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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. 101

    [[It seems to me that the thermal expansion wouldn't stop on a dime in response to what amounts at this point to an insignificant blip of a few years of recent cooling (assuming, for the sake of argument, that cooling has occurred). If you take a longer-term moving average, any recent cooling wouldn't even show up. ]]

    It will stop on a dime if the ocean temperature stops rising. And if the ocean cools, expansion will become contraction. There is no “inertia” to thermal expansion, or if there is, it’s measured in seconds, not years. Conduction of heat may be a slow process, but it’s not that slow. Nothing is. Look up figures for the thermal conductivity of seawater.

  2. 102

    [[So you're saying that warming causes CO2 increases, which causes warming, which causes CO2 increases, etc? Why has this perpetual feedback cycle not caused our planet to be uninhabitable prior to this point?

    Once again, asking because I want an answer, not to be contrarian. ]]

    It’s a converging series. Not all infinite series diverge. For example, 1 + 1/2 + 1/4… converges to 2 no matter how many terms you add.

  3. 103
    Lynn Vincentnathan says:

    RE #93, I suppose one mechanism that halts carbon increasing in the atmosphere (& concomitant warming increase) is that a large amount of fauna die off (there was a 90% die-off of life during the end-Permian extinction some 251 mya). And once the methane from their carcasses is all released, that’s it. Carbon releases plummet. Then eventually plants uptake that atmospheric carbon & we get back to a lower CO2 level & a cooler climate (assuming “we” as a species are around to see that day, which could come some 100,000 years into the future).

    The climate scientists hate my use of “venus effect” or “runaway warming” precisely because Venus has permanent runaway warming, while there is nothing at this time re earth that would put it into permanent runaway warming. Not until the sun turns into a very hot red ball some billions of years from now.

    Until then we have the possibility of hysteresis, in which natural (volcanic, etc) or human causes trigger such an amount of warming that nature is induced to release its vast (but finite) store of sequestered (frozen) carbon.

    So let’s not push our luck by pushing into this hysteresis scenario. Regular non-hysteresis global warming is bad enough.

    Re ocean warming, and new findings that methane clathrates are closer to the surface than heretofore thought, it seems to me if the ocean warming happens fast enough (in geological terms) and vast stores of methane are released (along with the permafrost methane also being released), we could enter a hysteresis scenario. Atmospheric methane (which is 23 times more potent a GHG than CO2) has about a 10 year lifetime, before it breaks down into CO2, etc, unlike CO2, part of which can stay thousands of years in the atmosphere. So if a huge amount of methane is released within 10 year timeframes that would compound to create a really bad case of warming.

    Which is why it is so very important that we slow our release of GHGs into the atmosphere & slow the rate of warming (which, I believe, is faster now than it ever has been in geological history).

    We are entering into a dark, unexplored forest here with beasts known and unknown. There is already momentum & we’re headed into the outskirts of the forest, like it or not. But we need at least to slow down (that is, drastically reduce GHGs), if not halt altogether (go to zero emissions — which would be impossible).

  4. 104
    Lynn Vincentnathan says:

    RE #42, re climate scientists & environmentalists being unhappy if GW is proven false, I sorta understand your point from your perspective. My husband thinks the same way, that GW believers (like myself) are somehow happier when evidence is pointing to GW.

    I do feel very happy today, after seeing yesterday that 20/20, Oprah, and Nightline had very good programs on GW (& not in the pro-con format). I used to watch them regularly in the early 90s, expecting them to adress GW. Also the televangelist programs, since AGW is a big moral failing, not just an inconvenient truth. But nada, nada, nada over the years, over the decade+. But yesterday, they (except the televangelists) finally came around.

    But I’m not gloating (despite what my husband & you might think); I’m just happy that the message is getting out, and perhaps NOW enough people will start doing something to solve this problem.

    I was also ecstatic 17 years ago around Earth Day, after learning about lots of things to do to reduce my GHGs (after spending a torturous lent after learning about AGW and that I was responsible, but having no idea how to mitigate it). Again to the outsider it may have appeared I was happy that there were awful environmental problems.

    However, I felt very sad — I cried actually — when the recent IPCC report came out. That surprised me, since I already suspected way in advance (actually from the time of TAR) they would say things are worse than they had thought & that they were more certain. Also bec I consider IPCC to be somewhat conservative.

    First of all science is conservative, requiring 90 & 95% certainty that a big problem is happening before claiming it so. And second, because the IPCC requires some level of consensus among a lot of nit-picking conservative scientists, so it’s even more conservative than a single scientific study (one of which BTW found 95% confidence AGW was happening back in 1995).

    So I cried, because if these conservatives can say it’s happening with 90%+ certainty, that’s it. Near nil chance of waking up from this really bad dream, because it’s not a dream.

    But today I’m happy, bec the world seems to be catching on, and maybe this problem can be mitigated enough to avoid the worst.

