A few months ago a paper by Jim Houston and Bob Dean in the Journal of Coastal Research (JCR) cast doubt on whether global sea level rise has accelerated over the past century or so. As things go these days, ‘climate sceptics’ websites immediately heralded this as a “bombshell”. A rebuttal by myself and Martin Vermeer has now been published in JCR.
The keystone of the argument by Houston & Dean is the fact that a prominent global sea level reconstruction (Church & White 2006) shows no acceleration since 1930. Which raises the question: why 1930, given the sea level data set starts in 1870? The reason becomes immediately evident when looking at the acceleration starting from any arbitrary date (Fig. 1).
Figure 1. Acceleration of sea-level rise (i.e., twice the quadratic coefficient) from different starting years up to 2001 in the global tide gauge data set of Church and White (2006; red line with uncertainty band). Note that after ~1960 the calculation gets excessively ‘noisy’ because the time interval gets too short to robustly compute acceleration. I graphed this right away after reading the Houston & Dean paper, and a few days later Tamino independently came up with a similar plot – it’s the obvious thing to do. The blue line shows the same quantity from the sea-level hindcast of Vermeer & Rahmstorf (2009) computed from global temperature data.
Around 1930 we see a unique minimum in the acceleration curve – I will explain the cause of this shortly. Other start dates either before or after this minimum show positive acceleration. Picking 1930 for this analysis is thus a classic cherry-pick, and according to the authors that is no accident. They write in the paper: ‘Since the worldwide data of Church and White (2006)…appear to have a linear rise since around 1930, we analyzed the period 1930 to 2010.’ The interval was thus hand-picked to show a linear rise rather than acceleration.
Connection to temperature
Houston & Dean use their result to question the future acceleration of sea level rise predicted by Vermeer & Rahmstorf (2009) for the 21st Century as a consequence of global warming. They argue that the 1930s acceleration minimum calls into question the semi-empirical link between global temperature and global sea level proposed by us in that paper. However, it is clear they never bothered to check this, because quite the opposite is the case: our semi-empirical formula predicts this acceleration minimum, as the graph above shows. As it turns out, this is an expected outcome of the mid-20th-Century plateau in global temperature.
If one subtracts out the non-climatic sea level change due to water stored in artificial reservoirs on land, as we did in Vermeer & Rahmstorf (2009), then the agreement between the acceleration curve predicted from global temperature with the actually observed curve is even better (graph below). Thus, the 1930s acceleration minimum pointed out by Houston & Dean supports our approach and projections rather than challenging them.
Figure 2. The same as Figure 1, but here the sea-level data are corrected for water storage in artificial reservoirs (Chao, Wu, and Li, 2008).
Regarding our projections of future sea level rise, Houston & Dean write:
it is not clear that the acceleration necessary to achieve these comparatively large projected rises in mean sea level over the course of the 21st century is evident in tide-gauge records.
That is a puzzling statement. Why would the acceleration we expect only for the 21st Century already show up in tide gauge records of the 20th? Since we expect a temperature rise to cause an acceleration of sea level rise, the acceleration in the 20th Century (which has seen only 0.7 ºC of global warming) must obviously be much smaller than that expected for the 21st Century, for scenarios of a many times greater warming.
Further issues raised by Houston & Dean
Houston and Dean raise a number of further points (beyond the Church & White global data set) on which we just cite the brief summary statements and refer the readers to our journal comment for more detail:
- Many U.S. tide gauges show a deceleration; since 1930, most of them do.
However, again, 1930 is a special choice, and U.S. tide gauges only provide a regional signal, not a global one.
- The authors’ extension of the Douglas (1992) sea-level compilation shows a sea-level deceleration for 1905–2010.
But this data set is not a properly area-weighted global average but is instead highly biased to the Northern Hemisphere. It is known that the twentieth-century acceleration is largely found in the Southern Hemisphere (Merrifield, Merrifield, and Mitchum, 2009), and the only two Southern Hemisphere groups in the extended Douglas data set indeed show acceleration.
- Decadal trends in tide gauge compilations show large variations over the full record, and the most recent decadal trends are not unusual.
