Ups and downs of sea level projections

Filed under: — stefan @ 31 August 2009

By Stefan Rahmstorf and Martin Vermeer

The scientific sea level discussion has moved a long way since the last IPCC report was published in 2007 (see our post back then). The Copenhagen Synthesis Report recently concluded that “The updated estimates of the future global mean sea level rise are about double the IPCC projections from 2007″. New Scientist last month ran a nice article on the state of the science, very much in the same vein. But now Mark Siddall, Thomas Stocker and Peter Clark have countered this trend in an article in Nature Geoscience, projecting a global rise of only 7 to 82 cm from 2000 to the end of this century.

Coastal erosion: Like the Dominican Republic, many island nations are
particularly vulnerable to sea level rise. (Photo: S.R.)

Semi-empirical sea level models

Siddall et al. use a semi-empirical approach similar to the one Stefan proposed in Science in 2007 (let’s call that R07) and to Grinsted et al. (2009), which we discussed here. What are the similarities and where do the differences come from?

For short time scales and small temperature changes everything becomes linear and the two new approaches are mathematically equivalent to R07 (see footnote 1). They can all be described by the simple equation:

dS/dt = a ΔT(t) + b     (Eq 1)

dS/dt is the rate of change of sea level S, ΔT is the warming above some baseline temperature, and a and b are constants. The baseline temperature can be chosen arbitrarily since any constant temperature offset can be absorbed into b. This becomes clear with an example: Assume you want to compute sea level rise from 1900-2000, using as input a temperature time series like the global GISS data. A clever choice of baseline temperature would then be the temperature around 1900 (averaged over 20 years or so, we’re not interested in weather variability here). Then you can integrate the equation from 1900 to 2000 to get sea level relative to 1900:

S(t) = a ∫ΔT(t’) dt’ + b t     (Eq 2)

There are two contributions to 20th C sea level rise: one from the warming in the 20th Century (let’s call this the “new rise”), and a sea level rise that results from any climate changes prior to 1900, at a rate b that was already present in 1900 (let’s call this the “old rise”). This rate is constant for 1900-2000 since the response time scale of sea level is implicitly assumed to be very long in Eq. 1. A simple matlab/octave code is provided below (2).

If you’re only interested in the total rise for 1900-2000, the temperature integral over the GISS data set is 25 ºC years, which is just another way of saying that the mean temperature of the 20th Century was 0.25 ºC above the 1900 baseline. The sea level rise over the 20th Century is thus:

S(1900-2000) = 25 a + 100 b     (Eq. 3)

Compared to Eq. 1, both new studies introduce an element of non-linearity. In the approach of Grinsted et al, sea level rise may flatten off (as compared to what Eq 1 gives) already on time scales of a century, since they look at a single equilibration time scale τ for sea level with estimates ranging from 200 years to 1200 years. It is a valid idea that part of sea level rise responds on such time scales, but this is unlikely to be the full story given the long response time of big ice sheets.

Siddall et al. in contrast find a time scale of 2900 years, but introduce a non-linearity in the equilibrium response of sea level to temperature (see their curve in Fig. 1 and footnote 3 below): it flattens off strongly for warm temperatures. The reason for both the long time scale and the shape of their equilibrium curve is that this curve is dominated by ice volume changes. The flattening at the warm end is because sea level has little scope to rise much further once the Earth has run out of ice. However, their model is constructed so that this equilibrium curve determines the rate of sea level rise right from the beginning of melting, when the shortage of ice arising later should not play a role yet. Hence, we consider this nonlinearity, which is partly responsible for the lower future projections compared to R07, physically unrealistic. In contrast, there are some good reasons for the assumption of linearity (see below).

Comparison of model parameters

But back to the linear case and Eq. 1: how do the parameter choices compare? a is a (more or less) universal constant linking sea level to temperature changes, one could call it the sea level sensitivity. b is more situation-specific in that it depends both on the chosen temperature baseline and the time history of previous climate changes, so one has to be very careful when comparing b between different models.

For R07, and referenced to a baseline temperature for the year 1900, we get a = 0.34 cm/ºC/year and b = 0.077 cm/year. Corresponding values of Grinsted et al. are shown in the table (thanks to Aslak for giving those to us!).

For Siddall et al, a = s/τ where s is the slope of their sea level curve, which near present temperatures is 4.8 meters per ºC and τ is the response the time scale. Thus a = 0.17 cm/ºC/year and b = 0.04 cm /year (see table). The latter can be concluded from the fact that their 19th Century sea level rise, with flat temperatures (ΔT(t) = 0) is 4 cm. Thus, in the model of Siddall et al, sea level (near the present climate) is only half as sensitive to warming as in R07. This is a second reason why their projection is lower than R07.

