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Doug Bostrom at 05:06 AM on 11 February 2010The role of stratospheric water vapor in global warming
Berényi Péter at 02:19 AM on 11 February, 2010 Here's a paper with a fairly comprehensive description of modern methods: Improvements to NOAA’s Historical Merged Land-Ocean Surface Temperature Analysis (1880-2006) Older but with some digestive aids: An Overview of the Global Historical Climatology Network Temperature Database -
Doug Bostrom at 04:29 AM on 11 February 2010Skeptical Science now an iPhone app
Echoing Jack Kelly, a genius move. Portable improvement of any discussion of this topic. -
Jeff Freymueller at 04:18 AM on 11 February 2010Working out future sea level rise from the past
#69 thingadonta, I have no idea if there is a general relationship between swell size/height and phase of the moon, either regionally or globally. Sounds interesting, and possibly testable. I think there are some sea state measurements that are made by satellite, based on the scattering properties of the ocean surface (roughness, basically). But I don't know where one would go to find such data. -
Jeff Freymueller at 04:07 AM on 11 February 2010Working out future sea level rise from the past
#66 Berényi Péter: "Could you just copy-paste the list of tide gauge station identifiers used in the Church et al. (2004) calibration procedure along with a pointer to full sea level histories of those gauges?" They show the stations used in a series of figures, not a list. But I was able to get Church et al. (2004) for free from home, so I think you can get that paper (the later one requires a subscription). The 2004 paper is in Journal of Climate. As for the data, they got all the data from the Permanent Service for Mean Sea Level (http://www.pol.ac.uk/psmsl). I think their entire catalog is freely available. -
scatter at 03:54 AM on 11 February 2010Skeptical Science now an iPhone app
Nice one! I'll echo the request for an Android version. Check out http://isites.us for easy Android app dev -
jonny_eh at 03:06 AM on 11 February 2010Skeptical Science now an iPhone app
Awesome stuff. But why do you require firmware 3.1.2? I'm still on 3.0.1 because of some bugs I've encountered with the later firmware. Plus, there are still iPod Touch users on the 2.x firmware since it costs them $10 to upgrade.Response: The app has just been updated on iTunes with a new version 1.0 that works on firmware 3.0. Thanks for the feedback. -
Bodo at 03:00 AM on 11 February 2010Climate sensitivity is low
Hello! You could add that Schwartz updated and corrected (in some aspects) his analysis. He now claims that climate response time is 8.5 ± 2.5 years. According to this climate sensivity is 1.9 ± 1.0 K. http://www.ecd.bnl.gov/pubs/BNL-80226-2008-JA.pdf Thus his estimate of climate sensitivity now is at the lower bound of the IPCC range.Response: Thanks for the link, I wasn't aware of Schwartz' response and have updated the article accordingly. -
Berényi Péter at 02:57 AM on 11 February 2010Working out future sea level rise from the past
#70. RSVP "Kepler didnt have computer" He didn't have an electric toothbrush either. So what? -
Berényi Péter at 02:19 AM on 11 February 2010The role of stratospheric water vapor in global warming
#73. Riccardo at 09:47 AM on 10 February, 2010 "here is the graph" Wow. I still have to look into the details. Any idea why the number of surface stations in GHCN dropped so dramatically from its 1970 peak value of 9403 to a feeble 1137 in this year? Looks like 88% of the stations are lost. This is the smallest number in the last 120 years. $ wget http://www1.ncdc.noaa.gov/pub/data/ghcn/v2/v2.mean.Z $ gunzip -c v2.mean.Z | cut -c13-16 | sort | uniq -c -
Riccardo at 02:08 AM on 11 February 2010Working out future sea level rise from the past
thingadonta, here's a picture -
Riccardo at 02:03 AM on 11 February 2010Working out future sea level rise from the past
thingadonta, it's the combined effect of the moon and the sun. It has been know for millennia and anyone living by the sea is well aware of it. -
stbloomfield at 00:54 AM on 11 February 2010Skeptical Science now an iPhone app
Add me to the "Android please" group! -
RSVP at 00:31 AM on 11 February 2010Working out future sea level rise from the past
"Berényi Péter Don't do that, please. Sice J. Kepler (1609) the issue is settled." Kepler didnt have computer. Besides, even Kepler didnt say this, as he was only talking about conservation of angular momementum. -
thingadonta at 00:06 AM on 11 February 2010Skeptical Science now an iPhone app
I wonder if we will get the same from Anthony Watts and co, he keeps me well informed on snow levels at various climate conventions etc. -
