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Comments 124251 to 124300:

124251. Charlie A at 16:03 PM on 10 February 2010
        Working out future sea level rise from the past
        Bern and Berényi Péter, I think that the key is not only the eccentricity, but also the timing of the perihelion with respect to northern hemisphere seasons. This is because changes in albedo over a year cycle are dominated by the changes in the northern hemisphere (the southern oceans don't change albedo much). The perihelion in January when the northern hemisphere has snow cover means that the total energy absorbed over a year is less than it would be if the perihelion was in July. Rather than muck up the explanation any further, I'll just point you to George White's explanation: http://www.palisad.com/co2/eb/eb.html See the section on albedo.
124252. Jeff Freymueller at 15:50 PM on 10 February 2010
        Working out future sea level rise from the past
        I decided to look up some old papers about the loading effect of rising sea level. Farrell and Clark (1976) proposed the classic form of the sea level equation, including the loading caused by rising sea level. Peltier (1994) modified this to include the fact that the extent of the ocean is time-dependent, because water comes up on the shelves, changing what is called the "ocean function" (the ocean function is 1 over the ocean, 0 over land). So the bottom line is that accounting for these effects has been standard for decades. The state of the art has moved past this paper now, but if anyone is interested in finding out more, Peltier's classic 1998 paper in Reviews of Geophysics is a good place to start, and is available free: http://europa.agu.org/?view=article&uri=/journals/rg/98RG02638.xml&t=rg,Peltier
124253. Charlie A at 15:44 PM on 10 February 2010
        Working out future sea level rise from the past
        GFW -- thanks. Makes sense now.
124254. Timothy Chase at 15:23 PM on 10 February 2010
        Could climate shifts be causing global warming?
        Constant Relative Humidity? part II of II Actually it might help to ask what the "assumption" of constant relative humidity is being used for. In a dry adiabat the lapse rate is roughly 9.8 °C per km. In a moist adiabat we might be speaking of 5 °C per km. But in either case the temperature drops with altitude. And what we are concerned with is what happens to the average temperature at the surface as the partial pressure of carbon dioxide increases. As the partial pressure of carbon dioxide increases, the altitude at which a given wavelength of thermal radiation is saturated will likewise increase. As the average altitude at which the spectrum most affected by carbon dioxide is saturated rises so will the effective radiating altitude. Given a positive lapse rate -- whether it happens to be 9.8 °C or 5 °C -- the temperature at the surface must necessarily rise. Generally, it is estimated simply based upon atmospheric column calculations that the temperature will rise by 1.1-1.2 °C per doubling simply as the result of the forcing of carbon dioxide by itself -- with perhaps a 10% margin of error. Now in terms of estimating the effects of the increasing partial pressure of carbon dioxide upon global average temperature not a great deal is going to be riding on whether a specific column of air has a dry or moist adiabat. It is what is happening to the climate system as a whole which matters most -- and somewhat well-behaved global averages will probably be more than enough. And as a matter of fact this is what Soden (2005) was concerned with. Near constancy not with respect to a given atmospheric column or the tropics, but globally over a 20 year period. Please see:

        Although substantial trends in T12 do occur regionally (31, 32), the globally averaged radiance record from HIRS shows little trend over the 20-year period. This lack of trend has been noted in previous studies (21, 33-36) and is insensitive to the intercalibration of the radiance records from individual satellites (21). The model simulations also yield little trend in global mean T12, implying that there is little change in global mean relative humidity over this period. In fact, the modelsimulated anomalies are nearly identical to those obtained if one repeats the calculation of T12 under the assumption of a constant relative humidity change in the model's water vapor field (21). This confirms that both the observations and GCM simulations are, to first order, consistent with a constant relative humidity behavior. pg. 842, Soden et al (4 Nove 2005) The Radiative Signature of Upper Tropospheric Moistening, Science, Vol. 310. no. 5749, pp. 841 - 844

        If you are looking for uncertainties you probably shouldn't be looking at the forcing but rather the feedbacks. Water vapor? For the most part, probably not. This is a large part of what both Soden (2005) and Gettelman (2008) is about. Aerosols? Perhaps. Clouds? Maybe. But that have come out suggest that clouds are a positive feedback. Meanwhile, we probably aren't really that interested in whether a given feedback is positive or negative, but more the climate sensitivity itself. Climate models based upon physical principles are all converging on a value of about 3 °C. A meta-study sythesizing the results of a fair number of studies for the past 420 million years centers on a value of about 2.8 °C. Please see: Dana L. Royer et al. (24 Mar 2007) Climate sensitivity constrained by CO2 concentrations over the past 420 million years, Nature 446, 530-532 A meta-study from the year before synthesizing still other evidence gives us a range of between 1.5-4.5 °C centering on roughly 3 °C. Please see: J. D. Annan, J. C. Hargreaves (2006), Using multiple observationally-based constraints to estimate climate sensitivity, Geophys. Res. Lett., 33, L06704, doi:10.1029/2005GL025259. When a given conclusion is supported by multiple, largely independent lines of argument, the justification for the conclusion is often far greater than what it would receive from any one line of argument considered in isolation from the rest. No one is able to propose a realistic model with a climate sensitivity of less than 1.5 °C -- not even with all the money at Exxon's disposal. Any such model would be incapable of explaining the swings that we see in the paleoclimate record from the glacials to the interglacials. And to a first approximation, forcing is forcing. If the climate system is more sensitive to solar radiation it will be more sensitive to carbon dioxide -- with the surface being warmed by its backradiation. * Bereni Peter states in 42:

        As far as I can see, relative humidity varies wildly in upper troposphere and lower stratosphere on all spatio-temporal scales. Even fractal-like structures are apparent.

