This is part 3.5 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.
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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 .
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…
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). 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.
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  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 , which covers the entire 20th century. What would happen if we replaced the HW04 data with the 2007 Holgate data (H07)? Take a look…
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.
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
The National Research Council has released a hard-hitting report about global sea level, and in particular, sea level along the western coast of the United States. Yup, they really nailed it down. They predict the sea level along California’s coast to rise somewhere between 4 and 30 cm (between 1.5 and 12 inches) between 2000 and 2030 (see page 5).
Their report is hundreds of pages long because they are very smart people. But if you want to save some time, you can get an idea of what is really happening by looking at the following three images. Click on each image to put it in animation mode in its own window. There is one animation for each of the coasts of California, Oregon and Washington state.
Be sure to notice the sea level rise rate centered above each graph. Keep in mind that a 30 cm sea level rise in 30 years requires an average of 10 mm per year.
We are already 12 years into the 30 from 2000 to 2030. As you can see from the above animated plots, there appears to have been a distinct lack of acceleration in the last 100 years or so. Roughly speaking, the sea level along the coast of California is rising at about 2 mm/year. So it looks like there will be a net rise surpassing the National Research Council’s lower limit of 4 cm in 30 years. On the other hand, it would require an extraordinary, nearly impossible acceleration to get to 15 cm, just half the NRC’s upper estimate of 30 cm, by 2030. But you can still pray to Gaia for a miracle.
A sure sign of poor scholarship
Here is a little hint for my obvious betters at the NRC: When you rely on the models of Stefan Rahmstorf to make your sea level rise predictions, one of two things will have happened by 2030. If you are lucky your report will have been forgotten. If you are unlucky people will simply be laughing at you.
Well, I suppose you can hope for that big earthquake that your report says (page 7) could cause the sea level to rise by an additional meter. You’d have it made if you could blame atmospheric CO2 for earthquakes. Your elite thinkers should start working on that paper now.
Some folks never give up. In the following video Stefan Rahmstorf says…
To me a tipping point in the climate system is like a sweet spot in the climate system, where a small perturbation can have a major, even qualitative effect. It’s like a small change in temperature moving, for example, the Greenland Ice sheet beyond the point where eventually it will melt down all together…from about 2 degrees global warming there would be a risk of the complete meltdown of the Greenland Ice sheet…I think this two degree limit agreed in Cancun by the politicians may not be enough to prevent a dangerous interference in the climate system.
Now let’s be clear about this: a “complete meltdown” of the Greenland ice sheet would raise the planet’s sea level 7 meters (7000 mm). The sea level rise rate today is about 3 mm per year and decreasing according to satellite data. A rational reading the tide gauge data is even less.
I guess in Greenland ice must melt at -25°C. Here is today’s temperature outlook…
Oh, I know, the scientifically
sophomoric sophisticated will tell us all about the rapidly accelerating glaciers. Well, their favorite journal, Science, throws a little icy cold water on their dreams of catastrophic nirvana. In 21st-Century Evolution of Greenland Outlet Glacier Velocities ( T. Moon, et. al., Science, 4 May 2012, Vol. 336, pp. 576-578) Moon et. al. produced “a decade-long (2000 to 2010) record documenting the ongoing velocity evolution of nearly all (200+) of Greenland’s major outlet glaciers.” They found that in some regions there was a glacier acceleration (SEE! SEE!), but not very consistently over the last 10 years. Here is their conclusion
Our observations have implications for recent work on sea level rise. Earlier research (33) used a kinematic approach to estimate upper bounds of 0.8 to 2.0 m for 21st-century sea level rise. In Greenland, this work assumed ice-sheet–wide doubling of glacier speeds (low-end scenario) or an order of magnitude increase in speeds (high-end scenario) from 2000 to 2010. Our wide sampling of actual 2000 to 2010 changes shows that glacier acceleration across the ice sheet remains far below these estimates, suggesting that sea level rise associated with Greenland glacier dynamics remains well below the low-end scenario (9.3 cm by 2100) at present. Continued acceleration, however,may cause sea level rise to approach the low-end limit by this century’s end. Our sampling of a large population of glaciers, many of which have sustained considerable thinning and retreat, suggests little potential for the type of widespread extreme (i.e., order of magnitude) acceleration represented in the high-end scenario (46.7 cm by 2100). Our result is consistent with findings from recent numerical flow models (34).
So, Rahmstorf is worried about a “complete meltdown of the Greenland ice sheet” which would lead to 7 meters (7000 mm) of sea level rise, but the data shows “sea level rise associated with Greenland glacier dynamics remains well below the low-end scenario (9.3 cm by 2100)” (93 mm by 2100). Does being off by a factor of 75 (7000/93) qualify as “alarmist?”
By the way, when Moon says “Earlier research (33) used a kinematic approach to estimate upper bounds of 0.8 to 2.0 m for 21st-century sea level rise” he is talking about Kinematic Constraints on Glacier Contributions to 21st Century Sea-Level Rise (Pfeffer, et. al., Science, 5 September 2008, Vol. 321. no. 5894, pp. 1340 – 1343). I discussed this paper at length two years ago in my “Reply to John Mashey.” (Still feeling smug, John?)
And finally, Moon’s last sentence says “Our result is consistent with findings from recent numerical flow models (34).” He is talking about Committed sea-level rise for the next century from Greenland ice sheet dynamics during the past decade (Price, et. al., PNAS, 31 May 2011, vol. 108 no. 22 pp. 8978-8983). Price, et. al. say
The modeling conducted here and some reasonable assumptions can be used to make approximate upper-bound estimates for future SLR from GIS [Greenland Ice Sheet] dynamics, without accounting for future dynamical changes explicitly. As discussed above, numerous observations indicate that the trigger for the majority of dynamic thinning in Greenland during the last decade was episodic in nature, as the result of incursions of relatively warm ocean waters. By assuming that similar perturbations occur at regular intervals over the next century and that the ice sheet responds in a similar manner, we can repeatedly combine (sum) the cumulative SLR [sea level rise] curve from Fig. 4B to arrive at additional estimates for SLR by 2100. For example, if perturbations like those during the last decade recur every 50, 20, or 10 y during the next 100 y, we estimate a cumulative SLR from GIS dynamics by 2100 of approximately 10, 25, and 45 mm, respectively…Addition of the estimated 40 mm of SLR from changes in SMB [surface mass balance] by 2100 would result in a total SLR from Greenland of 85 mm by 2100.
Holy cow! Rahmstorf is telling us to be worried about 7000 mm of sea level rise due to the “complete meltdown of the Greenland ice sheet,” but Price et. al. say maybe 85 mm due to Greenland by 2100.