pdt at 00:05 AM on 11 February 2010Skeptical Science now an iPhone app
Android version would be great! -
thingadonta at 00:01 AM on 11 February 2010Working out future sea level rise from the past
re#60: thanks Jeff, I was just wondering whether anybody had looked at it-ie the loading effect of rising sea levels. So it seems they have. It would have more bearing on eg flooded river deltas and such. Something else which is probably way off topic (I have always been interested in unusual oceanic features), various natives/locals/fisherman I have come across in the Indian Ocean are adamant that ocean swell size increases with the new moon. This assertion I have heard from areas separated by long distances and cultures. (They might also believe it increases at the full moon, but I havent heard it). I might just have dismissed this, excpet that they were usually right, at least in the short times I was there. Probably has nothing to do with changing sea levels (unless there is some sort of lunar-swell-tide relationship/cycle which has also changed over years/decades/centuries), but I doubt it. Just thought it was interesting. I have no real idea why they ?might be correct in their observation (?ocean current changes?, wind/swell energy combining with lunar tides??). -
Berényi Péter at 23:59 PM on 10 February 2010Working out future sea level rise from the past
#67. SNRatio Of course at least I. Newton (1687) is needed to handle the perturbation issue. The mathematical methods to treat effects of small orbital disturbances adequately took some time to develop even after that (a century or two) and with recent emergence of chaos theory, it is not finished yet. However, the case of eccentricity changes in Earth's orbit is simple. The main players are Jupiter & Saturn. Both have nearly circular orbit, Earth as well. Earth's orbit is also tiny compared to those of giant planets. Disturbances from forces other than radial cancel pretty well and radial forces do not change orbital angular momentum, so they leave orbital period alone. Q.E.D. -
Berényi Péter at 23:02 PM on 10 February 2010Could climate shifts be causing global warming?
Timothy, thank you for the long elaboration. However, it raises more questions than it answers. I would rather not overrun you with all of them in a sigle batch. If you would bear with me, I am going to serialize them. As a first remark. I am not stressing the ontological bases of operationism, in fact I am a realist (in medieval sense). However, an exact description of operations to get values for certain quanities is indispensable for quality assurance & debugging purposes, especially in calibration and remote sensing. http://en.wikipedia.org/wiki/Operational_definition For example remote sensing of atmospheric water vapor by satellites at first sight requires the solution of the unsolvable. Given the spatio-temporal distribution of pressure, temperature, humidity, trace gases and all the other ingredients of some relevance, it is a straightforward(?) process to calculate radiance spectra at TOA. However, in practice it should be done the other way around. You first measure radiation, then look for a distribution of state variables that would produce the same radiation signature. Unfortunately the transformation is not reversible, that is, a multitude of distributions can produce the very same radiation. The tricky part is to restrict the definition domain so as to make the transform invertible. It is done by constructing a model that does not allow for just any combination of state variables, but only a tiny subset, and if you are lucky, all states conforming to model would generate different radiation output. As you can see, a plethora of a priori assumptions go into choosing the particular model used to calculate atmospheric state backwards from radiance measurements. The question is what are the most important hidden assumptions behind model building for remote sensing purposes? How uniqueness is secured? To what extent "measured" (actually: calculated) values are dependent on model? -
Ned at 22:38 PM on 10 February 2010Skeptical Science now an iPhone app
That's fantastic, John. Thanks to you and to the people at Shine Technologies for doing this. Speaking of Tim Lambert and the debate ... someone could turn his global warming skeptic bingo game into an iPhone app. Then anyone with an iPhone could bring it to an event like the Lambert/Monckton debate and compete to see who gets the first "bingo". -
SNRatio at 22:25 PM on 10 February 2010Working out future sea level rise from the past
