Arguments
How much is sea level rising?
What the science says...
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A variety of different measurements find steadily rising sea levels over the past century. |
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Climate Myth...
Sea level rise is exaggerated
"We are told sea level is rising and will soon swamp all of our cities. Everybody knows that the Pacific island of Tuvalu is sinking. ...
Around 1990 it became obvious the local tide-gauge did not agree - there was no evidence of 'sinking.' So scientists at Flinders University, Adelaide, set up new, modern, tide-gauges in 12 Pacific islands.
Recently, the whole project was abandoned as there was no sign of a change in sea level at any of the 12 islands for the past 16 years." Vincent Gray).
Gavin Schmidt investigated the claim that tide gauges on islands in the Pacific Ocean show no sea level rise and found that the data show a rising sea level trend at every single station. But what about global sea level rise?
Sea level rises as ice on land melts and as warming ocean waters expand. As well as being a threat to coastal habitation and environments, sea level rise corroborates other evidence of global warming
The blue line in the graph below clearly shows sea level as rising, while the upward curve suggests sea level is rising faster as time goes on. The upward curve agrees with global temperature trends and with the accelerating melting of ice in Greenland and other places.
Because sea level behavior is such an important signal for tracking climate change, skeptics seize on the sea level record in an effort to cast doubt on this evidence. Sea level bounces up and down slightly from year to year so it's possible to cherry-pick data falsely suggesting the overall trend is flat, falling or linear. You can try this yourself. Starting with two closely spaced data points on the graph below, lay a straight-edge between them and notice how for a short period of time you can create almost any slope you prefer, simply by being selective about what data points you use. Now choose data points farther apart. Notice that as your selected data points cover more time, the more your mini-graph reflects the big picture. The lesson? Always look at all the data, don't be fooled by selective presentations.
graph from Church et al. (2008)
Other skeptic arguments about sea level concern the validity of observations, obtained via tide gauges and more recently satellite altimeter observations.
Tide gauges must take into account changes in the height of land itself caused by local geologic processes, a favorite distraction for skeptics to highlight. Not surprisingly, scientists measuring sea level with tide gauges are aware of and compensate for these factors. Confounding influences are accounted for in measurements and while they leave some noise in the record they cannot account for the observed upward trend.
Various technical criticisms are mounted against satellite altimeter measurements by skeptics. Indeed, deriving millimeter-level accuracy from orbit is a stunning technical feat so it's not hard to understand why some people find such an accomplishment unbelievable. In reality, researchers demonstrate this height measurement technique's accuracy to be within 1mm/year. Most importantly there is no form of residual error that could falsely produce the upward trend in observations.
As can be seen in an inset of the graph above, tide gauge and satellite altimeter measurements track each other with remarkable similarity. These two independent systems mutually support the observed trend in sea level. If an argument depends on skipping certain observations or emphasizes uncertainty while ignoring an obvious trend, that's a clue you're being steered as opposed to informed. Don't be mislead by only a carefully-selected portion of the available evidence being disclosed.
Current sea level rise is after all not exaggerated, in fact the opposite case is more plausible. Observational data and changing conditions in such places as Greenland suggest if there's a real problem here it's underestimation of future sea level rise. IPCC synthesis reports offer conservative projections of sea level increase based on assumptions about future behavior of ice sheets and glaciers, leading to estimates of sea level roughly following a linear upward trend mimicking that of recent decades. In point of fact, observed sea level rise is already above IPCC projections and strongly hints at acceleration while at the same time it appears the mass balance of continental ice envisioned by the IPCC is overly optimistic (Rahmstorf 2010).
Basic rebuttal written by doug_bostrom
This rebuttal was updated by Judith Matz on September 13, 2021 to replace broken links. The updates are a result of our call for help published in May 2021.
Last updated on 5 July 2015 by pattimer. View Archives
Do you mean short-term as in the last La Nina?
