April 7, 2011

Sea Level Rise: Still Slowing Down

Back in the summer of 2009, we ran a piece titled “Sea Level Rise: An Update Shows a Slowdown” in which we showed that the much ballyhooed “faster rate of sea level rise during the satellite era” was actually slowing down.

We suggested that this observation would help the IPCC to adjudicate an issue that it raised in its 2007 Fourth Assessment Report:

“Whether the faster rate [of sea level rise] for 1993 to 2003 reflects decadal variability or an increase in the longer term trend is unclear.”

In Figure 1 (below) reproduced from our 2009 WCR article, we superimposed the moving 10-yr rate of sea level rise as measured by satellites since 1993 upon the 10-yr rate of sea level rise measured from a collection of tide gauges from around the world since the early 20th century (as compiled by Simon Holgate, 2007).

Clearly, the behavior as measured by satellites since 1993 fit right in with the long-term behavior as measured by tide gauges. Such a result suggested that “decadal variability” had a strong hand in explaining why the (short-term) satellite measured rate of sea level rise was greater than the (long-term) tide gauge measured average.


Figure 1. Decadal rate of sea level rise from satellites (red curve) appended to the decadal rate of global sea level rise as determined from a 9-station tide gauge network for the period 1904-2003 (blue curve) and from a 177-station tide gauge network for the period 1948-2002 (magenta) (modified from Holgate, 2007).

At the time of our article, the available satellite data ran through early 2009. Since then, more data has become available. And an update to our Figure 1 recently found its way into the scientific literature in a paper by James Houston (Director Emeritus of the Engineer Research and Development Center of the Army Corps of Engineers) and Robert Dean (Professor Emeritus in the Department of Civil and Coastal Engineering at the University of Florida) and published in the Journal of Coastal Research. In their paper, “Sea-level acceleration based on U.S. tide gauges and extension of previous global-gauge analyses,” Houston and Dean incorporated satellite data through April 2010, and produced the rather familiar-looking (although not as colorful) figure below (Figure 2).


Figure 2. The 10-year moving averages of trends as measured by the altimeters (represented by black dots) plotted vs. Holgate’s data. The trend from 1993 to 2003 is represented by a dot at 1998, the trend from 1994 to 2004 by another dot at 1999, and so on with the final dot at 2005, representing the trend from 2000 to 2010 (from Houston and Dean, 2011).

Notice that the satellite-derived 10-yr average rate of sea level rise continues to fall.

This is how Houston and Dean describe their take on the situation:

When viewed in this historical perspective, the [satellite] altimeter measurements appear similar to several decadal oscillations over the past 100 years, and it is not possible to determine if the increased trend measured by the altimeters is the leading edge of acceleration or merely a typical decadal oscillation; however, the decreasing average suggests an oscillation. [emphasis added]

And since one good deed deserves another, we thought we’d take the opportunity to bring the Houston and Dean figure even more up to date by adding in the satellite altimeter data through September 2010—the most recent data available (see here for data source) (Figure 3)–and even more data should be available soon.


Figure 3. Update: Decadal rate of sea level rise from satellites (light red curve) appended to the decadal rate of global sea level rise as determined from a 9-station tide gauge network for the period 1904-2003 (blue curve) and from a 177-station tide gauge network for the period 1948-2002 (magenta). The satellite data runs through September 2010. The update to our previous update is shown (dark red) at the end of the satellite record. (modified from Holgate, 2007)

By now, this should come as no surprise—the rate of sea level rise continues to slow. The rate during the most recent 10-yr period is 2.32 mm/yr (or about 9 inches per century). This is not much above the 20th century average rate of 1.8mm/yr (7 inches per century), and FAR below the average rate of 10 mm/yr required to raise global average sea level by 1 meter (3.25 feet) by 2100—the new in vogue value for what the IPCC should have projected (rather then the ~15 inches that they did project) (see, for example, Grinsted et al, 2009; Vermeer and Rahmstorf, 2009).

So, in the time since the publication of the IPCC report in 2007, the observed rate of sea level rise has declined and all the while there has been a general clamor (from the more “concerned” among us) that the IPCC projections for sea level rise should be increased.

Go figure.

References:

Grinsted, A., J.C. Moore, and S. Jevrejeva. 2009. Reconstructing sea level from paleo and projected temperatures 200 to 2100AD. Climate Dynamics, doi: 10.1007/s00382-008-0507-2.

Holgate, S. J., 2007. On the decadal rates of sea level change during the twentieth century, Geophysical Research Letters, 34, L01602, doi:10.1029/2006GL028492.

IPCC, 2007. Climate Change 2007: The Physical Basis. Cambridge University Press, Cambridge, U.K., pp. 996.

Houston, J.R., and R.G. Dean, 2011. Sea-level acceleration based on U.S. tide gauges and extension of previous global-gauge analyses. Journal of Coastal Research, in press.

Vermeer, M., and S. Rahmstorf, 2009. Global sea level linked to global temperature. Proceedings of the National Academy of Sciences, 106, 51, doi: 10.1073/pnas.0907765106, 21527-21532.




No Comments

No comments yet.

RSS feed for comments on this post.

Sorry, the comment form is closed at this time.

Powered by WordPress