 3.0 ± 0.7 millimetres per year between 1993 and 2010, consistent with prior estimates from tide gauge records⁴. The increase in rate relative to the 1901–90 trend is accordingly larger than previously thought; this revision may affect some projections¹¹ of future sea-level rise.

I'm a bit bemused by this. Why would they use a different methodology for 1993-2010 to the one they used for 1901-90? Why would they want to combine data with "physics based and model-derived geometries"? Do the tide guages show any acceleration or not?

Perhaps the text of the paper will explain if someone can send it over or leave a comment.

Update on Jan 15, 2015 by

Bishop Hill

OK, I have a copy of the paper now. The authors have used an infilling mechanism to estimate SLR from 1901 to 2010. They have used the same mechanism throughout.

So the validity of the findings seems to rest on the validity of the infilling methodology. The authors asks us to draw comfort from the similarity of their 21st century trend to the trend calculated by others (including the satellite records) but suggest that previous 20th century estimates are too high.