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About 6 months ago, I wrote up a summary of how paleoclimatologists determine the temperature of the past, focusing primarily on oxygen isotopes Paleoclimatology Primer. It was relatively well received, so I figured I would continue the lessons on paleoclimatology. Today we will focus on the problems/opportunities inherent to the oxygen isotope system, and a few other systems that help us get a stronger handle on the climate of the past. I highly recommend you go back and read that post first, as this post builds upon what we learned 6 months ago.

 As a warning, almost all of the links I have provided here require a paid subscription (with a few exceptions), but almost all of the links are from major journals (Science, Nature, Geology, etc.) and your local library is likely to have a subscription. The abstracts of each paper are always free though.

While it has been a while since I posted, this post will hopefully be the first in a 6 part series I hope to put up over the next two months or so. The first two posts will principally focus on how scientists create temperature reconstructions in greater detail than the primer I posted earlier. The following three posts will be about the trends we see in the climate system on different time scales. The first of those three posts being the climatic trends over the last ~33 million years (hint: it has gotten steadily colder). The second post will focus specifically on the last million years (hint: it has gotten colder and more variable). The third post will focus on the trends we see just over the last 60,000 years through the last glacial to today. The final of the five posts will talk about the history of sea level change: how we study it, what has happened in the geologic past, what has happened in the instrumental past, and what is happening now. By the end of this series, you should be more than ready to school pretty much any one (who isn’t a climatologist of course) about the Earth’s natural climate cycles.

 In the primer on paleoclimatology I told you about oxygen isotopes and what they can tell us when we measure them in the CaCO3 tests of foraminifera. We extract temperature data from the 18O/16O ratios of the foram tests, but the ratios do not purely reflect temperature. They also reflect the 18O/16O ratio of the seawater in which the shells precipitated. The oxygen isotopic ratio of seawater reflects two components: how ‘heavy’ the ocean is with respect to oxygen isotopes caused by sequestration of light oxygen in ice sheets on the continents (which I told you about last time), and the evaporation/precipitation effect (erroneously referred to as the ‘salinity effect’ in many articles/books/papers). All three components (temperature, ice volume, and evap/precip) affect the 18O/16O ratio in the carbonate shells of foraminifera. So how do we extract the portion that is due solely to temperature?

 Let’s focus on the easy one first, extracting the ice volume effect from your oxygen isotope record. Ideally, if you can know the average oxygen isotope ratio of the seawater at any given time, than you could simply subtract that value from your data and you would be left with only two variables to account for. But unfortunately (for climate science, but fortunately for those of us who want to, you know, live), the active hydrologic cycling on our planet constantly changes the oceanic composition, so the glacial ocean no longer exists. There are a couple ways to deal with this though.

 Unfortunately, there aren’t a lot of options for direct measurement of ancient water (we will discuss those options a little further down). However, we have some means of addressing the problem indirectly. A rather clever attempt at addressing the changes in δ18O due to the ice volume effect was to look at the oxygen isotopic value of benthic foraminifera from places where the water can’t get any colder than it is today (just barely above the freezing point). There are a handful of places in the world’s ocean where the water temperature at the seafloor is between -1 and 0°C. Labeyrie et al. (1987) (Variations in mode of formation and temperature of oceanic deep waters over the past 125,000 years.) looked at the benthic δ18O record from the deep Norwegian Sea where temperatures are currently -1°C. The thinking was that the temperature of the deep water here could not possibly have gotten any colder, so any change in the δ18O record in the direction of heavier isotopes can be purely attributed to changes in the average value of seawater due to changes in ice volume. Labeyrie’s work showed a change of ~1.1‰ during the last glacial from today. Among the problems with this technique is in addition to assuming the water doesn’t get any colder, it also assumes the water doesn’t get any warmer. If it did, they could potentially be underestimating the ice-volume effect.

 Another attempt at determining the ice volume effect on the δ18O of seawater during the last glacial utilized the fact that certain modern species of coral have very specific depth habitats (<5 meters from the surface). Richard Fairbanks in 1989 (A 17,000-Year Glacio-Eustatic Sea-Level Record - Influence of Glacial Melting Rates on the Younger Dryas Event and Deep-Ocean Circulation.) used ancient coral deposits to determine the sea level curve coming out of the last glacial cycle. Once he had developed a sea-level curve, he merely used an equation that turned meters of seawater into the oxygen isotope value of seawater based on the mean values of ice in Greenland and Antarctica. He accounted for a seawater change of ~1.2‰ in the oxygen isotopes using this method. It is a crude method, true, but at the time, it was the best the scientific community had. Waelbroeck and others (2002) (Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records) did a similar calculation (sea level to oxygen isotopes) albeit from a much more complicated data set and algorithm. They posited a change of ~0.95‰.

 Of course, the ideal way to figure out the oxygen isotope ratio of an ancient ocean is to find some of the ancient water from that ocean sequestered somewhere safe where it could not be altered over time. When dealing with water values of the distant past (think millions of years), one place you can look is in evaporite deposits (Hardy 1996; Lowenstein et al. 2001). Evaporites are highly crystalline minerals that form when a water body evaporates. Think salt. When salt crystals (or gypsum or any of the other evaporites) are forming the crystals grow together in rather random directions. Sometimes, if you are lucky, the crystals grow together in such a way that they leave an open space in between them. This space frequently contains some water from the ocean basin in which they formed. This water is actually a geologically isolated sample of an ancient water body (thanks geology!) There are caveats though.

