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Comments 125951 to 126000:

125951. Tom Dayton at 04:27 AM on 20 December 2009
        Models are unreliable
        Allyrooney, saying that "modeling is the main evidence cited by the IPCC" is like saying "epidemiological models are the main evidence for the germ theory of disease." The true root and bulk of the evidence is basic physics, with details added in the form of progressively more advanced physics. But the media and public have gotten the misimpression that (a) scientists are merely guessing that human-produced greenhouse gasses are responsible for the portion of warming that scientists' models can't otherwise predict; and (b) there might be no unusual temperature rise needing to be explained, because the temperature hockey stick graph might be wrong. You will save yourself a lot of time and frustration if you read a quick overview of the wide range of evidence from cce's The Global Warming Debate. (Be patient, his server is slow, and sometimes gets completely bogged down; try again later). Then get a quick history from Spencer Weart's The Discovery of Global Warming; his summary Introduction is nicely short, but the rest of his site is quite rich. If you want to continue reading background material after that foundation, look at the Start Here section on RealClimate, which has links to materials categorized by level of technical background required. But if instead you then want to pursue pointed questions, this SkepticalScience site is a great place to turn next. Note there are two types of posts here: the concise Skeptic Arguments linked at the top left of the page (click "View All Arguments"), and the longer "Posts."
125952. Steve L at 03:41 AM on 20 December 2009
        Predicting future sea level rise
        neilperth @20 -- your points are not substantial, then. 1. Yup, sea level and temperature changed over time in the absence of anthropogenic forcing. 2. Yup, they will continue to change while humans are here and after humans are extinct. In the meantime, however, it's worth pointing out that temperatures and sea levels will rise (probably accelerating for the latter) into the foreseeable future because of anthropogenic CO2 (and human choices will influence the rate of that rise). All else being equal, if anthropogenic influences on climate were removed, these rises into the foreseeable future would not occur.
125953. Riccardo at 01:21 AM on 20 December 2009
        Predicting future sea level rise
        The only long term record i know of in the Netherland is Amsterdam (untill 1932 when it was separated from the sea). It shows a very slow increase of about 1.5 cm/century up to the second half of '800. Then, using also other coastal tide gauges, it started rising at about 17 cm/century up to today. It is quite similar to the world average during the same period. This points to a sea level rise along the Dutch coast similar to the world average, even if the noisier local record still cannot detect it. Indeed, as far as i know the Dutch have taken really seriously the threat posed to their country by sea level rise.
125954. allyrooney at 01:11 AM on 20 December 2009
        Models are unreliable
        I'm a medical doctor with no climatology experience beyond a recent lay interest. I've got some grounding in research and am doing an MD (a UK higher medical research degree) and a Cochrane review of a medical topic. I'm trying to bring these transferable skills to bear in helping me make my own mind up about anthropogenic global warming. I was concerned to hear our Prime Minister (no less) publicly dismiss those who question the scientific orthodoxy as "flat-earthers". My reading of this whole article (and sources referenced in the few balanced websites I can find - apart from this one, climatechangefacts.com and sourcewatch.org are good) is that the modeling can be criticised enough to plant 'reasonable doubt' regarding future projections. I think that this is a strong argument against AGW; correspondingly it requires a strong refutation. I don't think this article and thread has achieved this. Regarding global temperature data, the very simple point I'd like to make is that Hansen (2006), whose results you cite as the main defence of model prediction, themselves state that "a 17-year period is too brief for precise assessment of model predictions [because of inherent uncertainty within the model]". They continue, "close agreement of observed temperature changes with simulations [for scenario B] is accidental given the large unforced variability in the real world". I think this is appropriate scientific caution and does not necessarily disprove the model - yet this sense of balance is missing from your headline response to skeptics: "[climate models] have successfully predicted future climate change". I also note that the point at which scenarios A and B divide (ie discriminate between predictions) has not yet occurred, or is occurring now. Overall I would say the Hansen data is not irrefutable evidence that models work. Incidentally Hansen 2006 also suggest that the volcanic eruption estimated for the 1990s, (which you single out for special mention) was 'sprinkled' there - my reading of the paper is that the authors simply dispersed three eruptions across a 50-year period. Certainly any suggestion that the eruption was a spectacular success of the general climate model would seem to be misleading. I'm not sure that was your intention. This is very important because as I understand it modeling is the main evidence cited by the IPCC, which in turn is driving the current political process. If they are inaccurate (as, intuitively, they may well be if they do not include unknown forcing) then predictions are scientifically meaningless. As I say, the fit of the Hansen model is described, at best, as tentative by the authors themselves. I don't believe it's constructive to label critical questioning and rational scepticism as "denial", being "full of junk" or "spouting rubbish" as one blogger has done in this thread. I would also caution against automatically rejecting any article that is not peer reviewed. Peer review is also flawed; it is often not double-blind and therefore can be biased, and because peer-reviewed journals are extremely competitive, articles in them may tend to be those based on well-funded research; funding often following political agendas (and then there is the separate problem of publication bias). The source is simply something that must be weighed along with everything else. al
125955. FrankT at 23:02 PM on 19 December 2009
        Predicting future sea level rise
        "Meanwhile, we cannot detect climate change on the Dutch coast" is the heading (in Dutch) of a summary of a presentation given in March 2009 by one of Holland's main government advisors on sea-level (Douwe Dillingh), who works for Deltares (www.deltares.nl), the main Dutch research institute for everything related to water technologies. The graph on the link below shows an essential linear trend of appr. 15cm / century increase of sea-level from 1900 to today. The text asserts that this linear trend started earlier, and can be dated to at least 1800. In Dillingh's opinion the 30cm/century measured by sattelites is no reason to conclude that there is an increase in sea-level rise, since the measurement methods are too different (sattelite vs. tidal gauge locally). Bottomline: on the Dutch coast the sea level does rise, but exactly as it has been doing for the past 200 years. No sign yet of any increase due to CO2 based global warming. Of course, this is a local situation, and one can think up all sort of hypothesis why this is just a local peculiarity, if it is. The link is: http://www.waterforum.net/index.asp?url=/template_a1.asp&que=paginanr=6609 The website 'waterforum' is a news site for Dutch professionals involved in water management.