However, these variations in decadal tide gauge trends are not a climate signal but rather are dominated by sampling noise due to the inadequate number of tide gauges.
- The satellite altimeter record shows a slight deceleration since 1993.
But this time interval is far too short to draw any conclusions.
In our comment we conclude:
None of this supports a lack of acceleration in global sea-level rise, as compared to what is expected from global warming. Outside a few starting years around 1930, global sea-level reconstructions robustly show a modern acceleration of sea-level rise in conjunction with global warming.
For the evidence, just have a look at some of the references listed below.
p.s. I just see that JCR also carries a reply by Houston & Dean to our comment. This largely focuses on our supposedly “selective” use of data, because we show the acceleration of sea level rise ‘only’ for starting years from 1870 (the start of the data set) to 1970 (after which the computation is too noisy to be meaningful by anyone’s standard). This is slightly ironic given that Houston & Dean focused only on the rather unique start year 1930. Houston and Dean further argue that the data already become too noisy around 1940 because “decadal fluctuations begin to dominate records shorter than about 60 years, and accelerations become increasingly meaningless for starting years in Figure 1 greater than about 1940”. We disagree: while this may be true for individual records it is not true for the global sea level reconstruction shown. The 2-sigma range and the fact that the curve is smooth until then shows it is meaningful up to about 1960; we continued the graph up to 1970 in order to show (rather than just claim in the text) how the uncertainty explodes after 1960. In any case, by showing the plot until 1970, we allow readers to see the full potentially meaningful range and judge for themselves whether they see any significant difference between the data and our model. That our model is somehow called into question by the observed sea level acceleration was, after all, a key claim in Houston & Dean’s original paper.
Houston & Dean excuse the strong northern-hemisphere bias introduced by their simple averaging by saying that “this criticism would apply to any study of sea-level rise”. That is not true; the sea level data set we use (Church and White 2006) and also the temperatures (GISS) use an area-weighted averaging scheme that makes sure the northern and southern hemispheres are properly represented in proportion to their surface areas, regardless of the data density.
But at least on one thing we agree. As Houston & Dean state in their final sentence, we indeed predict a much larger acceleration of sea level rise in the 21st Century than is observed in the 20th Century. That is a direct logical consequence of the fact that we expect much larger warming in the 21st than in the 20th.
Update 24 July: A related case of “lack of acceleration” – also from the Journal of Coastal Research – is expertly treated by Tamino here: How Not to Analyze Tide Gauge Data. It does raise some questions about the quality of peer review at JCR.
Link
References
Church, J. A., N. J. White, 2006: A 20th century acceleration in global sea-level rise. Geophysical Research Letters, 33, L01602.
Douglas, B. C., 1992: Global sea level acceleration. journal of Geophysical Research-Oceans, 97, 12699-12706.
Houston, J., R. Dean, 2011: Sea-level acceleration based on US tide gauges and extensions of previous global-gauge analysis. Journal of Coastal Research.
Merrifield, M. A., S. T. Merrifield, and G. T. Mitchum, 2009: An Anomalous Recent Acceleration of Global Sea Level Rise. Journal of Climate, 22, 5772-5781.
Rahmstorf, S. and M. Vermeer, 2011: Discussion of: Houston, J.R. and Dean, R.G., 2011. Sea-Level Acceleration Based on U.S. Tide Gauges and Extensions of Previous Global-Gauge Analyses. Journal of Coastal Research 27, 784–787.
Vermeer, M., S. Rahmstorf, 2009: Global Sea Level Linked to Global Temperature. Proceedings of the National Academy of Science of the USA, 106, 21527-21532.
Der Spiegel takes a stab at sea levels. With some great pics.
http://www.spiegel.de/international/world/0,1518,774706,00.html
There seems an ongoing scientific debate concerning the potential loss of the Arctic sea ice: On the one hand the general consensus seems to be that we will see seasonally ice free Arctic waters by 2030 – 2050. On the other we have, for instance, Wiesław Maslowski predicting 2016.
It’s my understanding that the magnitude of sea ice volume and extent losses we’re currently seeing in the Arctic are not predicted by the consensus GCMs — or at least not for a couple more decades — isn’t this an indication that these GCMs have underestimated a positive feedback or overestimated a negative feedback?