 Model a [cm/ºC/year] b [cm /year] “new rise” [cm] (25a) “old rise” [cm] (100b) 25a+100b [cm] total model rise [cm] Rahmstorf 0.34 0.077 8.5 7.7 16.2 16.2 Grinsted et al “historical” 0.30 0.141 7.5 14.1 21.6 21.3 Grinsted et al “Moberg” 0.63 0.085 (15.8) (8.5) (24.3) 20.6 Siddall et al 0.17 0.04 4.3 4 8.3 8.3 (?) 7.9

Performance for 20th Century sea level rise

For the 20th Century we can compute the “new” sea level rise due to 20th Century warming and the “old” rise due to earlier climate changes from Eq. 3. The results are shown in the table. From Grinsted et al, we show two versions fitted to different data sets, one only to “historical” data using the Jevrejeva et al. (2006) sea level from 1850, and one using the Moberg et al. (2006) temperature reconstruction with the extended Amsterdam sea level record starting in the year 1700.

First note that “old” and “new” rise are of similar magnitude for the 20th Century because of the small average warming of 0.25 ºC. But it is the a-term in Eq. (2) that matters for the future, since with future warming the temperature integral becomes many times larger. It is thus important to realise that the total 20th Century rise is not a useful data constraint on a, because one can get this right for any value of a as long as b is chosen accordingly. To constrain the value of a – which dominates the 21st Century projections — one needs to look at the “new rise”. How much has sea level rise accelerated over the 20th Century, in response to rising temperatures? That determines how much it will accelerate in future when warming continues.

The Rahmstorf model and the Grinsted “historical” case are by definition in excellent agreement with 20th Century data (and get similar values of a) since they have been tuned to those. The main difference arises from the differences between the two sea level data sets used: Church and White (2006) by Rahmstorf, Jevrejeva et al. (2006) by Grinsted et al. Since the “historical” case of Grinsted et al. finds a ~1200-year response time scale, these two models are almost fully equivalent on a century time scale (e-100/1200=0.92) and give nearly the same results. The total model rise in the last column is just 1.5 percent less than that based on the linear Eq. 3 because of that finite response time scale.

For the Grinsted “Moberg” case the response time scale is only ~210 years, hence our linear approximation becomes bad already on a century time scale (e-100/210=0.62, the total rise is 15% less than the linear estimate), which is why we give the linear estimates only in brackets for comparison here.

The rise predicted by Siddall et al is much lower. That is not surprising, since their parameters were fitted to the slow changes of the big ice sheets (time scale τ=2900 years) and don’t “see” the early response caused by thermal expansion and mountain glaciers, which makes up most of the 20th Century sea level rise. What is surprising, though, is that Siddall et al. in their paper claim that their parameter values reproduce 20th Century sea level rise. This appears to be a calculation error (4); this will be resolved in the peer-reviewed literature. Our values in the above table are computed correctly (in our understanding) using the same parameters as used by the authors in generating their Fig.3. Their model with the parameters fitted to glacial-interglacial data thus underestimates 20th Century sea level rise by a factor of two.

Frosty legacy: We cannot afford to lose even a few percent of the land ice on Earth, which in total would be enough to raise global sea levels by 65 meters. (Calving front in Svalbard, photo by S.R.)

Future projections

It thus looks like R07 and Grinsted et al. both reproduce 20th Century sea level rise and both get similar projections for the 21st Century. Siddall et al. get much lower projections but also strongly under-estimate 20th Century sea level rise. We suspect this will hold more generally: it would seem hard to reproduce the 20th Century evolution (including acceleration) but then get very different results for the 21st Century, with the basic semi-empirical approach common to these three papers.

In fact, the lower part of their 7-82 cm range appears to be rather implausible. At the current rate, 7 cm of sea level rise since 2000 will be reached already in 2020 (see graph). And Eq. 1 guarantees one thing for any positive value of a: if the 21st Century is warmer than the 20th, then sea level must rise faster. In fact the ratio of new sea level rise in the 21st Century to new sea level rise in the 20th Century according to Eq. 2 is not dependent on a or b and is simply equal to the ratio of the century-mean temperatures, T21/T20 (both measured again relative to the 1900 baseline). For the “coldest” IPCC-scenario (1.1 ºC warming for 2000-2100) this ratio is 1.3 ºC / 0.25 ºC = 5.2. Thus even in the most optimistic IPCC case, the linear semi-empirical approach predicts about five times the “new” sea level rise found for the 20th Century, regardless of parameter uncertainty. 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.

Does the world have to be linear?

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.

A slightly longer answer is this. First we need to distinguish two things: linearity in temperature (at a given point in time, and all else being equal), and linearity as the system evolves over time. The two are conflated in the real world, because temperature is increasing over time.