65 BP: You might be well advised to take the step further to Newton. Kepler settled the issue in a kinematical sense, not a dynamical - that was Newton's contribution. You are making the tacit assumption that wr^2 = L = const independent on eccentricity e. In the case of Earth, I guess we must assume the total energy E=T+V is approximately constant, e varying. Solving this equation for L, is it still independent on e? I haven't looked into that, but intuitively I would guess not. Using r=a/(1+e*cos(theta)), and integrating out theta from r^2w=L also seems to me to result in an expression for L dependent on e. But this is just some thoughts on the fly, I haven't looked into it. It seems to me that your argument shows that we can concentrate on L=L(e) to look at the total irradiation. You did not mention the variable albedo with a non-vertical axis of rotation, but if that is approximately a periodic function of angle, it should integrate to zero over a period, so that's probably ok. -
Konfacela at 22:04 PM on 10 February 2010Skeptical Science now an iPhone app
I've downloaded the app and would like to take this opportunity to thank John Cook for this brilliant website. I follow a number of climate blogs but this one is my favourite hands down - reliable, informative, supremely accessible and well-organised. Thanks a lot! About the app - brilliant spin-off, and I like the fact that they've kept the layout and the nice crisp graphics. I wish the app included a Facebook/Twitter Share button so I can let the world know I'm using it.Response: The Facebook/Twitter buttons are great ideas, we'll look to put this into the next version. Thanks for the suggestion! -
Jack_Kelly at 21:42 PM on 10 February 2010Skeptical Science now an iPhone app
Genius! I think this is a great move. Any chance of an Android version of the app too?!? Pretty please? Of course, I understand this project is a hobby rather than a dayjob so please don't think I'm nagging. SkepticalScience is a great resource.Response: We're exploring the idea of an Android version. Will post on this when I have news... -
Berényi Péter at 21:11 PM on 10 February 2010Working out future sea level rise from the past
#48 Jeff Freymueller at 12:17 PM on 10 February, 2010 "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" Of course I should have done that. Unfortunately I have a daytime job outside climate science and those papers are behind a paywall. I could arrange for a university proxy, but even that takes time. Could you just copy-paste the list of tide gauge station identifiers used in the Church et al. (2004) calibration procedure along with a pointer to full sea level histories of those gauges? -
Berényi Péter at 20:56 PM on 10 February 2010Working out future sea level rise from the past
Bern at 15:22 PM on 10 February, 2010: "I beg to differ" Don't do that, please. Sice J. Kepler (1609) the issue is settled. In your calculation you should not divide the orbital period up into 1000 equal-length segments, but segments for which enclosed area between radii connecting endpoints to center of Sun and the orbital segment itself is constant, i.e. one thousandth of area enclosed by orbit. Redo, enjoy. -
RSVP at 19:40 PM on 10 February 2010Working out future sea level rise from the past
Bern It looks like your calculations assume a static model. The Earth spends less time in those segments nearer the Sun, and more time in those segments farther from the Sun. -
RSVP at 19:37 PM on 10 February 2010Working out future sea level rise from the past
"Charlie A at 16:03 PM on 10 February, 2010 Bern and Berényi Péter" #61 It is clear that radiation intensity increases for the Earth as it gets closer to the Sun. It is also clear that the Earth's tangential velocity increases as it gets closer to the Sun, and that net radiative forcing is thereby compensated. That is very different from the idea that these two tendencies lead to perfect cancellation. I dont see this as being necessarily the case because I think of the characteristics of electromagnetics and gravity (not to mention drivers of the Earth's heat budget) as being independent. Perhaps, however the math proves me wrong. -
Doug Bostrom at 17:53 PM on 10 February 2010Sea level rise is exaggerated
Neil, I don't wish to be unkind to Dr. Mörner, just want to point out what he says elsewhere in that interview as a bit of a reality check. I'm not sure what exactly the situation with him is, but quite clearly this is wrong: "Always the same thing: In about 1970, the sea fell about 20 cm, for reasons involving probably evaporation or something. Not a change in volume or something like that- it was a rapid thing. The new level, which has been stable, has not changed in the last 35 years. You can trace it so very, very carefully. No rise at all is the answer there." Much of the rest of the piece consists of accusations of lies, coverups, falsifications, too much to be believable. It's actually pretty sad, and I say that with sincerity. Sometimes you need to look at a narrative in sum and ask yourself, how -likely- is this? If I'm confronted with one man's word against hundreds and there is coherent consistency between what those many say that is completely inconsistent with the beliefs of the lone individual, I'm afraid I'm not going to believe him. There are just too many eye-popping anecdotes in Dr. Mörner's story to hold water. -