 If a body of water is evaporating, it probably is not in direct contact with the open ocean, and therefore is unlikely to reflect the true open ocean signature of the ice volume effect. Therefore the error bars are fairly large. In addition, aside from the difficulty in getting samples, dating when the crystals formed, and the age of the water contained within is notoriously difficult to do thanks to the ductile nature of salt and its tendency to flow under pressure. In addition, if you are interested in any of the other ions within the water sample (magnesium, boron, etc.), they will have been concentrated in the evaporation process, so you don’t have any other isotope systems to help you extract other data. However, in truly ancient paleoclimate systems, this data may be all you have.

 The last glacial cycle (~100,000 years) is special in that there is another place where we can look for geologically isolated water samples that is not impacted by the problems we have in halite inclusions. This technique, illustrated beautifully by Daniel Schrag and others (1996) (Pore Fluid Constraints on the Temperature and Oxygen Isotopic Composition of the Glacial Ocean) focused on the pore water within a sediment column drilled in the tropical Atlantic. Essentially, water at the bottom of the ocean can advect downward into the sediment column and become isolated from the ocean. Schrag performed oxygen isotopic analysis on the pore water fluids throughout the sediment column. After calculating the diffusion coefficient of the sediments at that site based on a number of parameters, including temperature and porosity, they managed to establish a model of fluid flow within the sediment column. This allowed them to discount upward advection/diffusion of water in the sediment column and identify the pore waters that were sequestered since the last glacial. The value they assigned to the δ18O of seawater during the last glacial was ~1.0 ‰ below today.

 Most of the paleoclimate community today uses ~1.1‰ when attempting to subtract the ice volume effect from their oxygen isotope curves for the last glacial. I know the values I have given you thus far mean nothing without their context; I might as well be measuring in hamsters. But I gave them to you for a reason. The results from the different methods range from 0.95 – 1.2‰. That is a spread of 0.25‰. Now if I told you that 1°C is approximately equal to 0.22‰ in the δ18O record (we will focus more on this fact next time), the reason for all the different techniques becomes clear. And before you ask, what is the point of arguing over a single degree, remember that the lower limit of human caused climate change we are facing by the end of this century is projected to be approximately 1.1°C on average. One degree of temperature change for our planet as a whole is a very major deal. In fact, the IPCC says that:

There is medium confidence that approximately 20 to 30% of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5 to 2.5°C over 1980-1999 levels. Confidence has increased that a 1 to 2°C increase in global mean temperature above 1990 levels (about 1.5 to 2.5°C above pre-industrial) poses significant risks to many unique and threatened systems including many biodiversity hotspots.

 As you can probably imagine, given all of this work just to figure out the change in the δ18O record of seawater during the last glacial maximum, trying to establish a comprehensive curve of seawater δ18O through time is remarkably difficult. It may even prove to be to complicated to accomplish. There have been a few attempts, such as Fairbanks and Waelbroeck’s referenced above. But the level of detail that may be needed to address short term events may prove prohibitively difficult. Ultimately, as scientists, we have to make educated guesses, and present our data in a range rather than discreet points to account for the uncertainty.

 Next time, we will go over how to strip out the evaporation/precipitation part of the δ18O signal, and wrap up what we know about paleotemperatures from a few other proxies.

Update:  I updated the diary to make clear that the 1°C comparison between the potential error in the reconstructions and human induced climate change is a comparison to the low end of the projections over the next 90 years.  The IPCC states that the temperature increase by 2100 will be between 1.1 and 6.5°C based on a range of societal and governmental responses to the threat of climate change.  I am not stating that 1°C is the most likely result, as the most likely result is probably higher.  I simply wanted to show how catastrophic the low range would be, because it is comparable to the error we were trying to work out in my field (which I think is pretty much taken care of at this point).  The point of this diary is not to address what makes the different IPCC reconstructions give different results (which might make for a good diary in the future, but I would need to joint write it to fill in some of the gaps in my own understanding of the physics).  The point was simply to make clear how the paleotemperature record is constructed.  I hope I accomplished that goal.

I also corrected a handful of spelling errors (he -> the, fro ->for, Paleontology -> Paleoclimatology).  You know, the common mistakes that spell check misses.

Originally posted to BlueberryTomatoSoup on Tue Feb 15, 2011 at 01:57 PM PST.

Also republished by SciTech, Astro Kos, and Community Spotlight.

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Comment Preferences

  •  Learning is fundamental (43+ / 0-)

    I know Einstein once said "Make everything as simple as possible and no simpler", but every once in a while, I find some complexity and explanation refreshing.

    All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident. - Schopenhauer

    by BlueberryTomatoSoup on Tue Feb 15, 2011 at 01:57:35 PM PST

    •  Very well done! (3+ / 0-)
      Recommended by:
      houyhnhnm, walkshills, ms badger

      How are the (alleged) discrepancies between the 18/16 ratios from Greenland vs Antarctic cores at the same ybp explained?

      If there be no real discrepancy that would be good!

      Exspectamus et vigilamus: quod nolite somnamus.

      by tapu dali on Tue Feb 15, 2011 at 05:46:49 PM PST

      [ Parent ]

      •  Your question is difficult to answer (1+ / 0-)
        Recommended by:
        walkshills

        without more detail.  Are you talking about timing discrepancies?  Climate discrepancies?  Are you talking in the ice cores or sediment cores?  Modern (last 100 years) stuff?