125956. neilperth at 18:28 PM on 19 December 2009
        Predicting future sea level rise
        Steve L, Pico. My points in relation to sea level changes and, by inference temperature changes, were that : 1- These change markedly over time due to natural causes. 2. Over time sea levels and temperature will rise and fall whether man-kind is on this planet or not. So I ask : do you consider statement 1 true or false? do you consider statement 2 true or false?
125957. Craig Allen at 17:25 PM on 19 December 2009
        Predicting future sea level rise
        neilperth: By your logic, given that people sometimes die in car accidents even when everyone is being responsible, it is therefore perfectly OK for drivers to get blind drunk and career around ignoring the speed limit. People will inevitable die either way right, so why be careful?
125958. Steve L at 16:12 PM on 19 December 2009
        Predicting future sea level rise
        neilperth @17 -- what's your point? People can die of natural causes, species can go extinct from natural causes, terrible living conditions can result from natural causes.... Therefore? neilperth @6 -- when did humanity make the biggest strides? Was it during the big swings in global climate and sea level or was it during the period of relative stability?
125959. neilperth at 14:31 PM on 19 December 2009
        Predicting future sea level rise
        It is a fact that sea levels can rise and fall over 100 metres due to NATURAL causes. This has happened in the past and no doubt will happen again in the future. If the sea level rises say only 5 metres over the next 1000 years, obviously this will cause problems for low-lying areas of the world. But the world was never designed to be optimal for human habitation. If you buy a house near the coast, you should be aware that over time there is the possibility that it will be flooded by the sea. If you buy a house in a city located on top of a Benioff Zone ( eg Seattle, Vanouver ), you should be aware that it may be destroyed by an earthquake. Of course people living in say Bangladesh have little option but to live in low-lying coasstal areas. But over time sea levels will rise and fall whether man-kind is on this planet or not.
125960. Riccardo at 10:01 AM on 19 December 2009
        Predicting future sea level rise
        jliungman, i think it's a success of this site if people like you come asking questions, read the papers and solve by themselves.
125961. jliungman at 08:49 AM on 19 December 2009
        Predicting future sea level rise
        Sorry, now that I actually read the paper I see that the authors do address my point: "In addition, highly nonlinear responses of ice flow may become increasingly important during the 21st century. These are likely to make our linear approach an underestimate."¨ As a non-physisist, I feel just a little bit proud for having seen that coming... ;-) John
125962. jliungman at 08:40 AM on 19 December 2009
        Predicting future sea level rise
        Thank you for your reply, Riccardo. However, the original posting also stated: "This calving process is accelerated by warming but the dynamic processes are not strongly understood." We attempt a theoretical model including glacial dynamics (and a lot of other parameters) but we find that those dynamics are hard to predict. So we try the "semi-empirical" approach instead, making the assumption that "highly non-linear events such as the collapse of an ice sheet" don´t happen. Then have we really solved the problem of collapsing ice sheets? NB. I´m not claiming that anyone is wrong, just trying to get my spontaneous objections resolved.
125963. Riccardo at 07:05 AM on 19 December 2009
        Predicting future sea level rise
        jliungman, actually the model is not linear. Whatever it is, extrapolation is always a tricky business and you need solid physical basis to be confident with it. If, for example, you push it too far to a situation in which there is no more ice anywhere the extrapolation will for sure be unjustified. But if you consider that the contribution to sea level rise is mostly due to only two processes (sea water warming and ice sheet melting, both in the end driven by GHG forcing) we might be confident enough that no dramatic changes will show up in a century. The model has also been tested tested against a simulation along a time span of 1000 years (fig.2 in the paper).
