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GFW at 10:41 AM on 10 February 2010Working 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. -
Riccardo at 09:47 AM on 10 February 2010The role of stratospheric water vapor in global warming
Berenyi Peter, here is the graph or you may like to read the whole procedure -
Riccardo at 09:38 AM on 10 February 2010Working 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". -
Berényi Péter at 09:28 AM on 10 February 2010The 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. -
Berényi Péter at 08:53 AM on 10 February 2010Working 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. -
Berényi Péter at 08:08 AM on 10 February 2010Working 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. -
Berényi Péter at 06:33 AM on 10 February 2010Could 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. -
Riccardo at 05:06 AM on 10 February 2010Working 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. -
Doug Bostrom at 04:48 AM on 10 February 2010Working 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. -
Doug Bostrom at 04:18 AM on 10 February 2010The 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. -
Berényi Péter at 03:57 AM on 10 February 2010Working 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. -
Berényi Péter at 03:51 AM on 10 February 2010Working 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. -
Timothy Chase at 03:43 AM on 10 February 2010Could 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. -
Timothy Chase at 03:31 AM on 10 February 2010Could 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. -
RSVP at 02:59 AM on 10 February 2010Working 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? -
Ani at 02:23 AM on 10 February 2010Could 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. -
Berényi Péter at 02:22 AM on 10 February 2010Could 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? -
andrewcodd at 02:12 AM on 10 February 2010Working 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. -
Riccardo at 01:22 AM on 10 February 2010Working 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). -
Riccardo at 01:17 AM on 10 February 2010Working 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". -
Ani at 01:12 AM on 10 February 2010Working 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. -
Berényi Péter at 01:01 AM on 10 February 2010Working 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. -
neilperth at 00:25 AM on 10 February 2010Working 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 ? -
Berényi Péter at 00:23 AM on 10 February 2010Working 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? -
Andreas at 23:39 PM on 9 February 2010The 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.) -
Riccardo at 23:26 PM on 9 February 2010Working 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. -
CBDunkerson at 23:15 PM on 9 February 2010Working 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. -
Jesús Rosino at 23:13 PM on 9 February 2010Working 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 -
Riccardo at 22:59 PM on 9 February 2010The 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. -
Ned at 22:43 PM on 9 February 2010Could climate shifts be causing global warming?
What's amazing about that 2003 image is the pattern over the US and downwind western Atlantic. CO2 concentrations are very high in this area ... but note the slight decrease over the eastern US. I assume this is due to sequestration of CO2 by regrowing forests in formerly cleared agricultural land. If we weren't regrowing all those trees, the eastern US would be as red as the West and the adjacent parts of the Atlantic. -
Working out future sea level rise from the past
While we're on this topic, what do we know about sea levels and temperatures this current inter-glacial? Is there a smilar plot to the first one above? -
Berényi Péter at 21:33 PM on 9 February 2010The role of stratospheric water vapor in global warming
doug_bostrom at 09:08 AM on 9 February, 2010: "all of the temperature signal displayed by the collective global measurement system is being affected by residing in the mid-domain of a single overarching slip event?" No. It is not just about surface temperatures, but all state variables of climate system, upper tropospheric specific humidity included. And not a single slip, but slips of a wide variety of magnitude distributed over all spatio-temporal scales. Present data homogenization techniques tend to identify some of these as results of undocumented instrumental changes and remove them from the record by adjusting data on either side of the "discontinuity", while in fact they are real jumps, parts of a climate feedback loop. Since the underlying dynamics is not time-symmetric, this procedure necessarily introduces a spurious trend. This is why time series "homogenized" by time symmetric statistical operators cannot be trusted. Of course there may be _some_ actual undocumented changes in instrumentation, so raw data should also be handled with care. But if the great majority of adjustments are in one direction (as it happens all the time with mainstram data torture), it is most probably due to this conceptual bias. -
Jesús Rosino at 21:32 PM on 9 February 2010Working out future sea level rise from the past
#21, GFW, In the Copenhaguen Diagnosis (p. 38, Fig. 17), they suggest that 3-5 m. could take place by year 2300 if temperature leveled at 3 ºC. Their source is this report from the German Advisory Council on Global Change (see p. 37, Table 3.1-1 and text). For this century, I think that the current best estimates would be close to 1 m. as global average (2 m. as an upper bound), but there will be regional deviations from that mean. -
stevecarsonr at 20:47 PM on 9 February 2010Working out future sea level rise from the past