Linearity in temperature is a very reasonable assumption often used by glaciologists. It is based on a heat flow argument: the global temperature anomaly represents a heat flow imbalance. Some of the excess heat will go into slowly warming the deep ocean, some will be used to melt land ice, a tiny little bit will hang around in the atmosphere to be picked up by the surface station network. If the anomaly is 2 ºC, the heat flow imbalance should be double that caused by a 1 ºC anomaly. That idea is supported by the fact that the warming pattern basically stays the same: a 4 ºC global warming scenario basically has the same spatial pattern as a 2 ºC global warming scenario, only the numbers are twice as big (cf. Figure SMP6 of the IPCC report). It’s the same for the heating requirement of your house: if the temperature difference to the outside is twice as big, it will lose twice the amount of heat and you need twice the heating power to keep it warm. It’s this “linearity in temperature” assumption that the Siddall et al. approach rejects.

Linearity over time is quite a different matter. There are many reasons why this cannot hold indefinitely, even though it seems to work well for the past 120 years at least. R07 already discusses this and mentions that glaciers will simply run out of ice after some time. Grinsted et al. took this into account by a finite time scale. We agree with this approach – we merely have some reservations about whether it can be done with a single time scale, and whether the data they used really allow to constrain this time scale. And there are arguments (e.g. by Jim Hansen) that over time the ice loss may be faster than the linear approach suggests, once the ice gets wet and soft and starts sliding. So ultimately we do not know how much longer the system will behave in an approximately linear fashion, and we do not know yet whether the real sea level rise will then be slower or faster than suggested by the linear approach of Eq. 1.

Getting soft? Meltwater lake and streams on the Greenland Ice Sheet near 68ºN at 1000 meters altitude. Photo by Ian Joughin.

Can paleoclimatic data help us?

Is there hope that, with a modified method, we may successfully constrain sea level rise in the 21st Century from paleoclimatic data? Let us spell out what the question is: How will sea level in the present climate state respond on a century time scale to a rapid global warming? We highlight three aspects here.

Present climate state. It is likely that a different climate state (e.g. the glacial with its huge northern ice sheets) has a very different sea level sensitivity than the present. Siddall et al. tried to account for that with their equilibrium sea level curve – but we think the final equilibrium state does not contain the required information about the initial transient sensitivity.

Century time scale. Sea level responds on various time scales – years for the ocean mixed layer thermal expansion, decades for mountain glaciers, centuries for deep ocean expansion, and millennia for big ice sheets. Tuning a model to data dominated by a particular time scale – e.g. the multi-century time scale of Grinsted et al. or the multi-millennia time scale of Siddall et al. – does not mean the results carry over to a shorter time scale of interest.

Global warming. We need to know how sea level – oceans, mountain glaciers, big ice sheets all taken together – responds to a globally near-uniform forcing (like greenhouse gas or solar activity changes). Glacial-interglacial climate changes are forced by big and highly regional and seasonal orbital insolation changes and do not provide this information. Siddall et al use a local temperature curve from Greenland and assume there is a constant conversion factor to global-mean temperature that applies across the ages and across different mechanisms of climate change. This problem is not discussed much in the paper; it is implicit in their non-dimensional temperature, which is normalised by the glacial-holocene temperature difference. Their best guess for this is 4.2 ºC (as an aside, our published best guess is 5.8 ºC, well outside the uncertainty range considered by Siddall et al). But is a 20-degree change in Greenland temperature simply equivalent to a 4.2-degree global change? And how does local temperature translate into a global temperature for Dansgaard-Oeschger events, which are generally assumed to be caused by ocean circulation changes and lead to a temperature seesaw effect between northern and southern hemisphere? What if we used their amplitude to normalise temperature – given their imprint on global mean temperature is approximately zero?

Overall, we find these problems extremely daunting. For a good constraint for the 21st Century, one would need sufficiently accurate paleoclimatic data that reflect a sea level rise (a drop would not do – ice melts much faster than it grows) on a century time scale in response to a global forcing, preferably from a climate state similar to ours – notably with a similar distribution of ice on the planet. If anyone is aware of suitable data, we’d be most interested to hear about them!

Update (8 Sept): We have now received the computer code of Siddall et al (thanks to Mark for sending it). It confirms our analysis above. The code effectively assumes that the warming over each century applies for the whole century. I.e., the time step for the 20th Century assumes the whole century was 0.74 ºC warmer than 1900, rather than just an average of 0.25 ºC warmer as discussed above. When this is corrected, the 20th Century rise reduces from 15 cm to 8 cm in the model (consistent with our linear estimate given above). The 21st Century projections ranging from 32-48 cm in their Table 1 (best estimates) reduce to 24-32 cm.

Martin Vermeer is a geodesist at the Helsinki University of Technology in Finland.