        Not so much on a global scale, apparently -- and that is what matters in terms of the argument. Besides, air pressure certainly varies from day to day -- but no hurricane as of yet has been observed that had an air pressure of less than 850 millibars. Not yet, anyway. And the fractal structures that I am aware of in weather are usually the result of self-organized criticality. Turbulence, perhaps. Not some sort of unbounded fractal structures. However, we should actually expect relative humidity to drop over time -- at least in the continental interiors. Oceans have greater thermal inertia than land. Consequently land has been warming more rapidly than ocean. The water vapor content of the atmosphere is primarily the result of evaporation, and as partial pressure at the surface of water increases by roughly 8% for every degree Celsius and roughly doubles for every 10 °C it is the tropical oceans which are most important in determining the water vapor content of the atmosphere. However, as moist air over is carried over land that is warming more rapidly than ocean the relative humidity will drop since the moisture content remains the same. The result? Less precipitation, more droughts and more severe droughts in the continental interiors.
124255. Bern at 15:22 PM on 10 February 2010
        Working out future sea level rise from the past
        Berényi Péter at 03:57 AM on 10 February, 2010 "Yes, definitely. The cancellation is exact, eccentricity variations have no effect on overall solar radiation forcing. Just on its seasonal timing." I beg to differ. The eccentricity does change the total amount of solar radiation. Just not by a huge amount. Dividing a year (orbital period) up into 1000 equal-length segments (about 8.76hrs each), I have calculated the relative total solar radiation input for various eccentricities, based on a simple 1/r^2 relationship between distance from the sun and solar radiation intensity: eccentricity relative radiation 0 1.00000 (circular orbit) 0.0034 1.00001 (min e of Earth's orbit) 0.0167 1.00017 (current e of Earth's orbit) 0.028 1.00045 (mean e of Earth's orbit) 0.058 1.00181 (max e of Earth's orbit) As I understand it, the eccentricity of Earth's orbit is currently decreasing from a value of ~0.02, and is expected to dip to ~0.003-0.004 over the next 20-30ky. The numbers above suggest that eccentricity actually increases mean solar radiation, though the effect is slight (<0.2% at most). This is because the semi-major axis of the orbit doesn't change, which means any increase in eccentricity results in periods where perihelion is closer to the sun, and the inverse square law means the radiation intensity increase at perihelion is greater than the decrease at aphelion, with the difference being about 1% by my reckoning.
124256. Timothy Chase at 15:20 PM on 10 February 2010
        Could climate shifts be causing global warming?
        Constant Relative Humidity? part I of II Bereni Peter wrote in 38:

        Then let me have my question. Why do you _assume_ constant RH?

        I responded in 41:

        As for the "assumption," it is a fairly good approximation of what we actually observe -- and while both dry and moist adiabatic lapse rate are roughly constant, the rate at which temperature changes with altitude is slower with moist air than dry air, so presumably if you had moist air below and dry air above the lapse rate might vary more with altitude. But as I've said, constant relative humidity with respect to altitude is a fairly good approximation.

        *Bereni Peter now asks in 42:

        How is this observation done?

        Nowadays? I would presume along these lines: Nasa JPL CIT AIRS: Water Vapor Multimedia Satellite imaging using multiple channels. Actually I just had to check:

        In this work we will use profile data for humidity and temperature from the Atmospheric Infrared Sounder (AIRS) to analyze how the atmosphere (mostly the upper troposphere) responds to changes in the underlying surface temperature. We equate this variation with a measure of the first part of the water vapor feedback: a change in climate state changes water vapor and its greenhouse effect. pg.3283, A. Gettelman, Q. Fu (1 Jul 2008) Observed and Simulated Upper-Tropospheric Water Vapor Feedback, Journal of Climate, Vol. 21, pp. 3282-9

        AIRS is an impressive machine:

        The 2378 independent channels on AIRS permit retrieval of an entire profile in the presence of up to 70% cloud fraction over the AIRS footprint. ibid.

        Their results?:

        These results from AIRS and CAM simulations indicate that as surface temperatures increase, water vapor in the upper troposphere increases in observations to maintain nearly constant relative humidity. Thus the water vapor feedback is positive, and yields near constant upper-tropospheric RH. Note that RH can decrease even if specific humidity increases as a result of the nonlinear change of saturation vapor mixing ratio with temperature. The result is consistent with analysis by Soden et al. (2005) using a different model and satellite observations of humidity (from the Special Sensor Microwave Imager) and temperature (from the Microwave Sounding Unit and the High Resolution Infrared Radiometer Sensor), indicating that simulated upper tropospheric temperature response over the observed record was similar to observations and to a constant RH assumption. The result is also consistent with the results of Minschwaner and Dessler (2004). The increase in temperature scales is like a moist adiabat, with increases larger at higher altitudes, similar to Santer et al. (2005). ibid.

