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Ocean Cooling. Not.

Filed under: — gavin @ 18 April 2007 - (Português) (Français)

A lot has been made of a paper (Lyman et al, 2006) that appeared last year that claimed that the oceans had, contrary to expectation, cooled over the period 2003-2005. At the time, we (correctly) pointed out that this result was going to be hard to reconcile with continued increases in sea level rise (driven in large part by thermal expansion effects), and that there may still be issues with way that the new ARGO floats were being incorporated into the ocean measurement network. Now it seems as if there is a problem in the data and in the latest analysis, the cooling has disappeared.

Ocean heat content changes are potentially a great way to evaluate climate model results that suggest that the planet is currently significantly out of equilibrium (i.e. it is absorbing more energy than it is emitting). However, the ocean is a very big place and the historical measurement networks are plagued with sampling issues in space and time. Large scale, long term compilations globally (such as by Levitus et al, 2001; Willis et al, 2004) and regionally (i.e. North Atlantic) have indicated that the oceans have warmed in recent decades at pretty much the rate the models expected.

Since 2000, though, ARGO – which is a network of floats that move up and down in the ocean and follow the currents – has offered the potential to dramatically increase the sampling density in the ocean and provide, pretty much for the first time, continuous, well spaced data from the least visited, but important parts of the world (such as the Southern Oceans). Data on ocean heat content from these floats had been therefore eagerly anticipated.

Initial ARGO measurements were incorporated into the Willis et al, 2004 analysis, but as the ARGO data started to dominate the data sources from around 2003, Lyman et al reported that the ocean seemed to be cooling. These were only short term changes, and while few would confuse one or two anomalous years with a long term trend, they were a little surprising, even if they didn’t change the long term picture very much.

The news this week though is that all of that ‘cooling’ was actually due to combination of a faulty pressure reading on a subset of the floats and a switch between differently-biased observing systems (Update: slight change in wording to better reflect the paper). The pressure error meant that the temperatures were being associated with a point higher in the ocean column than they should have been, and this (given that the ocean cools with depth) introduced a spurious cooling trend when compared to earlier data. This error may be fixable in some cases, but for the time being the suspect data has simply been removed from the analysis. The new results don’t show any cooling at all.

Are we done then? Unfortunately no. Because of the paucity of measurements, assessments of ocean heat content need to use a wide variety of sensors, each with their own quirks and problems. Combined with switches in data sources over the years, there is a significant potential for non-climatic trends to creep in. In particular, the eXpendable BathyThermographs (XBTs – sensors that are essentially just thrown off the side of the ship) have a known problem in that they didn’t fall as quickly as they were originally assumed to. This gives a warm bias (see this summary from Ingleby and Palmer or the paper by Gouretski and Koltermann) , particularly in data from the 1970s before corrections were fully implemented. We are still going to have to wait for the ‘definitive’ ocean heat content numbers, however, it is important to note that all analyses give long term increases in ocean heat content – particularly in the 1990s – whether they include the good ARGO data or exclude the XBTs or not).

There are a number of wider lessons here:

  • New papers need to stand the test of time before they are uncritically accepted.
  • The ARGO float data are available in near real-time, and while that is very useful, any such data stream is always preliminary.
  • The actual problem with these data was completely unknowable when Lyman et al wrote their paper. This is in fact very common given the number of steps required to create global data sets. Whether it’s an adjustment of the orbit of a satellite, a mis-calibration of a sensor, an unrecorded shift in station location, a corruption of the data logger or a human error, these problems often only get fixed after a lot of work.
  • Anomalous results are often the driver of fundamental shifts in scientific thinking. However, most anomalous results end up being resolved much more straightforwardly (as in the case, or the MSU satellite issue a couple of years back).