125964. jliungman at 06:23 AM on 19 December 2009
        Predicting future sea level rise
        Hello, and thanks for an interesting post! In the original post you state: "There are limitations to this approach. The temperature record over the past 120 years doesn't include large, highly non-linear events such as the collapse of an ice sheet." Isn´t the problem even more serious? If we view sea level as some kind of funtion of temperature, derived by looking at the evicence of the very narrow range of temperatures we have observed since 1880, how can we make any claims about a different range of temperatures? I´m not a scientist, but it seems to me that with so many variables involved, linearity would be the last thing to expect. The method seems interesting, but needs to be calibrated using more information about other temperatures and sea levels historically. And I don´t know if this information exists? Or am I mistaken? Thanks, John
125965. chris at 06:17 AM on 19 December 2009
        Predicting future sea level rise
        re #6 neilperth, your statement simply doesn't accord with the evidence:

        How can you blame man for sea levels rising when about 99% of that rise since the last ice age occurred before man built the pyramids, much less SUVs? A rise in sea level over the last century should not be surprising; it's been rising for the last 20,000 years.

        In fact the sea level rise from melting of polar ice during the last glacial to (present) interglacial transition was preetty much complete by a few thousand years ago. The evidence indicates that there has been little change in eustatic sea level since Roman times 2000 years ago, and if anything sea levels dropped somewhat (a small number of centimeters) in the nearly 2000 years up to around the middle of the 19th century, after which they've started to rise, increasingly so during the last century and especially during the last several decades: Pirazzoli PA (2005) A review of possible eustatic, isostatic and tectonic contributions in eight late-Holocene relative sea-level histories from the Mediterranean area Quart. Sci. Rev. 24, 1989-2001 “Finally, several data from tectonic and non-tectonic areas are consistent with nearly stable global eustasy since 6000BP, thus challenging the assertion of significant additional melting of Antarctica after the complete melting of the former Northern Hemisphere ice caps “ Lambeck K (2005) Sea level in Roman time in the Central Mediterranean and implications for recent change Earth Planet. Sci. Lett. 224, 563-575 “Part of this change is the result of ongoing glacio-hydro isostatic adjustment of the crust subsequent to the last deglaciation. When corrected for this, using geologically constrained model predictions, the change in eustatic sea level since the Roman Period is -0.13 +/- 0.09 m. A comparison with tide-gauge records from nearby locations and with geologically constrained model predictions of the glacio-isostatic contributions establishes that the onset of modem sea-level rise occurred in recent time at similar to 100 +/- 53 years before present.” Church JA et al. (2008) Understanding global sea levels: past, present and future Sustainability Sci. 3, 9-22 “While sea levels have varied by over 120 m during glacial/interglacial cycles, there has been little net rise over the past several millennia until the 19th century and early 20th century, when geological and tide-gauge data indicate an increase in the rate of sea-level rise.” Milne GA (2009) Identifying the causes of sea-level change Nature Geosci. 2, 471-478 ”The observed fall in sea level following the end of major melting (~7,000 yr bp; Fig. 3b) is due to isostatic processes52. A growing number of high-resolution records (Fig. 3c) detect an acceleration in sea level around AD 1850–1900 (refs 43–45)” etc...
125966. chris at 04:53 AM on 19 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        Re #26 HumanityRules, I was highlighting the fact that the evidence of a non-spatially homogeneous MWP, has been around for some time, and is not the recent proposal of Mann thst you suggested. I don’t disagree that there is limited S. hemisphere proxy temperature data. However, there’s rather a lot of data that supports the interpretation of a non-homogeneous MWP (temporally and spatially) either focussing on the N. hemisphere (see papers in my post above), or considering less quantitative paleoproxy data from the S. hemisphere and central latitudes. So, for example, data from Pacific corals indicate that the tropical Pacific was cool during the period of the high N. latitude MWP: Kim M. Cobb et al. (2003) El Niño/Southern Oscillation and tropical Pacific climate during the last millennium Nature 424, 271-276 And this data has recently been extended through the 20th century, to pin the paleoproxy data to the 20th century temperature record Nurhati IS et al. (2009) Late 20th century warming and freshening in the central tropical Pacific Geophys. Res. Lett. 36 Art # L21606 Temperature records from the mid-latitudes (Tibet) and S. hemisphere (Tropics; Andes) shows either an insignificant warming during the period of the high N. hemisphere MWP (tropics and Tibet) or a small warming that is non-synchronous with the N. hemisphere MWP (Andes; it lags by ~200 years) L.G. Thompson et al. (2006) Abrupt tropical climate change: past and present Proc. Natl. Acad. Sci. 103 10536–10543 Likewise analysis of S. hemisphere glacier advance (New Zealand) indicates that the N. hemisphere and S. hemisphere warming at the time of the MWP was temporally asynchronous: J. M. Schaefer et al. (2009) High-Frequency Holocene Glacier Fluctuations in New Zealand Differ from the Northern Signature Science 324, 622-625 Likewise, analysis of paleoproxy data from S. America has indicated non spatially coherent warming and little overall warming in the region compared to MWP in Europe R. Villalba, 1990 Climatic fluctuations in northern Patagonia during the last 1000 years as inferred from tree-ring records Quaternary Research 34 (1990), pp. 346–360 Recently reviewed: J.A. Boninsegna et al. (2009) Dendroclimatological reconstructions in South America: A review Palaeogeography, Palaeoclimatology, Palaeoecology 281, 210-228 and so on… Now one may quibble about the limited “quantitative“ paleoproxy data from the Southern hemisphere. However there is rather significant evidence that the Pacific was displaying La Nina like conditions during the period of the warm high latitude N. hemisphere MWP signature, and that Southern hemisphere and mid-latitude glaciers were not responding in a manner consistent with warming during the period of warming in the high Northern latitudes. This is quite different for the spatially-and temporally homogenous nature of 20th century warming. This evidence has been around for a long time…the recent data tends to reinforce this interpretation.