        * Bereni Peter continues:

        What is the operational definition of "constant" in this context?

        I am afraid I am not much for operationism.
124257. Philippe Chantreau at 15:03 PM on 10 February 2010
        The role of stratospheric water vapor in global warming
        BP, your last statement seems to imply that you're refering to a scientific, detailed analysis of the adjustments, can you give us the reference(s)?
124258. GFW at 14:35 PM on 10 February 2010
        Working out future sea level rise from the past
        Charlie, what you're missing is the first sentence of the abstract. "With polar temperatures ~3–5 C warmer than today, the last interglacial stage (~125 kyr ago) serves as a partial analogue for 1–2 C global warming scenarios." Knopp et. al. (2009) are concluding that 1-2 C of global warming from present would likely increase the rate of sea level rise from the current value (say 3.1 mm/y) to more than 5.6 mm/y and maybe as high as 9.2 mm/y. Without that 1-2 C of warming, there\'s no reason to expect such an increase. Conversely if AGW goes higher, say 3-4 C, one would have to expect sea level rise faster than those numbers. One background point you may not know - the interglacial before the current one just happened to be warmer than this one - that's why it can be used in the way that paper uses it. The reason it was warmer is because the underlying orbital forcing condition was stronger.
124259. GFW at 14:23 PM on 10 February 2010
        Working out future sea level rise from the past
        Jeff, thanks for #54 - exactly the point I was going to make about steeper rise in the last 25 years in Chao et. al. (2008), precisely the era in which the anthropogenic CO2 warming has dominated. I think Arno's comment has been disappeared because he made the exact same comment about Gore on another thread and ignored it when he was cor
124260. Doug Bostrom at 14:00 PM on 10 February 2010
        The role of stratospheric water vapor in global warming
        Berényi Péter at 09:28 AM on 10 February, 2010 "At least in case of surface station temperatures and upper troposphere radiosonde humidity there are considerably more upward adjustments than downward ones." Assuming your assertion about the distribution of individual adjustments is correct, that begs a another question: are more recent records adjusted upward more than older measurements, and as we approach the present do upward adjustments grow still more than all earlier ones? If not, or that is to say unless the adjustments can be shown to produce the trend we believe we see, looking to adjustments of measurements(temperature, tide, whatever) does not have explanatory power for upward trends. To put it another way, if all records through time are adjusted upward by a similar amount, no false upward trend will result. The modern,climate specific term for this pitfall might be termed "Watts' Fallacy".
124261. Charlie A at 13:55 PM on 10 February 2010
        Working out future sea level rise from the past
        From the Kopp 2009 abstract: "When global sea level was close to its current level 10m, the millennial average rate of global sea level rise is very likely to have exceeded 5.6 m kyr-1 but is unlikely to have exceeded 9.2 m kyr-1" If I interpret this correctly, 5.6m ky-1 is an average rate of 5.6mm/yr. Our current sea level rate of rise of around 1.7mm/yr (over all historical record) to 3.2mm/yr (over the shorter satellite record) is well below the 5.6mm/yr natural sea level rise rates expected at this point into the interglacial. We should therefore expect an significant acceleration of the sea level rate of rise, with or without anthropogenic global warming. Is this interpretation incorrect somehow?
124262. Jeff Freymueller at 13:45 PM on 10 February 2010
        Working out future sea level rise from the past
        Arno Arrak, what is different is that today Greenland is losing significant amounts of ice. Based on multiple independent data sets, by the way. It was not in the 1990s and before. Antarctica as a whole is most likely losing ice. In the 1990s and before it was not, as far as we could tell. So things HAVE changed. Chao et al. (2008) looks like a very solid paper, and you can see a plot of their sea level curve in the reply to comment #10. Prior to their work, there were unexplained real or apparent changes in rate in the middle of the 20th century. They showed that these could be explained by water impounded in reservoirs, which is the context of their linear fit. But look at the last 25 years of the data -- the trend is clearly steeper than average, and that is where you find the largest residuals to their linear fit. It appears that Chao et al did not test whether a model with a break in rate in the 1980s would be statistically justified based on the data or not -- they did not report on it or even hint that they tried it. This was not the focus of their paper, and certainly their conclusion does not rule out the possibility of recent acceleration in rate, as they stated explicitly in the last paragraph of the paper.
124263. Jeff Freymueller at 12:54 PM on 10 February 2010
        Working out future sea level rise from the past
        Slightly misspoke in my post #52. It is irrelevant to the acceleration, but not the whole reconstruction. But check out page 11 of Church 2008, and my first posting. The loading effect of sea level rise is included in the GIA modeling. For details, you would have to track back through previous papers.
124264. Jeff Freymueller at 12:36 PM on 10 February 2010
        Working out future sea level rise from the past
        #49 thingadonta, that effect can contribute to the average rate of sea level rise, but has no effect on changes in rate (acceleration) on the timescale of a century or two. Almost all of that sea level rise happened 6000 years ago or earlier, so the change in subsidence rate today due to that load is really, really tiny. It is irrelevant to the subject of Church 2008.
124265. SNRatio at 12:34 PM on 10 February 2010
        Working out future sea level rise from the past
