Posts Tagged ‘Vermeer’

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Rahmstorf (2011): Robust or Just Busted (Part 2) – Quadratic Fits of Laughter

July 6, 2012

This is part 2 of a multi-part series about “Testing the robustness of semi-empirical sea level projections,” Rahmstorf, et. al., Climate Dynamics, 2011. You can see an index of all parts here. I frequently refer to this paper as R2011.

I will refer to Stefan Rahmstorf’s “Testing the robustness of semi-empirical sea level projections”  as R2011 [1].

This post is all about fitting sea level data to a quadratic.

There is only one reason to fit sea level vs. time data to a quadratic: to highlight an acceleration trend.  It only makes sense to do so if you think that the trend is more or less uniform over time.  I have warned against reading too much into a quadratic fit, and especially against using a quadratic fit to imply a future trend in sea level.

I have seen something in R2011 that I have never seen before.  The use of a quadratic fit as a kind of “optical delusion.”

Consider the image at the right.  Do you see the triangle?  Sure you do.  Of course, it is not really there.  But what would you say if I insisted that the triangle really was there and said “The circles are shown merely to help the eye find the triangle?”

R2011 has done much the same thing with a quadratic data fit in their figure 1.   I would think what they have done was just a joke, if it weren’t such an obvious attempt to convince readers that the data says something that it does not say.  Take a look…

Figure 1 from "Testing the robustness of semi-empirical sea level projections" (Rahmstorf, et. al., Climate Dynamics, 2011)

Note the dashed grey lines through each data set.  As R2011 explains in their caption, these dashed  grey lines which pass through all the data sets, are actually the quadratic fit to just one of the data sets (CW06)[2].  They say

“The dashed grey line is a quadratic fit to the CW06 data, shown here merely to help the eye in the comparison of the data sets.”

The point the R2011 wants to make, of course, is that all of these data sets have the same acceleration trend as R2011′s preferred sea level data, CW06.

But that is not true.  In fact, if you fit any of the other data sets to a quadratic you will see that every single one of them has a lower trend than CW06 when projected through the 21st century. Every single one of them.

The following figure shows proper quadratic fits to all the sea level data sets used by R2011 in their figure 1.  The legend shows the sea level rise that would result for the period 2000 to 2100 if these quadratics were extrapolated to 2100.

Quadratic fits for all sea level data sets used by R2011 in their figure 1. The legend shows the sea level rise that would result for the period 2000 to 2100 if these quadratics were extrapolated to 2100
Quadratic fits for all sea level data sets used by R2011 in their figure 1. The legend shows the sea level rise that would result for the period 2000 to 2100 if these quadratics were extrapolated to 2100

Updated Holgate data

Science is about constant refinement of theories and data.  When Rahmstorf is faced with old data and new data from the same authors, he has a special method for deciding which data set is better.  The version that points to higher sea level rise in the 21st century is always considered to be better.  Thus his insistence that the 2006 Chuch and White sea level data is  better than the 2009 or 2011 Church and White data that incorporated Church’s and White’s data reduction improvements.

The same is true for Holgate’s sea level data.  Look at HW04 [3] plots in the above graphs.  This Holgate sea level data covers the mid-1950s to the mid-1990s.  It is a curious thing (not really curious if you understand Rahmstorf’s modus operandi) that R2011 chose this data over Holgate’s updated data from 2007 [4], which covers the entire 20th century.  What would happen if we replaced the HW04 data with the 2007 Holgate data (H07)?  Take a look…

Holgate data from 2004 has been replaces with Holgates updated data from 2007.
Holgate data from 2004 has been replaces with Holgates updated data from 2007.

Let me stress again, I do not recommend extrapolating sea level data with quadratic fit, and I am not endorsing any of the extrapolations shown above.  I am simply guffawing at Rahmstorf’s chuzpa in his figure 1.