Footnotes

(1) Siddall et al. use two steps. First they determine an equilibrium sea level for each temperature (their Eq 1, and shown in their Fig. 1). Second, they assume an exponential approach of sea level to this equilibrium value in their Eq. 2, which (slightly simplified, for the case of rising sea level) reads:

dS/dt = (Se(T) – S(t)) / τ.

Here S is the current sea level (a function of time t), Se the equilibrium sea level (a function of temperature T), and τ the time scale over which this equilibrium is approached (which they find to be 2900 years).
Now imagine the temperature rises. Then Se(T) increases, causing a rise in sea level dS/dt. If you only look at short time scales like 100 years (a tiny fraction of those 2900 years response time), S(t) can be considered constant, so the equation simplifies to

dS/dt = Se(T)/ τ + constant.

Now Se(T) is a non-linear function, but for small temperature changes (like 1 ºC) this can be approximated well by a linear dependence Se(T) = s * T + constant. Which gives us

dS/dt = s/τ * T + constant, i.e. Eq (1) in the main post above.

R07 on the other hand used:
dS/dt = a * (T – T0), which is also Eq. (1) above.
Note that a = s/τ and b = –a*T0 in our notation.

(2) Here is a very basic matlab/octave script that computes a sea level curve from a given temperature curve according to Eq. 2 above. The full matlab script used in R07, including the data files, is available as supporting online material from Science

% Semi-empirical sea level model - very basic version
T1900=mean(tempg(11:30)); T=tempg-T1900;

a=0.34; % sea level sensitivity parameter [cm/degree/year]
b=0.077; % note this value depends on a and on the temperature
% baseline, here the mean 1890-1909

% rate of rise - here you need to put in an annual temperature time series T
% with same baseline as chosen for fitting b!
dSdt = a*T + b;

% integrate this to get sea level over the period covered by the temperature series
S = cumsum(dSdt); plot(S);

(3) Here is a matlab/octave script to compute the equilibrium sea level curve of Siddall et al. Note the parameters differ in some cases from those given in the paper – we obtained the correct ones from Mark Siddall.

% Siddall et al equilibrium sea level curve, their Fig. 1, NGRIP scenario
A = 15.436083479092469;
b = 0.012630000000000;
c = 0.760400212014386;
d = -73.952809369848552;

Tdash=[-1.5:.05:2];
% Equilibrium sea level curve
Se=A*asinh((Tdash+c)/b) + d;
% Tangent at current temperature
dSe=A/sqrt(1+((0+c)/b)^2)/b;
Se0= A*asinh((0+c)/b) + d;
Te=dSe*Tdash + Se0;
plot(Tdash, Se, 'b', Tdash, Te, 'c', Tdash, 0.0*Se, 'k', [0 0], [-150 40], 'k')
xlabel('Dimensionless temperature')
ylabel('Equilibrium sea level (m)')
fprintf(1, 'Slope: %f m/K, Sensitivity: %f cm/K/year, zero offset: %f m\n\n', dSe/4.2, 100*dSe/4.2/2900, Se0);

(4) We did not yet receive the code at the time of writing, but based on correspondence with the authors conclude that for their values in Fig. 3 and table 1, Siddall et al. integrated sea level with 100-year time steps with a highly inaccurate numerical method, thus greatly overestimating the a-term. In their supporting online information they show a different calculation for the 20th Century with annual time steps (their Fig. 5SI). This is numerically correct, giving an a-term of about 4 cm, but uses a different value of b close to 0.12 cm/year to obtain the correct total 20th Century rise.

References

Church, J. A. & White, N. J. A 20th century acceleration in global sea-level rise. Geophysical Research Letters 33, L01602 (2006).

Grinsted, A., Moore, J. C. & Jevrejeva, S. Reconstructing sea level from paleo and projected temperatures 200 to 2100 ad. Climate Dynamics (2009).

Jevrejeva, S., Grinsted, A., Moore, J. C. & Holgate, S. Nonlinear trends and multiyear cycles in sea level records. Journal of Geophysical Research 111 (2006).

Moberg, A., Sonechkin, D. M., Holmgren, K., Datsenko, N. M. & Karlen, W. Highly variably Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature 433, 613-617 (2005).

Rahmstorf, S. A semi-empirical approach to projecting future sea-level rise. Science 315, 368-370 (2007).

415 Responses to “Ups and downs of sea level projections”

1. 351
Steve Fish says:

simon abingdon ~#347. Apparently, you are also clueless about what an ad hominem argument is. Hint– this is not an ad hominem.

Steve

2. 352

Wili #350, Hank #250,

The value of 10^18 cubic feet is released methane (under STP), not clathrate… divide by 160 ;-)

… 1) the global volume of methane contained in hydrate is huge—far exceeding the volumes of methane present in other forms …

Historically, estimates of the total volume of methane in natural gas hydrate have ranged widely, from roughly 100,000 trillion cubic feet (Tcf) to as much as 270,000,000 Tcf. In recent years, as more information is gained and real data slowly replace best guesses, estimates have tended to fall in a narrower range—from 100,000 to 1,000,000 Tcf.