Hello GFW, thanks for the welcome. And yet, response under #10 is maybe really really clear to someone who has studied the subject. But for the seekers it is one more piece of information and "hmm, how to weigh it up in the light of other things I have read?" Sometimes it is helpful to find out I am stupid, kind of a "wake up call". Some people have less thick skins and retreat. I'll be sure to study this (to me) new paper. Being slow it will take me a while to absorb it, so should I not ask questions until all papers referenced are fully understood? Because by then the debate is over and I have to wait until next time to ask my questions. But once again, it would be a shame if people with questions left early and missed the interesting stuff.Response: I will say it's not my intent to alienate any readers. Maybe I was a little snippy in my response to comment #17. As time goes on, I have made more effort to use less labelling and more focus on scientific arguments. Nevertheless, it's important that people are made aware of the dangers of a narrow focus that ignores the broader picture - lest they be misled by this practice. I will endeavour to communicate this message in a less alienating fashion.
By the way, the results of the Church 2008 paper have been available on the "sea levels aren't rising" page since I posted on the topic in May 2009. What I should've done was link to that page in my responses to #10 and #17 - I have now corrected that oversight. -
GFW at 20:28 PM on 9 February 2010Working out future sea level rise from the past
stevecarsonr, We welcome inquisitive and truly skeptical thought. The response to #17 was to someone making the "I don't see it in local raw data" argument, which really is a frequent device employed by deniers-who-call-themselves-skeptics. The person who wrote #17 could have looked at the response under #10, which is pretty darn clear. -
GFW at 20:24 PM on 9 February 2010Working out future sea level rise from the past
Arjen, I second what Riccardo says. Plan to deal with 1-2 meters by 2100, hopefully near the lower end of that, but an engineer has to be cautious... In a few more decades we'll have a much better idea what the rate of sea level rise will be in coming centuries. I'm thinking 2m/century from 2100 to 2600, although it could be less if we combat the CO2 problem aggressively. -
RSVP at 20:21 PM on 9 February 2010Working out future sea level rise from the past
"Berényi Péter at 02:59 AM on 9 February, 2010 Orbital eccentricity variations has no effect on annual average "solar radiative forcing". It is only the seasonal distribution of incoming radiation which changes." I do not see it this way. The more eccentric the orbit, the less time spent around the perihelion, and more time spent around the aphelion. This to me, would seem would favor cooling... comets being an example of this taken to the extreme. -
stevecarsonr at 20:13 PM on 9 February 2010Working out future sea level rise from the past
Re the response to #17: "..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.." Perhaps the information is not so easy to find. Perhaps "skeptics" are seeking information but not being climate scientists don't know where to find the latest research. I have been interested in this subject for a while - I've read about ocean heat content, I've read Willis, I've read Levitus - but I don't think it is easy to get to the bottom of. But if you want to run down "skeptics" you are welcome to do so, it's your website. But less "skeptics" will spend time here.. -
Riccardo at 20:09 PM on 9 February 2010Working out future sea level rise from the past
Arjen, the dynamics of ice sheets it not well known. The "linear" part of the response is relatively slow so I would expect that on average the melting of significant part of Greenland and/or West Antarctica will take several centuries. If i were a Dutch engeneer i'd not think about the 6 m for now.. But, i guess, even one or two meters in a century might be challenging and this rate is now believed to be possible. You should also consider that sea level rise is not uniform and as far as i remember measurments in the Netherland have show a smaller rate than the global average. You might be interested in this study: The Netherlands under a 5 m sea level rise. -
Berényi Péter at 18:37 PM on 9 February 2010Working out future sea level rise from the past
You can check sea level history for individual tide gauges. NOAA - Tides & Currents Mean Sea Level Trends for Global Network Stations http://tidesandcurrents.noaa.gov/sltrends/sltrends_global.shtml Acceleration is invisible.Response: As stated often on this website, 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. This comment is a classic example. One could take a few random selections of local tidal gauges as an indicator of global sea levels. Or one could look at peer-reviewed analysis that uses a global network of tidal data, taking into account local tectonic movements, compacting sediments and vertical land movement due to geological processes, combined with independently measured satellite observations (Church 2008). -
Arjen at 18:36 PM on 9 February 2010Working out future sea level rise from the past
As a Dutch engineer working in coastal construction, I'm very interested at the speed of mean sea level rise. What time frame are we talking about when we consider a 6 meter mean sea level rise? Even a 2 meter rise in 90 years is a very sobering thought for me. That would basically mean a complete redesign and the rebuilding/extension of all storm surge infrastructure and of about all ports. Even for rich countries that have the know-how, like the Netherlands, that is a major undertaking. When I try to contemplate a 6 meter mean sea level rise for only the port and city of Rotterdam, it boggles my mind. If it is feasible, it certainly would not be recognizable as the city and port it is today. -
Timothy Chase at 18:00 PM on 9 February 2010Could climate shifts be causing global warming?
