Being on the Level About Sea Level
Stuart Gaffin is a climate researcher at Columbia University and a regular contributor with his blog “Exhausted Earth”. ThomsonReuters is not responsible for the content – the views are the author’s alone.
Bjorn Lomborg is a Danish political scientist who makes a semi-career (if not career) out of countering claims about global warming. His brand of writing tends to throw major counter claims out there on quite big climate issues, in short pithy sound-bites, often without data, letting the reader try and figure it out.
A recent Lomborg editorial is an example and has many claims in it that one needs to take time to carefully analyze. Here I will just react to one of Lomborg’s deceptive suggestions that sea level has suddenly stopped rising:
Since 1992, we have had satellites measuring the rise in global sea levels and they have shown a stable increase of 3.2mm a year: spot on compared with the IPCC projection. Moreover, over the past two years, sea levels have not increased at all; actually, they show a slight drop. Should we not be told that this is much better than expected?
Without seeing the actual data, readers of this passage will think sea level rise from 1992-2006 was smoothly monotonic and then suddenly this stopped and is reversing. Here’s a graph of the data Lomborg is referring to (I thank Gavin Schmidt for this graphic):
In fact the short term 2-year trends are all over the place. This is due to the short term variations in weather like pressure, winds, currents and so forth, that cause small oscillations in sea level, just like they do in temperature.
Following Lomborg’s approach in 1998-2000 (or ’94-‘96 or in ’04-’06, etc) you might have concluded sea level had stopped rising (and things were therefore “much better than expected”), but this would have been meaningless for the long term, which is what counts. The fact is nobody should be claiming anything at all about long-term sea level based just on two-year trends and that’s why it doesn’t make any headlines.