Sea level rise – it’s still happening, isn’t it? Part 1

The recent reports in the media and the spin-off commentaries on sea level rise have been enough to confuse anyone. Here, I wish to set the record straight on a few key points.

Last week, a journalist emailed me with the following:

In a recent New Scientist article you’re quoted as saying that sea-level rise is accelerating. What data are you going by? Data from the Univ of Colorado suggests sea-level is rising linearly, but not accelerating.

I reproduce the U. Colorado chart above, which shows the change in global mean sea level (in mm) between 1992 and 2010, as monitored by satellite altimetry. As you can see, the journalist asked a valid question — the straight-line regression fits the data reasonably well, and there even seems to be a slight deceleration since 2006 (although the highest recorded anomalies in the whole chart come from 2010). The CSIRO also has a nice chart of these data, here, which includes regional trends and some nice animations.

They say the following:

Last two decades

High quality measurements of (near)-global sea level have been made since late 1992 by satellite altimeters, in particular, TOPEX/Poseidon (launched August, 1992) and Jason-1 (launched December, 2001) and Jason-2 (launched June, 2008). This data has shown a more-or-less steady increase in Global Mean Sea Level (GMSL) of around 3.2 ± 0.4 mm/year over that period. This is more than 50% larger than the average value over the 20th century. Whether or not this represent a further increase in the rate of sea level rise is not yet certain.

The New Scientist article that was referred to was Shape-shifting islands defy sea-level rise. It reports on a recent scientific paper which has used GIS analysis to show that the majority of Pacific coral atoll islands are not shrinking in the face of sea level rise, and indeed a lot are growing. I also made some comments to the NS journalist for that story, and later for ABC Radio in their coverage of this story, in which I said:

Well it is surprising in that sea levels are obviously rising. I think in the short term it suggests that there may be more time to do something about the problem than we’d first anticipated. But the key problem is that sea level rise is likely to accelerate much beyond what we’ve seen in the twentieth century.

Actually, I said a lot more that went unreported. One major point I made was that due to erosion, land was being lost along some areas and accreted along others — but this was not a ‘like-for-like’ exchange.  The new ‘land’ being created was the result of erosion and coral rubble and would be unlikely to be suitable for use by people or fauna/flora for some time. By contrast, the old land being lost or degraded due to regular flooding and  salt water intrusion was more likely to have had previous amenity, as beaches, for housing, or even as agricultural land.

There also came the attempts at ridicule from some — I wonder why they bother, or whether they really understand the point being made.

Anyway, how did I respond to the journalist’s question? I said this:

Sea level rise is indeed accelerating. Here is a recent review on the topic that summarizes the data:

Church, J.A. & White, N.J. (2006). A 20th century acceleration in global sea-level rise. Geophys. Res. Lett., 33, L01602.

Multi-century sea-level records and climate models indicate an acceleration of sea-level rise, but no 20th century acceleration has previously been detected. A reconstruction of global sea level using tide-gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea-level rise but no significant acceleration over this period. Here, we extend the reconstruction of global mean sea level back to 1870 and find a sea-level rise from January 1870 to December 2004 of 195 mm, a 20th century rate of sea-level rise of 1.7 ± 0.3 mm yr−1 and a significant acceleration of sea-level rise of 0.013 ± 0.006 mm yr−2. This acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed. If this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm, consistent with projections in the IPCC TAR.

This is also true in the Pacific, e.g.:

Gehrels, W. Roland, Bruce W. Hayward, Rewi M. Newnham, and Katherine E. Southall (2008). A 20th century acceleration of sea-level rise in New ZealandGeophys. Res. Lett., 35, L02717.

And

Merrifield, M. A., S. T. Merrifield, and G. T. Mitchum (2009). An anomalous recent acceleration of global sea level rise. J. Clim., 22, 5772.

So, the key is that small, short-term fluctuations in the rate of sea level rise are driven by events such as ENSO, whereas the trend in sea level rise must be assessed over the multi-decadal time scale. The 20th century rate of sea level rise averaged 1.7 mm per year, whereas over the last 15 years it has been >3 mm per year. This is an acceleration in the slope, and is not well characterised by a linear regression.

A SEAFRAME monitoring station

In addition to the satellite data, the Australian Bureau of Meteorology and National Tidal Centre is also measuring sea level in the Pacific, via their SeaFRAME network which uses an acoustic monitoring methodology that includes corrections for vertical land movement due to tectonics, etc. A summary of the recent results from the South Pacific are given here, with separate reports for each island. The net relative trend differs from station to station — around the Australian coastline it varies from as low as 1.3 mm per year to as high as 8 mm per year. Some examples from the Pacific islands include 5.7 mm/yr in the Cook Islands, 8.1 mm/yr in Tonga, 3.3 mm/yr in Kiribati and 5.3 mm/yr in Tuvalu.

In general, mean sea level has risen at relatively high rates in the southwest Pacific region and has fallen in the northeast Pacific, illustrating basin-wide decadal variability in the Pacific Ocean.

There has also been interesting recent work on this historical record which has attempted to eliminate some of the unexplained variation we see in the tidal gauge record of sea level rise. For instance, the 29,000 large dams and reservoirs that have been built since 1930 have stored so much water on land (nearly 11,000 cubic kilometres worth!) that they’ve masked the full extent of recent sea level rise — without them, it would have been ~30 per cent higher! There is a good review of the work on Mongabay.

So, that’s the recent observational record. Sea levels continue to rise, and indeed, on the multi-decadal scale, that rise is not steady, it’s accelerating (but not geographically uniform).