125967. Ned at 02:23 AM on 19 December 2009
        Predicting future sea level rise
        RSVP writes: But for the short run of 100 years, as oceans grow, would'nt that volume of extra water dampen global warming? (since the heat capacity of water is twice that of ice) Don't take this personally, but are you seriously suggesting that the change in the thermal mass of the ocean as a result of melting ice would have a significant effect on the rate of increase in global surface temperature? A few seconds with Google suggests that the mass of the oceans is 1.4 x 10^21 kg. (e.g., http://hypertextbook.com/facts/1998/AvijeetDut.shtml). The area of the ocean is 3.6 x 10^14 square meters. One cubic meter of water masses 1000 kg, so raising sea level by one meter adds 3.6 x 10^17 kg to the ocean. That presumably would increase the ocean's thermal mass by 0.0026%. Working that out took one or two easy Google searches, plus a small amount of very simple calculations. John, our host on this blog, tries to keep everything polite and I want to respect that. But I'd like to gently suggest that you, RSVP, could probably have figured out the answer to your question first, rather than throwing it out here as an objection that others then have to address. Okay, end of sermon.
125968. Ned at 01:58 AM on 19 December 2009
        Predicting future sea level rise
        neilperth: The IPCC AR4 predictions of future sea level rise were specifically designed to be conservative, by simply omitting processes that are difficult to predict but are known to contribute to sea level rise. In other words, they are a lower bound on SLR, and sure enough, as we see from the first figure in this post, actual SLR is nicely tracking the very uppermost range of the IPCC predictions. The Vermeer et al paper being discussed here makes a convincing argument for sea level rise of 7.5 to 19.0 mm/year over the next century. This is much faster than most pre-modern changes in sea level, and in fact is of the same order of magnitude as some of the extreme spikes that occurred during deglaciation. That's disturbing, because unlike the situation 14,000 years ago, there are now over 600 million people living within less than 10 m of sea level. Not to mention lots of nice stuff like cities, airports, shipping terminals, and other valuable infrastructure. None of that existed during past episodes of sea level rise. In wealthy countries, we can afford to move people inland (a 1 m rise in sea level might only cost the US something like $400 billion, though other estimates would put the price tag higher). In poor countries, this will mean vastly more hardship. Of course, in the worst-case scenario, if people fail to take action on climate now, and we keep burning more and more oil and coal, at some point we'll lose at least a large fraction of both the Greenland ice sheet and the West Antarctic ice sheet. Let's just hope they don't break up as fast as the portions of the Pleistocene ice sheets that were responsible for meltwater pulse 1A, when sea levels rose at rates of 50 mm/year for three centuries. Anything even close to that would be an immense disaster.
125969. RSVP at 01:40 AM on 19 December 2009
        Predicting future sea level rise
        Referring to Figure 3. Even with a total Venus style greenhouse runaway scenario, on an expanded time scale, the curve would have to flatten out, as there is only a finite amount of ice in our polar caps. But for the short run of 100 years, as oceans grow, would'nt that volume of extra water dampen global warming? (since the heat capacity of water is twice that of ice)... in which case the curve would be a little flatter. Or does more ocean mean more water vapor and more global warming?
125970. RSVP at 01:12 AM on 19 December 2009
        Predicting future sea level rise
        to neilperth Obviously, you dont surf.
125971. neilperth at 23:23 PM on 18 December 2009
        Predicting future sea level rise
        The IPCC tells us that warmer temperatures lead to higher sea levels. Fortunately, there is only one ocean. And while sea levels vary with tides over the year, averages are probably fairly reliable. The IPCC does present a chart of sea levels and its trend is more obvious than the temperature trend. It shows a steady rise of about 200 millimeters in the last 120 years. That's about eight inches. Is eight inches over 120 years significant or alarming? Better yet, scientists have produced a long-term graph of sea level changes, about 20,000 years worth. The data behind this graph are widely known and accepted. NASA, for example, accepts this data and the government of Canada publishes a similar graph. Firstly the graph ranges over about 120 meters (not millimeters), about 400 feet. On the graph by comparison, a change of 200 millimeters (or the change in the last 120 years as per the IPCC) would be would be about the width of your eyelash. When the seas were 400 feet lower, people could walk from Russia to Alaska and from France to England. Global warmists are taking their micrometer, literally, to the last 120 years on this chart, and from that, extrapolating that we are all about to die. If sea levels go along with global temperatures, as the warmists frequently remind us, then this chart makes blatantly obvious that •Man has just about nothing to do with global temperatures, •Any temperature changes in the last 100 years are insignificant compared to longer term changes, •And current trends are most likely just the final flattening out of temperatures after rising from the last ice age. How can you blame man for sea levels rising when about 99% of that rise since the last ice age occurred before man built the pyramids, much less SUVs? A rise in sea level over the last century should not be surprising; it's been rising for the last 20,000 years. If anything, looking at this chart would convince me that long term temperatures are cyclic and that we are coming near the end of the warming part of the cycle. In fact, it looks like we are near the peak of that warming and could be about to enter the cooling-down part of the cycle. Over the last 20,000 years, man did pretty well. His population grew from fewer than 10 million to almost 7 billion. He had an agricultural revolution, an industrial revolution and an information revolution. He started cities. He started writing. He started recording his own history. He walked on the moon. Over that time, the sea level rose about 120 meters. If the current trend continues, it will rise two meters in the next 1000 years. If man thrived like he did when the seas rose 120 meters, why would the world end if they rise another two?
