Posts Tagged ‘Rahmstorf’

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Sea Level Projections vs. Tide Gauge Data

February 28, 2016

Carbon dioxide, climate change, disaster, SEA LEVELS WILL RISE!

You can see all kinds of sea level rise predictions for the 21st century, with over-wrought images of houses and buildings under water.  One of the favorite predictions of the hand wringers is “1.8 meters” of sea level rise for the 21st century.  A major purveyor of this lurid climate-porn prediction is Stefan Rahmstorf (see here, here, and here).

Consider the following points

  • 75% of atmospheric anthropogenic CO2 arrived after 1950.
  • There has been no obvious acceleration in sea level rise rates since 1950 as seen from tide gauges.
  • Extrapolating tide gauge time series to 2100 would give about 15cm of sea level rise between 200o and 2100.
  • Projections of 1, 1.8 or 2 meters of sea level rise between 2000 and 2100 would require extraordinary rise rate accelerations.

Let’s compare the sea level data of the 20th century with these wild prediction for the 21st century.  The movie below will show all the tide gauge data sets available from NOAA that extend over at least 75 years.  In each case the trend is extrapolated to 2100.  Additionally, the likely local relative sea levels corresponding to 1 meter and 1.8 meter global sea level rises for the 21st century are shown.

Music is by Mechett and licensed under Creative Commons

The likely local relative sea levels are calculated by by assuming that the global anthropogenic sea level rise would be distributed evenly over the planet.  This assumption may not be entirely accurate but it is a good first approximation. Here is how the calculation is done.

Let

  • GSLR (20th century) be the 2oth century global sea level rise
  • LSLR (20th century) be a local 20th century sea level rise
  • GSLR(21st century) be the projected 21st global sea level rise
  • LSLR(21st century) be the projected local 21st century sea level rise

Then
LSLR(21st century) = LSLR (20th century) – GSLR (20th century) + GSLR(21st century)

Say the 2oth century global sea level rise was 18cm and the projected 21st century global sea level rise is 100cm.   And say the local 20th century sea level rise was 18cm at location A, 30cm at location B, and -10cm at location C.  Then the local projected 21st century sea level rises would be

Location A
Projected rise = 100cm = 18cm – 18cm + 100cm

Location B
Projected rise = 112cm = 30cm – 18cm + 100cm

Location C
Projected rise = 72cm = -10cm – 18cm + 100cm

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Uh, Oh! Karl, et. al., is bad news for Stefan Rahmstorf’s sea level rise rate.

September 25, 2015

Conclusion first

When the 20th century GISS temperature is modified according to Tom Karl, et.al., it causes the 21st century sea level predictions of Vermeer’s and Rahmstorf’s semi-empirical model to go down!

Details

I have written extensively about “Global sea level linked to global temperature,” by Vermeer and Rahmstorf (which I will refer to as VR2009).

VR2009 was a widely cited claim of using historical 20th century sea level and temperature data to calculate parameters that could be used to build a model to predict 21st century sea level rise for various 21st century temperature scenarios.  I reproduced the VR2009 model based on their description.  My code was verified by reproducing the VR2009 results using the same inputs that they used.

I spent a lot of time pointing out some of the bizarre results of their model that surely disqualified it form being taken seriously, some of which can be seen here, here, and here.

I also spent a lot of time pointing out that the VR2009 choices of 20th century sea level data sources left much to be desired.  For example, they used the 2006 Church and White sea level data that was already outdated.  If they had used the revised Church and White data, then their resulting sea level rise predictions for the 21st century would have been much lower.

They happily modified Church’s and White’s outdated sea level data by subtracting a reservoir correction (Chao, et. al.), which made their 21st century predictions for sea level rise go up. But they made no attempt to estimate a groundwater depletion correction. It turns out, unsurprisingly, that the groundwater depletion is of the same magnitude as the reservoir correction (Wada, et. al.), and including it would have made their 21st century predictions go down.

Nevertheless, Rahmstorf would later claim that his modeling approach was “robust!”  That is, it would give essentially the same result for the 21st century given different sources of 20th century sea level data.