An additional disagreement seems to be what happens when the ice does disappear? In Recovery mechanisms of Arctic summer sea ice by Tietsche, Notz, Jungclaus, Marotzke (2011) the authors conclude that
If the work of Tietsche, et al is based on models that are currently unable to adequately model the past 15 years of rapid volume and extent loss, can these models be relied upon to predict whether the ice can recover (short timescales or not)?
You replaced a poor analysis with another poor analysis. How to estimate velocities and accelerations in time series data is described in “Functional Data Analysis” by J.O. Ramsay and B. W. Silverman. Two of the key references are by Th. Gasser et al, 1991a, 1991b. There is much more primary literature. Code is available and is described in “S+ Functional Analysis User’s Guide” by D. B. Clarkson, C. Fraley, C.C. Gu and J.O. Ramsay.
> can these models be relied upon
“All models are wrong; some models are useful”
Different models, different results:
D Bernie, JA Lowe… – Progress in Physical …, 2011 – ppg.sagepub.com
… Concerning reversibility of Greenland ice-sheet loss, one model study incorporating a detailed ice-sheet model has found evidence for multiple stable states, representing effectively irreversible loss, even if global climate returns to its pre- industrial state (Ridley et al., 2010)….
and see https://www.realclimate.org/index.php/archives/2007/01/arctic-sea-ice-decline-in-the-21st-century/ (note when that was written–January 2007)
or at least look at the picture: https://www.realclimate.org/index.php/archives/2007/01/arctic-sea-ice-decline-in-the-21st-century/
https://www.realclimate.org/images/bitz_fig1.jpg
Kevin O’Neill wrote:
Purely amateur comments, but my impression is that many think that improving modeling of Arctic sea ice trends is mostly a matter of getting a *lot* of details right.
For instance, this paper from 2006 compares Arctic cloud characteristics from three different models with each other (and with in situ observations) seeking to understand how the cloud characteristics influence the sea ice:
http://journals.ametsoc.org/doi/pdf/10.1175/2007JCLI1614.1
A different sort of study is undertaken in the following paper–meticulous in situ measurements are made in order to derive better values for the transmission of solar radiation through the sea ice. The idea is that the previous values–based on a similar, but smaller and presumably less accurate study done in the late ’70s–are biased low, leading to a systematic underestimate of the amount of energy reaching the Arctic Ocean through the ice. (Possibly explaining why the sea ice is declining faster than the models had forecast? The authors don’t make that claim in the paper, but it seems an inescapable inference.)
http://psc.apl.washington.edu/publications/pubs/2006JC003977_transmission.pdf
Interesting thread abou communicating Climate Science over at Judith Curry’s Climate, etc blog. One commenter even taking an amusing swipe at this place;
“If climatology wants to be a grown-up science, it should foster skepticism instead of ducking it. Every time a climatologist or IPCC’s house organ, realclimate.org, points a gnarled finger at a skeptic, a denialist, a hack in the pay of Big Oil and coal, a Republican, or an unpublished ignoramus, climate science depreciates in the public eye.”
“Every time a climatologist or IPCC’s house organ, realclimate.org, points a gnarled finger at a skeptic, a denialist, a hack in the pay of Big Oil and coal, a Republican, or an unpublished ignoramus, climate science depreciates in the public eye.”
My response is Judith Curry and Republican eyes should be more open to science:
http://arctic.atmos.uiuc.edu/CT/animate.arctic.color.0.html
NE passage about to be open very early this year, not according to the skeptic plan, was it suppose to be regaining its extent? Cooling? Not following an ignorant skeptic rant? Are they, the contrarians magicians? Do they expect climate to behave according to their political agenda?
> Chas
Boring, no?
Wayne, that’s a meta-troll by Chas — taking a trolling post from JC’s joint, copypasting it over here, with a ‘shicked, shocked’ tskandalized tone yet.
Remarkable at least as among the most agonized mixed metaphors I’ve ever seen:
“… house organ … points a gnarled finger … in the public eye …”
Ewwwww.
Seems implausible, but “which shecan” is the Captcha.