What of future sea level rise? There’s been a lot of work in this area since 2005, and it’s definitely worth another post. Stay tuned for Part 2.

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51 Comments

  1. Very little awareness of sea level rise in Australian government or industry that I can see.Maybe we need another King Canute to demonstrate to the faithful in the Growth At Any Cost Church that nothing,but nothing,holds back the tide.

  2. I would have liked a little more “context”. The current trend of rising sea levels started about 20,000 years ago when the Laurentide ice sheet extended to where Ney York city is today. The sea level was 130 meters below present levels and over the next 12,000 years sea levels rose ~125 meters, for an average of 10 mm/year.

    For the last 8,000 years sea levels have been rising at a much slower pace as there is relatively little continental ice available for melting. Thermal expansion or contraction of ocean water is now a major contributor to sea level change.

    There is still plenty of ice left to melt so (as James Hansen loves to point out) the sea level can still rise another 70 meters. However at present (~ 3 mm/year) rates it will take 20,000 years to do so.

  3. Its the GRACE satellite data that is showing the acceleration in melting of ice in the arctic and in antarctica and in greenland. The last time I looked at the data it showed an approximate 8% per year acceleration that seems to be pretty steady.

  4. gallopingcamel,

    Don’t you think that adequate “context” when comparing sea level rise at the end of the Pleistocene glaciation to sea level rise observed now, would be to look at the global ice volume to melt volume ratio? I.e. I would assume that the rate of sea level rise now is much greater for the amount of ice there is on the planet.

    Also, with accelerated melt (of 8% per year if Gene Preston’s figure is correct), doesn’t this imply that the ~ 3 mm/year figure will fairly rapidly increase, particularly if global temperature continues to increase? I.e. the 20, 000 year figure could be out by, say, an order of magnitude.

  5. gallopingcamel, Gene, I will cover the issues of ice sheet contributions and the possibility of further acceleration in SLR in part 2.

    gallopingcamel, for now, I point out that:
    (1) New York city wasn’t there 20,000 – 12,000 years ago, so that natural SLR had no impact on urban environments

    (2) The rate of SLR in meltwater pulse 1A at ~13-14 ka was ~40 to 60 mm/yr, sustained for a period of 200-500 years

    (3) It’s not clear that there was any net SLR between about 6 ka and 200 years ago (perhaps 1-2 m at most, over a 6,000 year period, which is a rate of 0.1-0.3 mm/yr, which is more than an order of magnitude slower than current rates of SLR).

    (4) No credible analysis suggests that present rates of 3 mm/yr will continue for 20,000 years, given current forcings.

    More in Part 2.

  6. Another line of evidence is the recent paper describing observations of accelerated uplift of the margins of Greenland, Iceland, and Svalbard due to accelerated ice mass loss.

    Accelerating ice mass loss would tend to = accelerating sea level rise.

    A Science News account of the paper is here http://www.sciencedaily.com/releases/2010/05/100518170218.htm

    The abstract of the paper itself is here http://www.nature.com/ngeo/journal/v3/n6/abs/ngeo845.html

  7. The 20,000 year context of sea level rise shows that huge changes in sea level occur naturally and quite rapidly.

    As Barry points out there were no people living in New York city 20,000 years ago. My point was to show that ices ages are more to be feared than warm periods owing to the huge areas that are made uninhabitable by spreading ice sheets.

    While rising sea levels do present problems, the “cures” may be worse than the disease. I have no objection to local solutions such as those adopted in Holland through the building of sea walls. What I fear are solutions of a global nature that boil down to reducing the average global temperature.

    Be careful what you wish for…..you may get it sooner than you imagine.

  8. Brian that is the Washington TIMES, not the Post (maybe Barry could correct your post?)

    (The Washington Times is a far-right Moony paper.)

    [Ed: Done, thanks]

  9. GC said:

    What I fear are solutions of a global nature that boil down to reducing the average global temperature.

    I suppose I shouldn’t bite, but what the heck?

    There are no solutions in prospect that “boil down to reducing the average global temperature”. The most radical of proposed solutions hope to constrain average global temperature rises by the end of the century to no more than 1.5degC — which would mean of course that large parts of Africa and Latin America would get 2-3 degreesC of rises. It will almost certainly be more than a hundred years (if ever) before the humans living then can anticipate the temperature returning to what it was in 1880 which in turn was nothing like the temperature during which ice sheets covered large parts of North America.

    The idea that we might get our wish even for a stabilisation of average global temperatures, (leave aside a decline to ice age conditions) sooner than we would imagine is palpable nonsense. Most of us now alive and capable of wishing on the matter won’t be alive to see stabilisation, and our wishes, whatever they are, will be entirely moot.

  10. I think that Galloping Camel is truly deserving of the “King of the Red Herring” award. How many irrelevant arguments can one person make? This is not a matter of refuting incorrect arguments, but of asking, “What is the relevance to the present circumstances?”.

    Red Herring #1: Yes, G.C. sea levels have risen naturally in the past; however, they’ve been fairly stable for ~2,000 to 4,000 years (prior to the onset of 20th century warming), during which time a vast amount of human infrastructure has been built worldwide within a few meters of what WAS sea level. These facilities will be at risk with additional rapid sea level rise.

    Red Herring #2: Yes, climate change has occurred “naturally” in the past; however, contemporary climate change is being driven largely by anthropogenic greenhouse gases, so how is past (natural) climate change relevant to contemporary (anthropogenic) climate change. The fact that we are contributing to it gives us the opportunity to potentially do something to lessen the impact, if we deem it to be sufficiently important.