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1.  Rahmstorf, S., Perrette, M., and Vermeer, M., “Testing the robustness of semi-empirical sea level projections” Climate Dynamics, 2011

2. Church, J. A.,, and White,  N. J., “A 20th century acceleration in global sea-level rise,” Geophysical Research Letters, 33, 2006

3. Holgate, S. J., Woodworth, P.L., “Evidence for enhanced coastal sea level rise during the 1990s,” Geophysical Research Letters, 31, 2004

4. Holgate S., “On the decadal rates of sea level change during the twentieth century,” Geophysical Research Letters, 34, 2007
……..

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Rahmstorf (2011): Robust or just busted (Part 1)

June 30, 2012

This is part 1 of a multi-part series about Testing the robustness of semi-empirical sea level projections,” Rahmstorf, et. al., Climate Dynamics, 2011. You can see an index of all parts here. I frequently refer to this paper as R2011.

I don’t get many readers at my little blog, but it is nice to know that Stefan Rahmstorf has been keeping up with it. He has a great desire to prove that his claims of extreme sea level rise, and my comments (and equations, graphs, data, logic, etc.) have cast his conclusions into grave doubt. Besides showing in multiple ways that his models don’t make mathematical sense, I have also shown that when the best data is applied to his (bogus) model his sea level rise projections for the 21st century are cut down to size.

So, it seems his recent outing in Climate Dynamics (“Testing the robustness of semi-empirical sea level projections,” Climate Dynamics, November, 2011) is aimed squarely at that point, which he makes clear in the fourth sentence of the abstract.

“Lower projections are obtained only if the correction for reservoir storage is ignored and/or the sea level data set of Church and White (Surv Geophys, 2011) is used.”

You see, once upon a time (2007, 2009 ) Rahmstorf thought that the 2006 version of sea level data from Church and White was surely the finest data for figuring out the relationship between sea level rise rate and global temperature. When he used it in his silly 2007 and 2009 models to project 21st century sea level rise, the models gave alarmingly high results. Ergo, the models and input sea level data must certainly be correct. The problem was that Church and White were not as confident in their own sea level data as Rahmstorf was. By the time Vermeer and Rahmstorf were penning their widely quoted 2009 PNAS paper, Church and White had made serious corrections to their sea level data. But that corrected data never made it into the Vermeer’s and Rahmstorf’s paper. If it had, their sea level rise projections would have been way lower.

I raked Rahmstorf and company over the coals on this point. I ran their own model with the corrected data from their own source (Church and White) and published the results online. The result: vastly lower sea level projections for the 21st century. Their response: silence.

The above abstract sentence would have been more accurate if it had said…

Much higher projections are obtained if Church’s and White’s older, self-rejected, data is used than if Church’s and White’s newer, corrected data is used.”

The meaning of his chosen words was Rahmstorf’s way of telling his sycophants to close their eyes and stop thinking. Church’s and White’s out-dated data gives much higher 21st century predictions than their newer corrected data. That’s all you need to know to tell you that the old data is better than the corrected data. “These are not the droids you’re looking for. Move along.”

As is my custom, I will write a series of posts concerning “Testing the robustness of semi-empirical sea level projections.”  Stay tuned.

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Updated PSMSL sea level video

March 11, 2012

The following video shows all the PSMSL tide gauge data so you can search for a sea level rise acceleration.  It replaces an earlier version that was taken down by youtube because of music license violations.  This version has music with Creative Commons license.  The text and data are the same as before.

Vermeer’s and Rahmstorf’s “Global sea level linked to global temperature” (PNAS, 2009) relied on Church’s and White’s “A 20th century acceleration in global sea-level rise” (GEOPHYSICAL RESEARCH LETTERS, VOL. 33,) for their sea level data.  Church and White built their sea level time series from the Permanent Service for Mean Sea Level (PSMSL) tide gauge data.

There is no attempt to analyse the data here, but I have started that process and will report on it later.  The first two minutes may be a little boring, but please read along.  It livens up later.   For now, sit back and enjoy.

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