The Oracle knows.
# 106 illustrates the method of lying by using “if” and speaking as if things are the case which are not.
106, 107-110:
I’d translate it as “The more you fight, the more this is gonna hurt you.”
But as Pete points out, the reverse is likely true.
Hank and Pete, on the facts the contrarians have lost their cause a long time ago. Its now their strategy to turn climate in a purely partisan debate which has a chance to win because they channel money in the pockets of expert manipulators who do nothing else. World wide global temperatures are rising = sea ice vanishing = glaciers melting . If we remove ourselves from the equation, and present the facts vividly, it does not matter what they do or say.
Stefan,
It makes perfect sense that an acceleration in surface warming should cause a more rapid rise in sea level, due to both greater land-locked glacial melt and ocean thermal expansion. However the temporal response of both effects would seem quite complex (eg, the relative contribution of mountain glaciers versus ice sheets; rate of warming at different depths/tempratures in the ocean), and further complicated by issues like water mining and water storage in reservoirs. I note that Vermeer & Ramsdorf predict acceleration in sea level substantially greater than the IPCC AR4 predictions, and as best I can estimate from figure 6 in the paper, V&R project a rate of sea level rise of ~ 0.59 cm per year by 2020, and ~0.74 cm per year by 2030.
The satellite sea level record (1993 to present) shows a rate of ~0.31 cm/year, but with no obvious acceleration over the 18 year period. Two questions: Do you think the satellite record is accurate? Do you expect the trend in the satellite data to begin accelerating soon?
> substantially greater than the IPCC AR4 prediction
See the quote from Pilkey about the IPCC’s AR4 number:
https://www.realclimate.org/?comments_popup=8092#comment-210694
> over the 18 year period…. Do you expect the trend
I’ll add to those questions: how many years’ data is needed to assess whether a trend is found, for these particular satellite data sets? And does that vary across different parts of the planet?
this graph does not support the claim of “accelerated” sea level rise:
http://www.aviso.oceanobs.com/fileadmin/images/news/indic/msl/MSL_Serie_EN_Global_IB_RWT_NoGIA_Adjust.png
The real key here is that, as you focus more on the most recent data, the estimates of “acceleration” become less and less reliable: the short-term variation swamps any estimate of acceleration. You see this as well in the broad confidence band in the posted graph Only by cherry-picking can you detect any acceleration of sea level rise.
Tilo-san: unfortunately Barton was wrong. I used monthly data that came up to date, Barton used yearly data that didn’t. For some inexplicable reason Barton seemed to think that trending yearly data was more accurate than trending monthly data.
Me: If you let me use data sampled at the one-second level from 6 AM to 9 AM here in Pittsburgh, I can prove that the seas will boil in a few weeks. It’s appropriate to time-sample on scales consistent with the data being examined. For global warming, the proper sample size is 30 years or more. Annual data is fine for that. Chopping it up into months artificially balloons your significance (see the morning experiment proposed above).
Appears that Houston and Dean are not alone in their (misleading, misguided, whatever) way of looking at things…
http://www.theaustralian.com.au/news/nation/sea-level-rises-are-slowing-tidal-gauge-records-show/story-e6frg6nf-1226099350056
Stefan,
Your 2007 model assumes that sea level rise is a function of the temperature difference between the present period and a base period. In the current decade temperatures have not decreased, so one would expect that sea level rise should have continued at the same rate. In addition things like La Nina have to do with ocean temperatures which would affect Steric sea level rise, but would not impact volume changes. So the fact that sea level rise throughout the last decade is below the levels predicted by your models is interesting. You can reasonably argue that this is short term variation.
I would argue that this period is the first true out of sample test for your models. As so often happens in this types of things the most difficult time to predict is the future. We both know how often models are created based on historical data that immediately fail in current periods. So far this is happening with your model, but only time will tell whether this is a short term problem.