    Red Herring #3: The onset of an Ice Age would indeed be ominous, particularly if were to occur within 100 year time frame, (And please don’t tell me that the “Little Ice Age” was an “Ice Age”) What we are actually facing, however, is substantial anthropogenic warming on a 100-year time frame. And the relevance of an hypothetical Ice Age to our present situation would be…… (What?)

    Red Herring #4: You are correct that a substantial component of contemporary sea level rise is due to heating of the oceans (caused by enhanced greenhouse warming) and associated thermal expansion of the water. Also contributing to this rise is the accelerating melting of the Greenland and Antarctic ice sheets and mountain glaciers (also driven largely by anthropogenic warming). Now that we’ve agreed on that detail, what exactly is your point?

    Red Herring #5: At present rates, it would require thousands of years to completely melt Antarctica and Greenland. However, there’s ample scientific evidence that the contemporary rate of melting is accelerating. But even if it weren’t, why are you concerned about how long it would take to melt the Antarctic ice cap. Human civilization and natural ecosystems will be affected by much smaller sea level rises that are likely to occur within a few generations. So your argument is relevant how?

    It’s difficult to make progress in defining, understanding, and addressing REAL issues related to climate change, when distracted by irrelevancies.

  11. gallopingcamel,

    My comment actually pertained to the evidence for and interpreted cause(s) of recent sea level rise. The issue of response and remediation is quite another topic. It’s certainly an extremely important and valid question, but one that is well outside the scope of the current post, and not one that I’m particularly qualified to speak on.

    In any case, before we are able to address the question of response(s) to climate change, we first need to have a realistic understanding of what changes are actually occurring, what’s causing them, and how might they be expected to change in the future (taking uncertainty into account).

    I’ve found that in skeptical dialog about climate change, questions related to climate often become muddled together with questions relating to response, as if what we conclude about climate change depends in some way on what, if anything, we can or should do about it. I prefer to keep these issues separate. Otherwise we might allow bias to affect our scientific assessment of what’s happening and why.

    To be very candid, I do think that many skeptics allow concerns about possible response(s) to climate change to dictate their understanding of the science, to the extent that some (many?) go to extreme measures to refute the evidence. That’s just a general observation, which may not be pertinent in this case.

  12. gallopingcamel — What will occur, this being just physics and geology, is an S-shaped curve of average sea level over probably several millennia. I crudely estimate several tens of meters, but this will depend upon future CO2 emissions. The main point is that the growth will accelerate for centuries to come.

  13. Thanks to satellites we can make reliable measurements of sea level rise. Since the mid nineties the sea level change has averaged about +3 mm/year. The average for the 20th century was significantly less so “Yes”, it is plausible to suggest that sea level rise has accelerated recently.

    Sea levels rose about 130,000 mm from 20,000 before present to 1850. We can be sure that all of this increase was of natural origin even though the underlying causes are not well understood. The sharp temperature rise that triggered the initial rapid rise in sea levels preceded the rise in CO2 concentration (from 200 ppm to 280 ppm) so it is not plausible to suggest that CO2 drove the process.

    How much of the 285 mm rise in sea level since 1850 can be attributed to natural causes and how much is man-made?

    There are papers that attempt to answer this question. For example Jevrejeva, Grinsted, Moore (2009):
    http://www.glaciology.net/Home/PDFs/Announcements/anthropogenicforcingdominatessealevelrisesince1850

    Even if Jevrejeva et al. are right (there are many who doubt them) the rate of rise is unremarkable. Looking to the future, levels may continue to rise for the rest of the 21st century or they may fall as they did from 1450 to 1850.

    In the immortal words of Douglas Adams, “Don’t Panic”.

  14. “We need “somewhere” to pump all that off peak Nuclear generated desalinated water”

    Yes, because all of Australia’s dams are just so full that we couldn’t possibly pump desalinated water into them without breaking the banks.

  15. gallopingcamel, on 17 June 2010 at 12.49 — Excess CO2 from buring fossil fuels and deforestation is driving global temperatures upwards. This has been well understood for over 30 years now. While I can’t readily attribute SLR to human causation, there being also empondments and ground water depletion to account for, I can say something sensible about global temperatures:
    http://www.realclimate.org/index.php/archives/2010/03/unforced-variations-3/comment-page-12/#comment-168530

    Even if just current CO2 levels are maintained much existing ice will eventually melt as CO2 levels are about the same as those in the Milocene.

  16. David B. Benson,
    Thanks for that (rather long) link. Temperatures since 1850 have indeed risen but by such a small amount that one needs to forget about the actual temperatures and use sophisticated statistics to tease something out of the “anomalies” and “residuals”. For every Tamino there is a McIntyre.

    The radiative forcing caused by variations in atmospheric CO2 concentration is well understood by the Alarmists and Skeptics alike. However you are on shaky ground when you state:

    “Excess CO2 from buring (sic) fossil fuels and deforestation is driving global temperatures upwards.”

    CO2 does not drive global temperatures on any time scale from mega-years to decades.

    Getting back to sea level changes and the canard that CO2 causes ice to melt check out the Ice Age that occurred 450 million years ago when the CO2 concentration was ~4,400 ppm. The lengthy Ice Age that started in the late Carboniferous happened when CO2 concentrations were similar to today.