PS I figure seeing is believing, so I am including a link that may be of interest. The dark redder patches in the following satellite image are where there are higher levels of carbon dioxide at 8 km, and consequently the radiation that escapes to space gets emitted at higher, cooler altitude, decreasing the amount of thermal radiation that makes it to space at a wavelength of 15 ?m: Measuring Carbon Dioxide from Space with the Atmospheric Infrared Sounder http://airs.jpl.nasa.gov/story_archive/Measuring_CO2_from_Space/ And as you can see, the levels of carbon dioxide are highest where the winds would carry the gas away from more heavily populated areas (e.g., the east and west coasts of the United States) prior to dispersing it throughout the atmosphere. On this page you have an image of the distribution of carbon dioxide from July 2003 and July 2007: PIA11186: AIRS Global Distribution of Mid-Tropospheric Carbon Dioxide at 18-13 km Altitudes http://photojournal.jpl.nasa.gov/catalog/PIA11186 As you can see from either image, higher levels of carbon dioxide reduce the rate at which thermal radiation escapes to space -- and as you can see when the two images are side-by-side, there are higher levels of carbon dioxide in 2007 than in 2003.Response: Thanks for the links, here for the especially lazy reader are the images (but I recommend you click the links anyway):
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Doug Bostrom at 16:50 PM on 9 February 2010Working out future sea level rise from the past
Berényi Péter at 11:39 AM on 9 February, 2010 Just to clarify a couple of your points... While it is true that in certain areas affected by the last episode of continental glaciation local mean sea level is increasing due to isostatic adjustment, this effect should not be confused with eustatic or steric sea level rise, which of course are observed globally. Isostatic sea level is a special case that is regional in extent and should not be confused with sea level changes due to thermal expansion or bulk addition of water to the ocean. Ocean heat content does in fact continue to rise. Look at trends, as with any longitudinal data set don't be fooled by individual years: Ocean Heat Loads of heat being added there. More and more in the future the ocean will be responding with warnings on the debt we're running up in the way of heat storage. -
Timothy Chase at 16:49 PM on 9 February 2010Could climate shifts be causing global warming?