        All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident. - Schopenhauer

        by BlueberryTomatoSoup on Tue Feb 15, 2011 at 09:38:24 PM PST

        [ Parent ]

  •  I lurve me some complexity :) (13+ / 0-)

    But I also find it's helpful to occasionally do a larger explanation of something that comes up over and over, so you can use the link to it in subsequent battles.

    Nice stuff.

    Darwinic pilgrims claim the image fills them with an overwhelming feeling of logic. --The Onion

    by mem from somerville on Tue Feb 15, 2011 at 02:22:24 PM PST

  •  Can't you just drill a core sample (11+ / 0-)

    into the ocean like they do with Antarctic ice?

    looks around

    Why is everyone looking at me funny?

    In theory, there is no difference between theory and practice; but in practice, there always is a difference. - Yogi Berra

    by blue aardvark on Tue Feb 15, 2011 at 02:30:01 PM PST

  •  There's an invite coming atcha (2+ / 0-)
    Recommended by:
    walkshills, trashablanca
  •  Wow, that's quite a set up (5+ / 0-)

    I confess that I trust the science of how we know what temps were over the eons, and find the discussion about the actual waxing and waning of the glaciers a lot more interesting. Looking forward to the Parts that get to that.

    •  I promise I will get there (5+ / 0-)

      For some reason I felt the need to explain some science in much greater detail than needed.  

      I think it came from the fact that a lot of people don't realize just how complicated this stuff really is.  People ask for a temperature graph for the last 500 million years, and don't understand why we can't give it to them.  Or even how much work does into just the last 100,000 years.  A number of the graphs you see out there represent 1000's of man hours to produce the data that fits into one graph.  When I finally published my doctorate it was almost depressing to see four years of work put into just two graphs.

      All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident. - Schopenhauer

      by BlueberryTomatoSoup on Tue Feb 15, 2011 at 09:31:05 PM PST

      [ Parent ]

  •  I love this line: (6+ / 0-)
    I know the values I have given you thus far mean nothing without their context; I might as well be measuring in hamsters.

    There is nothing as wonderful as a scientist with a sense of humor.  :-)

    Behind every successful woman is a substantial amount of coffee. ~Stephanie Piro

    by sunspark says on Tue Feb 15, 2011 at 05:06:18 PM PST

  •  I can't wait for the last episode to see (3+ / 0-)
    Recommended by:
    walkshills, palantir, erush1345

    if you get tagged a "denier" because of your long term perspective.  

    If you lose your disc or fail to follow commands, you will be subject to immediate de-resolution. That will be all.

    by SpamNunn on Tue Feb 15, 2011 at 05:43:45 PM PST

    •  I hope that when I get to the climate stuff (2+ / 0-)
      Recommended by:
      wonmug, Hopeful Monster

      it will generate more comments.  I know that there isn't much people can contribute to a technical diary like this one.  

      My hope is that we are posting in a more or less reality based community, and when I tell people that not only the planet will survive, but so will human beings, they won't think I am diminishing the extent of the coming change.

      I have run into more than one person when talking about global warming where they don't understand the science behind climate change and they are freaking out about the end of the world.  And I have been called a denier on many occasions because I dare to mention that our planet has gone through things like this before.  Extraordinarily frustrating.  How do you even respond to such a comment?

      All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident. - Schopenhauer

      by BlueberryTomatoSoup on Tue Feb 15, 2011 at 09:36:35 PM PST

      [ Parent ]

  •  Let me pimp (2+ / 0-)
    Recommended by:
    walkshills, ms badger

    Smithsonian Leaf Margin Analysis

    Cool interactive on the lower right hand side.

    Today I had students analyze "ice cores" I made at home in the freezer. It needs a lot of tweaking.

    Light is seen through a small hole.

    by houyhnhnm on Tue Feb 15, 2011 at 05:58:03 PM PST

  •  No joke, I've wondered about "paleoclimatology" (0+ / 0-)

    lately, although I didn't know enough to use that term, when I read on some conservative websites about how high CO2 levels use to be (in the context of suggesting that current levels are historically low and therefor upward trend is nothing to be alarmed about, a la Inhofe).

    I haven't read the diary yet (I'm working late tonight), but hope to get an informed explanation for why what they (the conservative websites) are saying is bunk.

    Thanks.

    The ability to quote is a serviceable substitute for wit. Somerset Maugham

    by verasoie on Tue Feb 15, 2011 at 09:31:40 PM PST

  •  1 degree C! ???? (0+ / 0-)

    Re this statement:
    "And before you ask, what is the point of arguing over a single degree, remember that the human caused climate change we are facing is projected to be approximately 1°C on average. One degree of temperature change for our planet as a whole is a very major deal."

    Got a time frame and a reference to the lit for that number?

    It doesn't jibe with what I've read.  In fact it looks like we've already gone up by 0.8C, and we haven't come close to doubling CO2 yet, nor have all the effects of the existing anthropogenic GHG's percolated through the global system.  According to Hansen at NASA GISS we're looking at another 0.6C for the GHG's we've added thus far.

    The consensus opinion is that the DIRECT effects of doubling CO2 will be a 1C temperature rise, but the feedback effects will take us up to about 3C for a doubling of CO2, a level expected to happen about mid-century.  That could be a bit high, but it's more likely to be, given the probability curve, an underestimate.  See that long tail on the right hand side of the curve in figure 2, here:

    http://www.skepticalscience.com/...

    The climate change we are facing in the very near term (i.e. NOW geologically) is OVER 1C, and in 50 years it's likely to be 3C, but only if we're lucky.