        Look at the Antarctica situation - ice loss is accelerating there now. We don't know if it is a transient phenomenon, but we know that we are surprised. We also know that we have had sea level rise during years of little surface temperature increase, indicating imbalances. It takes very little acceleration to reach around 1m rise by the end of the century, and in fact we don't know if the forcing already in place will be enough. Fitting an exponential model, t=0 in 1900, L(0)=-5 L(t)=Lo+a*exp(kt) with the historical data plotted above, I get (R quickie) a=2.1, k=0.02 for L in cm. And L(200)=121 cm, ie 126 cm above 1900 level in 2100. For such a short time span and relatively modest rises, this process is perfectly possible. Of course, the 2.6 cm/year rise predicted from 2099 to 2100 by this "model" may seem extreme compared to the present rate of about .32 cm/year, but compare that to the rate of about 0.07 cm/year in the 1890es. Which, apart from some possible land use/GHG modifications should be the "natural" sea level rise in the "LIA recovery". Then somebody might say "exponential processes don't occur in relevant contexts in nature". Really?
124266. Jeff Freymueller at 12:27 PM on 10 February 2010
        Working out future sea level rise from the past
        One final point. Individual tide gauges have a LOT of variation that comes from things other than eustatic sea level rise. Most of these variations are not noise, strictly speaking. They are regional and local oceanography; real variations, but not what you want to tease out of the time series. It is VERY difficult to detect an acceleration in rate in any one such time series because you are not modeling those other variations but only treating them as statistical noise, and you should not expect to be able to do that with a few decades of data. It takes either averaging over the whole ocean (the altimetry approach) or averaging over several decades (best you can do with the tide gauges).
124267. thingadonta at 12:20 PM on 10 February 2010
        Working out future sea level rise from the past
        There doesnt seem to be any reference in Church 2008 to near-coastal isostatic adjustment to an extra 120-130m of water over the continental shelves since the last glacial maximum. Long coastlines (eg both sides of the Americas), areas of wider continetal shelves (eg Argentina), and shallow seas (Gulf of Carpentaria, Meditteranean, Bass Strait etc), and particularly those with weakly lithified strata/sediments, should display a measurable/partly predictable isostatic adjusment to an extra ~130m of water. Since the time lags of glacial rebound is long (still continuing), one would expect downward subsidence of coastal shelves to also be rather long. It might only be in the order of ?cms/thousand years, but it might still be occuring, or at least recuring since the rise in sea level in recent centuries. There doesn't seem to be any referance to this possible effect in Church 2008.
124268. Jeff Freymueller at 12:17 PM on 10 February 2010
        Working out future sea level rise from the past
        #29 Berényi Péter says that Church does not say which tide gauge set was used. But you have to follow up the references. It is clear from the text that they followed the method of Church and White (2006), which in turn followed Church et al. (2004), which outlines the selection procedure. They did not simply average over tide gauges. They used the tide gauge data with a decade-plus of satellite altimeter data. Specifically, they used the spatial correlations of the altimeter data to construct empirical orthogonal functions that they could use with the longer tide gauge record to reconstruct global sea level rise. if you want more details, read the papers. As for the satellite data, rather than respond to blanket statements I suggest checking out Steve Nerem's sea level pages at the University of Colorado: http://sealevel.colorado.edu/. The various links describe the calibrations and let you interactively explore the data. As for acceleration or not, focusing only on tide guages is a bit myopic. The altimetry is calibrated against the tide gauges and agrees with them at those points, but averages over (nearly) the entire ocean instead of just a few discrete points on the coasts. The rate from altimetry (1992-present) is 3.2 +/- 0.4 mm/yr, compared to 1.8 mm/yr for the 20th century from tide gauges. I don't recall the 20th century rate error bar off the top of my head, but the two estimates are distinct at a high level of confidence. And if you look at the altimetry time series you will see that the trend is fairly steady over nearly 20 years, aside from seasonal variations due to mass exchange between continents and oceans (think snow).
124269. Jeff Freymueller at 11:59 AM on 10 February 2010
        Working out future sea level rise from the past
        @thingadonta, #13. Yes, the loading effect of rising sea level can be important in determining sea level rise locally, and it is included in recent work. I'm not sure if the original sea level equation as outlined by Peltier in the 1970s accounted for it, but certainly everyone working on the problem accounts for it. If you look at recent papers by Jerry Mitrovica, in particular, you'll get a good idea of the state of the art, which includes the rebound of the sea floor that results from melting the ice, and also the change in shape of the earth that results from shifting the pole of rotation (slightly) as the mantle rebounds.
124270. GFW at 11:08 AM on 10 February 2010
        Working out future sea level rise from the past
        Oops, I badly miscalculated my second scenario. If I start at 3.1 mm/y increasing at 2%/y, but each year the % goes up by 0.05% (so it's 2.05% in year two, 2.1% in year three, etc.) after 90 years, total rise is 2274 mm! Trying to tone that down a bit ... If I start at 3.1 mm/y increasing at 1.5%/y, but each year the % goes up by 0.03% (so it's 1.53% in year two, 1.56% in year three, etc.) after 90 years, total rise is 1041 mm.
124271. GFW at 11:00 AM on 10 February 2010