3. 353
simon abingdon says:

#345 Ray

As far as I’m aware all the Andrill (www.andrill.org) sites are off-shore. I stand by my #342 “we have not a clue about what is under several kilometres of Greenland or Antarctic icecap”.

Ray, if you can disabuse me of this belief, please do so. (BTW the Antarctic ice sheet is about one-and-a-half times the area of the USA 13,720,000/9,161,923 sq km).

4. 354
simon abingdon says:

#351 Steve, I think you’ll find …

5. 355
Mark says:

“If one wants to pick a credible argument with me it’s best to make it over something I actually said as opposed to the argument they want to have.”

It would be good for Rod B to follow his own advice too…

6. 356
Hank Roberts says:

Simon: http://www.ncdc.noaa.gov/paleo/icecore/iicdc.html
How are you managing to stay so badly informed? What source are you relying on for your belief that these facts aren’t easily available? Who do you trust?

7. 357
Mark says:

No, that you don’t understand ad hom is evident from your claim of it.

Calling you out on your lack of understanding is not ad hom, it’s a statement of fact.

Else spelling the dry areas of the Sahara “dessert” is not wrong, since you can’t say it is without saying I’m wrong to spell it that way and you take that as an ad hom attack and a priori evidence that your correction should be ignored and considered by default (and no need to check) wrong.

8. 358
simon abingdon says:

#356 Hank

Hank, I humbly admit my ignorance. Thank you for the link and for drawing my attention to a field of knowledge of which I had previously been unaware.

And Ray, please accept my unreserved apologies.

9. 359
sidd says:

Mr. Abington writes:
“Moreover sea level rise or fall is to me obviously almost exclusively due to thermal expansion/contraction.”

Mr. Abington ought to read the thread more carefully. I pointed out in comment #19 that mass change outstrips steric effects.

10. 360
Brian Dodge says:

Actually, what Simon said was “And on topic may I say that we have not a clue about what is under several kilometres of Greenland or Antarctic icecap and what their response to an increase of temperature might be.”
So, does he believe that the icecaps might not actually melt as the temperatures rise, because he doesn’t know whether it’s basalt, or sedimentary rock, or turtles all the way down? Maybe if we close our eyes, plug our ears, and tuck our heads under the covers, nothing bad will happen.

11. 361

Simon,
Apologies accepted and my sincere apologies for what was probably an over-reaction. I take back half the nasty things I said about you. ;-)

12. 362
stevenc says:

I have a question regarding the concept of an expanding earth: Shen, Chen, Li 12/2007 AGU. They state that the Earth is expanding at a rate of around 0.6mm per year. I have been trying to conceptualize how this would be taken into account in the checks and balances of satellite altimetry and, having failed miserably, thought I would just ask. Has the concept of an expanding Earth already been included in calculations? If not would this be picked up as rising sea levels or satellite drift?

13. 363
Hank Roberts says:

Simon, _where_ have you been getting your information?

Seriously, it helps everyone if you’ll say what sources you have been relying on, where you found them, and why you found them trustworthy up til now — because other people will be relying on them too.

Note the page I pointed you, referencing ice core drilling to bedrock, is a decade old (I emailed the maintainer and asked them whether they have an update somewhere).

Looking out for bad information, telling people who maintain it that it needs correction, and letting readers know whether sites _do_ try to update — is part of the game where we’re all playing on the same side, to the extent we want the science to be understood by people.

So — where’d the bad info come from?

14. 364
Hank Roberts says:

stevenc, where did you hear or read about that paper, that left those questions you ask unanswered?

Here it is; you can see they addressed some of your questions right there:

15. 365
Martin Vermeer says:

stevenc #362: thanks, that’s an interesting nut to crack!
The abstract is here.
First off, my hunch is that this is nonsense. Unfortunately I have not found the article itself.
To first answer your question, it would be picked up as rising sea level by the altimetry, but not by the tide gauges. The common time base of those two systems is still too short to decide the matter.

One immediate problem I see with their idea is, they say they derive the change in principal moments of inertia from the spherical harmonic coefficients of the Earth’s gravitational field, specifically C20, C22 and S22. The problem is that this inversion is degenerate: the external field contains no information on the radial mass distribution.
This means that you cannot unambiguously fix the principal moments of inertia based on those spherical harmonic coefficients. Especially their claimed equal increase in all three principal moments is unobservable from spherical harmonics alone.
If they looked at the change in spherical harmonics, converting it naively to a change in moments of inertia, part of the effect they claim to see may be due to the Laurentide glacial isostatic rebound, which is known to produce a secular increase in C20, but no significant change in C22 or S22. But that’s not what they find… so what are they really doing? No idea.