I know you attempted out of sample testing in your 2007 paper, but as I pointed out in an earlier article it didn’t really work out.
http://nierenbergclimate.blogspot.com/2009/04/published-comments-on-rahmstorf-2007.html
#75 tph “in order to get 1000 mm by 2100, that is an average of 10 mm/yr for the century – that means a significant acceleration is to come”. Why doesn’t this just beg the question? You infer that “a significant acceleration is to come” from your assumption that predicted sea levels for 2100 are already set in stone. Says who?
simon asks:”#75 tph “in order to get 1000 mm by 2100, that is an average of 10 mm/yr for the century – that means a significant acceleration is to come”. Why doesn’t this just beg the question? You infer that “a significant acceleration is to come” from your assumption that predicted sea levels for 2100 are already set in stone. Says who?”
The best available research and the apparent ostrich head in the sand approach to dealing with unpleasant realities, so that business as usual is going to be the “plan”. The sea level data over the past century has a signal to noise ratio that is too high to detect any changes in acceleration over the past 130 years, mainly because the driving force is too weak compared to natural fluctuations and the observations too poor for most of the time period. By mid century both of these factors will be such that we may even analyze the third derivative of global sea level.
#121 tph “By mid century both of these factors will be such that we may even analyze the third derivative of global sea level.” Again, to what other evidence do you cross-refer to make such a confident prediction?
#121 “a signal to noise ratio that is too high to detect any changes”. ?
A report published in JCR by Watson shows that sea levels are decelerating in Australia and New Zealand. The report is based on tidal records going back from 1897 t0 present (Fremantle Western Australia), 1903 to present (Auckland NZ), 1914 to present (Sydney Australia) and Newcastle (NSW Australia). This seems to support the findings of Houston and Dean
Sorry I should have put the URL in for the story
it is
http://www.theaustralian.com.au/news/nation/sea-level-rises-are-slowing-tidal-gauge-records-show/story-e6frg6nf-1226099350056
[Response: He seems to have done the exact same cherry pick as H&D…. – gavin]
[Response: He seems to have done the exact same cherry pick as H&D…. – gavin]
Gavin, could you expand on this point? This paper is getting a some attention in Aus.
I am no stats man but I read it and could not figure how they could sensibly apply a quadratic to what looked like ‘stepped’ data.
err, on comment 121 make that signal to noise too low. Or noise to signal too high.
> exact same cherry pick
Careful, it’s likely Watson didn’t say what the newspaper suggests.
That’s “The Australian” — http://scienceblogs.com/deltoid/2011/07/the_australians_war_on_science_66.php
The Australian’s War on Science 64: Respect The Science!
“The Australian regularly shows its contempt for science, scientists and the scientific method ….”
Beware the newspaper’s spin. The story refers explicitly to H’n’D, it’s not saying Watson made the comparison. Further down they mention that Watson has twice told them something — but whatever he said didn’t make it through to the article clearly enough to understand. Wanta bet the newspaper’s wrong?
Below the story, the first comment on that page says:
“This is a complete misrepresentation of Phil Watson`s views. See for example the Pittwater Council`s website.”
Looking there I find this presentation appears: http://www.pittwater.nsw.gov.au/__data/assets/pdf_file/0015/34620/Phil_Watson.pdf
Don’t ever assume a news story has described a scientist’s work correctly.
Hank is correct, at a science site like this we should be looking at the research paper published by Watson, not a newspaper story about it.
The Watson paper is at
http://www.jcronline.org/doi/full/10.2112/JCOASTRES-D-10-00141.1
It looks like a reasonable paper to me, with quite a fair literature review.
He looks at the 3 sites in Australia and one in New Zealand with continuous tide gauge records for at least 80 years. They show a very slight deceleration.
Hank, a bit more balanced article here.
IA, as Gavin says, the cherry pick is the same as in H&D, and so is the refutation: see above. The same model that we used in our 2009 paper to describe sea-level rise as a simple function of global temperature for the past instrumental period — and which projects the “comparatively large” sea level rise values out to 2100 that H&D have a problem with –, has no difficulty at all reproducing also the near-zero “acceleration” for 1930-now (or 1940-now) noted by H&D. There is no contradiction.
@ Martin
thanks for the link – definitely more balanced.
The thing I dont really understand is why the authors fit a simple quadratic when there is a discontinuity in the data from the 1960’s/70’s onwards. The weight of earlier data in the series means you get a good r-squared but to then say the the rate of change is declining seems…odd?