  5. 105
    Marcus says:

    Re: #98: Henry Molvar: Well, to take one example, water is densest at 4 degrees Celsius. If you take a mass of water at 4 degrees, and use Maxwell’s demons to move heat around such that half of the water is at 2 degrees and half is at 6 degrees your new volume will be larger than the old one, even though you have added no heat to the system (we’ll ignore the entropy laws this violates). This is an example of what I meant by non-linear density to heat content relationship.

    I have no idea what effect pressure might have on this relationship.

    However, if you read my full post, you will also note that I doubt that these sorts of 2nd order effects can matter on the large scale.

  6. 106
    James says:

    Re [So you're saying that warming causes CO2 increases, which causes warming, which causes CO2 increases, etc? Why has this perpetual feedback cycle not caused our planet to be uninhabitable prior to this point?]

    I’d think that a big part of the reason this hasn’t happened in the past is that there’s only so much CO2 dissolved in the oceans, and even if you got it all into the atmosphere, the amount just isn’t enough to cause such a runaway warming.

    That’s the point to keep in mind: basically all of the increase in CO2 over the last century comes from carbon that was taken out of the system (as coal & oil) over many hundreds of millions of years, and is now being dumped back in all at once.

  7. 107
    Ray Ladbury says:

    Re 42 and subsequent discussions among Lynn and Rod.
    Rod, why do you assume we WANT the climate to change. What we want is irrelevant–it’s what the evidence tells us that matters. As a technophile and science geek, I strongly regret that much of the next century’s greatest minds will be distracted from fundamental science, by a need to adapt and survive. I also realize that some of the lifestyle changes that may be needed will not be easy. Nonetheless, if humans cannot anticipate and adapt to a challenge, then the mass of neurons on the end of our spinal columns seems to serve little adaptive purpose. Yeast cells can do as well–growing until they render their environment uninhabitable to themselves.
    On the other hand, as I have pointed out, I am happy when the models work–as that at least provides us with some guidance as to what to expect and means we are not flying blind. A working model is always better than a nonworking model–even when you don’t like what the model is telling you.

  8. 108
    Henry Molvar says:

    Re: #105 Marcus: *…water is densest at 4 degrees Celsius. If you take a mass of water at 4 degrees, and use Maxwell’s demons to move heat around such that half of the water is at 2 degrees and half is at 6 degrees your new volume will be larger than the old one, even though you have added no heat to the system (we’ll ignore the entropy laws this violates). This is an example of what I meant by non-linear density to heat content relationship.
    However, if you read my full post, you will also note that I doubt that these sorts of 2nd order effects can matter on the large scale.*

    Your insight is well noted.

    Any water, e.g. Arctic, that is between 0C and 4C will contract and get denser as it warms until it reaches 4C. This will reduce the volume of the oceans by some amount during warming periods counteracting the warming and expansion that occurs above 4C.

    To what extent this retarding effect is happening now I don’t know.

    Anyone?

  9. 109
    gerard mc aree says:

    Bit off topic but have seen comments before about bets. Leading Irish bookie Paddy Power will give you 7/2 for this to be hottest year on record in the UK and 5 to one that Ireland has its hottest year on record. Now, let´s see who has the courage of their convictions!?

  10. 110

    [[But yesterday, they (except the televangelists) finally came around.]]

    Actually, Pat Robertson, of all people, recently said he believes it’s really happening. I’m not a big Robertson fan, but at least he’s got this issue right.

  11. 111
    tamino says:

    According to Wikipedia, because of the salinity of seawater, it does not expand at temperatures below 4 deg.C. However, the density variations with temperature are much less at low temperatures than at higher temperatures, so the upper layers of the ocean have a much greater expansion due to warming than the lower levels, on a per-kilogram basis.

    This means that we can expect the thermal expansion of deep-ocean water to depend on heat permeating to massive volumes of the deep ocean. There’s plenty of deep-ocean water, so the effect can be sizeable — but it will take a long time to accumulate the necessary thermal energy. Therefore it would seem that on short timescales, thermal changes in the upper ocean will dominate those of the deep ocean.

    This makes it even more incongruous that upper-ocean cooling would coincide with sea level rise.

  12. 112
    Paul M says:

    What is inherently wrong with this whole situation is with the “flattening of the world” economywise and the concurrent climate change there needs to be international cooperation for success. This is possible, but I see one huge issue that could spell disaster for the world and humanity in general. To say it nicely, some countries may try to control space, and others might not like it too much. Get the picture?. The next decades or so should be ones of cooperation, and if we don’t work together civilized human existence could be highly problematic. I also see the ice sheets falling off, but to combat those problems we need the world to work together. Humanity has one chance here, are we going to screw this up?

  13. 113
    Dan Fregeau says:

    Ocean Warming. Yes, but is it Really CO2?

    1. Earth orbital geometry is currently approaching coincidence of perihelion and solstice. In fact, this will occur roughly within next thousand years, i.e. coincidence at opposite phase every half-precessional cycle. Precessional cycles are in turn modulated by orbital eccentricity, i.e. the envelope of precession.