    Technically, our planet is still in an Ice Age as there are ice caps at both poles. For much of Earth’s history, average temperatures were 7 degrees Kelvin above today and naturally there were no ice caps at the poles. The eustatic sea level was ~75 meters higher back then.

  17. gallopingcamel, on 21 June 2010 at 8.44 — CO2 certainly drives temperatures on the scale of mega-years:
    http://www.globalwarmingart.com/wiki/File:Five_Myr_Climate_Change_Rev_png
    on the scale of 40–120 millennia:
    http://en.wikipedia.org/wiki/File:Carbon-dioxide-temperature-plot.svg
    down to the decadal scale. This is fundamental atmospheric physics first understood by Arrhenius, whose formula I used. Richard Alley gave a very good talk about it at last fall’s AGU meeting; the video is available on-line. In essense, the scientific understanding was complete by 1979:
    http://books.nap.edu/openbook.php?record_id=12181&page=R1
    and little more has been added since. I suggest you learn this basic application of the laws of thermodynamics and radiative properties of triatomic (or more) molecules.

    Configuration of the continents and the dim early sun explain
    http://en.wikipedia.org/wiki/Snowball_Earth
    etc. Eearly high concentrations (above 1000 ppm of CO2) have recently been brought into most serious question.

    Yes, the entire
    http://en.wikipedia.org/wiki/Quaternary
    has been an ice age. However, agriculture and civilization depends upon remaining in the stable climate of the
    http://en.wikipedia.org/wiki/Holocene
    or at least not departing from it very rapidly. Unfortunately, we are now heading quite quickly towards the
    http://en.wikipedia.org/wiki/Neogene
    and SLR of several tens of meters (about 70 m maximum). Those conditions existed before lines leading to humans split off from other primates. Whtever, this rapid change is not good for the continuance of civilization, IMO.

  18. Galloping Camel,

    It’s hard to have a meaningful dialog unless we are all “speaking the same language”.

    The term “alarmist” describes “a person who tends to raise alarms, esp. WITHOUT SUFFICIENT REASON, as by EXAGGERATING dangers or PROPHESYING calamities.” (from http://dictionary.reference.com/browse/alarmist?db=dictionary, with emphasis added.) I understand the term “prophesying” to refer not to rational, science-based predictions, but to irrationally-inspired beliefs. They’re not necessarily wrong,… just not scientifically supportable.

    This might describe a very small subset of overly zealous environmentalists, or opportunistic media people who engage in sensationalism and exaggeration, but it certainly would not describe the vast majority of climate scientists who earnestly try to understand contemporary climate change, and to predict, with appropriate levels of uncertainty. what the future may hold in store. As such, I disagree with your assessment that “Alarmists” understand the scientific basis for climate change attribution and prediction. In general, they don’t.

    I would agree with you that there are indeed skeptics who understand the scientific basis for AGW, yet remain skeptical regarding human impact. But here we are talking about an exceedingly tiny proportion of the climate science community. In general, their voices are drowned out by the overwhelming din of Denialists, who seem to understand little of the actual scientific basis for AGW, and are so biased in their approach that their acceptance or rejection of scientific evidence is dictated not by the evidence itself, but by whether it conforms to their rejection of AGW. One of the strongest indicators of Denialism, by the way, is reliance upon specious “reasoning”, especially Red Herring and Straw Man arguments.

    Thus, I’m puzzled by your statement, “The radiative forcing caused by variations in atmospheric CO2 concentration is well understood by the Alarmists and Skeptics alike.”. By using the article “the”, it makes it sounds like these two groups represent widely held views on climate change, when in fact both groups are very small. Moreover, in the case of alarmists, your statement is commonly false.

    The statement, “Excess CO2 from burning fossil fuels and deforestation is driving global temperatures upwards.” is most assuredly NOT on shaky ground. This, after all, is the principal conclusion of the IPCC TAR and AR4, which is based upon a compilation of hundreds of peer-reviewed scientific studies. (You could look it up.)

    If this conclusion were actually on shaky ground, then why do you not present evidence to support your position rather than citing the same sort of irrelevant Red Herring arguments that I commented on previously. Can we make no progress here?

    Actually, what you’ve done is make a “Straw Man” argument, that is, misrepresenting what climate scientists actually say about climate change, for the sole purpose of “debunking” it. For example, what makes you think that competent climate scientists believe that CO2 is the ONLY factor that drives climate change? No competent climate scientists say this…. at least none that I’ve ever heard. If you believe they say this, then you have a great deal of work to do to understand the fundamentals of climate science.

    Do you not realize how much you undermine your own credibility as a skeptic? If you actually have valid skeptical criticisms of climate science, then why use Red Herring and Straw Man arguments? This only makes me suspect that you don’t actually have a valid basis for doubting AGW, and thus are constrained to making flawed arguments.

    Finally, let’s not play with language in an apparently (?) intentional effort to create ambiguity and confusion. We use the term “Ice Age” to refer to recurring periods in the Earth’s past when global temperatures have been significantly colder, and continental ice sheets significantly more extensive than they are today. During the Pleistocene ice ages, CO2 levels consistently have been significantly lower than they are today. We are presently in an “Interglacial” period. If you’re unsure what “interglacial” means, you could look it up.

  19. David B. Benson,
    You really need to be more skeptical about Wikipedia. William Connolley’s malign influence still prevails there.

    Just consider your first argument (40-120,000 years). This falls within the Vostok ice core record which shows a clear correlation between temperature proxies and the CO2 concentration. This is graphed in your Wikipedia reference and in Al Gore’s movie (An Inconvenient Truth).