Continuing with the above comment... Now a little bit about absorption spectra may be in order. First, absorption occurs in bands and bands consist of lines, but the lines themselves are not infinitely thin. They have a wavelike shape to them -- and this helps to understand why even at the surface increasing the partial pressure of a given greenhouse gas generally has the capacity to increase the optical thickness of the atmosphere. At sufficiently low partial pressures of a given greenhouse gas, increasing the partial pressure of the gas will result in a linear increase in the absorption. This will occur right around the center of a sharp peak of absorption. However, as one increases the partial pressure of the greenhouse gas the central peak becomes saturated, but increasing the partial pressure causes the peak to broaden. The range over which absorptivity is nearly 1 broadens, but there are the slopes over which absorptivity gradually drops towards zero. Thus at moderate levels of saturation absorption increases as the square root of the partial pressure. At the surface, methane's central peaks are only moderately saturated, so absorption increases as the square root of the partial pressure -- and consequently so does radiative forcing. At still higher levels saturation more of the additional absorption takes place in the "wings" of the spectral "line." At this point absorption increases as the logarithm of the concentration. This is where both carbon dioxide and water vapor are at, and as a consequence forcing is a logarithmic function of their partial pressures. Please see for example:For gases such as halocarbons, where the naturally occurring concentrations are zero or very small, their forcing is close to linear for present-day concentrations. Gases such as methane and nitrous oxide are present in such quantities that significant absorption is already occurring, and it is found that their forcing is approximately proportional to the square root of their concentration. For carbon dioxide, parts of the spectrum are already so opaque that additional molecules are almost ineffective; the forcing is found to be only logarithmic in concentration. http://www.global-climate-change.org.uk/6-5-1.php
Here are some posts over at Eli's which show how the spectral absorption of carbon dioxide varies according to temperature and pressure — and which point you to an online tool where you can create your own graphs: Temperature Wednesday, July 04, 2007 http://rabett.blogspot.com/2007/07/temperature-anonymice-gave-eli-new.html Pressure broadening Thursday, July 05, 2007 http://rabett.blogspot.com/2007/07/pressure-broadening-eli-has-been-happy.html High Pressure Limit. . . . Sunday, July 08, 2007 http://rabett.blogspot.com/2007/07/high-pressure-limit.html However, what matters most in terms of the enhanced greenhouse effect under current anthropogenic global warming isn't increased absorption near the surface but rather how the effective radiating altitude rises with the increasing partial pressure of carbon dioxide. Most of the relevant spectra in which carbon dioxide acts is already saturated by water vapor at the surface, thus if one were to only increase the partial pressure of carbon dioxide at the surface it would have very little effect. However, water vapor tends to stay much closer to the surface than other gases. It has a scale (or "e-folding") height of roughly 2 km as opposed to 8 km which would be more typical of other gases, including carbon dioxide. It is at the higher altitudes that raising the level of carbon dioxide will really matter. The effective radiating temperature of the earth is roughly -17°C. This corresponds to an effective radiating altitude of roughly 5 km. But by raising increasing the partial pressure of carbon dioxide at the surface, one increases the partial pressure of carbon dioxide at higher altitudes, increasing its absorptivity and therefore raising the altitude where of the atmosphere to thermal radiation one increases the altitude where a photon is radiated without being reabsorbed, that is, where its energy is radiated for the last time and finally escapes to space. However, the higher the altitude the colder it gets -- reducing the emission. Consequently the we have a radiation imbalance in which more radiation is absorbed by the earth's climate system than is emitted to space as thermal radiation. The apparent (or "brightness") temperature of the earth -- as it is viewed at a distance -- decreases because less radiation is able to escape to space. But by the principle of the conservation of energy this implies that the actual amount of energy in the earth's climate system is increasing. For a new thermodynamic equilibrium to be achieved the temperature of the effective radiating layer must increase. But what this implies is that the rate at which radiation is emitted at the surface must increase. How much? Interestingly enough, the temperature drops roughly as a linear function of altitude, and the rate at which temperature drops with altitude. As altitude increases, the atmospheric pressure decreases. 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. So if the effective radiating altitude rises by a certain distance, one can divide that distance by the lapse rate to arrive at the temperature. Tamino goes into this in more depth here: Lapse Rate, July 16, 2007 http://tamino.wordpress.com/2007/07/16/lapse-rate/ Prior to any feedbacks the warming of the surface turns out to be about 1°C per doubling of carbon dioxide. But of course at higher temperatures ice melts -- decreasing the albedo of the earth and increasing the absorption of sunlight. Likewise, water evaporates, with the absolute humidity at the earth's surface increasing by roughly 8% for each additional degree Celsius and roughly doubling for every ten degrees Celsius. Once one takes into account all the feedbacks doubling the partial pressure of carbon dioxide is more likely to raise the temperature by roughly three degrees Celsius. Incidentally, I would recommend checking out: A Saturated Gassy Argument 26 June 2007 http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument/ ... and: Part II: What Ångström didn't know 26 June 2007 http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/ Anyway, I hope this helps... -
Timothy Chase at 15:09 PM on 9 February 2010Could climate shifts be causing global warming?