Arno Arrak at 16:29 PM on 10 February 2010Sea level rise is exaggerated
I did not realize that you had posted a comment to my comment until now. I want to emphasize that factoring in water impoundment gives the true rate of sea level rise that would exist if no water were impounded. I don't know why you bring in the other curves especially since the slope, and hence the predicted rate or rise, is essentially the same. And none of this has any significance whatsoever on the fate of retreating ice sheets. That is a totally different issue and depends upon the causes of arctic warming. In the case of the Antarctic the West Antarctic ice sheet is melting because it is being undermined by warm water rising up from below in the Amundsen Sea. This is because prevailing winds are from land to sea and blow away the cold surface water which is then replaced by warmer Antarctic bottom water. It has collapsed before, most recently 1500 years ago, and may collapse again if this keeps up. In the Arctic we are now in the middle of more than a century long warming period that started abruptly at the start of the twentieth century. This abrupt beginning rules out any greenhouse effect as its cause and indicates that a rearrangement of North Atlantic current system that directed warm water to the north took place at the turn of the century. Since we know that the Gulf stream now brings warm water to the Arctic it is likely that it assumed its present northerly course at that time. It is futile to try to predict any of this from computer models using the old carbon dioxide global warming paradigm. They produce nothing but GIGO. -
Charlie A at 16:06 PM on 10 February 2010Working out future sea level rise from the past
The link to Kopp in the head post leads to a paywall. The full paper is freely available at http://www.princeton.edu/step/people/faculty/michael-oppenheimer/research/Kopp-et-al-%282009%29-Probabalistic-assessment-of-sea-level-during-the-last-interglacial-stage-.pdf -
Charlie A at 16:03 PM on 10 February 2010Working 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. -
Jeff Freymueller at 15:50 PM on 10 February 2010Working 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 -
Charlie A at 15:44 PM on 10 February 2010Working out future sea level rise from the past
GFW -- thanks. Makes sense now. -
Timothy Chase at 15:23 PM on 10 February 2010Could 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. -
Bern at 15:22 PM on 10 February 2010Working 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. -
Timothy Chase at 15:20 PM on 10 February 2010Could 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. -
Philippe Chantreau at 15:03 PM on 10 February 2010The 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)? -
GFW at 14:35 PM on 10 February 2010Working 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. -
GFW at 14:23 PM on 10 February 2010Working 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 -
Doug Bostrom at 14:00 PM on 10 February 2010The 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". -
Charlie A at 13:55 PM on 10 February 2010Working 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? -
Jeff Freymueller at 13:45 PM on 10 February 2010Working 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. -
Jeff Freymueller at 12:54 PM on 10 February 2010Working 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. -
Jeff Freymueller at 12:36 PM on 10 February 2010Working 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. -
SNRatio at 12:34 PM on 10 February 2010Working 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? -
Jeff Freymueller at 12:27 PM on 10 February 2010Working 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). -
thingadonta at 12:20 PM on 10 February 2010Working 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. -
Jeff Freymueller at 12:17 PM on 10 February 2010Working 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). -
Jeff Freymueller at 11:59 AM on 10 February 2010Working 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. -
GFW at 11:08 AM on 10 February 2010Working 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. -
GFW at 11:00 AM on 10 February 2010Working 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.
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