Scientists working in a field build up a certain intuition about how things ‘work’. This intuition can come from a gut instinct, deep theoretical understanding, robust model results, long experience with observations etc. New results that fall outside of that framework often have a tough time getting accepted, but if they are solid and get subsequent support they will generally be incorporated. But that intuition is also very good at detecting results that just don’t fit. When that happens, scientists spend a lot of time thinking about what might be wrong – with the data, the analysis, the model or the interpretation. It generally pays to withhold judgment until that process is finished.


282 Responses to “Ocean Cooling. Not.”

  1. 251
    Ray Ladbury says:

    Dan. Satellite measurements of GCR fluxes are not changing–they oscillate, but they are not changing. Neutron fluxes are not changing. So if your putative cause is not changing, how can it produce a change?

  2. 252
    Dan Fregeau says:

    #246 (Blair Dowden) Significance
    Thanks for clarifying cyclical hemispheric insolation differential.

    Opposite data in paleoclimatic record – what data proxy are you looking at? The current models makes critical assumptions between various proxies, glaciation and temperature.

    Re. Irrelevance – small effects are insignificant if they do not cumulate. But if heat from annual insolation increases is being trapped in an oceanic reservoir, then the cumulative effect of that trapping would be more significant than the annual effect, perhaps even on a relatively short timescale, would it not?

  3. 253
    Hank Roberts says:

    Dan, where do you see this happening?
    http://www.osdpd.noaa.gov/PSB/EPS/SST/climo.html

  4. 254
    Dan Fregeau says:

    #235 (Ray Ladbury) Major Climate Factors
    We agree that the sun is most important, and then H20 (in all of its phases) after that. These are the basics.

    Since Svensmark hypothesis specifically addresses how these two may be coupled, via solar wind, to modulate clouds, i.e. H2O vapour, with potential large impact to albedo, then it might be valuable to get to the bottom of this one, not to mention oceanic heat capacity and heat-transporting currents, and their long-term modulation by astronomical cycles. Agree?

  5. 255
    tamino says:

    Re: #252 (Dan Fregeau)

    if heat from annual insolation increases is being trapped in an oceanic reservoir, then the cumulative effect of that trapping would be more significant than the annual effect, perhaps even on a relatively short timescale, would it not?

    The important part of this is, “IF.”

    The precession cycle alters the seasonal distribution of insolation, but has NO EFFECT on the annual total. So, the cumulative effect of zero being zero …

  6. 256
    William Astley says:

    Re: Comment 246 “In fact, at the present time the southern hemisphere receives 6.7% more radiation averaged over the year than the northern hemisphere.”

    I believe this commment is not correct. The earth’s orbital differences average out over the year. The orbital eccentricity changes whether one season is relatively warmer and the other proportionally relatively colder. The forcing effect is balanced. The total amount of energy received by the earth, from the sun, in both hemispheres is equal. The current affect on planetary temperature due to orbital eccentricity, is that there is less seasonal temperature difference in the Northern Hemisphere than the Southern Hemisphere. (i.e. Earth is closer to the sun during January and farther from the sun in June.) Does this statement make sense?

    Milankovitch’s hypothesis, which I believe based on paleoclimatic evidence is not correct, is that insolation changes at specific critical latitudes triggers the glacial/interglacial cycle. As you stated the insolation changes are gradual, the ocean should smooth out any changes.

    The following are some very basic fundamental questions, which can not be explained by Milnakovitch’s hypothesis.

    Why does the interglacial period occur roughly every 100 kyrs now and prior to 700 kyrs ago occurred every 41 kyr? Why are there semi-periodic abrupt climate changes of 2C and greater? (The glacia/interglacial cycle is 5C. These are very large changes.) Why does the entire planet cool and warm rather than a single hemisphere? Why did the interglacial cycle start at event 11 before the insolation increased at the 60degree N?

    The fundamental explanation of past climate changes is relevant to a discussion of expected future short term changes in the planet’s temperature, as the models have been tuned based on a hypothesis (i.e. Orbital changes cause the glacial/interglacial cycle) that appears to have first order deficiencies. From a model standpoint, an unstable system is required, that is very sensitive to small changes in forcing to create the interglacial/cycle. (i.e. Positive feedback is required to amplify small forcing changes.)