    •  I had a long reply (0+ / 0-)

      that got erased when I clicked on a link, so because I have to feed my children, this has to be shorter.

      My source was the IPCC which reports a projected temperature increase of 1.1 to 6.5°C over the next century.  I rounded from 1.1°C for ease of use.  While is is the lower range of the projections, and is likely to be low from reality, it is the only temperature increase we can be sure will happen.  

      There is no consensus around the 3°C number.  It is true that the average of the models comes out to 3°C, but that doesn't mean that is the right number.  An equivalent statement would be my students last semester had a range of 27 to 101 on their final with an average of 78, so all of my students this semester will get a 78.  This is, of course ridiculous.  There is a consensus on the range of 1.1-6.5°C, but there is vigorous debate on where in that range the final number will pop up.  

      As for the doubling of CO2, there is definitely no consensus that there will in fact be a doubling.  There were 6 projections commissioned by the IPCC, only 3 of which included a doubling (560 ppm) in its range, including one which had a range of 485-570 ppm, making a doubling unlikely.  It may well happen, it is within the range of projections, but it is not a guarantee, and I think the consensus is that it is less likely than likely to happen.

      I would also like to draw attention to a trap that the site you linked to falls into and frequently happens in people who follow science as a hobby.  The site cites James Hansen as saying he feels the 3°C number is most likely as 'proof' of consensus.  I don't want to take anything away from Hansen, he is very nice and I had a very interesting (albeit short) conversation with him when I met him 2 years ago.  His work is beyond reproach.  But his word is not gospel.  He is a rock star in the scientific community, like Stephen Jay Gould (RIP), Carl Sagan (RIP), or Stephen Hawking, which makes him a great face for the public.  However, when it comes to the science he is one voice among many.  And he happens to have an interest in pushing the 3°C number, since he ran one of the models for the IPCC, and that is the number his put out.  But his model is just one of six, and the consensus is with the range, not with whatever number James Hansen's computer puts out.  He can be wrong.

      Lastly, I will just say that the IPCC report states that a temperature increase of 1.5°C would be very likely to lead to a mass extinction of 20-30% of all life on this planet.  So you don't have to call on the high end of the range for this to be a major major problem.  Even a 1°C change would be devastating.

      All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident. - Schopenhauer

      by BlueberryTomatoSoup on Wed Feb 16, 2011 at 06:51:57 AM PST

      [ Parent ]

      •  delta 1C = delta10% rice yield... (1+ / 0-)
        Recommended by:
        BlueberryTomatoSoup

        ...that's going to have an impact on a wide swath of humanity.

        (-9,-9) pragmatic incrementalist :-P

        by Enterik on Wed Feb 16, 2011 at 08:11:24 AM PST

        [ Parent ]

      •  Keeping it real. (0+ / 0-)

        (Firstly, if you really are on the side of the angels on this issue, take the following as constructive discussion and critique, and ignore the condescending tone which is tit for tat due to your comment "I would also like to draw attention to a trap that the site you linked to falls into and frequently happens in people who follow science as a hobby."  It's clear to me that the person you diss there has a grasp of the science well beyond your own.)

        "My source was the IPCC which reports a projected temperature increase of 1.1 to 6.5°C over the next century.  I rounded from 1.1°C for ease of use.  While is is the lower range of the projections, and is likely to be low from reality, it is the only temperature increase we can be sure will happen."

        Really? So given a range of values (1.1 to 6.5C) in a model projection based on statistical analysis you believe that the smallest value of that 95% confidence interval, on what is thought to be a normal curve is more "real" than the others?.  (I musta' been dreaming in Stat 101, I thought they said that peak in the middle of a normal distribution was the most likely value.)  Now a probability distribution can be skewed I suppose, but there is no reason to believe this one is, and you don't suggest that as your reason for your seemingly arbitrary choice of 1C  (I suggest that 6.5 C is just as likely as 1C,  so you should base your writings on THAT number, by the same logic.)

        "There is no consensus around the 3°C number."

        There most certainly is, go back and actually READ that link to Skeptical Science I sent.

        "The site cites James Hansen as saying he feels the 3°C number is most likely as 'proof' of consensus."

        It says no such thing, it links, ultimately, to dozens of researches using different approaches who all seem to be converging around a value of 3C for climate sensitivity.  Hansen's point is that the 3C figure is only the result of fast feedbacks.  By the time equilibrium is reached the real value will be 6C.

        "The site cites James Hansen as saying he feels the 3°C number is most likely as 'proof' of consensus."

        Says no such thing.  They cite a 1988 study by Hansen that predicted a climate sensitivity of 4.2C. Indeed Hansen was off in his estimate back then, it turns out to be about... guess what... yep ... 3.0C.

        They also cite a 2008 study by Hansen et al at NASA GISS that says that the long term feedback is more likely to be 6.0C.

        You can say what  you wish about Hansen, but if you're honest what you will say is that by-and-large he has been right, chillingly right, for thirty or more years.  Even though Hansen is NOT basing his statements on what he "feels" if anyones "gut" feeling in this area is to be given serious consideration, it's Hansen's.

        Ok... we got the sensitivity issue out-of-the-way? (There IS a narrowing consensus, right around 3C, multiple researchers, multiple methods say so.)

        So the next issue is the likely emissions scenario, because:

         "Climate sensitivity is the amount the planet will warm when accounting for the various feedbacks affecting the global climate.  The relevant formula is:

        dT = λ*dF

        Where 'dT' is the change in the Earth's average surface temperature, 'λ' is the climate sensitivity, usually with units in Kelvin or degrees Celsius per Watts per square meter (°C/[W m-2]),..."