Sorry should have said 80’s/90’s onwards…
The article in the Australian does seem to accurate portray Watson’s paper. The following quotes are taken directly from the journal:
‘the analysis finds there was a “consistent trend of weak deceleration” from 1940 to 2000.’
‘Mr Watson’s research finds that in the 1990s, when sea levels were attracting international attention, although the decadal rates of ocean rise were high, “they are not remarkable or unusual in the context of the historical record at each site over the 20th century”.’
‘He said further research was required, “to rationalise the difference between the acceleration trend evident in the global sea level time-series reconstructions (models) and the relatively consistent deceleration trend evident in the long-term Australasian tide gauge records”.’
Here’s the agency response, as a Letter to the Editor
http://www.environment.nsw.gov.au/media/DecMedia11072205.htm
Letter to the Editor …
“I refer to today’s article titled, Sea-level rises slowing: tidal records.
Your article has misrepresented our Mr Phil Watson’s research paper by saying that ‘global warming is not affecting sea levels’. This is untrue and misleading and it is not what Mr Watson told your journalist. Mr Watson’s research looked only at measurements of historical data. It specifically did not consider predicted linkages between sea level rise and global warming predicted by climate models….”
Click the link for the full text.
Comment: Looks to me like this is the agency responsible for protecting heritage sites along the coastline, which has to decide when and where to protect or move structures as sea level changes. They are interested in site-specific numbers for their local responsibilities.
Note, that Letter to the Editor I posted above, from Watson’s agency, hasn’t appeared in the responses to The Australian’s site.
“All indications, from the Arctic and worldwide surface temperatures, melting and movements of the Greenland/Antarctica ice sheets perimeters, Arctic and worldwide sea surface temperatures, Arctic sea ice extents/areas/volumes, atmospheric CO2 concentrations and the oceans (limited and apparently reduced) capacity to uptake these increased CO2 concentrations in a warming climate…”
A shameless plug for the other CO2 problem, just to be fair:
http://www.pmel.noaa.gov/co2/story/Ocean+Acidification
Hank, the Australian repeated their own crap in the editorial instead
http://scienceblogs.com/deltoid/2011/07/the_australians_war_on_science_67.php#more
Well H&D had this presentation given to the FSBPA on February 9, 2011;
http://www.fsbpa.com/2011TechPresentations/Dean%20Robert.pdf
Using, you guessed it, their quadratic relationship, which has absolutely no physical science basis whatsoever.
They then go on to use this exercise (no make that excuse) in curve fitting “model” to extrapolate from 2010 to 2100 for several locations in Florida.
Curev fitting ~90 years worth of data and then extrapolation ~90 years from this dubious exercise in statistical math… (using OLS, no less, when the time series are quite clearly of a non-stationary nature).
Words can’t describe what these two are doing to the field of science.
Also, another reply to H&D at JCR;
http://www.jcronline.org.pinnacle.allenpress.com/doi/abs/10.2112/JCOASTRES-D-11-00098.1?journalCode=coas
and H&R’s reply to this reply;
http://www.jcronline.org/doi/abs/10.2112/11A-00010.1?prevSearch=%5BAllField%3A+sea+level+rise%5D&searchHistoryKey=
(both currently behing paywall)
Note the dates of of the H&D reply;
“Received: May 26, 2011; Accepted: May 22, 2011; Published Online: July 22, 2011”
(accepted 4 days before receipt, what’s up with that?)
Heads up – tamino reanalyzes the Watson work.
http://tamino.wordpress.com/2011/07/22/how-not-to-analyze-tide-gauge-data/
The latest IPCC panel on ocean rise is deliberating their predictions. I noted that they stated that at this time in the last interglacial the worlds temperature was 2C hotter and the oceans 6 metres higher. This seems like a contradiction as it is meant to be mankind that will cause this problem, yet it happened before according to the scientists at the IPCC. Gavin do you have an explanation for this contrary information.
Re #33, “…we favor relating sea level to temperature, not time)”
Okay but then come up with a definition of what such a math result represents because that AIN’T ‘acceleration’ in anybody’s vernacular.