    I believe there is evidence that there are significant damping mechanisms that work together to regulate the planet temperature. (i.e. Ocean, atmosphere, and clouds.) If the hypothesis that there are significant negative forcing functions that resisted change is correct, it has two implications:

    First, a much stronger global forcing function is required to explain the glacial/interglacial cycle and the abrupt climatic changes. The insolation changes and orbital changes cannot have caused the observed changes.

    Second, the will be less change in the earth’s temperature, from increases or decreases in forcing.

  7. 257
    Hank Roberts says:

    Dan, how much of the AIP history have you read?
    I don’t see anything in what you’re raising that isn’t already well studied.
    What do you believe is contributing to current rapid changes, that isn’t being studied?
    Where are you getting what you believe to be true?

    I can’t tell if you’re asking for reassurance, or if you’re raising points you believe nobody has studied, or if you have theories you believe need to be taken seriously that aren’t.

    Can you focus a bit on what your information is, and where it comes from? What do you know now and how?

  8. 258
    William Astley says:

    Ray, the following is in reply to your comment and line of reasoning.

    “William, the problem with a GCR driven mechanism is that it has to be operative at the time of the effect it tries to explain–and GCR fluxes simply are not changing–based on either satellite observations or neutron monitoring.”

    For short term periods (say for example the last 100 years), there is evidence that solar changes can module planet cloud cover by directly affecting GCR or by the electroscavenging mechanism (The jury is still out as to whether the solar changes did cause a significant portion of the 20th century temperature rise, however, as there is not scientific consensus, concerning the supporting data, although the earthshine data in addition to the satellite data helps the case.)

    Your line of reasoning is correct, that over the long term solar changes could not have directly caused long term cloud changes and could not therefore have caused the glacial/interglacial cycle via the GCR mechanism. (Assuming the GCR/electroscavenging mechanism works.) There is an alternative to the insolation hypothesis as to what drives the glacial/interglacial cycle, which I think is relevant to the current climate change discussion.

    This paper hypothesizes that geomagnetic field changes modulate the GCR which causes the glacial/interglacial cycle (The paper below also discusses the problems I mentioned in my comment concerning Milanokovich’s hypothesis.) I find their hypothesis, that GCR modulated by the geomagnetic field, more persuasive as there is evidence that “the geomagnetic intensity drops suddenly by a factor of 5-10 and the local direction changes dramatically ” The ‘normal’ state of the geomagnetic field, dominate by an axial dipole, seems to be interrupted every 30 -100 kyr: it (my comment, the geomagnetic field) may not therefore be as stable as we thought. ” These important results paint a rather different picture of long-long term behaviour of the field from the conventional one of a steady dipole reversing at random intervals instead the field spends up to 20 per cent of its time in a weak, non-dipole state (Lunde et al. 1998)” (Quote from paper is the geomagnetic field unstable?)

    Paper “Glacial Cycle and Cosmic Rays”

    http://arxiv.org/pdf/physics/0407005

    “There is growing evidence for close links between climate changes in the Holocene (approximately the last 10 kyr) and variations of the cosmic ray flux (see, for example, [17, 18, 19]). A high GCR flux is associated with a cold climate, and a low flux with a warm climate. On these 100 yr timescales, variations of the cosmic ray flux are thought to reflect changing solar activity (increased solar magnetic activity reduces the GCR flux). However, recent high-resolution paleomagnetic studies suggest that short-term geomagnetic variability may in fact control a significant fraction of the GCR modulation within the Holocene, even on 100 yr timescales [20]. Moreover, we will present evidence here that shows climate changes are also linked to variations of the cosmic ray flux caused by changes of geomagnetism. This indicates that GCRs directly influence the climate, rather than merely serve as a proxy for solar variability.”