        The LOWEST of the SERS marker emissions scenarios given in AR4 is 1.8 C by 2100.  (Unless you want to select the model runs for zero emissions after 2000 because you want to stick to "reality.")

        I could go on for pages picking holes in your diary and comments, but I think you get the main point.

        One more thing, if your worried about people sticking to "reality" and not being alarmists, you might examine this statement of yours, and compare it to what the text of IPCC AR4 actually says below it:

        "Lastly, I will just say that the IPCC report states that a temperature increase of 1.5°C would be very likely to lead to a mass extinction of 20-30% of all life on this planet." -BlueBerryTomatoSoup

        Risks to unique and threatened systems. There is new and stronger evidence of observed impacts of climate change on unique and vulnerable systems (such as polar and high mountain communities and ecosystems), with increasing levels of adverse impacts as temperatures increase further. An increasing risk of species extinction and coral reef damage is projected with higher confidence than in the TAR as warming proceeds. There is medium confidence that approximately 20 to 30% of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5 to 2.5°C over 1980-1999 levels. Confidence has increased that a 1 to 2°C increase in global mean temperature above 1990 levels (about 1.5 to 2.5°C above pre-industrial) poses significant risks to many unique and threatened systems including many biodiversity hotspots. Corals are vulnerable to thermal stress and have low adaptive capacity. Increases in sea surface temperature of about 1 to 3°C are projected to result in more frequent coral bleaching events and widespread mortality, unless there is thermal adaptation or acclimatisation by corals. Increasing vulnerability of indigenous communities in the Arctic and small island communities to warming is projected. {5.2}

        •  For starters (0+ / 0-)

          don't question people's motivations, or their grasp of a subject.  It doesn't contribute in anyway other than to drive emotion into a discussion that is based on facts.  

          That being said, either in my haste I didn't type things clearly enough, or you misread what I wrote.  When I said

          My source was the IPCC which reports a projected temperature increase of 1.1 to 6.5°C over the next century.  I rounded from 1.1°C for ease of use.  While is is the lower range of the projections, and is likely to be low from reality, it is the only temperature increase we can be sure will happen.

          I didn't say anything about the probability of other values.  I am only saying, as the lower end we can guarantee that any thing that would happen at 1°C is going to happen.  If the correct number is 3°C, you still have to go through 1°C to get there.  If the answer is 100°C, you still have to go through 1°C to get there.  That is not the same as the upper end of the range.  So the only number that you can guarantee will happen is the low end of the range.  I wasn't saying anything about where the final temperature will end up in 2100.  Can we agree on that?

          You are also wrong about your probability distribution claim.  Your statement of the highest probability being at the middle of the peak is only correct if you have a random data set, which this range most certainly is not.  It consists of 6 different models, each with different inputs and sensitivities.  You cannot simply take the average of those model as the most probable answer because they do not start with the same inputs.  Think of the probability curve of this range as 6 different and overlapping curves, resulting in a very complex equation.

          I stand by the claim that there is a lot of hero worship of Hansen.  Yes, his numbers have been very good in the past.  But that doesn't mean you should throw out everyone else's models just because they give a different number than Hansen's model does.  If you really think that his record is so great, maybe everyone else should just quit the IPCC and we will let him write it.  He is a great scientist, but just because he has a great track record in the past doesn't mean that he will always be right.  You have to concede that point.  Otherwise, what is even the point of scientific inquiry?

          As for when you said this:

          They cite a 1988 study by Hansen that predicted a climate sensitivity of 4.2C. Indeed Hansen was off in his estimate back then, it turns out to be about... guess what... yep ... 3.0C.

          How do we know what the answer turned out to be?  It isn't 2100 yet.  3.0°C is simply what his latest model says.  No doubt Hansen will continue to refine his models in ways he hasn't even thought of.  And how do we know that his model 5 years from now won't say the answer is 2.4°C?  Or maybe 4.4°C?  We won't know until he designs his next model.  Unless you think he is retiring from science, I think we can trust he will always be making his models better and not simply stating that this one is 'good enough'.

          You said:

          There IS a narrowing consensus, right around 3C, multiple researchers, multiple methods say so.

          This statement is true and you will never see me argue it.  But the key word here is 'narrowing' and the fact that the range is centered on 3°C.  The range that the community is agreed upon is narrowing.  But there is no consensus on 3°C being the answer.  The consensus of the community is that, by 2100, the temperature will have increased by 1.1 to 6.5°C, with the average value being 3°C.  

          I love SkepticalScience, I send people to them all the time, but one website does not a consensus make, no matter how smart they are.  I am a paleoclimatologist, actively doing research and publishing in major journals.  I participate in these debates.  I was in San Francisco in December at the American Geophysical Union Meeting having these very discussions (though nobody there accused me of not knowing what I am talking about), and I can tell you from personal experience there is a range of values bandied about for 2100, but they are all in that range.  You are not going to convince me of a consensus using someone else's opinion when I have first hand experience in the matter.  Unless you want me linking to dozens of models that come up with numbers different from 3.0°C.

          I ask you to go back and look at the actual IPCC data before saying the lowest scenario is 1.8°C.  The lowest model result (B1) gives a range of 1.1 to 2.9°C with a median result of 1.8°C.  You stated that you can't throw out the whole range for one number.  This is the same case here.  