        Working out future sea level rise from the past
        A quick experiment in Excel using a non-linear (exponential) model: If I start with a sea level rise of 3.1 mm/y, increasing by 2%/year for 45 years, then by 3%/year for 45 years, I get 930 mm by the end. Let me try a smooth variation in the strength of the exponential ... If I start again at 3.1 mm/y increasing at 2%/y, but each year the % goes up by 0.05% (so it's 2.05% in year two, 2.1% in year three, etc.) after 90 years, total rise is 1210 mm I'm not saying that's exactly what will happen, but it's very plausible under business-as-usual emissions.
124272. GFW at 10:41 AM on 10 February 2010
        Working out future sea level rise from the past
        Berényi Péter, I have a couple of useful points for you. Much of North America is still rebounding from the weight of the gigantic Laurentide ice sheet that once covered it. However, the eastern seaboard of the US was not so covered and thus was elevated ("forebulge effect") by the same glacial weight that depressed land further inland. So that part of the US is now sinking. Now probably most US tide gauges are on the east coast (way more people) so if the forebulge relaxation rate is (a) noisy, or (b) decelerating, it would easily obscure any sea level rise acceleration so far. There is no reason to expect that the rate of acceleration during the 21st century will be a constant, nor that the 20th century would share that acceleration. It is only since the 1970s that AGW has started to dominate other climate signals. The temperature is still going up, and the amount of temperature rise "still in the pipeline" is also still going up. The real kicker though is the dynamic ice sheet effects whereby due to local geography, a tipping point can be reached dramatically accelerating basal melt rates. Greenland is kinda bowl shaped, and once the melt gets past the surrounding ring of mountains, it's very likely to speed up a lot.
124273. Riccardo at 09:47 AM on 10 February 2010
        The role of stratospheric water vapor in global warming
        Berenyi Peter, here is the graph or you may like to read the whole procedure
124274. Riccardo at 09:38 AM on 10 February 2010
        Working out future sea level rise from the past
        Berenyi Peter, #7 in #17 John already pointed you to a relevant article if you dare reading it. You claim the opposite with no reference but a bunch of irrelevant local data. Accusing me of appealing to authority is absurd, let alone invoke working through understanding and invite people "to understand first what was said".
124275. Berényi Péter at 09:28 AM on 10 February 2010
        The role of stratospheric water vapor in global warming
        Riccardo at 22:59 PM on 9 February, 2010: "corrections made to the raw readings can be up or down, globally they average to zero" No, they are not. At least in case of surface station temperatures and upper troposphere radiosonde humidity there are considerably more upward adjustments than downward ones.
124276. Berényi Péter at 08:53 AM on 10 February 2010
        Working out future sea level rise from the past
        doug_bostrom at 04:48 AM on 10 February, 2010: "Dense but satisfying, like a high quality chocolate cake" It is. The section relevant to the present discussion can be found here in html: IPCC Fourth Assessment Report: Climate Change 2007 Climate Change 2007: Working Group I: The Physical Science Basis 5.5.2.4 Interannual and Decadal Variability and Long-Term Changes in Sea Level http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch5s5-5-2-4.html "Interannual or longer variability is a major reason why no long-term acceleration of sea level has been identified using 20th-century data alone (Woodworth, 1990; Douglas, 1992). Another possibility is that the sparse tide gauge network may have been inadequate to detect it if present (Gregory et al., 2001). The longest records available from Europe and North America contain accelerations of the order of 0.4 mm yr–1 per century between the 19th and 20th century (Ekman, 1988; Woodworth et al., 1999). For the reconstruction shown in Figure 5.13, Church and White (2006) found an acceleration of 1.3 ± 0.5 mm yr–1 per century over the period 1870 to 2000. These data support an inference that the onset of acceleration occurred during the 19th century" If we accept the high end value for acceleration given by Church and White (2006) for a 130 year interval, it is 0.018 mm/y^2. Should this acceleration continue, by the end of this century it would give an additional 81 mm rise to whatever linear trend already exists. The low end value would work out to be 36 mm, while Ekman (1988) & Woodworth et al. (1999) gives 18 mm. Not scary. Acceleration should somehow increase at least tenfold in the near future to cause harm. However, we are not talking about contingencies here, but foresight based on past observations.
124277. Berényi Péter at 08:08 AM on 10 February 2010
        Working out future sea level rise from the past
        Riccardo at 05:06 AM on 10 February, 2010: "you keep making assumptions without even noticing" Riccardo, try to understand first what was said, please. Having done that it is much easier to proceed. 1. It has nothing to do with the US being one nation under God. If there is no long term acceleration in US coastal tide gauge station signals and sea level rise is still accelerating, it implies the entire US is accelerating upward. Most unlikely. 2. I was not talking about "recent" acceleration, but supposed acceleration during the last century. Anyway. What should recent acceleration mean with all this internal variability? We are trying to make long term predictions, so the high frequency part of the signal has to be removed. 3. The average rate of sea level rise at individual stations has nothing to do with acceleration. First and second derivative are not the same. 4. There is no need to correct for vertical land movement if you are interested in acceleration. The only hidden assumption is that vertical acceleration of crustal segments, either positive or negative, are negligible on this time scale. Should be true for most US coastal locations, except some tectonically active regions perhaps (like California). Mantle viscosity is a bit higher than that of seawater. 