    [Response: FWIW, this paper was rejected after peer review and never resubmitted. -gavin]

    Paper: “Is the geodynamo unstable?”

    http://eprints.whiterose.ac.uk/archive/00000416/01/gubbinsd4.pdf

    I have found other papers that support the assertion that the geomagnetic field is unstable and that it can change extraordinary rapidly (The drop in geomagnetic intensity appears to follow a rapid unsuccessful attempt to reverse, followed by a gradual increase back to normal geomagnetic strength.) For example:

    Oregon rapid field change.

    http://scholar.google.com/url?sa=U&q=http://www.nature.com/nature/journal/v374/n6524/abs/374687a0.html

    Acton’s Near Instantaneous Geomagnetic Reversal

    http://scholar.google.com/url?sa=U&q=http://www.geo.edu.ro/~paleomag/PDF/00-180-225.pdf

    What do you think of the two hypotheses? 1) Large drops in the geomagnetic field intensity have happened. 2) Large drops and a return to normal geomagnetic field strength could have caused the glacial/interglacial cycle.

    [Response: The changes in the geomagnetic field do not correlate to climate. Look up the Laschamp excursion for instance. - gavin]

  9. 259
    Rod B. says:

    Ray (248), a minor point/question: I thought there was very little mixing of the atmosphere between the north and south hemisphere’s.

  10. 260
    Chuck Booth says:

    RE 259 (Rod B)
    I’m no expert on this, but: Winds from the southern and northern hemisphere converge near the equator at the intertopical convergence zone (ITZ). The ITZ oscillates north and south, but is generally north of the equator, esp. in the Northern Hemisphere summer, when it moves up over Asia. In the fall, it moves south, sometimes dipping below the equator.

  11. 261
    William Astley says:

    In reply to “The changes in the geomagnetic field do not correlate to climate. Look up the Laschamp excursion for instance.”

    The Laschamp excursion is the lowest geomagnetic field intensity, in the last 70 kyrs. A lower geomagnetic field will result in higher GCR, however, there is a point where the GCR mechanism saturates so that additional GCR does not cause additional clouds. Also as the planet was very cold, already during the Laschamp excursion (it occurred during glacial part of the cycle) there was less moisture in the atmosphere for the GCR mechanism to create additional clouds.

    As to whether the geomagnetic field changes are cyclic, there is disagreement. There is agreement that the geomagnetic field abruptly and severly drops and that the excursions in the field were cyclic for a period of time, but not for the entire period. See the attached paper. There appears to be correlation with the start and termination of glacial periods with high and low intervals of geomagnetic field intensity.

    http://www.geo.uu.nl/~forth/publications/Langereis99.pdf

    Excerpt from the above paper:

    “Channell et al. therefore concluded that their record provides evidence that the Earthâ��s obliquity influences geomagnetic field intensity, with a period of around 41,000 years. They suggested that this is caused by the effect of obliquity on precessional angular velocity and hence on precessional forces in the Earthâ��s core. Does this hypothesis take us back to the early 1970s? Not according to Guyodo and Valet2. They performed a spectral analysis of Sint-800, comparing every 400,000-yearlong interval, in steps of 100,000 years, over their entire record, and found no evidence of any dominant stable periodicity in palaeomagnetic intensity. This, however, is no doubt a debate that will run for some time.

    Another feature of Sint-800 is the occurrence of many intervals of low geomagnetic intensity. Low intensities of Earthâ��s dipole favour the incidence of geomagnetic excursions, both in direction and intensity, because the non-dipole contribution of the field becomes significant. But it is not clear whether excursions should be considered as increased secular variation or as aborted reversals; and because of the imprecision of published excursion ages, it has even been speculated that excursions correlate with climate, for example with cold periods. (Worm, H.-U. Earth Planet. Sci. Lett. 147, 55â��67 )”

    Summing up what is known. This paper and other papers support the hypothesis that the geomagnetic field suddenly drops and that the drop in the field intensity are sever. The geomagnetic field instablity started 700 kyrs ago, which happens to be when the ice age cycle changed from 41 kyr to 100 kyr.