          The last bit you had in there, I don't see you disagreeing with anything I said.  In fact I see you making my point even further.  As far as I can see, I said exactly what the bolded text says.  The resulting change would be a disaster.  This is why we have to do something, because even the low end (1°C) results in the destruction of the coral reef ecosystem, the tropical rainforest system and 20-30% of all life on this planet.  I don't see your problem here.

          When I am talking about alarmists I am talking about the people who believe that all life on this planet will go extinct and we as a species will go extinct.  We are remarkable adaptable as a species, we will absolutely survive as a species even the worst case scenario, but it will be civilization changing.  By making the Armageddon claims you end up looking like the loon on the corner wearing a sandwich board that no one listens to.  Be honest and state that even small changes will destroy whole ecosystems.  Isn't that bad enough for you?

          I will state one last thing about your following quote:

          I could go on for pages picking holes in your diary and comments, but I think you get the main point.

          Bring it on, especially the diary.  There is nothing in there that is incorrect.  I will even email you pdf's of every one of those references if you want to pour through them.  I may make an error here or there in comments when I am rushing to type, but my diary is well researched.  You could submit it to a dissertation committee if you want.  You won't find any errors.

          I regret using the 1°C number.  I knew it was the low range of projections when I used it, but that is because I was trying to show how important it is to work these issues out.  If I had not been lazy and changed

          And before you ask, what is the point of arguing over a single degree, remember that the human caused climate change we are facing is projected to be approximately 1°C on average. One degree of temperature change for our planet as a whole is a very major deal.

          to

          And before you ask, what is the point of arguing over a single degree, remember that the low end of human caused climate change we are facing is projected to be approximately 1°C on average. One degree of temperature change for our planet as a whole is a very major deal.

          you wouldn't have had one thing to say about my diary.  Because that is the only thing you have criticized in my diary, the rest was all from just one comment that I had to write quickly because the other one was erased.  And I clearly didn't write it very well, because you misinterpreted half of the points I was making.

          All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident. - Schopenhauer

          by BlueberryTomatoSoup on Wed Feb 16, 2011 at 10:08:34 PM PST

          [ Parent ]

          •  Ok... let me decompress this, at least little... (0+ / 0-)

            Having now read your previous diaries, and considered your comments, it's clear you're not trying to mislead anyone, and my knee-jerk first comment was perhaps a bit confrontational.

            "I regret using the 1°C number."

            Good enough.  Thank you sir, that wasn't so hard after all, was it?  To be honest, I was still in combat mode over your original stipulation ("...the human caused climate change we are facing is projected to be approximately 1°C on average") had your original diary had the nuance that you added in your first reply, that "it's the only temperature increase we can be certain of." I would likely have seen some sort of merit in that interpretation, as misleading as it might be.

            Going forward, I haven't really deeply considered your discussion of isotopic ratios in reconstructing paleoclimate.  I scan read it, just like I pretty much scanned the original papers on the Vostok Ice Cores when they came out (Yep, I'm THAT old) but I did read the abstracts and struggled through their conclusions.  Your explanation of the reconstruction method sounded just fine to me. To be honest it was a bit over my head, and probably over the heads of  most others here.  (I AM tempted to take you up on your offer of finding further errors in your diary, but that's not my field, and I really do have a life somewhere else.)

            Some other random stuff from you last comment:

            "I ask you to go back and look at the actual IPCC data before saying the lowest scenario is 1.8°C.  The lowest model result (B1) gives a range of 1.1 to 2.9°C with a median result of 1.8°C.  You stated that you can't throw out the whole range for one number.  This is the same case here."

            Dude, that is exactly what I asked you to do in my first comment.  Find me ANYTHING that says a 1C AGW is what we are facing, and to specify your time frame, because if you weren't talking about 2000 to 2100, you may well have been bang-on. As it is, you were wrong.   I said nothing about "throwing out a whole range of numbers" those are your words, which you seem to be happy to substitute for the words of others whenever you are faced with a vexing argument. (As you did with the "hobbyist" post at Skeptical Science.)

            What I did say was you can't take a number at the EXTREME LOW END OF THE ESTIMATE and imply that's the likely scenario, but since you've backed off of your original claim and now say it's a 'minimum expected' I might not argue with that, even if it's still low by 0.8C, in the most favorable scenario out of 6 representative IPCC scenarios.  And that median result for B1 of 1.8C? It's referred to as the BEST ESTIMATE, note that the best estimate is NOT the number at the low end of the range.

            To make my point in another context, if the best models available said that Green Bay was going to beat Pittsburgh by 3 points in the Super Bowl, with a range of 1 to 6 points, would you tell people that 1 point is most likely scenario?

            Have I beat this to death enough for you yet?   You seemed to have gotten it with  your "I regret..." statement above, then you slither back and try to justify it once again.

            "I stand by the claim that there is a lot of hero worship of Hansen.  Yes, his numbers have been very good in the past.  But that doesn't mean you should throw out everyone else's models just because they give a different number than Hansen's model does."

            Actually, what's popular in many circles is to attack Hansen.  I guess mostly because he's gone over to what seems like a crusade... unseemly for a scientist.  Personally I can't blame him, he didn't go looking for a political confrontation, he was doing science, the political confrontation came to him. And as you say, Hansen's work, and the work of the dozen-or-so other researcher/co-authors on his papers, is "beyond reproach." (Though at first blush that seems an odd stipulation for someone who thinks Hansen et al are wrong by at least 300 percent in their predictions.)

            "As far as I can see, I said exactly what the bolded text says."