It’s a conference presentation, not peer reviewed I believe.

16. 366
William says:

Ray #339
Looks like China has figured out that Nuclear power is is one way to minimize CO2 and they have plans to build dozens of nuke plants. Too bad the USA has a failure of leadership to do the same. See below:
DALIAN, China, Sept. 11 /PRNewswire-FirstCall/

Mr. Kearney’s panel at the World Economic Forum’s Annual Meeting of the New Champions, known as “Summer Davos, entitled “The New Climate Framework: What Will Copenhagen Mean for Tomorrow’s Global Companies?” focused on the possible global business implications of a new climate change accord. Executives joining Mr. Kearney on the panel to share their expertise included:
Yvo De Boer, Executive Secretary, United Nations Framework Convention on Climate Change; Mark Norbom, President and Chief Executive Officer, GE, People’s Republic of China Caio Koch-Weser, Vice-Chairman, Deutsche Bank Group, Deutsche Bank, United Kingdom; and Wu Changhua, Greater China Director, The Climate Group, People’s Republic of China. “Two of the most promising ways the world can drive increased energy capacity while also addressing climate change are increased investments in nuclear power and efficiency improvement technology for the broader power sector,” said Mr. Kearney in addressing the panel. “Nuclear power is proven, safe and emits zero greenhouse gases, while generating the kind of base load power advanced economies require. China is rapidly building new nuclear capacity. The U.S., which has not built a new nuclear plant in 30 years, needs to do the same.
Thanks
William

17. 367
Hank Roberts says:

Stop plopping your stuff in every science topic. Please.

18. 368
stevenc says:

Hank, that’s exactly what I was looking at. The answers to my questions I could not get from the text although perhaps there is something there I am misinterpreting or just missing somehow.

Martin, yes I was confused over the idea that they gave a published date but I now see that would be the published date of the abstract they gave the presentation from and not an indication of being peer reviewed. I actually do look for the peer reviewed labal before buying. Thank you for your thoughful response.

19. 369
20. 370
wili says:

Thanks, Martin V.

So maximum possible drop in sea level would be more like 65mm or so, and probably some fraction of a percent of this for real annual decreases even if considerable amounts are released. I suppose the calculation gets further complicated since much of the methane would be dissolved in the water. Presumably this would increase the volume of the water? Enough to off set the tiny sea level drop?

21. 371

stevenc, yes, Hank’s question, just curiosity: how did you find out about this paper? Did you stumble over it all by yourself?

wili, yes, some 6 cm (your numerical precision is a stretch), corresponding very roughly to 6000 ppm of the atmosphere.

Most of this would be converted quickly, I would assume, to CO2 by reacting with atmospheric oxygen (if not, we’re in even greater trouble). Then we’re already talking CO2 concentrations causing over ten degrees of warming… Then I wouldn’t worry too much about centimetre precision sea level any more ;-)

22. 372
CM says:

Martin, stevenc, (#362, 365),

The reference in the last line of the Shen & al. abstract to “the Dirac large numbers postulate”, in the context of extending their expanding-earth claim from ten years to geological time, sort of trips my crank alarm. But I’m not a physicist.
http://en.wikipedia.org/wiki/Dirac_large_numbers_hypothesis

23. 373
stevenc says:

Martin, I can’t actually remember how I stumbled on the expanding earth page. I was not directed there. The expanding earth was either mentioned in something I was reading causing me to look for more information or this paper showed up in a search I conducted on a different topic. It’s location in my saved list indicates it was probably months ago that I found it.

24. 374
stevenc says:

CM, I took the last sentence as saying that the hypothesis of Dirac’s large number postulate meant that it could have been happening for a long time as opposed to the calculations for the last ten years meaning that the hypothesis was correct.

25. 375
Mark says:

stevenc, I remember reading a paper about how the earth is expanding. By maybe as much as 0.6mm a year.

Can’t remember where I read it or why it’s expanding, but until the IPCC models include a shrinking earth, they aren’t correct.

Now, is that roughly what you have?

26. 376

CM, stevenc, quick calculation:

0.6 mm/yr = 600 km / Gyr = 3000 km since the Earth formed… actually I remember reading about such theories many years ago when I was little. It seems that most of them require that either the strength of gravitation G varies strongly over time, or that the total mass of the Earth does. That would certainly have been noticed in Earth satellite motion, way before the radial expansion itself!

http://en.wikipedia.org/wiki/Expanding_Earth

27. 377
Hank Roberts says:

The ‘expanding earth’ is a notion to explain how the Americas and Europe got separated, from folks who can’t find time in their religious beliefs for continental drift to occur. As an alternative to continental drift, it explains all those parallel lines in the seabed as stretch marks and the matchup between the continent shapes as indicating how much smaller the Earth was when it was created without changing the landforms at all. Kind of like painting them on a balloon, waiting for the paint to harden, then blowing up the balloon.