    There is agreement that say a sudden 70% drop in the geomagnetic field would result in increased GCR. There is evidence that GCR changes affect planetary cloud cover.

    To me there still seems to be a reasonable and defendable hypothesis. I will ask Richard Muller, to see why as you state the paper “Glacial Cycle and Cosmic Rays” was withdrawn and will get back to you.

  12. 262
    Dan Fregeau says:

    #253 (Hank Roberts) SST Data shows southern ocean not warming

    Measuring sea surface temperature, which is in constant flux as the graphs clearly show, is not a good measure of increased long-term oceanic heat absorbtion. For that you need to go deeper.

    Gille, Warming of the Southern Ocean since the 1950′s (Science 2002, 295:1275)

    Autonomous Lagrangian Circulation Explorer floats recorded temperatures in depths between 700 and 1100 meters in the Southern Ocean throughout the 1990s. These temperature records are systematically warmer than earlier hydrographic temperature measurements from the region, suggesting that mid-depth Southern Ocean temperatures have risen 0.17°C between the 1950s and the 1980s. This warming is faster than that of the global ocean and is concentrated within the Antarctic Circumpolar Current, where temperature rates of change are comparable to Southern Ocean atmospheric temperature increases.

  13. 263
    Dan Fregeau says:

    #252 (Tamino) Annual global insolation – zero

    Yes, solar variation aside, total annual global insolation remains the same irrespective of orbital variations – but this is irrelevant. The issue is that heat from this relatively constant insolation is not being absorbed and retained/released uniformely, regionally and over time. The heat is being absorbed and retained more efficiently in certain regions during certain periods, due to the variable composition of the earth and its variable heat capacity.

  14. 264
    James says:

    Re #261: [A lower geomagnetic field will result in higher GCR, however, there is a point where the GCR mechanism saturates so that additional GCR does not cause additional clouds.]

    I hope you realize that what this amounts to is fitting the hypothesis to the desired result. You want to explain climate changes by GCR and geomagnetic field changes, therefore you’re postulating a mechanism that conveniently switches off and on just when it needs to in order to match observations. Seems to me that that’s about half a step away from invoking the benevolent hand of God :-)

    To me the more interesting question is one of psychology: why are some people so obsessed with finding some alternate theory? Surely they can’t all have their entire retirement savings invested in fossil fuel stocks?

  15. 265
    Dan Fregeau says:

    #251 (Ray Ladbury) GCR not changing

    As you say, short-term satellite measurements show an oscillation inline with the solar cycle. But this is too short a timeframe to detect the longer-term trend. Be10 and C14 proxies suggest that they are changing, or perhaps even oscillating with longer astronomical cycles, as well. Do you altogether dispute those proxies?

  16. 266
    Hank Roberts says:

    Dan, where do you find evidence for a mismatch between hemispheres, that you claim should be happening according to your theory differently than what the climatologists have described?

    You seem to be pulling up bits and pieces and claiming they show something, but — like saying “you have to go deeper” and quoting one study — it’s just bits and pieces.

    Of course there’s deep water warming; even the abyssal depths turn out to show a warming signal, earlier than expected, from one Japanese transect I recall. The deep ocean currents don’t stop at the equator!

    So are you arguing there’s a level at which the ocean somehow only goes around the Antarctic, not too deep, and not too shallow, in which somehow this warming you expect will appear unique to the Southern hemisphere? If so how would it get warmed up, if not from deep circulation or insolation?

    I just can’t tell if you’re suggesting you have a theory that others ought to look into, or that there’s a body of work being ignored that you’re revealing one bit at a time, or that there must be an explanation, try this…. now this ….