125972. gubisoul at 23:08 PM on 18 December 2009
        An overview of Antarctic ice trends
        Is it possible to get data for land ice somewhere easy? I would like a longer periode to analyse on. For me 5 years isnt really enough to show a trend. Because if 5 years was enough for that, you could cherry pick and find data that actually shows that co2 has nothing to do with global warming. So a period of 40-50 years of data around land ice would be super, if anyone could help me with finding the right place to look.
125973. Riccardo at 20:28 PM on 18 December 2009
        Predicting future sea level rise
        Those of you who have acces to Nature and are less inclined to the mathematical details of the anlysis should take a look at the published version of Kopp 2009 paper.
125974. Riccardo at 19:23 PM on 18 December 2009
        Predicting future sea level rise
        HumanituRules, the thermal expansion coefficient of sea water actually increases with pressure; hence, heat going into the deep ocean has a larger effect on sea level. The fact that current model do not include warming in the deep ocean is one more contribution to the underestimation of sea level rise.
125975. HumanityRules at 12:13 PM on 18 December 2009
        Predicting future sea level rise
        I guess that temperature could be replaced with energy in this article. The important issue being that with warming globe sea level rise will depend on where that energy is flowing (into sea/land ice, land, atmosphere, shallow or deep water etc). In your post "Understanding Trenberth's travesty" you reported on recent work to suggest that some of the energy is following into the deep ocean. My understanding is that old theories ignored deep oceans as an unimportant energy sink, being relatively stable. Energy into here, due to the higher pressures, has little affect on sea level. I was wondering whether is work is intergrated into estimates of sea-level rise. On a broader point Trenberth seemed unable to balance both the energy bugget and observed sea-level rise based on what we presently know. Suggesting there may be room for an unknown in the energy budget equation. I was wondering what impact that has on the work you present here. Trenberth's paper
        Response: The issue of heat being sequestered into the deep ocean has no bearing on the semi-empirical method. I'm not sure to what degree it will affect the kinematic study but the general sense I get from both papers is that thermal expansion becomes less of a contributing factor as time goes on. The newly released paper on the last interglacial (Kopp 2009) backs this up, finding ice sheets are vulnerable to sustained warm temperatures.
        
        Pfeffer 2008 is freely available online (you can register on Science for a free account) so I leave this one as an exercise for the reader :-)
125976. Riccardo at 09:44 AM on 18 December 2009
        Is Pacific Decadal Oscillation the Smoking Gun?
        farwalker, to be honest, i do not have the will to go through the 55 pages of that (unpublished?) paper. But just from the first few pages you may realize that the whole reasoning is based on a faulty assumption: recovery from the LIA. What does it mean recovery? Is there any predefined climate state that have to be restored? Does it happen without any forcing? This argument would make even the skeptics crazy, they who love the sun so much! Indeed, there has been an increasing sun activity from the Maunder minimum but it has stopped about 60 years ago. The temperature increase from the mid 19th century up the the mid 20th century is surely due in part to the sun; but from then on it can not be the sun. Another faulty claim is that global warming has stopped in the last decade. There are good reason to believe that it's not cooling; and there's no way to support this claim based on temperature data. (Also here).
125977. Riccardo at 08:58 AM on 18 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        SNRatio, this is where it all started in #14: "Apropos sensitivity: Who is quite sure that a 3 deg sensitivity at the doubling from 140 to 280 ppm necessarily implies a 3 deg sensitivity at the next doubling, to 560 ppm? I'm not :-)" Here you are linking sensitivity and temperature. It's correct, they are by DT=lambda*DF. So the issue is wether the forcing is logarithmic or not. If it is, whenever CO2 concentration happens to double, you'll get 3 °C. Now, maybe I misunderstood your question. Are you asking if climate sensitivity can be assumed constant? Then in #20 you mention absorption band overlap. In my mind sensitivy is defined by the relation above. Then overlap has nothing to do with climate sensitivity but, eventually, with the forcing. This is the rationale of my comment #29. CO2 forcing does not depends on overlap, it's already considered. Maybe I misunderstood again or maybe we call sensitivity two different things. In #30 you explicitly say that "100 year sensitivity may be only about half of equilibrium sensitivity". This sensitivity can not be used to compare different time span or different situations; for example, even keeping everything else constant the next 100 years you'll get a lower "sensitivity", given that the process of reaching equilibrium is not linear. So, you can use this different definition of sensitivity just for inter-model comparison ot to compare them with reality in the very same situation and time span.