5. I do not _assume_ that sea level rise is linear, I prove it. Of course I neglect both temperature and glaciers in this study. They have nothing to do width tide gauges. A tide gauge can work pretty well, provided the water column in it does not get frozen. If that happens, some data points are lost. 6. I do like satellites. They are wonderful devices. But they need calibration as any other device and errors just happen. There is no law of nature stating the quality of satellite data is always superior to in situ measurements. You always have to check the details. And it is inherently more difficult to see things from a distance accurately, isn't it? This is why one has a closer look if interested in something. 7. I dare you to show increase in rate of sea level rise using tide gauge data. Simple pronouncement is not enough. To appeal to authority is impermissible. Science is supposed to work through understanding.
124278. Berényi Péter at 06:33 AM on 10 February 2010
        Could climate shifts be causing global warming?
        Timothy Chase at 03:31 AM on 10 February, 2010: "it [constant RH] is a fairly good approximation of what we actually observe" How is this observation done? What is the operational definition of "constant" in this context? As far as I can see, relative humidity varies wildly in upper troposphere and lower stratosphere on all spatio-temporal scales. Even fractal-like structures are apparent.
124279. Riccardo at 05:06 AM on 10 February 2010
        Working out future sea level rise from the past
        Berenyi Peter, you keep making assumptions without even noticing and make a kinematic analogy which is, again unsupported. But there's more. - You quoted just US costal stations, great nation but it's not the whole world - 50 years averaging smooth everything out, the recent acceleration would disappear anyway. - you didn't notice that many of those stations show higher rates than the numbers you use and some show a decreasing trend, there must be more than just this. - even if not explicitly stated, there is no correction for vertical land movements - global sea level rise is not linear in time as you assume. The zeroth order aproximation says it's linear in temperature (neglecting glaciers and ice sheets). We can make anything aproximately linear but need to understand what we're doing. - your last claim ("No meaningful acceleration of sea level rise is detected in last century") is not true. Even with just tide gauges (you don't like satellites, do you?) there has been an increase in rate. - your conclusion is consequently wrong You keep trying to dismiss science with a few random observations. Using our own knowledge to understand what science says is a good thing, but we should be well aware of our limits.
124280. Doug Bostrom at 04:48 AM on 10 February 2010
        Working out future sea level rise from the past
        You can get an excellent snapshot of difficulties with measuring sea level as well as the challenges of picking up any possible acceleration, warts and all, here at the IPCC AR4 WG1 report chapter 5: Observations: Oceanic Climate Change and Sea Level Dense but satisfying, like a high quality chocolate cake. The moral of the story is, we should have gotten our best instrumentation in place before setting fire to all the fossil fuel. Sure would have made things easier, but it's still not impossible to tease out useful information.
124281. Doug Bostrom at 04:18 AM on 10 February 2010
        The role of stratospheric water vapor in global warming
        Berényi Péter at 21:33 PM on 9 February, 2010 I don't find your argument persuasive, though as always you've provided me some enlightenment on things I might never have known. Thank you.
124282. Berényi Péter at 03:57 AM on 10 February 2010
        Working out future sea level rise from the past
        RSVP at 02:59 AM on 10 February, 2010: "are you saying" Yes, definitely. The cancellation is exact, eccentricity variations have no effect on overall solar radiation forcing. Just on its seasonal timing.
124283. Berényi Péter at 03:51 AM on 10 February 2010
        Working out future sea level rise from the past
        Riccardo at 01:17 AM on 10 February, 2010 "the single gauge data are pretty noisy, the linearity is just the lowest order aproximation. Taking that as given is hardly justifiable" Turns out part of the job is already done. NOAA Tides & Currents has "Variation of 50-Year Mean Sea Level Trends" for 25 US sites. http://tidesandcurrents.noaa.gov/sltrends/50yr.shtml?stnid=8574680&name=Baltimore&state=Maryland (scrool down on page for more) These graphs are much less noisy and they also have pretty error bars. They are not about sea level, but rate of change (in mm/y) averaged for fifty years intervals. Absolute values can safely be ignored for our purposes, it is the slope that counts. If it is increasing, it means acceleration. Let's calculate backwards. If current sea level rise rate is 3 mm/y and sea level is supposed to increase by 1 m (1000 mm) till the end of this century, the acceleration is 0.18 mm/y^2. With this acceleration at 2100 the instantaneous rate of sea level rise would be more than 19 mm/y (almost 2 cm). If this acceleration is projected back to the XX. century, with the CO-OPS graphs spanning fifty or so years the average increase would be some 9 mm/y from beginning to end. Nothing like that is observed, not even close, not for a single site. Tha actual acceleration can't be more than one tenth of this value, probably less. Current 3 mm/y average increase rate is also doubtful. No meaningful acceleration of sea level rise is detected in last century, based on past history 1 m rise by end of this century is dismissed.
124284. Timothy Chase at 03:43 AM on 10 February 2010
        Could climate shifts be causing global warming?
        I had written in 35:

        Consequently a parcel of air will expand and in expanding it will lose potential energy and cool. And assuming a constant relative humidity, the rate at which temperature decreases with increasing altitude - known as the lapse rate - will remain roughly constant under an enhanced greenhouse effect.

        Bereni Peter wrote in 38:

        thank you for the thorough discussion of radiation issues. I would never have the patience. Then let me have my question. Why do you _assume_ constant RH?

        Thank you for the compliment. As for the "assumption," it is a fairly good approximation of what we actually observe -- and while both dry and moist adiabatic lapse rate are roughly constant, the rate at which temperature changes with altitude is slower with moist air than dry air, so presumably if you had moist air below and dry air above the lapse rate might vary more with altitude. But as I've said, constant relative humidity with respect to altitude is a fairly good approximation.
124285. Timothy Chase at 03:31 AM on 10 February 2010
        Could climate shifts be causing global warming?
        Thank you for putting the graphics up John. But I wouldn't necessarily recommend it with what is below... I found something else that may be of interest: a movie showing monthly global carbon dioxide distribution for the months September 2002 to July 2008. Please see:

        The AIRS data show the average concentration (parts per million) over an altitude range of 3 km to 13 km, whereas the Mauna Loa data show the concentration at an altitude of 3.4 km and its annual increase at a rate of approximately 2 parts per million (ppmv) per year. Aqua/AIRS Carbon Dioxide with Mauna Loa Carbon Dioxide Overlaid http://svs.gsfc.nasa.gov/vis/a000000/a003500/a003562/

        Given the fact that measurements are being taken from 3 km to 13 km, at any given time a great deal depends upon the path of the jetstream -- the influence of which you can see in the movie. Likewise you can see the seasonal variation as plants in the northern hemisphere take up carbon dioxide in the spring and summer months and release it in the fall and winter months. They have also overlaid the daily counts an Mauna Loa.
        Response: That animation of CO2 distribution from 2002 to 2008 is an even clearer visual depiction of what's happening with CO2 levels, thanks again! I figured this would surely be on YouTube and sure enough, it is. I've embedded it below and also tweeted the YouTube URL.
        