CBDunkerson wrote in 27:"... in short, the emissivity of the Earth's atmosphere has decreased due primarily to the increase in carbon dioxide and the positive feedback effect that has with water vapor."
I think part of the problem here is that people may be equating emission and absorption with emissivity and absorptivity. Emission is the actual rate at which radiation is emitted, either independently of the frequency or in the case of spectral emissivity and spectral absorptivity as a function of the frequency of the radiation. In contrast, emissivity and absorptivity consist of the capacity to emit or absorb radiation, and particularly in the case of greenhouse gases it is important to speak not simply of emissivity or absorptivity, but of spectral emissivity and absorptivity -- as these are very much a function of the frequency -- as indicated by the specific absorption spectra of greenhouse gases. Emissivity and absorptivity are equal under local thermodynamic equilibrium, and as higher levels greenhouse gases increase absorptivity they also increase emissivity -- in the bands in which they act. However, the emission and absorption will typically not be equal. And as a matter of fact, local thermodynamic equlibrium means essentially that emission is independent of absorption as emission is simply a function of the intrinsic properties of matter and the temperature of matter. Please see:"local thermodynamic equilibrium – (Abbreviated LTE.) A condition under which matter emits radiation based on its intrinsic properties and its temperature, uninfluenced by the magnitude of any incident radiation. "LTE occurs when the radiant energy absorbed by a molecule is distributed across other molecules by collisions before it is reradiated by emission. LTE is needed for Planck's law and Kirchhoff's law to apply, and is typically satisfied at atmospheric pressures higher than about 0.05 mb. Laser radiation is an example of non-LTE emission." Glossary of Meteorology, American Meteorological Society http://amsglossary.allenpress.com/glossary/search?p=1&query=local+thermodynamic+equilibrium
The reason why emitted radiation is independent of incident radiation is because absorbed incident radiation is thermalized. Photons are absorbed by molecules that enter a quantized state of of excitation (e.g., bending or stretching which are jointly referred to as "vibrational," rotational, or rovibrational), but then the energy is lost due to collisions with the surrounding molecules before the molecule that absorbed the photon has a chance to spontaneously decay. At 20 mb, a molecule may already be undergoing perhaps a million collisions during the half-life of a given state of excitation. So the wavelength, intensity and angle of the incident radiation is more or less irrelevant. Typically, local thermodynamic equilibrium conditions remain in place until 70 km or above. At lower altitudes the high frequency of collisions will insure the equipartition of thermal energy, resulting in the brightness temperatures associated with different degrees of freedom (e.g., translational motion and a given mode of vibrational excitation) being equal and will be equal to the temperature associated with translational motion. However, at certain wavelengths it may begin to break down as low as 40 km -- at which point non-local thermodynamic equilibrium conditions may then apply. Under local thermodynamic equilibrium conditions, given the equipartition of energy, for each quantized state of excitation a certain number of molecules will always be in that of excitation at any given time. The spontaneous decay of such states of excitation are independent of the length of time that a given molecule has been in that state of excitation. As such a certain percentage of molecules will decay due to spontaneous radiation over any given period of time. Thus the thermalization of absorbed radiation -- in which almost all molecules that absorb photons lose energy through collisions rather than by emitting photons, collisions do not prevent photons from being emitted as such. * But what then are emissivity and absorptivity? Absorptivity is the easiest to define. It is the ratio of incident radiation that is absorbed by a given body, and in the case of spectral absorptivity refers to the ratio of incident radiation at a given frequency that is absorbed by the body. Thus the absorptivity of a true black body would be 1 at any given frequency as it would absorb all radiation. And it is in the context of this last statement that it is easiest to understand the definition of emissivity:"emissivity – The ratio of the power emitted by a body at a temperature T to the power emitted if the body obeyed Planck's radiation law." Glossary of Meteorology, American Meteorological Society http://amsglossary.allenpress.com/glossary/search?p=1&query=emissivity