125978. timbo1235 at 08:33 AM on 18 December 2009
        Predicting future sea level rise
        Problem with this, and this goes to most PR/comms with the public from science (and is a big failure in engagement with the public by science) is that these numbers have zero immediacy with the public. I'm far from being a skeptic (I bled concern at heresysnowboarding.com/blog) but I look at 2050 and see anything from 20-60cm and I think, so what. What science needs to do is make it clear in terms of lost land (i.e. X%) or number of people displaced, amount of arable land lost etc etc. Putting up values of 4cm, 10cm etc doesn't mean much to fat, lazy, ignorant, unconcerned Western consumer...
125979. adrianco at 08:02 AM on 18 December 2009
        Predicting future sea level rise
        I just finished reading James Hansen's new book (Storms of my Granchildren) where he talks a lot about sea level rise and references a bunch of papers. Could you do a review and summary of Hansen's position vs. the other researchers in this area? Thanks.
125980. farwalker at 05:55 AM on 18 December 2009
        Is Pacific Decadal Oscillation the Smoking Gun?
        I think this is they correct place for this question, has anyone examined Akasofu's paper claiming that we are now in the cooling phase of the multi-decadal oscillation? http://people.iarc.uaf.edu/~sakasofu/pdf/two_natural_components_recent_climate_change.pdf Is there any merit to his arguments? It looks convincing but perhaps a little too neat.
125981. Patashu at 02:22 AM on 18 December 2009
        Climate's changed before
        Right; there are positive feedbacks, but they are not boundless. Water vapour can only be added into the atmosphere up to saturation point, counterbalanced by a tendency to rain more the more there is. Greenhouse gasses trapped under permafrost, ice, in the ocean and wherever else can only be released once, and there's only so much ice to melt to diminish Earth's reflectivity. One of the things that can counteract an excess of CO2 is excess growth/adaption of plants, and IIRC this is what eventually causes the atmosphere to bounce back and temperatures with it.
125982. Ned at 01:11 AM on 18 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        Batsvensson writes: "If CO2 can make the planet come out from an ice age isn't it also a plausible idea that CO2 can prevent the planet from entering an ice age as well? " As far as I understand it, there's a lot of disagreement as to the probable timing of the next glacial cycle in the absence of human intervention. Most people (but not all) now think that the current interglacial would have been longer than the Eemian (basically, cooling over the past millennia would have dipped towards the tipping point for initiation of a new glacial cycle, but probably not gotten cold enough). The next tipping point comes in ca. 50,000 years from now, when the Milankovich forcing almost certainly would be sufficient to start glaciation. Depending on how much CO2 we emit over the next 200 years, it's entirely possible that there will still be enough in the atmosphere to prevent the next glacial cycle from starting 50,000 years from now. That's a pretty astonishing thought, IMHO. See Clausen et al (2004), Did Humankind Prevent a Holocene Glaciation? Climatic Change, 69: 409-417. Not everyone agrees, however. I haven't discussed this with them, but my former colleagues Steve Vavrus and John Kutzbach have a paper out (coauthored with Bill Ruddiman) which allegedly confirms Ruddiman's hypothesis that we would already have started a glacial cycle if it weren't for the initiation of agriculture several millennia ago: Vavrus et al., 2008, "Climate model tests of the anthropogenic influence on greenhouse-induced climate change: the role of early human agriculture, industrialization, and vegetation feedbacks" Quaternary Science Reviews, 27: 1410-1425.
125983. Ned at 00:46 AM on 18 December 2009
        Skeptical Science housekeeping: Twitter and double-posts
        pico writes: Lately I've been seeing 'skeptics' trotting out their lame argument that because there were vinyards in England during the Roman period, therefore global warming isn't happening. But you don't have that on your hottest skeptic arguments. Perhaps it is just too lame to add to your list, but it would be handy to be able to point them at a concise rebuttal. I like this rebuttal: Medieval warmth and English wine and a brief follow-up: English vinyards again To summarize: (1) Before 1200, there were at least 50 vinyards in England, all located south of a line running from Cambridgeshire to Gloucestershire. (2) During the 19th century, vinyards almost disappeared from the UK. In the 1800s, only 8 were reported. (3) In the 1950s, vinyards started reappearing, and they have increased in numbers rapidly over the past few decades. There are now over 400 in England, extending much further north than ever before (e.g., Yorkshire and Lancashire). English vinyards are probably not actually a good climate proxy, since they're affected by other factors like trade, the economy, consumption preferences, etc. But if one insists on using them as a proxy, they nicely agree with the consensus view: the North Atlantic experienced a mild Medieval Warm Period, a cool LIA, and a rapid warming post 1950, now to levels greater than the MWP (if you go by vinyards).