        
124286. RSVP at 02:59 AM on 10 February 2010
        Working out future sea level rise from the past
        Berényi Péter Please picture a diagram of an ellipse with its major axis horizontal, and with the Sun situated at one focus. Now draw a vertical line where the Sun is. I am sure you would agree that the Earth would be spending more time on one side of the line than on the other. More time on the "cooler" side, and less time on the "hotter" side. The more eccentric the orbit, the more pronounced this effect (however small it may be). Or are you saying that the energy loss and storage rate is perfectly compensated by 1/r^2?
124287. Ani at 02:23 AM on 10 February 2010
        Could climate shifts be causing global warming?
        Just a technicians point of view. Climate shifts would just be the earth trying to reach an equalibrium. Seems rational to me, but the very first post describes what looks like is happening. So it seems to me they cannot account for global warming in the long run.
124288. Berényi Péter at 02:22 AM on 10 February 2010
        Could climate shifts be causing global warming?
        Timothy Chase at 16:49 PM on 9 February, 2010: "assuming a constant relative humidity" Timothy, thank you for the thorough discussion of radiation issues. I would never have the patience. Then let me have my question. Why do you _assume_ constant RH?
124289. andrewcodd at 02:12 AM on 10 February 2010
        Working out future sea level rise from the past
        In response to #2. Wouldn`t it be that flat ice shelves displace less water than the same volume of chunky shaped ice? I guess newest ice shelves form a flat skin and grow thicker. Older ice shelves may displace more water. Displacemet should be measured not just by looking at ice sheets and shelves but looking at each age strata, the daily, anual, other cyclical and geological scales.
124290. Riccardo at 01:22 AM on 10 February 2010
        Working out future sea level rise from the past
        neilperth, to answer your question one should have the crystal ball. All the projections for the end of the century assume no varyiation in natural forcing (sun and volcanoes).
124291. Riccardo at 01:17 AM on 10 February 2010
        Working out future sea level rise from the past
        Berényi Péter, the single gauge data are pretty noisy, the linearity is just the lowest order aproximation. Taking that as given is hardly justifiable. This clearly brings you to assume that "most show no sign of acceleration", "appending possibly ill-calibrated satellite data", "a small piece does not fit into the broad picture, the whole thing is doomed to collapse.", etc. They all depends on the first unjustified assumption. Altough a bit more sophisticated is the same thing as saying ehi, in my place temperature rose then "the whole thing is doomed to collapse".
124292. Ani at 01:12 AM on 10 February 2010
        Working out future sea level rise from the past
        I appreciate articles like this because it gives us one more tool to use and try to forecast the sea level rise. Thats science advancing to the next level. To me this shows that reality is setting in. If you live in Miami Beach and increasing rates of buildings and homes flooding, it doesnt matter if you believe in warming or not. Tough choices ahead for the next generation.
124293. Berényi Péter at 01:01 AM on 10 February 2010
        Working out future sea level rise from the past
        RSVP at 20:21 PM on 9 February, 2010: "I do not see it this way" You should. Semimajor axis of a planetary orbit is pretty stable, not subject to perturbations. Orbital period T depends on semimajor axis, also constant. Eccentricity can vary. According to Kepler's second law of planetary motion "the line joining a planet and the Sun sweeps out equal areas during equal intervals of time". That is, r^2w=const (r is distance to Sun, w angular velocity). Incoming solar radiation flux is proportional to 1/r^2, also proportional to w. Integrating w from 0 to T, i.e. for an entire orbital period lends 2Pi, which does not depend on excentricity.
124294. neilperth at 00:25 AM on 10 February 2010
        Working out future sea level rise from the past
        Sea level rise during the last interglacial was due to natural causes. What is the outlook for sea level rises or falls due to natural causes in the future ?
124295. Berényi Péter at 00:23 AM on 10 February 2010
        Working out future sea level rise from the past
        Hostmaster response to Berényi Péter at 18:37 PM on 9 February, 2010: "the one thing most skeptic arguments have in common is a tendency to focus on narrow pieces of the puzzle rather than step back and take in the broader picture" I know. "Now faith is the substance of things hoped for, the evidence of things not seen. For by it the elders obtained a good report" (Hebrews 11:1-2) http://etext.virginia.edu/etcbin/toccer-new2?id=KjvHebr.sgm&images=images/modeng&data=/texts/english/modeng/parsed&tag=public&part=11&division=div1 Is that what you mean? Well, not even peer reviewed scrip is scripture. And it is rather healthy to have a look of your own, whenever parcticable. In science sheer authority is not in high esteem. The tide gauges I was referring to are not just a random cherry-picked set, but 45 NOAA/CO-OPS operated GLOSS-LTT (Long Term Trend) gauges and 114 PSMSL (Permanent Service for Mean Sea Level) ones. Spatial coverage is reasobnable. Church 2008 does not state which tide gauge set was used to calculate multidecadal global sea level trend in that paper. If this one, we've got a problem. If not, the selection has to be specified & justified. Yes, the problem we have got. Linear trend of said tide gauge set varies between wide margins. However, most show no sign of acceleration. If you take the average of several linear functions, the linearity is preserved. So. To squeeze out an accelerating trend from these data, some nonstandard nonlinear averaging procedure is needed. Nothing of the kind is mentioned in Church 2008, except appending possibly ill-calibrated satellite data to historic tide gauge series. The only other option is to suppose an aligned ever diminishing sinking rate for all coastal regions which will turn into swelling eventually. So, compared to them the accelerating sea level rise accidentally looks linear. Scary enough, but unlikely. Also, Earth-swelling can't be man-made. "Broader picture" is not for science, it is for journalists. In this realm of human endeavor if a small piece does not fit into the broad picture, the whole thing is doomed to collapse. This kind of method is called analytic, a rather ruthless procedure. It would be nice to have these tide gauge data in tabular numeric format. Anyone?
124296. Andreas at 23:39 PM on 9 February 2010
        The role of stratospheric water vapor in global warming
        Looking at figure 3, it seems to me that the slight dip in forcing due to changes in stratospheric water vapor may explain the perceived lack of global temperature rise just after 2000. In the case such an explanation is viable, it would actually strengthen the case for antropogenic global warming. (but in reality I guess it's more complex than that.)
124297. Riccardo at 23:26 PM on 9 February 2010
        Working out future sea level rise from the past
        stevecarsonr, i'd like to add my opinion about how to deal with skeptics. I think the response strongly depends on the attitude they show in the comment. If you ask questions i think you will easily find answers, more informations to think about, and this will improve your knowledge and contribute to form your personal opinion. The latter may well different from what other people here think, but it's ok. If, instead, you show up here just to counteract our host's opinion you will easily get harsh replies. It also generates confusion in the readers because the discussion tend to polarize on yes or no, true or false, instead of strength and weaknesses or on what some data may tell us. Is it plausible that the so called "consensus view" is wrong in general _and_ in all the details? It is really unproductive when people always say no.
124298. CBDunkerson at 23:15 PM on 9 February 2010
        Working out future sea level rise from the past
        Bruce Cooke, you can find a good summary of sea level rise during the current interglacial here; http://www.giss.nasa.gov/research/briefs/gornitz_09/ As in the plot at the top of the article the zero baseline is the current sea level. Recent changes are tiny in comparison to the increase after the last ice age ended, but accelerating as shown in the graphs John attached to comment #10.
124299. Jesús Rosino at 23:13 PM on 9 February 2010
        Working out future sea level rise from the past
        #25 Bruce Cooke, There's one in Wikipedia: http://en.wikipedia.org/wiki/File:Post-Glacial_Sea_Level.png Comparison with 20th century and satellite-measured trends: http://www.theoildrum.com/uploads/12/holocene_with_29.jpg *Another one here: http://geology.uprm.edu/MorelockSite/morelockonline/3_image/holcrv.gif
124300. Riccardo at 22:59 PM on 9 February 2010
        The role of stratospheric water vapor in global warming
        Berényi Péter, you representation of how undocumented jumps are corrected for is inaccurate, they do not just trivially get rid of them by shifting the data on one side of the jump whenever one shows up at a single station. You should also be aware that the corrections made to the raw readings can be up or down, globally they average to zero.

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