    2. Current phase is perihelion close to summer solstice in southern hemisphere, and perihelion close to winter solstice in northern hemisphere. Seasonal effect of current perihelion-solstice approach is hotter summers in southern hemisphere, and also warmer winters in northern hemisphere. This seasonal effect will reach a maximum at coincidence.

    3. Usual Milankovitch analysis of insolation at high-latitude is much too simplistic for understanding current warming climate situation which is being forced by increased oceanic summer heat absorbtion in mostly oceanic southern hemisphere, and also by decreased oceanic winter heat loss in northern hemisphere.

    4. Effect of southern hemispheric perihelion-solstice approach is gradual global oceanic warming with corresponding adjustment of current and air flows, oceanic thermal expansion with gradual shift in oceanic-atmospheric CO2 balance (with more CO2 being released on top of anthropogenic addition), increased polar melting, particularly at the margins where ice is most affected by nearby warming oceanic temperature, and of course corresponding sea level rise.

    5. This climatic effect is exacerbated when eccentricity is very low, as is currently the case, and as was the case 400,000 years ago during the long MIS-11 Interglacial. At that time, the evidence indicates that sea levels were 15-20 meters (50+ feet) higher than today! This too, was “Real Climate”, and with CO2 levels under 300 ppm, suggesting that CO2 did not cause that period of “Global Warming”.

    6. MIS-11 was a period of much warmer climate in Europe, given that we have fossils of Hippopotamus amphibius (hippos), Elephas antiquus (elephants), and Bubalus murrenis (water buffalos) in Northern Germany, Northern France and also England, all dated from this period. Clearly, Europe was then a much warmer place than it is today, and without the benefit of anthropogenic CO2.

    7. While some more anthropogenic CO2, per the IPCC, will increase sea levels by a few centimeters, I strongly suggest that if you are really interested in understanding the scope of future climate change, then you should all carefully read:

    Earth’s Climate and Orbital Eccentricity, The Marine Isotope State 11 Question. Droxler, Poore, Burckle. AGU Geophysical Monograph 137, 2003.

    The Climate of Past Interglacials. Sorocko, Claussen, Sanchez Goni, Litt. Developments in Quaternary Science 7, Elsevier, 2007
    Particularly the following articles:
    - Eustatic sea levels during past interglacials, Siddall
    - Mammalian faunas from the interglacial periods …, Koenigswald

    After reading these volumes, one of clear mind might question the IPCC’s current obsession with anthropogenic CO2, and its resultant recommendations and priorities, given the implications of accepted paleoclimate research and scientific evidence.

    But then again, people have often been known to ignore the lessons of the past many times before. I commented on this previously under – IPCC Sea Levels .. #49.

  14. 114
    Craig Truglia says:

    Didn’t the latest research fine that the Oceans were neither cooling nor warming? If the ocean is not warming and the troposphere according to RSS and UAH is not warming like the surface, we have some major problems with the models.

  15. 115
    Richard Vineski says:

    Re #68: I think you miss the point. The 800 year lag between rising temperatures and increasing CO2 is used by some anti AGM people as “proof” that carbon dioxide levels have nothing to do with the earth’s temperature. This may be hard for us scientists to imagine, but I have met people (some of whom are highly educated) who argued exactly that. So I have to go back to basic chemistry and an explanation of how a greenhouse actually works, which some people still can’t imagine being applicable to something on the scale of the earth’s climate.

  16. 116
    Mark A. York says:

    “I’m just happy that the message is getting out, and perhaps NOW enough people will start doing something to solve this problem.”

    Boy Howdy, Lynn. That’s what I thought last night watching the ABC line-up. Good deal. It’s a shame some folks just don’t want to know the truth about anything and hold fast to ideas that just aren’t true only becasuse they have them. That’s a failure to adapt which, is terminal.

  17. 117
    Henry Molvar says:

    Re. #111: tamino: *According to Wikipedia, because of the salinity of seawater, it does not expand at temperatures below 4 deg.C. However, the density variations with temperature are much less at low temperatures than at higher temperatures, so the upper layers of the ocean have a much greater expansion due to warming than the lower levels, on a per-kilogram basis.*

    Thanks for the adjustment regarding the temp at which expansion of cold seawater starts to commence. I take it that your view is that this effect is negligible in the grand scheme of things?

  18. 118
    Hank Roberts says:

    > try to control space

    Already too late, according to the models of, again, basic physics; even before China added 10% to the space debris, there was already enough junk to expect a cascade of collisions to start eventually, producing more, and leading to loss of use of low earth orbit for satellites. I’m not sure if geosync is also expected to become a debris belt or not.

    Although the official website for the joint intergovernmental group on space debris still says China’s hosting this year’s meeting right about how:

    http://www.iadc-online.org/index.cgi?item=home

    News sources say China suddenly cancelled the meeting. Perhaps proof they’re capable of embarassment, or simply don’t want to admit they were capable of being so uncoordinated as to make an already marginal situation utterly disastrous.