125984. edivimo at 00:24 AM on 18 December 2009
        Skeptical Science housekeeping: Twitter and double-posts
        Man, I send you a tweet last day thanking you for your efforts, let me thank you here again. Excellent Site
125985. SNRatio at 22:47 PM on 17 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        #27 batsvensson "If CO2 can make the planet come out from an ice age isn't it also a plausible idea that CO2 can prevent the planet from entering an ice age as well? " Sure. And we may already be past that point, relative to the variations of the other factors during the last 500000 years. With values in the upper tail of the current estimated probability density function for CO2 sensitivity, we probably are.
125986. SNRatio at 22:36 PM on 17 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        #29 Riccardo It IS about sensitivity, at least I think so! :-) My initial question was whether a 3 deg sensitivity at the 280-560 ppm doubling would imply the same sensitivity at the next doubling. This is not irrelevant for the current theme: If, for instance, sensitivity falls with increasing ln(CO2), CO2 may actually have played a bigger role in the climate variations of the reconstruction period than assumed - CO2 was, most of the time, lower than now. It is also a question of how to define 'sensititity'. Some model runs indicate that 100 year sensitivity may be only about half of equilibrium sensitivity, which may take several hundred years to reach. It's not quite implausible that the more radiative overlap, the longer the system may take to reach equilibrium. And the relevant indicator here is the observed radiation balances, not the expected. And because the H2O/CO2 ratio varies so much spatially and temporally, I think it may be hard to make good estimates of the net effects of overlapping. Making too simplistic assumptions can lead us very far astray.
125987. Riccardo at 19:11 PM on 17 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        SNRatio, you can't be so generic about band overlap. For example, the main contribution to CO2 absorbtion in the atmosphere is at about 600 cm-1 where there's no overlap with water vapour; other bands do overlap and there there's almost no contribution by an increase in CO2 concentration. For this reason CO2 absorption is essentially independent on H2O concentration. This was about forcing and the reason why it is more or less logarithmic. Then comes feedbacks and climate sensitivity, but it's a completeley different story.
125988. Craig Allen at 16:35 PM on 17 December 2009
        Skeptical Science housekeeping: Twitter and double-posts
        Thanks for that tip John. Is it possible to add a search box to that feature so that the lists in the drop-down boxes get filtered by a search term applied to the pages they refer to?
        Response: That's a clever idea, I've added a search form to the Link To Us page. Many thanks for the suggestion!
125989. Bern at 15:13 PM on 17 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        batsvensson @ 27: I think that it sounds pretty plausible to me. But what happens if we aren't heading into an ice age, and we throw that additional forcing on top? That seems to be the issue at present. WAG @ 23: a colleague of mine summed it up nicely. There have been climate changes in the past, many were quite large. The difference is that we weren't around to see them. 'We' being 'human civilisation' - there were hunter-gatherers around at the end of the last ice age, but the entire development of human civilisation has taken place in a relative stable period of climate history.
125990. Craig Allen at 15:00 PM on 17 December 2009
        Skeptical Science housekeeping: Twitter and double-posts
        By the way, I just noticed the 'link to this post' link that John has at the top of each of his posts. Up til now I've been typing out the links manually - doh! Use it people, It'll significantly enhance your wack-a-mole capability.
        Response: Even more useful is the "Link To Us" page (look for the link in the top navigation links) which generates up to 5 URLs for you. It also gives you the option to either generate a plain URL, HTML link or even a short answer along with the URL.
125991. Craig Allen at 14:56 PM on 17 December 2009
        Skeptical Science housekeeping: Twitter and double-posts
        That may have been me Em, I'm constantly pointing people here. John provides the most incisive, concise explanations of the science anywhere. Thanks John! Lately I've been seeing 'skeptics' trotting out their lame argument that because there were vinyards in England during the Roman period, therefore global warming isn't happening. But you don't have that on your hottest skeptic arguments. Perhaps it is just too lame to add to your list, but it would be handy to be able to point them at a concise rebuttal.
        Response: The general argument is addressed indirectly when answering the argument "The Medieval Warm Period was warmer than today". The answer is that while certain regions show past warmth comparable to recent decades, the global average temperature is cooler over the past 1,700 years (Mann 2008).
125992. batsvensson at 14:08 PM on 17 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        "a positive feedback system which enabled our planet to come out of a global ice age." If CO2 can make the planet come out from an ice age isn't it also a plausible idea that CO2 can prevent the planet from entering an ice age as well?
125993. Em at 12:56 PM on 17 December 2009
        Skeptical Science housekeeping: Twitter and double-posts
        I was lead to this site by somebody posting a comment on The Age website, and I am so glad I found it! I had been reading comments made by sceptics on forums like The Age, and trying to make informed comments myself, but the whole tone was so shrill and relied in the end to name calling and be-littlement of people with opposing views (the amount of times I was told to go and "educate" myself for having a view that sided with scientific results not conspiracy theories!). This site is like a drink of cold water - very refreshing!
