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31
Aug
Sea Level Acceleration
Posted by David Stockwell in All, Climate

Table of contents for Sea Level Acceleration

Sea Level Acceleration

Having now submitted a review of the empirical support for weakening of the Walker circulation to the Journal of Geophysical Research, I can get back to the “Is the sea level rise accelerating?” article. The abstract is below:

No Significant Basis for Acceleration in Sea level Rise Last Century

Abstract: Various authors have claimed that sea level rise is accelerating. This assumption is responsible for the high end projections for sea level by the year 2100. We evaluate three main datasets, and two studies, finding no support for an acceleration term in models fit to sea level over the 20th century, and a significant deceleration in satellite altimeter readings from 1993. The only empirical basis for sea-level acceleration arises from the inclusion of data prior to 1900, which cannot be attributed to the influence of greenhouse gases. Moreover, core references for projected sea level rise contain errors and imprecision that bias upward projections for sea level in 2100. We conclude that acceleration of sea level rise both in observations and the projections of climate models cannot be substantiated at this time. We find broad justification and agreement for empirical linear models, greatly reducing CI projections based on linear extrapolation.

It was interesting to find a reservation in the post at RealClimate today about projections for the future — something you won’t find in the published articles.

How do we know that the relationship between temperature rise and sea level rate is linear, also for the several degrees to be expected, when the 20th century has only given us a foretaste of 0.7 degrees? The short answer is: we don’t.

In other words, this is an admission that the models are based on speculative assumptions. When we stick to the facts, it will become clear, there is no basis for belief in non-linearity (aka acceleration) either over temperature or time.

The other interesting admission below, identifies the RC team as advocates, and hence not the place to look for scientific objectivity. If one were equally cautious that would be objective, but Rahmstorf then goes on to justify a bias. It sounds like to them, erring on the high side is unbiased.

In our view, when presenting numbers to the public scientists need to be equally cautious about erring on the low as they are on the high side. For society, after all, under-estimating global warming is likely the greater danger.

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Andrew

One of my frustrations with claims of "acceleration" occurring in this or that variable, is that they do not know the correct way to interpret a positive trend in the differential of the data. The following situations would be diagnosed as "acceleration" when in fact no such thing is occuring:

A data set starts with no change and then starts rising a constant rate.

A data set goes from going down to going up suddenly, and the rates before and after the switch are constant, but have opposite signs.

That's not even including the situations in which tide gauge trends for a hundred or more years are compared to the trend in altimeter data for the last 15 or so years, which are mathematical travesties in their own right.

The ignorance of some of these people to concepts which are so intuitively obvious to anyone who has thought about the maths is striking.

This same problem occurs with the temperature data. Consider this graph, which originates with the IPCC's SPM:

http://noconsensus.files.wordpress.com/2009/04/...

It leaves the impression of accelerating warming. The reality?

http://i23.photobucket.com/albums/b370/gatemast...

davids99us

That's exactly right, and source of some of the acceleration hype I am
mentioning. I haven't studied the new papers in the posts mentioned in RC,
but the errors you mention are on the record and not retracted as far as I
know.

davids99us

The empirical evidence for the long time lags to equilibrium is another
issue I should look at, as its a big part of the recent papers. To me, it
looks like SL stabilizes around 30 years after a temperature rise. after
all, it is flat at times during the last century, so the time to equilibrium
can't be longer than that. The fact that the satellite record is now
decellerating significantly tells me that the effect of temperature rise
since 1960 is just about done.

sherro

"How do we know that the relationship between temperature rise and sea level rate is linear"

Intuitively, it should not be linear because expansions of the oceans are not just upwards but sideways as well. I have not seen an estimate of the various volumes of water that would cause successive 1 mm rises on addition, taking into account the shape of the basins to be filled.

Then there is the problem of the whole ocean. Strictly, a thermal increase in volumes requires all of the volume, on average, to be heated. It is not adequate to show that the top x metres have heated. It is also required to show that the rest of the oceans have not cooled. I suspect that the data are too sparse to model whole ocean temperatures for expansion, given that currents are altering grid cell temperatures all the time; and that some currents have too few data points, like those that flow under ice.

Then there is lag. I have not seen a paper that uses buoy data to estimate thermal lag with depth, though it should be possible to get some idea from day/night changes. There might be papers, I just have not seen them. If you have a delta T at the surface, how long does it take to propagate to X, Y, Z, m depth? And then the reverse movement as it cools? Surely one needs a handle on this to try to dissect causation.

Finally, I have grave uncertainty about the meaning and accuracy of SST. Is it merely a parameter that has no great significance but has a convenient shape with time as Andrew notes?

davids99us

It is what it is. SL is strongly linear with temperature, rate of SL rise is not correlated with temperature.

Andrew

"Finally, I have grave uncertainty about the meaning and accuracy of SST. Is it merely a parameter that has no great significance but has a convenient shape with time as Andrew notes?"

This concern is well placed. I won't get much into the data quality issues (Buckets and Inlets etc.) But the physical interpretation of a relationship between SST and sea level is pretty tricky. From the surface temperatures, one could not tell if the bulk of the ocean increased in heat content or just a shallow layer-the thermal expansion depends on the total heat content of the oceans, not the temperature at the surface. Over long time scales this may not be a big issue. But that begs the question of how quickly heat diffuses from the surface to lower layers, or vice versa. My understand is that this is tied into lots of other climate issues, including sensitivity.

cohenite

You would also think that sea level rise from temperature increase would be non-linear because ice-melting does not have a direct relationship with temperature increase; glaciers can expand in warmer conditions. The RC constants for long term and short term sea level responses to temperature would also seem to be defeated by the historical relationship between temperature and sea level;

http://4.bp.blogspot.com/_TDdxO2FHJPs/SQ2wsVEvo...

Andrew

Glacial melt is mostly secondary for sea level. Thermal expansion is the big effect. So while this is a good point, it is trivial in comparison to the more serious issues with regard to temperature and sea level relationships.

cohenite

That is true enough but the alarmists are saying that glacial melt especially fom the Pine Island Glacier and various Greenland and Alaskan glaciers will inundate us all. However, things are not going to AGW plan because OHC is actually declining and the rate of sea level increase is also declining; all at a time whem CO2 is still increasing, although Watts did recently notice something interesting about that;

http://wattsupwiththat.com/2009/03/21/recent-oc...

Andrew

I have got to remember to do my "How temperature changes are related to rates of CO2 increase" idea one of these days. I think it may help to demystify that issue.

Fun fact about Greenland:

At the current rate of ice loss (.4% per century) Greenland won't melt entirely for 25 thousand years!

Andrew

"In our view, when presenting numbers to the public scientists need to be equally cautious about erring on the low as they are on the high side. For society, after all, under-estimating global warming is likely the greater danger."

This really grinds my gears. Experts are all like this. The Knowledge Problem has been known now for at least eighty years. Being an "expert" doesn't make one any better a planner than the market is, in fact, their limited knowledge makes them worse almost a priori. They don't even think they "know" that underestimating is more dangerous. It's blindness to their own ignorance, blindness to the possibility that overestimating warming is more dangerous than they can conceive...or, considering the political implications of their belief that the should decide which information is useful for planning, it's Far-Left politics.

That quote is, to those of us "in the know" the most revealing look at RC's ideology one can get.

davids99us

Yes, I think such people should not be employed as scientists. Go work for
Greenpeace or something.

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