    It is all very impressive stuff for the masses who don’t bother to check what the real science says. As measuring techniques have improved, time resolution of the Vostok data has improved to the point that we can see that Carbon Dioxide concentrations lag temperature changes by about 900 years. As cause precedes effect it is therefore proven that CO2 concentration does not cause temperature changes on this time scale.

    Here is a summary that may help you understand this issue:
    http://joannenova.com.au/global-warming/ice-core-graph/

    There are a number of respected scientists who do not but the CAGW hypothesis and they have much more credibility than Wikipedia. Your critique on the following video would be appreciated:
    http://video.google.com/videoplay?docid=-5576670191369613647#

    We can go on trading links from either side of the CAGW debate but I suspect that neither of us will be persuaded to change our opinions.

  20. TreeDoctor,
    The use of labels such as “Alarmist” or “Skeptic” in the context of climate change can be helpful. In my mind these terms are no more derogatory than “Liberal” or “Conservative”. Note that I avoided the “Denier” label that was intended to equate with “Holocaust Denial”. I am not trying to hurt your feelings by using such terms so try not to be offended.

    When it comes to IPCC reports you won’t get much argument from me if you quote from AR1. That report included the work of Hubert Lamb and recognised the “Medieval Warm Period” and the “Little Ice Age”. Later reports such as TAR and AR4 are a disgrace to the fundamental traditions of science owing to their exaltation of junk such as Mann et al. 1998 & 1999 and supporting papers.

    You can go on believing this rubbish but within the next 30 years it will be all too obvious that the IPCC’s predictions of “Catastrophic Anthropogenic Global Warming” are driven by a political agenda rather than facts that can be verified scientifically. This thread is about sea level rise; AR4 predicts an increase of 180 to 590 mm by 2100 while the “Copenhagen Diagnosis” says that these estimates are “too low”.

    While the term “Ice Age” causes confusion, I use this term to describe periods such as the Pleistocene Epoch that started 1.6 million years ago.
    This epoch has been characterised by a series of cold periods interspersed with “Inter-glacial” warm periods. The current inter-glacial is technically part of an ice age as polar ice caps still exist. Can we at least agree on this?

  21. I think it’s important to make a distinction between “skepticism” and “denialism”. The way I used the terms is becoming increasingly, widely accepted. I don’t think it’s valid to say that all those who accept AGW as likely are “alarmists”, nor to describe all those who reject AGW as “skeptics”.

    I use the term denialism (little “d”) as a generic term to describe the rejection of widely accepted conclusions for which there is an abundance of supporting evidence. AGW Denialism and Holocaust Denialism are two examples. Similar rhetorical methods are used in all forms of denialism, but I’m not implying that adherence to one form implies sympathy for or advocacy of any other. All varieties of denialism emerge from a pre-existing political/social ideology, which explains the relative absence of political content in climate science, but the overwhelming political content evident in AGW Denialism.

    I object to the use of the term “alarmist” to refer to scientists who have a rational basis for predicting future adverse impact of climate change, as it is simultaneously unwarranted and insulting. The term “catastrophe” is rarely used in scientific discussions of climate change, whereas this word is frequently encountered is in “straw man” criticisms of climate science. I don’t think the express goal of most climate scientists is to frighten or raise alarm. Shouting “Fire!” in a crowded theater constitutes alarmism if there’s no fire. If there IS a fire, then it’s a responsible and appropriate action.

    The climate science community has moved past MBH-98. MBH-98 appeared in the TAR, but not in AR4. I wish the skeptical community would forget about it, but it’s simply too rich of a target. The take-away conclusion from MBH-98 that contemporary warming is unprecedented still seems valid to me, whether or not the MWP and LIA are “smoothed over”. By the way, there is a lot of really good science in the TAR and AR4. Seizing on a limited number of examples of errors, is “cherry picking” (another commonly used method in AGW Denialism.) Throw out MBH-98 entirely and the theory of AGW still stands strong.

    Yes, I will agree that the term “Ice Age” may be used to describe longer time periods that include both “glacial” and “interglacial” intervals. This is not, however, how the term “ice age” is commonly used and understood. The important aspect is that CO2 is just one factor that contributes to glacial/interglacial cycles. There are positive and negative feedback processes that enhance or suppress cooling & warming. The important points is that higher CO2 levels in the distant geologic past do NOT disprove the role of CO2 in enhancing warming during the present Pleistocene to Recent “ice age”. It was this aspect of your argument that I was objecting to.

  22. gallopingcamel, on 21 June 2010 at 14.06 — Wm Connelley edited the climatology related pages, not the geology; he did well to keep it sanely balanced. Jeez. But of course one only starts with Wikipedia and goes on to more authoritative sources, as with any encyclopedia. I particular I provided you with a link to the Charney et al. 1979 NRC/NAS report. (Which it seems you didn’t bother to read, did you?)

    As for cause and effect, during glacial cycling, CO2 acted as a feedback to enhance the size of the cycles. In close accord to the Arrhenius formula. Jeez again. Nobody with any understanding of the physics doubts the formula is (approximately) correct.

    I recommend learning some actual climatology. Try starting with “The Discovery of Global Warming” by Spencer Weart:
    http://www.aip.org/history/climate/index.html
    after reading Andy Revkin’s review:
    http://query.nytimes.com/gst/fullpage.html?res=9F04E7DF153DF936A35753C1A9659C8B63

    Until you actually understand some of the science, your opinions are worthless. Just like all too many who fail to understand that the role of CO2 in paleoclimate is thoroughly understood and not subject to debate. What I read from you is long debunked, tirsomely so, talking points from the modern version of the Flat Earth Society. Sorry.