    China Junks Space Debris Meeting=April 20, 2007
    http://www.livescience.com/blogs/author/leonarddavid
    “China has canceled the hosting of the 25th meeting of the Inter-Agency Space Debris Coordination Committee (IADC). The China National Space Administration was slated to host the IADC April 23-26 at the China Academy of Space Technology in Beijing.”

    Commentary here: http://onemansblog.com/2007/02/11/china-destroys-satellite-adds-10-more-debris-to-orbit/
    quoting a NYT article:

    “Today, next year or next decade, some piece of whirling debris will start the cascade, experts say.

    �It�s inevitable,� said Nicholas L. Johnson, chief scientist for orbital debris at the National Aeronautics and Space Administration. �A significant piece of debris will run into an old rocket body, and that will create more debris. It�s a bad situation.�

    Those old enough to remember the Cuban Missile Crisis will recall both the US and the USSR “tested” nuclear weapons in space during those critical days, supposedly as mutual threat
    http://www.vce.com/crisis.html
    apparently the results (widespread EMP, damage to satellites, whatever else) convinced both governments that actually using a larger number would be an utterly stupid move —- the long-delayed treaty banning nuclear tests above ground finally was signed shortly thereafter.

    They moved to killing satellites by throwing rocks. That should be safe, duh?

    “Take the machine gun aboard Salyut-3…. It weighed about 40 kg, was 2 meters long, and fired 200 gram projectiles at rate of 900 rounds per minute and a velocity of 780 m/se…… the USSR sowed the spacelanes with a dozen clouds of shrapnel from killer satellite tests in the late 1960′s which were lingering threats to navigation for decades. These small fragments were too small to track and too numerous to dodge, so important vehicles were just armored against them.

    “This was the preferred kill mechanism for many anti-satellite (ASAT) weapons, from the Soviet space-to-space â��killer satelliteâ�� of the 1960â��s and 1970â��s which used a shrapnel charge aimed at its target to the air-launched U.S. ASAT missile of the 1980â��s, which used precise guidance to directly ram the target.”
    —- excerpted from: http://www.jamesoberg.com/06122001pearlharbor_pol.html

    Well, now _that’s_ proven utterly stupid, as we’ve already exceeded the amount of garbage in orbit to predict more collisions, leading to more garbage …. it’s another chicken-and-egg argument. Too damn many, can’t stop them from multiplying.

    This is the outcome of attempting to control anything by being best at breaking it. Mutually assured destruction works as a threat, not as an incremental, ongoing strategy applied tactically.

    Imagine their surprise:

    “What? We can _share_ it but we can’t _own_ it or _control_ it??? That’s politically unacceptable ….”

    “But, Mr. Administrator, it’s basic physics ….”

    “Guards! …..”

  19. 119
    B Buckner says:

    Much of the discussion on this thread relates to Gavin’s statement that sea levels would not continue to be rising if in fact the sea temperatures have stopped rising or fallen slightly. The time period referenced in the Willis el al paper is mid 2004 to mid 2006. A look at the actual sea level data points in the data provided in post #95(ignoring the time related smoothing curve) during this period, with all of their scatter, does in fact suggest sea levels have not risen in this time period. With that said and has Gavin has stated, the time period is too short as yet to come to any conclusions as the data remain firmly in the long term upward trend. So the descrepancy between the sea temperatures and levels may not in fact exist.

  20. 120
    tamino says:

    Re: #113 (Dan Fregeau)

    Consider how slowly the astronomical cycles act. The fastest of them (the precession cycle) has a period which varies between 19000 and 23000 years.

    Consider how slowly climate changes during the natural warmings and coolings of glacial cycles. A reasonably rapid deglaciation warms the planet by about 5 deg.C in 5000 years. That’s a rate of 0.1 deg.C/century, while the warming rate during the modern global warming era is about 1.8 deg.C/century — 18 times faster.

    The extremely rapid climate change we’re experiencing now cannot be due to the cycles of eccentricity, obliquity, or precession. After reading your post, one of clear mind must doubt your clarity of mind.

  21. 121
    tamino says:

    Re: #117 (Henry Molvar)

    I misspoke; the sources I’ve seen indicate that seawater continues to contract as temperature is lowered, all the way to the freezing point, but the rate of contraction is much smaller at low temperatures than it is at near-surface temperatures.

    I don’t think the effect (heating of deep ocean water) is negligible in the grand scheme of things, but it seems clear to me that the effect is dramatically slower than the effect of heating upper-ocean water. So, long-term (many centuries) projections of sea level rise may be strongly influenced by the deep ocean, but short-term (the next 50 years) are likely to be dominated by the upper ocean.