So, I also implemented the VR2009 technique using several different sources of sea level data, which should have given similar results, according to Rahmstorf’s claim of robustness.  In fact, they gave widely varying results, and every combination of sea level data, reservoir data, and groundwater depletion data that I tried gave lower results than VR2009’s chosen combination.

New Temperature Data!

The widely reported nearly two decade long pause in global warming was causing suicidal ideation among hard-core global warming alarmists.  Something had to be done to stop them from slitting their wrists with shards of glass from their shattered thermometers.

Just in the nick of time – revised temperature data!   Like all proper revisions of temperature data, this revision caused the reported temperature change of the 20th century to go up.

This was a result of a paper by Tom Karl, et. al. (Nature) based on very thin reasoning (see for example) that argued for such revision.  The folks at GISS (who provided VR2009’s temperature data) glommed onto Karl’s logic and subsequently revised their temperature data accordingly.  Other temperature data source like UAH and RSS did not.

Which means we must ask ourselves, what happens to 21st century sea level rise predictions based on the VR2009 model using the now modified GISS data?

VR2009 applied their model to six families of temperature scenarios for the 21st century form the IPCC’s 4th Assessment Report.  Let’s see what happens to each of those scenarios when we update the 20th century GISS temperature data.

The IPCC temperature scenarios that VR2009 used for prediction of 21st century sea level rise.

Case 1.

Sea level inputs are identical to what VR2009 used: Church’s and White’s sea level with the Chao reservoir correction.  The old GISS temperature data is replaced with the new GISS temperature data.  The table below shows that the new GISS data yields 21st century sea level rises that are about 17% less than when the old GISS data is used.

Old GISS vs New GISS

It is a shame that after Tom Karl went to all the trouble to increase the temperature rise of the 20th century it just makes VR2009’s model predict LOWER sea levels for the 21st century.  This must be a great disappointment to Vermeer and Rahmstorf, so you can be pretty sure they will never tell you this result. But I just did.

Case 2

As I pointed out previously, VR2009 chose to use outdated 2006 Church and White sea level data, instead of Church’s 2009 data.  They also neglected a groundwater depletion correction.  When these improvements are included the VR2009 model yields 21st century sea level rises that are only about 55% of VR2009.  When the new GISS temperature data is included in the mix this drops to about 45%.

New GISS CW2009 Chao Wada

Case 3.

Lest Vermeer or Rahmstorf argue that their large sea level rise rates are saved by another update of the Church and White data in 2011, I have include these results also.  The difference between 2009 and 2011 Church and White sea level data was small.  Here is how the 2011 Church and White sea level data version plays out in the VR2009 model. The resulting 21st century sea level rise predictions are only about 43% of the VR2009 predictions.

New GISS CW2011 Chao Wada

The trend continues.

It seems that no matter what combination of inputs that are used in the VR2009 model, the predicted sea level rise for the 21st century is always smaller than with VR2009’s choice of inputs.  I wonder what that implies?

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Vermeer and Rahmstorf paper rejected

January 31, 2014

Vermeer and Rahmstorf had a paper rejected by the journal “Climate of the Past.” This news is 16 months old, but I just heard about it, and could find very few references about it on the web.

This paper, On the differences between two semi-empirical sea level models for the last two millennia,  promoted their earlier sea level rise models.  They couldn’t seem to get traction with this paper.

Here are some reviewers’ comments…

One of the major problems with this work is the decidedly biased analysis and presentation.

Highly biased analysis and presentation.

It currently takes significant effort to figure out which pairs of models and training data sets the authors use, and whether they have evaluated all the relevant combinations of the same.

No surprise here.  Rahmstorf has a history of alluding to all kinds of data sets and implying that he has taken them into consideration, but only presenting results for those that support his thesis.

And the final blow…

In the light of the two negative reviews and one comment which all require new analyses and point to fundamental flaws in the methodology of the current paper, I regret to inform you that my conclusion is to support rejection. I strongly dissuade the authors from submitting responses and a revised version.

Here is the paper…

Click for full PDF version

Here is the reviewers’ discussion that lead to the the rejection.

Of course, Vermeer and Rahmstorf do not give up that easily, and similar papers have been shopped around to other journals