    I can’t watch video and wouldn’t bother in any case, but since you can, watch/listen the Richard Alley’s; he is the professional here.

  23. gallopingcamel, on 21 June 2010 at 14.06 — Oh yes. The CO2 lag is not from VOstok ice core, but from marine cores in the Pacific Warm Pool. And just from the end of LGM. If you check the beginning of MIS 11 (or is it 13?) you’ll there find indications of a lead.

    Paleoclimatology is not for the gullible, along with many another portion of geology.

  24. TreeDoctor,
    Peace on the “Alarmist” and “Denier” thing. I defer to your arguments.

    Actually, the “Hockey Sticks” did not go away either in AR4 or even the “Copenhagen Diagnosis” that was issued before the big conference:
    http://www.copenhagendiagnosis.com/
    Take a look at Figs. 19,20 & 21.

    In your last paragraph you mention feedbacks and that is a huge unresolved issue. My understanding of the radiative forcing due to a doubling of CO2 concentration is 4.2 Watts/sq. meter measured at the Earth’s surface. While there is no agreement on the effect that this has on global temperatures I will not throw a “hissy fit” if you suggest 1.2 degrees Kelvin.

    But are the feedbacks positive or negative? If you believe Lindzen & Choi, 2009 and a paper by Spenser due to be published any day now, the feedbacks are negative so the measured temperature rise will be ~0.2 to 0.4 degrees Kelvin.

    If you look at the dozen climate models quoted by the IPCC, the feedbacks will be positive so temperature rises will be in the range 4 to 7 degrees Kelvin (per doubling).

    The highest temperature the Earth has seen over the last 500 million years appears to be 22 degrees Centigrade or roughly 7 degrees above present. Given that CO2 concentrations have been above ~3,200 ppm for long periods (3 doublings relative to 400 ppm), the high temperature increase numbers are implausible.

    David B. Benson,
    As a physicist I have no difficulty with the theory of radiative forcing, thermodynamics and the basics of climate models. My research and teaching experience is in electro-optics, so when I feel the need to improve my understanding of climate science I spend time at blogs such as the “Science of Doom” where the resident gurus do not make fun of my relative ignorance.

    Take a look at:
    http://scienceofdoom.com/2010/06/12/venusian-mysteries/#comment-2953

    You will see a lively discussion involving notables such as SOD, DeWitt Payne, Chris Colose, Leonard Weinstein and many others. We don’t always agree but the discussions are helpful (at least to me).

    De Witt Payne drew my attention to a treatise by Rodrigo Caballero which I found very useful:
    http://maths.ucd.ie/met/msc/PhysMet/PhysMetLectNotes.pdf

    It is clear that you have studied the subject in some depth so I would be very interested to hear your comments.

  25. gallopingcamel, on 22 June 2010 at 13.16 — As
    http://www.realclimate.org/index.php/archives/2010/03/unforced-variations-3/comment-page-12/#comment-168530
    the already observed tempeerature response to CO2 forcing, normalized to 2xCO2, is over 2 K, so Lindzen is once again demonstrably wrong. As is further indicated by the about 2 K higher temperatures during the Eemian interglacial. Anyway, Knutti & Hegerl state that the warming just due to CO2 acting alone, without water vapor+clouds feedback would be 1.2 K. Water vapor increase abouts doubles that, and indeed that’s what my parameter estimation exercise shows; it all hangs together.

    For a more professional look at (part of) the instrumental record, study Tol, R.S.J. and A.F. de Vos (1998), ‘A Bayesian Statistical Analysis of the Enhanced Greenhouse Effect’, Climatic Change, 38, 87-112.

    As for concentrations of CO2 greater than 1000 ppm, there is recent evidence against that from around 3.4 billion years ago. For more recnet times, leaf stomata do not provide aq reliable prozy above about 1000 ppm. The net effect is not to believe stuff about paleoclimate even if it has made its way into geology textbooks. That includes claims of previous times being up to 7 K warmer than now. I’m highly skeptical of the claim and have yet to see a convincing proxy establishing that figure.

    Oh. Except maybe during the End Permian mass extinction. Please read Peter D. Ward’s “Under a Green Sky”. As for the effects of each degree of warming, please read Mark Lynas’s “Six Degrees”, which Professor David Archer assigns as reading in his class on climate for non-majors. He is a CO2 specialist and so must think the book is about right.

  26. David B. Benson,

    I can accept your argument that CO2 proxies on the >100 Mega-year time scale are unreliable with very large “error bars” and yet even the lowest estimates are much higher than today until the late Carboniferous.

    While I consider 1.2 K/doubling is more plausible than 2K/doubling both values fall within the wide range in the published literature. In hard science we like to have 3 sigma or better accuracy but in climate “science” one is lucky to get even 1 sigma accuracy, as in this case.

    I could not access that Tol paper but please be aware that when you need advanced statistical analysis to tease out a relationship between GHGs and global temperatures the effect may be unimportant. Before we get into a fight over statistics please be aware that my tutor was J.C.P. Miller

    Gabriele used to have an office 100 yards from my lab before she moved to Scotland. You should have noticed that “Knutti & Hegerl” was merely a review paper that leaned heavily on thoroughly discredited tree ring proxies; no new science at all. Her reputation is simply not comparable with Richard’s. Your “off the cuff” dismissal of L&C09 is based on a flawed critique by Kevin (Travesty) Trenberth. Kevin should “lawyer up” and stay off television as he comes across very badly.

