IPCC 1990 : “there is no convincing evidence of an acceleration in global sea level rise during the twentieth century”

9 Responses to IPCC 1990 : “there is no convincing evidence of an acceleration in global sea level rise during the twentieth century”

1. daveburton says:

   January 11, 2014 at 5:28 am

   Even the IPCC’s Third Assessment Report (2001) noted the “observational finding of no acceleration in sea level rise during the 20th century.”

   Here are some other noteworthy papers on this subject:
   http://sealevel.info/papers.html

   Reply
2. gator69 says:

   January 11, 2014 at 2:04 pm

   “observational finding of no acceleration in sea level rise during the 20th century.”

   This is why they switched to models and adjustments.

   Reply
3. Aslak Grinsted says:

   January 11, 2014 at 2:11 pm

   This is fully consistent with both process modelling and semi empirical modeling of Sea level rise. It can be explained by timing of major 20thC volcanic eruptions.
   See
   http://www.nature.com/nature/journal/v438/n7064/abs/nature04237.html

   Reply
   • Billy Liar says:

     January 11, 2014 at 7:02 pm

     You have used the shibboleth ‘fully consistent with’ which identifies you as a warmist. I suspect you also believe ‘global warming is real, and it’s happening now’.

     Reply
     • Aslak Grinsted says:

       January 13, 2014 at 7:54 am

       I suppose so if that is your definition of a warmist.

       Reply
   • daveburton says:

     January 12, 2014 at 12:17 am

     I’m glad you acknowledge the lack of acceleration in sea-level rise, Aslak, but that is inconsistent with your defense of the discredited Rahmstorf “semi-emperical modeling” nonsense.

     Rahmstorf, the “semi-emperical modeling” guy, claimed that the rate of sea-level rise is proportional to the global mean temperatures, relative to some baseline. In other words, according to him, the warmer it gets the faster sea level will rise.

     But the rate of sea-level rise is no greater now than it was 80 years ago. There’s been no increase at all in the rate of sea level rise in response to anthropogenic GHG emissions. Nearly 100 ppm of additional CO2 has not caused any detectable increase in sea-level rise.

     That means there’re only two possibilities:

     1. There’s been no overall global warming, anthropogenic or otherwise, in more than 80 years. Or,

     2. Rahmstorf’s “semi-emperical model” is falsified.

     Which do you think it is, Aslak?

     Reply
     • Aslak Grinsted says:

       January 13, 2014 at 8:15 am

       Semi-empirical models fit by design the observational record they are tuned to. So ofcourse Rahmstorf 2007’s model fits the data.

       Here’s link to a plot from another semi-empirical model (Jevrejeva et al. 2009) where you can see the effect of volcanoes. http://tinypic.com/r/2jcsz2b/5

       – without volcanoes the model shows a clear acceleration over the 20th century. However, when volcanic forcing is included then the 20th century sea level rise is much more linear (just like the observational records). This is very similar to what you see for steric expansion in “proper” ocean models (see Church et al. linked in my previous comment).

       Also note that Rahmstorfs model is simply dS/dt = a*T+b . if you choose a=0 then the rate of sea level rise is constant.

       Reply
       • daveburton says:

         January 13, 2014 at 3:20 pm

         Aslak wrote, “without volcanoes the model shows a clear acceleration over the 20th century. However, when volcanic forcing is included then the 20th century sea level rise is much more linear (just like the observational records)”

         Volcanoes are irrelevant. They’re not irrelevant to temperature, of course, since they do cause dips in temperature (though not as much as most models suggest). But they are irrelevant to the issue of the claimed relationship between global warming and sea-level rise because, in the context of the climate debate, they’re just a temperature forcing. Volcanoes are not claimed to affect sea-level except by affecting temperatures. (They might also affect rain patterns, which could affect sea-levels for a year or two, but that’s irrelevant to any long-term sea-level/temperature relationship.) So if you have measurements for temperatures, you can and should ignore the myriad of possible forcings which caused them, if you’re trying to detect an hypothesized long-term relationship between temperature and sea-level rise.

         Just about everyone agrees that (regardless of volcano activity) global mean temperatures have been, on average, significantly higher over the last 20 years than they were, on average, in the 20th century as a whole. Yet the rate of sea-level rise is no higher that it was for the 20th century as a whole (unless you compare apples to oranges). So any study which claims that higher temperatures cause accelerated sea-level rise, at least on timescales of less than several decades, is obviously wrong.

         The end of the Little Ice Age did coincide with an apparent very slight increase in the rate of sea-level rise over the following 60-80 years, but on sub-century timescales there’s no apparent positive correlation between global mean temperatures and sea-level rise.

         Aslak also wrote, “Rahmstorf 2007?s model fits the data.”

         No, Rahmstorf 2007 does not fit the data. In fact, even he grudgingly admitted as much:

         “In hindsight, the averaging period of 11 years that we used in the 2007 Science paper was too short to determine a robust climate trend…” –[Stefan Rahmstorf’s 2009 mea culpa, on the RealClimate blog site]

         Rahmstorf made many mistakes, but his first mistake was that he used Church & White’s 2006 global sea-level data. C&W 2006 was an outlier: by its own admission it was the only extant study to report any 20th century acceleration in sea-level rise. So that choice by Rahmstorf ought to raise eyebrows.

         It turns out that all of the C&W 2006 reported acceleration in rate of sea-level rise occurred before 1925 — i.e., before there was much anthropogenic contribution to GHG levels. Since GHG levels have been going up substantially, there’s been no acceleration in sea-level rise at all.

         It also turns out that the C&W 2006 reported net 20th century acceleration was just an artifact of their tide station selections. C&W’s own 2009 data showed no acceleration in sea-level rise even for the entire 20th century; in fact it showed a very slight deceleration.

         (Also note that C&W used a lot of poor quality data, including even sea-level records from tide stations which were operational for as little as three years… GIGO!)

         C&W 2006 was also a poor choice, because, although they reported a rate of global mean sea level rise, they didn’t actually report the measured rate of sea-level rise at all. Instead, they added a fudge factor to their calculated rate, to inflate the number to match what they thought it should be. Here’s the quote from their 2006 paper:

         “An additional spatially uniform field is included in the reconstruction to represent changes in GMSL [Global Mean Sea Level]. Omitting this field results in a much smaller rate of GMSL rise…” Church & White 2006

         Plus, note that, according to Dr. Church, the “spatially uniform field” (fudge factor) which they added wasn’t even temporally uniform.

         Rahmstorf’s approach amounts to creating a humbug equation with enough tuneable knobs (delay periods, averaging periods, weights, baselines) that you can tweak the knobs to make it generate a result which approximates a chosen limited snippet of history. That approach is worse than useless for forecasting.

         “With four parameters I can fit an elephant, and with five I can make him wiggle his trunk.” John von Neumann

         Other “semi-emperical models,” which use indirect forcings like volcanic eruptions, GHGs, anthropogenic particulates, etc., which affect temperature, instead of using actual measured temperature, just multiply the number of knobs to be tweaked, with no plausible improvement in predictive power.

         Aslak also wrote, “Also note that Rahmstorfs model is simply dS/dt = a*T+b . if you choose a=0 then the rate of sea level rise is constant.”

         But he didn’t do that, did he? a=0 would mean sea-level rise is independent of temperature, and irrelevant to the climate debate. Since you have written that, “Rising sea level is probably the most important impact of anthropogenic climate change over the coming century” I don’t think you believe that.”
4. Ben says:

   January 13, 2014 at 6:42 pm

   Aslak Grinsted is an anagram for “Streaking Lads”

   Reply