I first came across it when I was proofreading for a well respected magazine and an editor slapped a caption on a photo of seafloor spreading saying it illustrated the expanding Earth. I know the details in the, er, theory are more, er, elaborate than that. But that’s the idea in an, er, nutshell.

28. 378
Hank Roberts says:

> Dirac’s large number postulate

SttevenC — try looking it up. This should tell you something, I think.

The software here doesn’t handle quoted strings properly so I can’t give you a clickable link, but put the line below into a Google Scholar search box

That searches for all scholarly articles that mention Dirac and this string:

Dirac “large number postulate”

Short answer: nobody else does, just these authors.

They might be talking about — the notion that — over the age of the universe, for values of ‘age’ considerably in excess of 6K years, some physical constants may have varied. Or maybe not. Pretty flaky stuff to be tossing out in any discussion about climate change. Think of the time scales involved.

29. 379
stevenc says:

Hank, actually the material I have read on the expanding earth requires a considerable amount of time. Perhaps there are those that incorporate it in their beliefs and how they do this I am not clear on since I seldom wander into the religious aspects of science.

I would agree that it seems unlikely the hypothesis is correct in it’s entirety. I would be more likely to wonder if periods of expansion and contraction would be possible based on the balance between crust being created and destroyed within the framework of the tectonic plate theory.

30. 380
stevenc says:

Mark, you are confused. “If” the earth is expanding or contracting then it is expanding or contracting regardless of whether it has been given permission to do so or not. Now please stop thowing rocks at me, it does grow tiresome. I am trying to have intelligent conversations and learn things in the process.

31. 381
Mark says:

There is also a “young earther” theory that the world is expanding and that is why the continents are spread as they are: not because of continental drift but because the world is expanding in size.

32. 382
simon abingdon says:

#363 Hank

Be assured there was no “bad info”. I drew false conclusions from my own inadequate knowledge. And I now see how posting might have been misleading and irresponsible. Shall be more circumspect in future. Thanks for the advice. Respectfully, simon.

33. 383
wili says:

There has been some recent discussion about the effects of melting ice sheets on vulcanism as the declining mass shifts the distribution of weight on the tectonic plates (if I understand this correctly).

I was wondering about the other end:

As sea levels rise, should we expect the increased water weight on the continental shelves to cause more earth quakes?

34. 384
Hank Roberts says:

Wili, where do you find this stuff? “There has been some recent discussion” — where?

35. 385
Hank Roberts says:

But, Simon — when you write

“we have not a clue about what is under several kilometres of Greenland or Antarctic icecap”

All you meant to say was that you didn’t know??

36. 386
Hank Roberts says:

Simon, even _this_ guy can show up at the AGU:
http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=ja08&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Fja08%2Fja08&maxhits=200&=%22V31A-06%22
One has to wonder what kind of stuff the AGU rejects, since this made the cut. He’s got a website, even more glorious.

37. 387
stevenc says:

Hank, Robin McKie has an article in the Observer 6 sep 09 regarding melting ice and natural disasters. Perhaps this is the source wili is referring to.

38. 388
CM says:

Re “expanding earth”, it seems their idea is indeed that as the universe ages, gravity weakens, and the planet elastically expands, explaining continental drift without plate tectonics.

Martin #376, your calculation was probably meant ad absurdum. But it seems one L. Egyed (1956?, 1970?) in all seriousness derived the 0.6mm/yr figure over 4.4 billion years from paleogeography data, fitting together bits of the Earth’s crust that could have formed the seamless surface of a far smaller early Earth.

Hank #377, Mark #381, that means it’s not just a young-earther thing. These theories seem to have been fairly respectable in the 1970s, just look at this 1978 textbook. Hank, you will find journal articles and book chapters linking Dirac and expansion.

To sum up, I doubt anyone measuring sea-level rise needs to lose sleep over this one. But contrarian ideas seem to attract each other, so I’m sure it will come up again from the more creative fringes of denialism.

39. 389
wili says:

Sorry, Hank. Here’s the link:

http://volcanism.wordpress.com/2009/09/06/climate-change-scientists-warn-of-tectonic-volcanic-geo-apocalyptic-mega-mayhem/

From the article:

“the disappearance of ice caps will change the pressures acting on the Earth’s crust and set off volcanic eruptions across the globe.”

40. 390
Hank Roberts says:

wili, why not read the link provided there to the university symposium? You could sum up the science if it’s relevant.

41. 391
wili says:

OK, so I looked at the flyer for the symposium, and under session three I found the following:

“Short time-scale drivers of geological and geomorphological hazards

Addresses environmental processes and mechanisms with the potential to trigger geological and geomorphological hazards at short time-scales, which may also have implications for climate modulation of hazardous Earth processes at longer time scales. Examples include tidal, meteorological and ocean loading effects on volcanism and seismicity.”