    You mention David Archer, one of my favourite experts. He makes bold predictions based on long term climate models (The Long Thaw) and I love that. So you won’t have to read the whole book check out “Archer & Ganopolski” 2005. The Ice Age has been postponed “indefinitely”. David considers that to be a “Catastrophe”.

    I could go on but the above is intended to show that the science is far from settled. You end up trying to weigh the reputation of dozens of scientists and that is a fruitless pissing contest.

    I was hoping to get your comments on the Rodrigo Caballero treatise that replaces the lecture notes I lost many years ago. His explanation of the “Greenhouse Effect” makes sense. Thank God for the Irish.

    You come across as an intelligent individual but don’t fall into the trap of believing that people who disagree with you have never read a book, published a peer reviewed paper or earned a Ph. D in physics.

  27. gallopingcamel, on 23 June 2010 at 14.38 — The CO2 proxies can, it now seems, only inform one that the concentration was at least 1000 ppm without stating anything about how much more. What is quite new (and surprising) is that rocks formed about 3.4–3.8 billion years ago could not have been laid down in a concentration exceeding 1000 ppm. Of course, in between then and the start of the Cenezoic the concentrations could have indeed been higher, but I’d certainly want to read, in detail, about the proxy used to establish that in the light of these recent discoveries.

    Knutti & Hegerls’ value of 1.2 K for 2xCO2 is for just thew CO2 without accounting for the water vapor + cloud cover feedbacks. (That is all I need just now from that paper.) So that much one can directly check a srather simple physics is all that is required. Rather harder is the water vapor positive feedback for which some understanding of atmospheric physics and the global warming (so-clled greenhouse) effects of H2O are required; the answer is about double, so without clouds one has 2.4 K. Estimating the cloud effect is very hard as low clouds cool but high clouds (cirrus) warm. So I measured it, using the most straightforward of parameter estimation methods and found of the instrumental period 2.28 K suggesting more low cloud effect.

    First of all, the physics of CO2 as a global warming (so-called grreenhouse) gas is well established; no statistics there. Similarly for the water vapor; no statistics there either. The only statistics used are a link to BPL’s correlation, hardly advanced statistics, and I mentioned autocorrelation which is just another correlation; hardly advanced statistics. The parameter estimation method does not use any statistics at all. So I plead not guilty although I’m trying to learn a little statistics from Tamino:
    http://tamino.wordpress.com/

    The question of the response is of course closely connected to the matter of the equilibrium climate sensitivity for which Knutti & Hegerl provides a useful review, one which doesn’t actually depend upon the (prefectly good) tree ring studies.

    Tol & de Vos (1998) is available from Dr. Tol’s publications page; that”s where I obtained a copy. They go on in a rathr ineteresting fashion to obtain an estimate of ECS, using advanced statistics.

    My dismissal of Lindzen’s so-called iris effect comes directly from studiying about the Eemian, an important period in human development and not second hand by anybody. In all comes from noting the above measured value of the climate response to date, vastly in excess of anything claimed by Lindzen, and in good agreement with Tol & do Vos. And I certainly don’t care about his reputation (which he recently has been tranishing); when you are wrong, you’re wrong. Richard Feynman had something to say about that.

    I have recentlystudied Archer & Ganopolski for the third time now.

    I don’t know when I’ll find the time to read Rodrigo Caballero’s lecture notes, but I’ll give it a try.

    Diaagree with me? I’m an amateur at climatology, only helped along by being a life-long amateur geologist. What I object to is people constantly repeating long debunked denialist talking points which flatly contradict climatology, the known portions of the behavior of he climate, or cast aspersions on techniques, such as tree rings, about which they have almost no knowledge. As for that last, one of the most interesting aspects of climatology is the clever use of a variety of proxies to tease out some of the facts; much cleverer than the hard rock geologists.

  28. David B. Benson,
    We were discussing sea level rise. In my opinion the present unremarkable rate of rise is likely to continue or perhaps decline. You seem to think that the rate will accelerate owing to an increase in global temperatures driven by rising CO2 concentrations.

    So far we have not even been able to agree how the “Greenhouse Effect” is supposed to work which is why I was hoping to get your comments on the Rodrigo Caballero treatise. OK, you don’t want to read the whole thing so let’s cut to the chase. The relevant section is 5.17 that starts on page 132:

    Here is the link again:
    http://maths.ucd.ie/met/msc/PhysMet/PhysMetLectNotes.pdf

    Is this your understanding of how the “Greenhouse Effect” works or do you have an alternative explanation?

  29. gallopingcamel, on 24 June 2010 at 12.52 — SLR will accelerate just as it did during the transition from LGM to Holocene; an S-shaped curve now just getting underway.

    I still have no time for finding page 132 given my defecient pdf reader, so where is some simplified physics:
    http://bartonpaullevenson.com/Greenhouse101.html
    http://bartonpaullevenson.com/NewPlanetTemps.html
    and then there is also the Arrenhius formula in my note. That’s how it works for CO2 although other simplifying formulae are required for other global warming (so-called greehouse) gases.

  30. David,
    I hope you won’t mind me using your first name. Arrhenius’ predictions were way too high although as you correctly point out his logarithmic relationship is still widely used today. For example, I used it earlier when I mentioned that three doublings (from 400 ppm to 3,200 ppm) would imply implausibly high temperatures prior to the Devonian era using the IPCC’s sensitivity estimates.