The whole basis of climate prediction itself is founded on the principle of what will happen IN TIME, no?
Absolutely read Tamino’s How Not to Analyze Tide Gauge Data”.
Mike M. asks:”Re #33, “…we favor relating sea level to temperature, not time)”
Okay but then come up with a definition of what such a math result represents because that AIN’T ‘acceleration’ in anybody’s vernacular.
The whole basis of climate prediction itself is founded on the principle of what will happen IN TIME, no?”
No. Climate prediction is based on physics. The assumptions are that humans will continue to emit CO2 in the future, which has the first order physical effect of raising temperature. The reason for relating sea level to temperature is because most sea level rise is caused by increased temperature. Temperature, while having an underlying trend upwards (because of the unrelenting increase in CO2 which causes increase in temperature) has a noise component. The same factors that add noise to temperature adds noise to sea level.
> Mike M
> that AIN’T …
is so:
ac·cel·er·a·tion/akˌseləˈrāSHən/
Increase in the rate or speed of something….
rate/rāt/
A measure, quantity, or frequency, typically one measured against some other quantity or measure: “the crime rate”.
141, Mike M. The whole basis of climate prediction itself is founded on the principle of what will happen IN TIME, no?
No. Some of the statistical models are based on the analysis of time series. The physical models predict temperature change as a result of CO2 change. These latter are the models relevant for assessing changes in the energy economy and reforestation. Time enters these models because of the rate of change of CO2 concentration.
Going slightly OT for a minute, I just had a look at Sivan 2004 and Lambeck 2004 – both archaelogical studies of past sea level. Results from both are depicted in Kemp et al. 2011, Fig.3 but I’m wondering if they’ve been incorrectly plotted.
In the two papers figures are given as ‘before present’ (BP) for reference. By convention I think ‘BP’ = ‘1950’ but the plot in Kemp et al. appears to use 2000 as the ‘present’ reference point instead which moves everything upwards by about 10-15cm.
Neither the Sivan or Lambeck paper explicitly define ‘BP’ as ‘1950’ so I could be wrong about this but I’ve been reading a bit about past sea levels and this apparent discrepancy was a source of confusion. For Stefan, Martin or Mike, I realise you probably wouldn’t have worked on this part of the paper but do you have any idea whether or not my interpretation might be correct?
#139 – I just read tamino’s post, and you are right – it is really excellent. Anyone seriously interested in Watson’s analysis should read it.
If global sea levels are rising due to thermal expansion, may we not reasonably conclude that the planet’s diameter is increasing? Basic physics tells us that as the diameter increases, the rate of rotation will slow in order to conserve angular momentum. This affects the length of day and can be measured to a very high degree of precision.
I am quite aware that tectonic plate movements, changes in ocean currents, as well as astronomical influences can and do affect the Earth’s rate of rotation but these are reasonably well understood and can be calculated.
Looking at records of the changes in length of day since 1860, e.g. here [http://www.john-daly.com/press/lods1860.gif] it’s clear that there is no discernible trend which would suggest long-term or accelerating increase in the Earth’s diameter.
Are global sea levels really rising?
Why would we conclude that, reasonably or not? I don’t quite grasp the connection between the [comparatively small] thermal expansion of the oceans and your proposed expansion of the whole planet.
Scottie (#148)
The change in diameter due to thermal expansion is way down in the noise. What is measureable, though, is the change in the Earth’s oblateness due to redistribution of mass from the Greenland and Antartcic Ice Sheets – mass from near the axis or rotation is distributed around the Earth. See, for example:
Nerem, R. S., and J. Wahr (2011), Recent changes in the Earth’s oblateness driven by Greenland and Antarctic ice mass loss, Geophys. Res. Lett., 38, L13501, doi:10.1029/2011GL047879.
There is a bit more background on this in:
Munk, W (2002), Twentieth century sea level: An enigma, PNAS, 99, doi:10.1073/pnas.092704599
and
Mitrovica et al. (2006), Reanalysis of ancient eclipse, astronomic and geodetic data: A possible route to resolving the enigma of global sea-level rise. Earth Planet. Sci. Lett. , 243, 390.
Neil White