    Where’s the science here? Do you have it collected on a website somewhere in a focused way?

  17. 267

    Is this ‘Dan Fregeau’ the executive vice president of Document Sciences Corporation? Just wondering. An IP associated with Document Sciences Corporation recently hit my website.

  18. 268
    Dan Fregeau says:

    #266 (Hank Roberts)
    Hank, I am frankly, like you and many others, just trying to better understand our climate change situation, in particular the amount of natural versus anthropogenic warming, which seems to have been the crux of the ongoing (and very confusing) scientific and political debate of the past years.

    If warming was much greater during previous interglacials, when there was no anthropogenic component, which seems to have been the case on the basis of purported sea levels and distribution of fauna (e.g. MIS-11), then I am trying to better understand what might have caused that amount of warming and sea level rise, and whether this might also likewise be occuring today, in addition to the critical GHG forcing component which we all agree on.

    It seems, based on all the responses, that the concensus of this blog and its scientific community is that the GHG forcing is sufficient to account for all currently occuring global warming, and that it is very unlikely that there are any other significant types of natural forcing occuring today based on the scientific research of all other possible warming mechanisms.

    Thus, we should make every effort to focus on reducing global GHG emissions, and such actions if implemented at sufficient levels, should by themselves significantly reduce global warming in the coming decades, centuries, etc.

  19. 269
    William Astley says:

    Re: Comment 264 (James).

    James you seem skeptical concerning the “Geomagnetic field intensity changes drives the glacial cycle” hypothesis.

    Attached is a review Paper: “Time Variance in Geomagnetic Intensity” by Jean-Pierre Valet. See page 4-24, figure 9, entitled “Field variations during the past 75 kyrs.”

    The Laschamp magnetic field excursion occurred roughly 41 kyr ago, at which time the geomagnetic field intensity dropped to roughly 20% of its current value. As shown in figure 9 a) the geomagnetic field gradually recovered from the Laschamp low point. The high point in the geomagnetic field strength in the last 75 kyr matches the Holocene interglacial period.

    http://ssn.dgf.uchile.cl/home/informe/2001RG000104b.pdf

    The sea floor sediment geomagnetic paleodata for the last 75 kyr can be checked against volcanic data. Note for this short period the low point in the geomagnetic field does occur during minimum orbital obliquity.

    My interest from a scientific standpoint: Is what is causing the abrupt changes in the geomagnetic field? I believe I have found the mechanism and understand the reason for the periodicity of the geomagnetic field changes. I am looking at paleoclimatic data to try to prove the hypothesis. I am also interested in long term variations in the solar cycle. (Maunder type minimums and super solar flares. I am looking at data from stellar studies of other stars which are similar to the sun.)

  20. 270
    Blair Dowden says:

    In my opinion, Dan makes a valid point that the southern hemisphere is mostly covered in ocean, therefore has a lower albedo, and should cause the Earth to warm at points in the precession cycle (like now) when southern summer occurs when the Earth is closest to the sun.

    But paleoclimate evidence shows the mid-Holocene was warmer than today, and as I understand it climate theory predicts that we should be in a period of slight cooling without anthropogenic influences. I can’t explain this contradition. Maybe someone else can help.

    While understanding interglacial periods such as the Eemian or MIS-11 are important for understanding the mechanics of climate, they are less relevant for understanding the impact of the current anthropogenic warming. Different interglacials have different patterns, the current Holocene natural pattern is almost flat, or declining slightly. So my suggestion to Dan is that he is not taking into account the timescales – the timescale of the orbital changes that drive the ice age cycles is much longer than the century or two relevant to global warming.

  21. 271
    tamino says:

    should cause the Earth to warm at points in the precession cycle (like now) when southern summer occurs when the Earth is closest to the sun

    No, this is not the case. When southern summer coincides with perihelion, the souther hemisphere has a hotter summer and a colder winter. Furthermore, because planets move faster along their orbits when closer the the sun, the southern hemisphere also has a shorter summer and longer winter.