Likewise, spectral emissivity is the ratio of radiation emitted at a given frequency by the body relative to the amount of radiation that would be emitted by a black body at that frequency. Anyway, for those who are interested, here is a derivation of Kirchoff's law for spectral emissivity and absorptivity: Radiative Transfer http://www.cv.nrao.edu/course/astr534/Radxfer.html The author shows why Kirchoff's law applies under thermodynamic equilibrium and then shows how this can easily be extended to local thermodynamic equilibrium conditions. -
Tony O at 15:04 PM on 9 February 2010Working out future sea level rise from the past
Just to add a little more uncertainty. From http://vulcan.wr.usgs.gov/Volcanoes/Antarctica/description_antarctica_volcanoes.html Despite its size, Antactica ranks below all other regions in number of dated eruptions, and only the Pacific and Atlantic Ocean regions have fewer historically active volcanoes. It's historical record is brief, and 75 percent of its eruptions are from this (last) century. Precise dating of past eruptions is difficult -- much of the landscape is glacier-covered, travel is daunting, and the wood needed for radiocarbon dating does not grow in this extreme climate -- and the region has the highest proportion of volcanoes with uncertain status. We had a couple of eruptions last century so I guess we will have a couple this century. Which ones and when might be a rather critical issue. Then we add to the mix that glacial melting increases volcanic activity. Could this affect the SLR this century? Of course then the pro polluters will blame the volcanoe. -
thingadonta at 14:53 PM on 9 February 2010Working out future sea level rise from the past
I'm just wondering if there is any studies on the depression of land from the extra weight of water over near-coastal areas with rising sea levels since the last ice age; it is well-known that the coast is still rising in areas formerly depressed by thick ice, I suspect that areas inundated by rising sea levels should also be subsiding, thereby raising sea levels in these areas further. -
stevecarsonr at 14:19 PM on 9 February 2010Working out future sea level rise from the past
I have a couple of questions. The first about the "Milankovitch" cycles. There is a nice page on wikipedia with the various cycles over 1M years, but does anyone know of a resource where the data is available in a higher resolution over the last 200,000 years? Second, noting in passing that the IPCC AR4 says there is a huge uncertainty in the ice melt (p339): "Estimates for the overall mass balance of the Antarctic Ice Sheet range from +100 to –200 Gt yr–1 (–0.28 to 0.55 mm yr–1 SLE) for 1961 to 2003, and from +50 to –200 Gt yr–1 (–0.14 to 0.55 mm yr–1 SLE) for 1993 to 2003." So the IPCC summary says we aren't sure about the sign. Of course we can take the mid point.. If temperature rises stopped today what would sea level be likely to be in 2100? -
Berényi Péter at 12:33 PM on 9 February 2010Could climate shifts be causing global warming?
CBDunkerson at 04:34 AM on 9 February, 2010: "and I'm not sure why you are suggesting otherwise" I tell you. Emissivity/absorptivity of materials depend on wavelength. Snow is white in the visible while pitch black (has high absorptivity) in IR. If you put more "greenhouse gases" (the ones having some absorptivity in IR, being transparent otherwise) above an IR-bright surface (which has low absorptivity in the infrared, like quartz sand), the scene starts to look "darker" from above in IR, i.e. the absorptivity is increased. So does emissivity, according to Kirchoff. Well. Your statement "the emissivity of the Earth's atmosphere has decreased due primarily to the increase in carbon dioxide" is not true. Carbon dioxide, as any other "greenhouse gas" increases emissivity. If global effective temperature is constant, average photosphere temperature should decrease. It has to decrease even more to achieve an imbalance between ASR & OLR, provided shortwave albedo (1-absorptivity) does not change. -
Bern at 12:12 PM on 9 February 2010Working out future sea level rise from the past
Berényi Péter: "Antarctica is gaining somewhat" Actually, John has covered that previously - the most recent measurements are indicating that Antarctica as a whole is losing ice mass, not gaining.
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