  22. 122
    tamino says:

    Re: #119 (B Buckner)

    My analysis of the data referenced in post #95 indicates that during the period 1993 through most of 2006, the average rate of sea level rise was 3.1 +/- 0.2 mm/yr. Using just the data from mid-2004 to mid-2006 gives a rate of 5 +/- 2 mm/yr, and that result is most assuredly statistically significant.

    So your statement that “sea levels have not risen in this time period” is mistaken.

  23. 123
    Blair Dowden says:

    Re #120 (tamino) and #113 (Dan Fregeau): tamino has shown that the long time scale of orbital changes make them largely irrelevant for understanding present climate change or ocean temperature. I would argue further that Dan has the effect backwards. The northern hemisphere is more sensitive to changes in insolation because it has more land mass and sea ice cover. The paleoclimate record shows that the northern hemisphere drives global climate, which was warmer 8 thousand years ago (when northern summer occurred while the Earth was closest to the sun) in spite of the presence of continental ice remaining from the previous ice age.

    So the influence of orbital cycles for the past few thousand years has been in the direction of global cooling. This has been offset by anthropogenic changes, which if you believe William Ruddiman, has been happening for up to eight thousand years.

  24. 124
    Ken Winters says:

    Re: #113 (Dan Fregeau)

    Countless Forest Fires have historically been caused by natural means. Does that mean humans shouldn’t be considered the cause of any Forest Fires? Of course not. But that’s the basic logical flaw many skeptics use. Just because a previous climate change was caused by natural causes doesn’t mean the current one is. And since the current one is happening much more rapidly than any detected in the historic record, it seems quite reasonable to look beyond natural causes for the explanation. That’s what’s been done the past 30 years and the evidence indicates a human let a campfire run astray causing the current forest fire (to further my analogy).

  25. 125
    James says:

    Re #113 & following arguments re orbital cycles, CO2-temperature lag, etc: It seems that everyone is discussing this from the point of view that global warming is an observed phenomenon (or possibly observed, for the skeptics), and the task is to find an explanation – CO2, solar variation, orbital changes, cosmic rays, or little green men – that best fits the observations. That’s taking things exactly backwards: AGW is a prediction which was first made IIRC half a century or so before there was data to confirm it.

    To continue the analogy of #124, we know this forest fire was caused by careless humans, and are now using computer modelling to predict how the fire will spread. (Which is something that is actually being worked on, BTW.)

  26. 126
    Dan Fregeau says:

    Re. #120 (Tamino)

    “A reasonably rapid deglaciation warms the planet by about 5 deg.C in 5000 years. That’s a rate of 0.1 deg.C/century, while the warming rate during the modern global warming era is about 1.8 deg.C/century — 18 times faster.”

    - This is a rather uniformitarian view of the global climate process.

    Please consider the Younger Dryas termination/transition to Pre-Boreal, when the northern hemisphere was similarly close to perihelion-solstice coincidence. Then, per the original work of Dansgaard (The Abrupt Termination of the Younger Dryas event, Nature 339, 1989), and since further refined, the temperature drop in the North Atlantic region was around 7 deg in 50 years, with the bulk of the temperature change occuring in just 2 decades. Of course, this was also accompanied by a massive reorganization of Atlantic currents.

  27. 127
    Dan Fregeau says:

    Re. #124

    Dear Ken, I am not skeptical about global warming, nor that some level of anthropogenic GHG forcing is contributing to the warming process.

    But what I dispute is the conclusion that CO2 is the main causal of this current warming phase, on the basis of the reality of the MIS-11 Interglacial when CO2 was quite normal, but sea levels were much higher due to extensive deglaciation well beyond what has occured so far, or projected to occur by the IPCC.

    The fact that the current Holocene is quite similar to MIS-11 from an orbital geometry standpoint should alert one to the possibility that there may be other significant factors at work, and with forcing potential well beyond that of anthropogenic CO2.
    Dan

  28. 128
    DaveS says:

    The 800 year lag between rising temperatures and increasing CO2 is used by some anti AGM people as “proof” that carbon dioxide levels have nothing to do with the earth’s temperature.

    Well… no. Most people who cite the fact that CO2 naturally lags warming are responding to the unsubstantiated insinuation popularized by Al Gore’s movie, by which an ancient correlation is subtely passed off as evidence that CO2 *causes* the warming. The mythology here didn’t start on the “skeptical” side.

    It is also often cited in response to the assertion that increasing CO2 will triger an infinite feedback cycle (which has already been brought up in this thread)–where CO2 causes warming, which causes more CO2, which causes more warming, etc. It is actually an excellent demonstration of the fact that such a thing only exists in the virtual world described by computer models, and that CO2 has naturally increased in response to warming in the past without ever actually triggering runaway warming.

    [Response: No models predict 'runaway warming' and positive feedback in the climate sense of the term does not lead to unbounded solutions. See here for a discussion: http://www.realclimate.org/index.php/archives/2006/07/runaway-tipping-points-of-no-return/ -gavin]

  29. 129
    Dan Fregeau says:

    Re. #123 (Blair Dowden)

    Yes, you are quite correct that the northern hemisphere was closest to the sun (perihelion) at summer solstice around 10,000 years ago. This caused much warmer summers in the north as well as significant and abrupt climate change including the advent of the Holocene, i.e. this interglacial.