    The effect of the precession cycle is to increase the seasonal contrast, but it has no effect on cumulative insolation at any location on earth.

  22. 272
    Hank Roberts says:

    Dan, you keep dropping these statements, like this:

    “… If warming was much greater during previous interglacials …”

    Would you _please_please_please_ say where you are getting your ideas?

    Did you read that somewhere? If so, where, and why do you consider it a reliable source?
    Did you make it up as a hypothetical? If so, there’s no end to what-ifs, but it’s just noise with no data.

    You can look this stuff up. Instead of just doing the endless “what-if” stuff with ideas lacking any cite, lacking any source, lacking any theory —– could you please try to say what you’re thinking and what your sources are?

  23. 273
    James says:

    Re #269: [James you seem skeptical concerning the "Geomagnetic field intensity changes drives the glacial cycle" hypothesis.]

    Skeptical is far too mild a word. I’ve occasionally brought up some of my questions re the whole GCR-climate connection hypothesis. These range from the short term (particle fluxes change considerably during solar flares: shouldn’t we see obvious short-term correlations?) to the long term (many millions of years of geomagnetic data from e.g. mid-Atlantic Ridge spreading, but AFAIK no correlation to climate) to the basic mechanism. If I can ask such obvious questions, and get no better answer than that the effect is modulated just the way it needs to be to match observations… Well, can you see how I’d be skeptical of such a theory, even if it were presented in isolation?

    It’s not presented in isolation, though, but as an alternative to a mechanism which was derived from basic theory, and which predicted the current warming well before evidence of it was available. It seems that the only advantage GCR has as a theory is that it absolves humans from any responsibility for the current changes, and thus any need to change their behavior. That’s why I go beyond skepticism to a very cynical suspicion.

    (I should probably add that this just applies to the invocation GCR/geomagnetic/climate connection, not to basic research into the geomagnetic field and its reversals. I think that’s an interesting area of science, just not relevant to the current climate. And on a quick read-through, I didn’t see anything about climate in the paper you linked.)

  24. 274

    Would you _please_please_please_ say where you are getting your ideas?

    We all know where Dan Fregeau is getting his … er … talking points.

  25. 275
    Blair Dowden says:

    Re #271: tamino, I think I was misinformed by these lecture notes that say eccentricity causes a temperature imbalance between the hemispheres, which I assumed could only because of eccentricity. I appreciate you correcting my errors, but could you please point me to a reliable reference so I can understand this properly, and not continue to mislead readers of this forum?

  26. 276
    tamino says:

    Re: #275 (Blair Dowden)

    Alas, the lecture notes you link to are just plain dead wrong on this point. It’s quite clear that the lecturer simply computed the difference in midsummer insolation between the hemispheres, ignoring the change in the length of seasons. Furthermore, even if there was no change in length of seasons, his estimate of the hemispheric difference (7% at present eccentricity) is inflated — you can’t just extrapolate the midsummer value to the entire year. Frankly, this doesn’t bode well for the students.

    Technical expositions can be found in Vernekar (1972, Long-term Global Variations of Incoming Solar Radiation, Meteor. Monogr. No. 34), Vernekar (1977, Variations in Insolation Caused by Changes in Orbital Elements of the Earth, in The Solar Output and its Variation, O.R. White ed., Colorado Associated University Press, pp. 117-130) Berger (1978, Long-term Variations of Caloric Insolation Resulting from the Earth’s Orbital Elements, Quat. Res. 9, 139-167) and Berger (1979, Long-term Variations of Daily Insolation and Quaternary Climate Changes, Jour. Atmos. Sciences, 35, 2362-2367). I’ve computed it myself, and arrived at exactly the same formulae. For a less technical expose, maybe I’ll do a post on the topic on my blog.