            No.  The bolded text has a number of  qualifiers, it has "medium confidence" that the (unspecified) "plant and animal species assessed so far"  are  "likely to be at increased risk of extinction" and they're likely talking about sensitive species (that's my interpretation, though the language isn't explicit)  that is VASTLY different from your  "...very likely to lead to a mass extinction of 20-30% of all life on this planet."

            A scientist wouldn't make that and other sloppy mistakes that you have made.  This isn't a a peer reviewed journal, so dropping the endless qualifiers, and a bit of rounding, and using shorthand are perfectly acceptable. But Einstein advised "Make everything as simple as possible, but not simpler." And we still have an obligation to the facts.

            •  We are still miscommunicating (0+ / 0-)

              I will try one more time.  I do NOT believe that 1°C is the most likely scenario.  I personally believe the most likely number will be closer to 2.4°C with a range of ~1.5°C to 3.8°C, as projected by model B2.  That doesn't mean I think Hansen is wrong, on the contrary, his model results are within the range of the B2 results.  It is just from my analysis of the model inputs, I think B2 is going to best represent the way we will approach the problem (decrease our rate of fossil fuel usage increase, but not decrease our usage itself).  Below is a description of the different model inputs.  

              The A1 storyline assumes a world of very rapid economic growth, a global population that peaks in mid-century and rapid introduction of new and more efficient technologies. A1 is divided into three groups that describe alternative directions of technological change: fossil intensive (A1FI), non-fossil energy resources (A1T) and a balance across all sources (A1B). B1 describes a convergent world, with the same global population as A1, but with more rapid changes in economic structures toward a service and information economy. B2 describes a world with intermediate population and economic growth, emphasising local solutions to economic, social, and environmental sustainability. A2 describes a very heterogeneous world with high population growth, slow economic development and slow technological change. No likelihood has been attached to any of the SRES scenarios. {WGIII TS.1, SPM}

              This is why you can't just make a simple probability distribution out of the total range from the 6 scenarios.  When trying to figure out what the correct projection is, you need to decide which input most accurately reflects how the world will react to the coming crisis.  Then you look at the results from that model.  This isn't Stats 101, its more like Stats 240.

              I will reassess which model I think best represents our projected climate change when the AR5 report comes out.  That doesn't mean I think the other models are incorrect, in science it is possible to believe that one model is more likely than another while accepting that other models could be right.  We won't know the actual result until 2100.  I don't expect to make it that long, but we should have a reasonably good idea where we are going by ~2030.  

              The real point where we aren't communicating is you think I am trying to say that 1°C is the most likely scenario, when I am saying that the change will be at least 1°C.  To use your Superbowl analogy, I would not say that 1 point was the most likely result.  I would say that the Packers will win by at least 1 point.  This way you can't be wrong, whether they win by 1 or 6, you covered all of those options by saying they will win by at least 1.  That is all I am saying here.  The temperature change is going to be at least 1°C.  So we can guarantee that the changes associated with 1°C will happen.  That doesn't say anything about 2 or 3 or 6°C changes.  Those happen in addition to the changes that we know will happen because the globe will warm by at least 1°C.

              The whole point is you have to report the ranges of the projections.  If you only report the most likely result, it is not hard to end up wrong.  If you say the number is 3°C and the number is 2.8°C, you are wrong.  If you say the number is between 2.5 and 3.5°C centered around 3°C, and the answer is 2.8°C you were right.  That is how science works.

              As for the extinction thing, you are kidding right?  The IPCC had to define all of these terms,

              Where uncertainty is assessed more quantitatively using expert judgement of the correctness of underlying data, models or analyses, then the following scale of confidence levels is used to express the assessed chance of a finding being correct: very high confidence at least 9 out of 10; high confidence about 8 out of 10; medium confidence about 5 out of 10; low confidence about 2 out of 10; and very low confidence less than 1 out of 10. ...  Where uncertainty in specific outcomes is assessed using expert judgment and statistical analysis of a body of evidence (e.g. observations or model results), then the following likelihood ranges are used to express the assessed probability of occurrence: virtually certain >99%; extremely likely >95%; very likely >90%; likely >66%; more likely than not > 50%; about as likely as not 33% to 66%; unlikely <33%; very unlikely <10%; extremely unlikely <5%; exceptionally unlikely <1%.

              because they were reporting results in as scientific and quantitative way possible.  Are you actually insisting that I have to do the same for my blog posts?  Now you are just being deliberately difficult.

              A scientist wouldn't make that and other sloppy mistakes that you have made.

              That was a unnecessarily jerky thing to say.  I am a scientist, and have dedicated my life to climate sciences.  You have read a few websites and maybe scanned a few abstracts and think you are an expert.  You are right that I would never try to publish anything I wrote for a scientific publication.  What I submit is written in a technical matter, generally goes through 7 or 8 drafts, and has long discussions about sources of error and ranges.  You know how many times I edit my diaries?  1.  How many times I edit my comments?  0.  So because of the fact that I don't write my blog posts like scientific papers I am not a real scientist?  The internet would be empty if you held that standard to everyone, including yourself.  

              In addition, the whole point of submitting science to a blog like this is exactly to cut through the clutter, like defining modifiers for the word likely so that the science can be accessible to a general audience.  So yeah, I do simplify some aspects of my post for the sake of accessibility.  And some of those oversimplifications I would never make in a scientific paper.  But I don't have to because I am publishing for people with backgrounds in the field so they understand the complexities.  Most of the people who read my posts will not have much of a background in climate science or even science technical writing.  Some will, but most won't and I have to cut through the clutter for them.