    Today, the opposite is true – the southern hemisphere has much warmer summers instead of the northern. But what you fail to realize is that the northern hemisphere is now also closer to the sun (perihelion) at winter solstice, which makes for warmer northern winters in addition to somewhat less warm summers, but still more warm overall.

    Therefore, when the earth is near perihelion-solstice coincidence, now or 10,000 ago, both polar regions are warmer on a seasonal basis. This is why polar deglaciation is synchronous in both hemisphere.

    With respect to having it “backwards” – please note that water aborbs (and retains) heat quite well, because it has very low albedo. Oceanic albedo is below 5%, whereas most land albedo is 10-40%, and ice and snow from 40 to 90%. Since the southern hemisphere is mostly water, do you not think that it would absorb heat far more efficiently than the northern hemisphere?

  30. 130
    Ray Ladbury says:

    So, Dan, what might those “other significant factors” be? Until you have real candidates, you don’t even have what mounts to a scientific hypothesis. What is more, if your candidate mechnanisms turned out to be important, there would be the additional problem of explaining why a greenhouse gas should not behave like a greenhouse gas.
    After all, we can measure insolation–and that doesn’t come close to explaining things. What else would you propose?

  31. 131
    tamino says:

    Re: #126 (Dan Fregeau)

    per the original work of Dansgaard … the temperature drop in the North Atlantic region was around 7 deg in 50 years, with the bulk of the temperature change occuring in just 2 decades…

    Dansgaard’s paper claims a 7 deg. temperature drop in south Greenland. That’s not the north Atlantic region, it’s nowhere near as big as (nor does it have the thermal inertia of) the ocean, and it’s certainly not the world.

    Frankly, your contention that the global average ocean temperature changes are being driven by orbital changes just doesn’t hold water.

  32. 132
    Dan Fregeau says:

    Re. #125 (James)

    I agree with you AGW was theorized a while back, and forces climate to an extent, and that modelling future climate change due to AGW makes very good sense. Go for it.

    However, I also think that modelling future climate change on the basis of well-measured past climate change makes even more sense, particularly if past climate change analog (MIS-11) was significantly greater than current AGW climate change, per the geological record, i.e. the prehistoric Real Climate.

    Otherwise, modelling future climate change on the basis of AGW alone might be largely inconsequential, might it not?

  33. 133
    Mark A. York says:

    So why aren’t the experts saying this is Milkanovichian this time around? Just wanted to overlook it? One has to wonder why it is CO2 defenders try so hard to blame something else, the oldest of which is it happened before and thus is natural. That strikes me as simplistic as well.

  34. 134
    pete best says:

    Re #127

    Take a look at this graph. Even the Antartic experts are telling us that its CO2.

    http://home.btconnect.com:80/objectcomx/IPCCAnt_small.jpg

    If we get to 550 ppmv then all current ice sheets will be in danger and remember it is not just CO2 but methane and others contribute to.

  35. 135
    Rod B. says:

    Lynn, a minor quibble with a small part of 104. I don’t see the IPCC as a bunch of conservative scientists. Nor is it correct to say because there is a big bunch per se, conservative or otherwise (ignoring the large mass of politicos), the answer is going to be either more conservative or “better.” To paraphrase an old saw, with a half-dozen or so good scientists you might get a good scientific theory/law; with 1000 good scientists you can have some grapes stomped and get some good wine.

  36. 136
    Hank Roberts says:

    Dan, you’d need to identify _two_ unknown significant factors, wouldn’t you?
    One unknown to subtract from the known CO2 forcing, to zero it out (since CO2 is enough to explain current warming).
    Plus another unknown equal to the known CO2 forcing, to explain current warming.

    Why do you think sea levels were much higher? What source are you relying on, can you give us your cite and why you consider it good info?

    I looked for recent articles
    http://scholar.google.com/scholar?q=%22MIS-11+interglacial%22&hl=en&lr=&scoring=r&as_ylo=2002

    I found references to an older idea that sea levels were higher during that period, a known paradox being studied.

    More common recently are a series of refutations—-for examples from that search, one area formerly considered evidence of a sea level change has apparently been uplifted,
    http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm06&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm06%2Ffm06&maxhits=200&=%22PP51B%22
    another site referred to, when restudied, appears to be evidence of a major tsunami,
    http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm06&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm06%2Ffm06&maxhits=200&=%22OS33E-06%22

    Where are you finding the info you rely on? I’m always _very_ interested in sources, and very few people ever reply by giving their cites, so I’d much appreciate knowing where you got yours. I’d like to look into it further; I’m just another casual reader here, but I dearly love footnotes (grin).