  27. 277
    Dan Fregeau says:

    #272 (Hank Roberts) Sources
    My main sources for the idea that past interglacials may have been warmer than the current Holocene are:

    - The Climate of Past Interglacials. Sorocko, Claussen, Sanchez Goni, Litt. Developments in Quaternary Science 7, Elsevier, 2007
    - Earth’s Climate and Orbital Eccentricity, The Marine Isotope State 11 Question. Droxler, Poore, Burckle. AGU Geophysical Monograph 137, 2003.

    These books contain several papers that seem to suggest a warmer climate (at least in some areas) during some parts of past interglacials based on evidence of higher sea levels and, in the case of the long MIS-11 interglacial, based on recovered fossils of warmer climate-adapted species in Northern Europe.

    As was pointed out, the sea level evidence appears less secure because of other geological factors although I believe the IPCC agrees that sea levels were higher than today during MIS-5. In any case, the latest IPCC report appears to provide a very thorough review on Paleoclimate (Chapter 6), and reading that will hopefully provide more clarity on the relationship between past sea levels and past global temperatures.

    On perihelion-soltice coincidence, I want to clarify that according to Kukla, Gavin (Milankovitch Climate Reinforcements, Global and Planetary Change, 2004), precessional coincidence actually occured around 1250 AD, and so I was incorrect in my earler statement about approach, given that the earth is already past that special orbital point.

    Therefore if there is no long-term oceanic heat retention/accumulation mechanism then it would also be true that southern summers should now be getting cooler on the basis of the natural forcing component, exclusive of any anthropogenic GHG forcing, which I believe is your position based on the feedback provided.

  28. 278
    Hank Roberts says:

    I suppose there’s some reason to question a file of “old notes” even left publicly available. The latest cite I noticed was “The correlation between cosmic rays and cloudiness was discovered by Svensmark and Friis-Christensen in 1997.”
    These notes may date from a decade ago.

  29. 279
    Blair Dowden says:

    Re #276: Thanks, tamino. I seem to occupy a middle ground where the standard simplified explanations are not good enough, but I am not at a level to understand a full technical book (such as the ones you suggest) intended for a specialist. If you choose to cover it in your blog, that would be great.

    I have a web page of my own on the subject, which I am using as an attempt to collect information to understand the climate change issue. You may recognize a small part of it – I lifted it from one of your helpful responses.

  30. 280
    Hank Roberts says:

    Dan, you wrote — after giving some references saying some areas were warmer during some interglacials:

    > “… Therefore if [X]* then it would also be true that southern summers should now be getting cooler which I believe is your position …”

    I don’t have a “position” — I’m a reader here; I’m trying to understand the science, and where people get what they believe to be true, by asking questions about their sources, checking cites, looking for the science behind what’s being said.
    ________
    * “if there is no long-term oceanic heat retention/accumulation mechanism” (Now, where did this come from? Who said that the ocean _doesn’t_ retain heat over the long term? Earlier you were talking about some separation of heat somehow between the hemispheres, quite a different idea. I think.)

  31. 281

    Re #279 — Blair, that is a very nice web page you’ve put together on the Milankovic cycles. The balance between text and graphics is just about perfect, and the writing is clear and to the point.

  32. 282
    Blair Dowden says:

    Re #281: Thanks, Barton. I found this interesting page on The Length of the Seasons” which talks about orbital variations in great detail, so I will be updating my page. It states

    The Northern Hemisphere dominates global weather patterns because it contains most of the land area. With its Summer being the longest season and getting longer, while Winter is the shortest season and getting shorter, for the next several millennia there will be an unavoidable cumulative trend toward global warming.

    The argument was made that the southern hemisphere has more ocean area, with lower albedo, thus absorbs more energy. But I think what drives climate change is the change in albedo, which is greater in the northern hemisphere due to the vulnerability of sea ice and snow cover on land. But this idea is not consistent with the fact that the mid Holocene was a relatively warmer period.


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