              As a scientist I do have an obligation to the facts.  Which is why I talk about ranges, rather than absolute numbers.  I also want to point out to you, because you seem to have forgotten, that when projecting the future you aren't dealing in facts, you are dealing in probabilities.  

              And as a clarification; I do NOT regret making a comparison between the degree of uncertainty that the field has found itself in to the lower limit of projected human induced climate change.  I do regret not clearly designating it as the lower limit of the projections.  I will edit that now.

              If you have a legitimate question about the science or my interpretation of it, I will be happy to answer you.  But if you are going to continue attacking my writing style and accusing me of saying things I didn't say (or mean to say as is clear from clarification), then don't bother.  I won't be responding to you on this or any other diary.

              All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident. - Schopenhauer

              by BlueberryTomatoSoup on Thu Feb 17, 2011 at 08:04:58 AM PST

              [ Parent ]

  •  You'll be putting that +/-0.5C in context? (0+ / 0-)

    As in, we will see what percentage of the deduced temperature changes over time it represents?

    (-9,-9) pragmatic incrementalist :-P

    by Enterik on Wed Feb 16, 2011 at 08:13:02 AM PST

  •  real science (0+ / 0-)

    This is just what I've been looking for. Some hard core science with global warming.
    I'm just a novice but the articles RollingStone mag. are a little incomplete for my taste.
    I'm sick of people that scoff at warming and science than go use electricity made by a nuclear powerplant. Isn't that science ?

    "There is more stupidity than hydrogen in the universe, and it has a longer shelf life." Frank Zappa

    by da888 on Wed Feb 16, 2011 at 12:23:04 PM PST

    •  no, having reduced themselves to a pre-tech state (1+ / 0-)
      Recommended by:
      BlueberryTomatoSoup

      by choice becoming functionally illiterate. It is now magic.

      two quotes by Arthur c. Clarke seem about right here.

      I would defend the liberty of consenting adult creationists to practice whatever intellectual perversions they like in the privacy of their own homes; but it is also necessary to protect the young and innocent.
      1984: Spring (1984)

      and his laws:

      Clarke's First Law: When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
      "Hazards of Prophecy: The Failure of Imagination" in Profiles of the Future (1962)
      Perhaps the adjective "elderly" requires definition. In physics, mathematics, and astronautics it means over thirty; in the other disciplines, senile decay is sometimes postponed to the forties. There are, of course, glorious exceptions; but as every researcher just out of college knows, scientists of over fifty are good for nothing but board meetings, and should at all costs be kept out of the laboratory!
      "Hazards of Prophecy: The Failure of Imagination" in Profiles of the Future (1962; as revised in 1973)
      Clarke's Second Law: The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
      "Hazards of Prophecy: The Failure of Imagination" in Profiles of the Future (1962)
      Clarke's Third Law: Any sufficiently advanced technology is indistinguishable from magic.
      Profiles of the Future (revised edition, 1973)

      Clarke's Law of Revolutionary Ideas: Every revolutionary idea — in science, politics, art, or whatever — seems to evoke three stages of reaction. They may be summed up by the phrases:
      (1) "It's completely impossible — don't waste my time";
      (2) "It's possible, but it's not worth doing";
      (3) "I said it was a good idea all along."

      fact does not require fiction for balance (proudly a DFH)

      by mollyd on Wed Feb 16, 2011 at 01:38:00 PM PST

      [ Parent ]

      •  bummer (0+ / 0-)

        Ah come on. Senile decay in your forties. Not here. I'm 53 and feel more intellectual than ever.
        I love reading theoritical physic's and most any book that gives me a new perspective on a topic, particulaly history.
        I know what you mean though. It's just something I like to throw in the face's of people who poo poo science.
        " Oh really, do you realize where your flu shot comes from, or your electricity, not to mention most all medical test ?" On and on and on.
        Sometimes, rarely I'll admit, a person is quite intelligent but ignorant. Ignorance is bliss you no. So I will keep trying.
        I read Bill Bryson's History of Nearly Everything lately and it sure makes you admire scientist and engineers.
        Like I said I'm only a novice but I like to think I could trigger some people to read a little and be curious.

        "There is more stupidity than hydrogen in the universe, and it has a longer shelf life." Frank Zappa

        by da888 on Fri Feb 18, 2011 at 06:25:51 PM PST

        [ Parent ]

      •  And don't forget Clarke's definition of an (0+ / 0-)

        intellectual as, 'a person educated beyond their intelligence.', my personal fave. ;-)

        Information is abundant, wisdom is scarce. The Druid

        by FarWestGirl on Tue Feb 22, 2011 at 09:49:42 AM PST

        [ Parent ]

  •  I study in a similar discipline (0+ / 0-)

    So congrats on a very well written introduction to the field.

    There's another technique we use to learn about what kind of ecology an area such as the early Great Lakes or Lake Agassiz might have been like.

    Although marine isotope stages can tell us a lot, I'm particularly interested in temperatures around the glacial margins, which you can't learn from those kinds of indicators. Lacustrine sediment, pollens, and insects can tell us a lot: the insects particularly, as they can be very, very sensitive to temperature.

    Since the insects of the recent stages were all pretty much modern, the presence or absence of insects can make for some pretty compelling evidence with regards to temperature and the length of the growing season.

    If apes evolved from humans, why are there still humans?

    by Bobs Telecaster on Thu Feb 17, 2011 at 07:20:48 PM PST

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