The last bit suggests that there are or could be tidal and ocean loading effects on volcanism and seismicity. Is that what you wanted me to find?

I have to apologize if I’m just being completely dense, here.

Were you suggesting that issues of possible effects of sea level rise would not be relevant to a discussion of sea level rise? Hey, at least I’m not talking about an expanding earth or endlessly harping on nuclear power;-]

42. 392
Hank Roberts says:

I’m just asking if there’s anything there yet, Willi. Is it a future event? A publication already available? Something with anything we can read? Just a promise of something to come? Named speakers or authors? Look them up in Scholar and see if their papers are available. Do they mention probabilities? climate forcing, how much difference any of these events might make in temperature trends?

43. 393
Hank Roberts says:

Willi, shorter answer: I’m just another reader, I know nothing about it, it’s interesting, you found it, you can probably describe it well enough after you read up on it to attract the attention of a scientist or two to help you. Ask informed and helpful questions, and likely you can to attract their attention.

44. 394
Martin Vermeer says:

wili #383

I was wondering about the other end:
As sea levels rise, should we expect the increased water weight on
the continental shelves to cause more earth quakes?

Wili, most certainly. And there will also be a “wedge effect”: the greater weight on the sea floor will try to depress it, and the displaced material will try to uplift the adjoining continents. But expect all this to be fairly minor.
It is similar to the small tremors that often accompany filling artificial reservoirs. And in Fennoscandia, seismic activity has been attributed by some to the ongoing post-glacial uplift.

45. 395
Martin Vermeer says:

CM #388
> Martin #376, your calculation was probably meant ad absurdum.
Actually, no… just showing how the abstract referred to fitted in with Dirac’s notion of a changing G and expanding-Earth ideas based on (or related to) it.
But yes, the idea itself is absurd based on current knowledge. Like, can you say ‘mechanism’? And plate tectonics, with subduction, is real, period. And then, we now know the universe to be 13.6 Ga old… those ideas could have more traction when the age of the universe was still held to be only slightly more than that of the Earth and Solar system, i.e., 4.6 Ga… crank stuff.

46. 396
CM says:

Wili #383 asked: “As sea levels rise, should we expect the increased water weight on the continental shelves to cause more earth quakes?” Bill McGuire at UCL has been raising that possibility in the popular press (NS, Guardian), making reference to the end of the last ice age. Don’t know about the published science (a Keating and McGuire paper in Adv. Geophysics 47 may be relevant). Presumably after the symposium you link to, more will be known…

47. 397
Mark says:

“The last bit suggests that there are or could be tidal and ocean loading effects on volcanism and seismicity. Is that what you wanted me to find?”

How does that reading make this statement:

“Were you suggesting that issues of possible effects of sea level rise would not be relevant to a discussion of sea level rise?”

Since that earlier prognosis doesn’t say anything about sea level rise and the selected quote from the symposium doesn’t say that tidal is a cause for sea level rise.

The tide is about moving the ocean about. Unless you have some way of keeping the tides high in an area, this doesn’t change sea levels in anything more than the trivial way that waves cause sea level rise.

48. 398
Mark says:

“Hank #377, Mark #381, that means it’s not just a young-earther thing. These theories seem to have been fairly respectable in the 1970s, just look at this 1978 textbook.”

That it was used for valid purposes doesn’t make it not a young-earther thing any more than the “miracle of the eyeball” being used doesn’t mean you’re not facing an IDer.

It *WAS* validly used as a counter to the evolution, but even Darwin had an answer. That someone uses it still is indication enough.

49. 399
Mark says:

“Mark, you are confused. “If” the earth is expanding or contracting then it is expanding or contracting regardless of whether it has been given permission to do so or not”

You’re confused, steven. I haven’t said it needs permission. Need some more straw?

And the earth isn’t likely to be expanding at an average of 0.6mm a year, or even 0.006mm a year. Or century.

“Now please stop thowing rocks at me, it does grow tiresome.”

Please stop talking  because it’s tiresome countering all the half-assed ideas you come up with. “Oh, they don’t have the World Turtle in their model, so maybe they’ve got it wrong with AGW!!!”.

50. 400
stevenc says:

CM, if the Earth expands by 0.6mm per year for a deacade then contracts by 0.6mm per year for the next decade, then the satellites would register that as a 0.6mm decrease in the rise of sea level. I don’t see this as an issue that can be written off based on the numbers. The methodology of the researchers appears to be the real issue but that is difficult to follow for me period and for those that understand it better based on the information available.

Martin, or anyone, did you have any thoughts on the possibility that the Earth may expand and contract based upon the amount of crust being formed and dissolved? I understand it is widely accepted that the Earth has a long term trend of contraction but most trends in nature fail to follow a straight line.