Which trend in sea level do "skeptics" want to use?
This question was asked recently: c8kslxq
(the above is a tinyurl append to the question, I am not sure if Y!A will allow me to include a full link, will add one in a comment anyway)
I answered and have since been blocked. I am not sure what was so contentious about my answer, other than providing good reasons why the questions were badly premised - however I can still sign out and look at the question, just can't edit my answer any more.
One of the recent edits by the author Pat was to suggest that the 200mm sea level rise since the beginning of the tide record shows a trend of 1.54 mm/year, I suppose to be a big "AHA!" to me in that continuing that trend produces an even *smaller* GMSL change in a 100 years than the trend over the satellite record.
But, the blog post from Tamino's clearly shows an acceleration in the trend to roughly match the trend over the satellite period, so I see this as dishonest.
I also see it as self-defeating, since it's now so easy to show that the trend of 1.54 mm/year has been essentially doubled. It only helps the narrative that sea level trend is increasing, to try to extrapolate the 1.54 mm/year trend - which would "skeptics" _really_ like to use?
2013-01-12T21:07:42Z
Here's the link in full: http://answers.yahoo.com/question/index;_ylt=ApmWMGQsYGYtivNW75UMtT7sy6IX;_ylv=3?qid=20130112181543AAAp9UA
2013-01-13T09:45:21Z
flossie - it's a bit confusing with the mix between his desire to be considered a member of the House of Lords and the appendage given to his name from being Viscount - "Lord." But you're correct.
Ian2013-01-13T00:12:36Z
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I have no problem using satellite even though it's adjusted upwards the most. The University of Colorado says 3.1mm/year - 0.3mm/year for glacial rebound gives approx 2.8mm/year.
Well, it's not like denialists are using any kind of reason or logic to form their beliefs.
For the benefit of anyone reading Ian's answer and mistaking it for a reasonable statement, allow me to point out that he is ignoring variables such as thermal expansion and ice melt rates. Does anybody really expect ice to melt at a continuous rate for the next century? Thermal expansion may also tend to vary in the rate at which it drives changes in sea level. Ironic that someone like Ian, who complains abut predictive climate models because of the variation in parameters, will just completely ignore all the parameters regarding sea level rise and assume a linear change.
The target audience you seek ("skeptics") does not live here. The Deniers that do live here do not concern themselves with the messy details of science and, consequently, they have no understanding of, or interest in, your question. They can only answer questions that involve copying-and-pasting something they know nothing about from some source that is either lying or just as ignorant as they are - hence, their constant repeating of the same lame, misinformed, misleading, dishonest, and stupid comments about the Vostok ice cores, Mann's Hockey Stick, the Medieval Warm Period and Little Ice Age, and Al Gore.
A real skeptic - meaning someone who either by aptitude or through experience has some level of skill and comfort dealing with complex issues - would want to look at all relevant sources of evidence because, as Trevor's answer illustrates, different measures provide different perspectives and different information. Even if one method is considered to be better in some way, to some extent, its relevance and validity depends on the coherence of its results with the results from other independent analyses - and Deniers could not care less about any of that.
--- You missed us, huh?
It's good to see that you appear well and still sane.
Ian, you thoughts seem reasonable until you try to extrapolate 100 years out not accounting for any difference in climate, the acceleration in sea level rise, etc. Most scientist recognize that the system is not static and develop scenarios based on little change, most likely change and extreme change scenarios. You cannot extrapolate over 100 years the way you do without modeling changes in the factors that affect sea level. Take your estimate as a "low end": estimate (~0.3 meters in 100 years). What is the"most likely" estimate? what is the "high end" estimate? Which estimate would you use for planning purposes? Why?
Your question relates to one that was raised by Pat, which I guess is a question he posted as a follow up to various emails that Pat and myself have been exchanging in the last day or so.
Whichever global temperature record you look at they’re all pretty much the same, it makes life easier. The same can’t be said for GMSL records and it’s easy to see where confusion can arise.
The long-term records use tidal-gauges that are positioned at various locations around the world, depending which record you look at you’ll get very different responses. One or two of them record a drop in MSL of up to 0.4mm a year (Sweden), some show rises of up to 31mm a year (Bangladesh), the overall average based on the last 100 years or so is 1.8mm a year.
The advent of satellite telemetrics has enables us to obtain a true global perspective of how sea-levels are changing and we now have millions more datapoints to work with. As a result the satellite record is much more accurate, and this shows that sea-levels are rising at 3.2mm a year (now revised to 3.3mm).
If you look at the tidal gauge record for the last 30 years or so there has also been a significant increase in the rate at which MSL is rising, these data provide a figure of about 2.8mm a year with a significant margin of error (sorry, can’t recall what the figure is).
Another way to calculate sea-level rise is to do so mathematically. We know that the average loss of polar ice is about 520 billion tonnes per year over the last 30 years – 220Gt from Antarctica and 400Gt from Greenland. The surface area of the world’s oceans is 360 million km² and therefore sea-level rises will be 1.444mm a year.
We also know that the average temperature of the world’s oceans is rising. Given that the coefficient of volumetric thermal expansion of water is 0.000207/°C, the volume of the oceans is 1.3 quintillion m³, the average depth is 3,790 metres and area 360 million km² we can calculate that thermal expansion will add a further 1.511mm a year to the GMSL.
Add the two together to get 2.955mm per year, then factor in the 01.mm due to isostatic rebound and you come out with 3.055mm per year.
Whether it’s calculated mathematically, determined by observations at ground level or measured from space, the answers are all close to each other (2.8 to 3.3mm per year), with the mean being 3.1mm.
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EDIT – ADDED DETAILS
Just to clarify re Lord Monckton. He is a Viscount, a hereditary title, Viscounts are not Lords but the correct form of address is “Lord”. Viscounts cannot call themselves Lord and they are not automatically a member of the House of Lords (the upper house of the UK Parliament). Lord Monckton claims to be both a Lord and a member of the House of Lords, he is neither. He could become a member of the House if he were to be elected, he’s stood for election four times and received no votes.