Is Sea Level Falling?

The latest of many “sceptic” claims about global warming is that sea level is falling.  Satellite altimetry (measuring sea-surface heights from satellite radar systems) supposedly shows the steady rise of sea level has reversed.  Well, no, sea level is rising faster than ever.

Up-to-date reputable data can be found at  http://ibis.grdl.noaa.gov/SAT/SeaLevelRise/LSA_SLR_timeseries.php

Here is a recent plot from that site.  It shows sea level continuing to rise at 3 mm/year.

Sea level measured by satellite altimetry by NOAA

 

 

 

Before 1990 sea level was rising at only 2 mm/year.  The change can be seen in a plot by Stefan Rahmstorf, Potsdam Institute for Climate Impact Research  http://www.sciencexpress.org / 1 February 2007 / Page 1 / 10.1126/science.1136843

Sea level from 1970 to 2007

 

 

 

In this plot the satellite data (blue) overlap the older tide-guage data (red).  You can see they correspond.  This is significant because the two data sources are subject to different sources of interference and have different global coverage, so if they are consistent is increases confidence that they are correct.

This plot also shows that the current rate of rise is at the top of the range of predictions of the Intergovernmental Panel on Climate Change (IPCC), whose projections are shown as dashed lines and the grey-shaded band.  This is consistent with other evidence that the effects of global warming are accelerating, and are now happening faster, in some cases much faster, than projections made even a few years ago.

It is true sea level is falling in some areas relative to the local land level.  This is usually because the land is actually rising, due to local tectonic forces or, in some cases, due to the loss of glacier ice on land which used to weigh it down more.

There are the usual claims that the scientists involved in producing the above plots don’t know how to do their job.  If that were true, those who claim sea level is falling should be getting their work published in mainstream scientific journals.  Of course there are the usual claims of a wicked conspiracy blocking publication of contrary views.  Like most conspiracy theories, that is nonsense.

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2 thoughts on “Is Sea Level Falling?

  1. janama

    Geoff – a sceptical scientist would naturally try to find more than one interpretation of sea level rise.

    here’s one from http://www.climate4you.com – the source of the data is clearly reported.

    Here’s another one from Colorado

    Both my charts are different to yours, not only in data but in resolution. Neither of my charts show increasing sea level rise.

    here’s a quote from a recent article in the Australian

    http://www.theaustralian.com.au/news/nation/science-is-in-on-climate-change-sea-level-rise-17mm/story-e6frg6nf-1225795202916

    “According to the most recent report by the Bureau of Meteorology’s National Tidal Centre, issued in June, there has been an average yearly increase of 1.9mm in the combined net rate of relative sea level at Port Kembla, south of Sydney, since the station was installed in 1991.

    This is consistent with historical analysis showing that, throughout the 20th century, there was a modest rise in global sea levels of about 20cm, or 1.7mm per year on average. ”

    Nils Morner has his own view regarding sea levels and by the look of his bio he appears to be in a pretty good position to make a statement about it, which he did in an open letter to the President of the Maldives.

    http://network.nationalpost.com/np/blogs/fpcomment/archive/2009/10/20/maldives-president-all-wet-on-sea-level.aspx

    So as I feel I’ve clearly pointed out in this post, using 4 separate sources, your statement about increasing rates of sea level rise is totally false and you should cease your insipid scaremongering.

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  2. Geoff Davies Post author

    Janama –

    The graphs you link to both show sea level rising at an average around 3 mm/year since the early 1990s, which is consistent with the NOAA graph above. The speed-up from 2 mm/year occurred around 1990 (see second graph above), so your graphs don’t cover the change.

    There is a slight decrease in the RATE of increase within the last few years, but that’s not the same as saying sea level is DECREASING, which what some people are claiming. Anyway short-term fluctuations are not the issue, it’s the longer-term trend that’s important – see my post on so-called cooling since 1998.

    SImilarly, we need to look at global averages, and data from a single locality like Port Kembla are not sufficient to judge the global trend. There are many subtle causes of local variations, of which I mention only a couple in my post.

    If Nils Morner is well-qualified then let him argue his case in the scientific literature.

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