That's what the Colorado University Sea Level Research Group said. How short term that is remains to be seen.Are you sure you're taking everything into account with this back-of-the-napkin calculation?
I think the "Back-of-the-Napkin" assessment is accurate I also think that with respect to the information given in the Executive Summary of the AR4's Chapter 5 it's not likely to be that far off the mark. The Chapter 5 Executive Summary quote is in regard to the empirical record and Table 10.7 is a projection, and the 6.8 mm/yr is worst case. Worst case is often what is reported in the popular press. So it ought to be realistic. So how realistic is it that in the next 89 years that the thermal expansion component of sea level rise will go from 0.36 mm/yr to 6.8 mm/yr?Well, observations show the thermal (steric) component of sea level is rising at 0.69mm per year over the last 6 years,
Is rising 0.69 mm/yr or is 0.69 mm/yr? It does make a difference. In any case, do you have a link for that observation? Even at 0.69 mm/yr is it reasonable to expect a possible 6.8 mm/yr due to thermal expansion by 2100?
so your calculations appear to be missing important details - I see a glaringly obvious one in your calculations.
And that glaringly obvious one is?
Camburn ... I think you are overestimating sea level rise. Envisat data, which at this time is the most advanced, iindicates a sea level rise of approx 1.78mm/yr if memory serves me
The IPCC tells us that Over the period 1961 to 2003, global ocean temperature has risen by 0.1°C from the surface to a depth of 700 m. The IPCC also tells us, in table 10.7, that by 2100 we can expect thermal expansion to account for as much as 6.8 mm/yr. I'm questioning if those two facts are compatible. The graph that Albatross put up is nearly a straight line. In order to achieve the 6.8 mm/yr it's going have to change. So, how likely is it that it will begin a sharp upward trend resulting in that 6.8 mm/yr contribution from thermal expansion the IPCC tells us could happen by 2100? As I pointed out earlier, 6.8 mm/yr is worst case, but that's what the popular press will report, so it ought to be reasonable. Is it?
[DB] You continue to be disingenuous with your graph. Envisat data is actually shown here:
[Source]
[DB] "This thread is about sea level rise...right? And one has to look at all the data available....right?"
Excellent point. One in which the entire thrust of your point is lacking in. So, let's look at ALL of the data, shall we? You mean like this, right?
Or this, right?
Or this, right?
Or this, right?
Multiple sources, using the all of the data available, rightly show the long term trend is far worse than your dissembling, cherry-picked case.
That's being a little bit silly. Data is useless without analysis.
Analysis without any data is even more useless.
The point was that your simplistic calculations bore [no] relationship to reality.
What doesn't bear any relationship to reality is the mismatch of claims within the IPCC's AR4.
So, is it reasonable or is it an exaggeration to project that the thermal component of sea level rise by 2100 might be over ten to nearly 20 times what it is today?
Well climate modeling sure suggests an increase in the thermal component.
Climate modelers can most likely make sure their models do whatever they want.
It's to do with the greater temperature rise expected this century.
We are over ten years into the century and certainly sea level is not demonstrating any positive change in trend. this graph
certainly doesn't and if you plot out the tide gage data from PSMSL you will find that the timeline over the last 120 is nearly as straight.
Much more than the 20th century. Like this study for instance: Note the inset portion, where the thermal component reaches 6mm per year by 2100.
The IPCC no doubt got their value for table 10.7 from such a study. I assume they got the value for the observed 0.1°C over 42 years in that 700-meter layer of ocean from a legitimate source.
I'm questioning whether or not it's reasonable that the empirical record described in the Chapter 5 Executive Summary of the AR4 could lead to the worst case projected outcome in table 10.7. If it's reasonable, then the annual rate of sea level rise, and it's claimed that it's mostly thermal expansion, has to change very dramatically in the next few years. The only place I see that happening is in the models. World temperatures have been on an upward trend for 120 years but the sea level trend during that time has remained relatively constant. It's on course for about 275 mm or less than a foot.