125994. HumanityRules at 11:32 AM on 17 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        Chris #17 I agree the Nature blog isn't peer reviewed I did suggest it as a jumping off point because it does give a view of the development of the hockey stick idea as well as linking to some peer reviewed papers that questioned the science. I can accept that Mann didn't stumble on the MWP as a regional phenomenon in 2009 but I'd question the validity of the papers you present Crowley 2000 - The main conclusion of this paper is that the MWP can't be described as warmer than 20th century. It describes MWP as occuring in the NH only because it recognises insufficient data in the SH. You can't say something is regional just because you don't have data for the other regions. Bradley 2003 - Again this paper bemoans the lack of records in the tropics and SH. Concludes that evidence of a MWP is safest in Europe. Again MWP as a regional phenomenon can't be deduced due to the poor spread of data. Jones 2004 - "Regional conclusions, particularly for the Southern Hemisphere and parts of the tropics where high-resolution proxy data are sparse, are more circumspect." Osborn 2006 - This states it is an analysis of the NH. It is impossible to draw conclusion on SH. They are generally working with averaged data from 14 proxys and make no attempt to define spatial variation. Based on averaged data they find evidence of a MWP. Wanner 2007 - I don't fully follow this 38 page blockbuster again I'll stick to one quote to prove my point. "It is still an open question whether the MWP–LIA transition was caused by external forcing, and its spatial extent is still not entirely clear" It appears the MWP is a northern Hemisphere phenomenon only because we have data for the NH. It is funny that with essentially the same data sets Mann in 2009 can draw such definitive maps of the globes temperature 1200 years ago. It should be remembered he is still working with only a handful of proxy data sets in the tropics and whole of the southern hemisphere. I assume he uses modelling to fill in the huge gaps. Mann's desire for certainty in his work is his shortcoming.
125995. trout at 10:40 AM on 17 December 2009
        Skeptical Science housekeeping: Twitter and double-posts
        I just wanted to say thanks also for this great site, its a invaluable tool, filled with science, logic, reasoning and critical thinking. Keep up the great work.
125996. yocta at 09:41 AM on 17 December 2009
        Skeptical Science housekeeping: Twitter and double-posts
        You're right NewYorkJ. I only started coming to this site a little over a month ago. I was appalled at the media's grab at the "controversial" science around global warming and couldn't believe how quickly people lapped it up. So even if it is a sad result it has forced me to do proper research on global warming so I can actually fight back with facts and openness. (and yes part of the spike in web traffic is to do with me, my family and friends I have forwarded the link to which has to be a good thing!) Thanks John!
125997. NewYorkJ at 08:55 AM on 17 December 2009
        Skeptical Science housekeeping: Twitter and double-posts
        On a general topic, web traffic to your site (according to alexa.com) has increased significantly over the last couple of months. This is true of most blogs on climate science (or those pretending to cover climate science) and is likely a sad result of the stolen emails incident. A big chunk of the population doesn't care about science unless there's some juicy gossip being perpetuated by an eager media machine. The traffic increase here appears to be a bit sharper relative to previous traffic than with other sites. I think the expansion to a blog format is a good thing. This site helps inform visitors what the science says, allowing them to cut through the spin they might be reading elsewhere. Keep up the good work. Not a big deal or at all high priority, but you might want to update the following skeptical argument at some point (see my last post in the comments section): http://www.skepticalscience.com/1934-hottest-year-on-record.htm
125998. Phil at 07:59 AM on 17 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        Mizimi @21 H2O and CO2 have the same number of IR active vibrations - 3. An absorption band at a given frequency is due to a specific vibration. For example the 650cm-1 CO2 absorption is due to the (doubly degenerate) bending mode. So more asymmetry in a molecule does not mean more absorption at a given wavelength. It usually means more wavelengths at which it absorbs. However asymmetry will complicate the rotational-fine structure of a particular IR absorption, however H2O's rotational fine structure will be quite dispersed because of its light mass (18 compared to CO2's 44)
125999. jebjones42 at 07:20 AM on 17 December 2009
        Climate's changed before
        I'm curious. Do we know what caused the reversal in past warm periods in the Earth's history? What made it get cool again? Clearly, despite CO2 having a positive feedback loop, we didn't get runaway warming. We're not living on Venus. Even if we're headed for higher temps, rising sea levels, drought, mass extinctions, catastrophic loss of human life, etc. At some point won't it top out an head back to another ice age? What's prevented a runaway greenhouse effect in the past?
126000. chris at 06:36 AM on 17 December 2009
        Hockey sticks, 'unprecedented warming' and past climate change
        re #21 It depends on a lot of things. Obviously it depends on the wavelength - you are really only talking about wavelengths where the CO2 and water vapour absorption bands overlap. In such a case the relative absorption is chracterised by the (wavelength-specific) absorption coefficient. Water vapour does have a stronger absorption than CO2 over the range of longwave IR wavelengths/frequencies relevant to the greenhouse effect (the wavelengths/frequencies appropriate for surface heat dissipation to space). All of that is "accounted for" in analysis of the greenhouse effect and the effect of raising greenhouse gas levels.

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