    The important equations are shown in the Rodrigo Caballero treatise but here they are again in a presentation by Scott Denning (by courtesy of Bart Verheggen) to a recent ICCC meeting:

    http://ourchangingclimate.wordpress.com/2010/05/21/scott-denning-to-iccc-heartland-%E2%80%98conference%E2%80%99-gathering-%E2%80%9Cbe-skeptical%E2%80%A6-be-very-skeptical%E2%80%9D/

    You should note that Denning’s audience included Richard Lindzen and other Skeptics, yet he was not torn limb from limb.

  31. gallopingcamel, on 25 June 2010 at 12.53 —

    Dear Joe, :-)
    SLR predictions for 2010 CE rnage from 0.8 m (considered most likel) to 2 m (considered highly unlikely). Three different groups of enginerrs independently are using values in the range 1.3–1.5 m to setting out plans of defenses against the SLR.

    If we suppose 0.9 m, that’s an average of 1 cm per year, so the current rate of SLR is certainly expected to increase.

  32. I’m belatedly replying to GallopingCamel (22 June 2010 at 13.16 ; http://bravenewclimate.com/2010/06/14/sea-level-rise-1/#comment-75578.

    You say the “hockey stick did not go away”.

    But it did.

    I looked at the three diagrams (Figs 19, 20 & 21) trom “The Copenhagen Diagnosis”. There’s nothing wrong with these diagrams from the standpoint of currently available scientific evidence. Figure 19 is the current version of the 2000 year proxy temperature reconstruction, showing the Medieval Warm Period(s), and the Little Ice Age(s). Also included in this diagram, on the right hand side, is the current observed global temperature trend from CRU. The proxy data show more scatter partly because they don’t represent global averages. Variance in the proxy data was captured in the very large “error bars” in the original MBH-98 graph.

    Figure 20 represents Arctic air temperatures over the last 2,000 years based on proxy records from lake sediments, ice cores and tree rings. This trend shows much less variability, as it represents a more restricted geographic area. If you have some specific criticisms of this diagram, you might share them.

    Finally, Figure 21 shows basically the same average trend as Figure 19, but rescaled to show projected temperature increases to 2100, which puts the current and predicted warming trend into historical perspective.

    You are correct that the feedbacks have the greatest impact on projected warming, but simply to note that they are uncertain is insufficient basis to ignore them. They are each based on a specific set of assumptions, for which there are varying degrees of supporting evidence. Just as weather forecasting has continually improved, I expect climate prediction to continue to improve.

    And why, in heavens name, would I believe Lindzen & Choi 2009? Even Richard Lindzen acknowledges errors in this paper. It was a nice try (from a skeptical perspective), that got as far in the peer review process as getting published in a reputable journal, before getting shot down by valid scientific criticism. And holding out your hopes that Roy Spencer will save the day is really grasping at straws.

  33. TreeDoctor,
    Thanks for your interesting comments. It may take another 20 years before one or other of us is proved right.

    At least we agree that the feedbacks (positive or negative) make a huge difference. With negative feedbacks the temperature rise due to CO2 by 2100 could be as low as 0.3 Celsius which will be hard to measure with any confidence.

    The IPCC predicts rises up to 7 Celsius by 2100 in their “worst case” scenario. I regard the 7 degree number to be absurd as that would bring the planet to its highest temperature in at least 1 million years. The IPCC can keep on making absurd predictions but will reality take any notice? If the IPCC is right some pretty dramatic warming is imminent!

    With regard to your comments on the “Hockey Sticks” in the “Copenhagen Diagnosis”, those temperature plots are almost flat up to 1850 so I don’t agree that they do justice to the MWP or LIA.

  34. I’m a bit late to this thread, but maybe someone will pick up my question:

    Referring to the debate on orbital cycles: if orbital cycles warm the poles, why don’t they warm the entire planet? Obviously, orbital cycles could affect the poles more than the equator. So you have a high dT (d=delta) at the poles and a low dT at the equator at the initiation of a warming cycle, and dT stays roughly constant, then you’d see a slower change in T at the equator, and thus temperature change at the equator need not be driven by CO2. I suppose this has already been addressed. If so, please inform!

    Thanks,
    j

  35. James Harvey,
    Changes in orbital cycles that warm the poles should warm the entire planet but there are factors that “amplify” warming in the high latitudes.

    As ice melts, more land is exposed and that leads to less of the sun’s radiation being reflected into space. Changes in Earth’s albedo are considered a “positive” feedback in this situation.

    At low latitudes, a small increase in temperature causes a large increase in the atmospheric load of water vapour and this tends to moderate the temperature increase. More water vapour in the atmosphere means increased precipitation which is one of the mechanisms that moves heat from low latitudes to high latitudes.

    In climate science our ignorance is far greater than our knowledge so take what I say with a pinch of salt.

  36. Pingback: Climate change basics II – impacts on ice, rain and seas « BraveNewClimate

  37. How much is “sea level rise” affected by local conditions?
    Busselton, in south west WA is flat, low-lying, and close to sea level. The current coast line is about 250m north of where it was in the 1840s.

    Similarly an old shipwreck north of Bunbury, that was exposed up to the early 1970s, is now buried by sand.

    Grant you, only local examples, but not a lot of evidence for recent sea level rise.

    I wonder how IPCC modelling accounts for it?

  38. Pingback: Kakadu – a climate change impacts hotspot « BraveNewClimate

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