  37. 137
    B Buckner says:

    Re:122 (tamino)

    Perhaps you used a different starting point, but from the second half of 2004 through the end of the data series I get a trend of -0.002mm/yr +/-5mm. There is a lot of scatter in the data and I am not sure how you came up with a standard deviation of only +/- 2mm.

  38. 138

    But what I dispute is the conclusion that CO2 is the main causal of this current warming phase, on the basis of the reality of the MIS-11 Interglacial when CO2 was quite normal, but sea levels were much higher due to extensive deglaciation well beyond what has occurred so far, or projected to occur by the IPCC.

    Gosh, I don’t know where to begin here. First of all, if the present warming continues, on the timescales that you are referring to, all of the ice is going to melt, not just Greenland and the West Antarctic – presumed 20 meter or so rise to which you refer. So we can establish easily that natural forcing, left to it’s own over geological time, can melt Greenland and/or West Antarctica. Clearly then 383 ppm rising at 2 ppm/year will melt all the ice. Are you with me so far?

    Now, clearly a 100 ppm per century (on average) rise of carbon dioxide concentration is not natural, and we have good evidence that humanity is perturbing the carbon cycle on a grand scale. We know that carbon dioxide traps heat. We’ve quantified that carbon cycle to approximately first order, constructed sophisticated mathematical models running on sophisticated computational systems of our own design, using a fairly sophisticated second order set of physical principles derived over several hundred years, and we have achieved a moderate amount of empirical success with the technological systems that we have.

    What particular processes do you think we have missed? New physics?

  39. 139
    David B. Benson says:

    Re #127: Dan Fregeau — I encourage you to read

    David Archer & Andrey Ganopolski
    A moveable trigger: Fossil fuel CO2 and the onset of the next glaciation
    Geochemistry, Geophysics, Geosystems. v. 6 #5 (2005 May 5)

    The paper is easy to find via web trawling, but there is also a link in a comment in the What triggers ice ages thread.

    The similarities between MIS-11 and the Holocene are not directly discussed in this paper, but it will help you to understand the magnitudes of the natural and anthropogenic effects…

  40. 140
    tamino says:

    Re: #133 (B Buckner)

    I got the data from the link provided in the post you referred to (http://sealevel.colorado.edu/). There are four data sets: with or without “inverted barometer” correction (to correct for the effect of air pressure), and with or without the seasonal trend removed. Analyzing data from 2004.5 to 2006.5 by linear regression, I get a statistically significant trend for all four datasets.

    The scatter in the data itself is around 5mm, but it’s generally true that the uncertainty in the result of a trend analysis will be far less than the raw data scatter. I even allowed for the effect of auto-correlation in the data, to be sure the results were statistically significant.

  41. 141
    Ike Solem says:

    Regarding the role of orbital variations, carbon dioxide and ice sheets in the glacial cycles, it still seems that CO2 variations are a primary driver in the glacial cycle, and that the ice sheet dynamics lag behind changes in CO2. It also seems clear that CH4 and N2O can play important roles in short-term variability. See Ice, Mud Point to CO2 Role in Glacial Cycle by Richard A. Kerr and The 100,000-Year Ice-Age Cycle Identified and Found to Lag Temperature, Carbon Dioxide, and Orbital Eccentricity, Shackleton 1999

    “Shackleton sees the lockstep of eccentricity, greenhouse gas, and temperature as a sign of cause and effect. In his view, at the beginning of glaciation changes in eccentricity–presumably by shifting the distribution of sunlight across the globe–could have decreased atmospheric carbon dioxide, weakening the greenhouse and cooling the ocean and atmosphere. At the end of an ice age, the changes are in the opposite sense. Those changes are relatively rapid and would appear to coincide; the sluggish ice volume would lag behind. That delay rules out ice as a prime mover, Shackleton says; it’s only a follower….

    Shackleton’s results impress many researchers who specialize in sorting out the cause of the ice ages. The paper “is really well argued,” says geophysicist Richard Peltier of the University of Toronto. “It has inevitable drawbacks because of the short record,” but it would appear that “carbon dioxide is a primary driver, not just a weak feedback.”

    Peltier says his own computer models reinforce that conclusion. Hoping to show that ice sheets themselves were crucial to glacial cycles, he developed a model that included not only orbital forcing and carbon dioxide variations but also the way ice sheets grow and decay. The ice turned out to be essential for the distinctively abrupt end of an ice age, but not crucial the way carbon dioxide seems to be. “The model only works because it includes the forcing from carbon dioxide,” Peltier says. “If we exclude that, we get no glacial cycle. The ice dynamics just doesn’t do it for you at all without carbon dioxide.”

    We’ve strengthened the greenhouse effect through the use of fossil fuels; now we’re wondering how the oceans and ice sheets and hydrologic cycle (and the biosphere) will respond. Sort-of-trustworthy data says that currently, the oceans aren’t warming at their earlier rate, and are not cooling either.. but the Earth is still in energy imbalance of 0.85 +/- 15 Watts/m^2 ; where is that energy going, if not into the ocean? (over 10,000 years, that’s enough to melt enough ice to raise sea level ~1 km). If only one could measure the planetary energy imbalance directly… but the Deep Space Climate Observatory has been grounded. The satellite has already been built, but won’t be launched, due to NASA’s “competing priorities”. Why? “Four hundred million dollars have been cut to pay for shuttle flights to the International Space Station and to return astronauts to the Moon.” Maybe NASA should rethink priorities?

  42. 142
    Steve Reynolds says:

    Re 128> Ray: “Until you have real candidates, you don’t even have what mounts to a scientific hypothesis.”

    How about this hypothesis (for discussion, I’m not necessarily claiming it is correct):

    Actual climate sensitivity to CO2 is 1.0C (GHG positive feedbacks are effectively canceled by negative feedback from clouds), not the 3C calculated mostly from insolation changes (including volcanic solar dimming).

    The higher positive feedback with insolation change is due to previously unconsidered effects that may only respond to insolation. A possible example is ocean emissivity changes with wind:
    http://aerosols.lanl.gov/conf2006/talks/files/Volz.pdf

    Any discrepancy with 1C sensitivity and current measured temperature increase is a combination of natural variation and measurement error (including UHI effects not properly accounted for).

  43. 143
    Blair Dowden says:

    Re #129: (Dan Fregeau): The precession cycle does not change total insolation over the course of a year. So the ocean in the southern hemisphere may well absorb the increased summer insolation, but it will lose the same amount of energy from the decreased winter insolation. Therefore no net change. The same is true in the northern hemisphere, except for the large amount of sea ice. Here the timing is critical; the summer warmth may melt more ice (thus reduce albedo and absorb more energy) than the winter cooling will cause it to freeze. That is why global temperature is driven mainly by changes in the northern hemisphere.

    You are incorrect to assume the precession cycle changes the amount of energy received over the course of a year. Because of the seasonal effects, our present position in the precession cycle is one of slight global cooling, not warming as you claim. And the magnitude of this change is very small compared with anthropogenic greenhouse gases over the century timescale that we are concerned with.

    So while the precession cycle is important for understanding past climate, it is not having much influence over the present climate changes. Anthropogenic changes are the main driver at this time.

  44. 144
    Blair Dowden says:

    Re #142: Steve, the problem with a climate sensitivity of one, as you suggest, is that it is hard to explain how the large changes in climate occurred during the ice ages when the forcings caused by the orbital cycles are relatively small. For example, it is hard to understand how the large temperature swings during the Younger Dryas period could happen without a significant feedback from somewhere. If changes in cloud cover canceled the feedbacks, the climate would be much more stable than it actually is.

  45. 145
    Paul M says:

    The ice sheets at antarctica slipping off and creating catastrophe, or most marine life dying off, or plants and insect relationships failing, or permafrost thawing, we need to work together to tackle this. Sputnick spurred competition, the initial catastrophe will spur cooperation. Poor Bangledesh. We created the bomb because Hitler was allegedly working on it, now we need to save the planet. The initial catasrophe will change everything.

  46. 146
    Steve Bloom says:

    Re #128: The “CO2 has naturally lagged warming amd the same must be true now” argument predates the Gore movie considerably. IIRC it was raised by the usual fossil fuel-funded suspects (e.g. Pat Michaels, Steve Milloy) just as soon as the first ice core papers came out. It’s fallaciousness was pointed out immediately, but since it is sometimes effective in fooling the ignorant it has become one of the stock denialist arguments. BTW, Gore did not get this point wrong.

  47. 147

    the forcings caused by the orbital cycles are relatively small.

    Do you honestly expect us to believe that?

  48. 148
    tamino says:

    Re: orbital forcing

    The obliquity and precession cycles alter the latitudinal and seasonal distribution of incoming solar energy, but have no effect on the solar energy intercepted by earth averaged over the entire year. Only the eccentricity cycle alters this, but its effect is small; the eccentricity-induced change in average insolation generally amounts to less than 0.5 W/m^2, and the cycle takes about 100,000 years.

  49. 149
    Steve Bloom says:

    Re #147: Thomas, the orbital forcings aren’t large enough by themselves to drive the glacial cycles. Feedbacks are required to make things work.

  50. 150

    Clearly orbital forcing is the pacing element. Carbon dioxide forcing and other feedbacks are measured in Watts (per square meter), whereas the integrated solar forcing from orbital variations is measured in tenths of Watts (per square meter), but insolation at latitude varies by tens of Watts (per square meter). Clearly orbital forcings are neither insignificant nor even ‘small’, since they drive the oscillations. That’s why orbital variations drive the processes, and feedbacks do the amplification. I hope that clarifies a hopelessly naive statement.

    Please don’t tell me that carbon dioxide is driving orbital variation. I suppose things would be a lot simpler if the ice caps where at the equator, but I can’t imagine trying to live on a planet like that.


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