The 800-Year Lag

Until I watched the Global Warming Swindle, I had confined my criticisms of anthropogenic global warming theory to two general areas:  1)  The models for future warming are overstated and 2) The costs of warming may not justify the costs of preventing it.

The movie offered an alternate hypothesis about global warming and climate change that, rather than refute the magnitude of anthropogenic global warming, provided a counter hypothesis.  You should watch the movie, but the counter hypothesis is that historic temperature changes have been the result of variations in solar activity.  Rather than causing these changes, increased atmospheric CO2 levels resulted from these temperature increases, as rising ocean temperatures caused CO2 to be driven out of solution from the world's oceans.

I thought one of the more compelling charts from Al Gore's pPwerpoint deck, which made the movie An Invconvienent Truth, was the hundred thousand year close relationship between atmospheric CO2 levels and global temperature, as discovered in ice core analysis.  The Swindle movie, however, claims that Gore is hiding something from that analysis in the scale of his chart -- that the same ice core analyses show that global temperature changes have led CO2 concentration changes by as much as 800 years.  (short 2-minute snippet of this part of the movie here, highly recommended).

Well, this would certainly be something important to sort out.  I have not done much real science since my physics days at Princeton, but my sense is that, except maybe at the quantum level, when B follows A it is hard to argue that B caused A.

So I have poked around a bit to see -- is this really what the ice core data shows, or is Swindle just making up facts or taking facts out of context ala the truther hypotheses about 9/11?  Well, it turns out that everyone, even the die-hard global warming supporters, accept this 800-year lag as correct (Watch the Al Gore clip above -- it is clear he knows. You can tell by the very careful way he describes the relationship).  LuboÃ…¡ Motl summarizes in his blog:

However, the most popular - and the most straightforward - explanation
of the direction of the causal relationship is the fact that in all
cases, the CO2 concentration only changed its trend roughly 800 years
after temperature had done the same thing. There have been many papers
that showed this fact and incidentally, no one seems to disagree with

The whole "group" at RealClimate.ORG
[ed: one of the leading sites promoting the anthropogenic theory] has agreed that there was a lag. But they say that in the first 800
years when the influence of temperature on CO2 is manifest, it was
indeed temperature that drove the gases. But in the remaining 4200
years of the trend, it was surely the other way around: CO2 escalated
the warming, they say.

Frequent readers will know that I have criticized forward looking climate models on many occasions for being too reliant on positive feedback processes.  For example, in the most recent IPCC models, over 2/3 of future warming come not from CO2 but from various positive feedback effects (section 8.6 of the 2007 report). 

The folks at are similarly positing a positive feedback mechanism in the past -- "something" causes initial warming, which drives CO2 to outgas from the oceans, which causes more warming, etc. 

I am not sure I have ever done so, so let me take a minute to discuss positive feedbacks.  This is something I know a fair amount about, since my specialization at school in mechanical engineering was in control theory and feedback processes.  Negative feedback means that when you disturb an object or system in some way, forces tend to counteract this disturbance.  Positive feedback means that the forces at work tend to reinforce or magnify a disturbance.

You can think of negative feedback as a ball sitting in the bottom of a bowl.  Flick the ball in any direction, and the sides of the bowl, gravity, and friction will tend to bring the ball back to rest in the center of the bowl.  Positive feedback is a ball balanced on the pointy tip of a mountain.  Flick the ball, and it will start rolling faster and faster down the mountain, and end up a long way away from where it started with only a small initial flick.

Almost every process you can think of in nature operates by negative feedback.  Roll a ball, and eventually friction and wind resistance bring it to a stop (except, apparently, on the greens at Augusta).  There is a good reason for this.  Positive feedback breeds instability, and processes that operate by positive feedback are dangerous, and usually end up in extreme states.  These processes tend to "run away."   I can illustrate this with an example:  Nuclear fission is a positive feedback process.  A high energy neutron causes the fission reaction, which produces multiple high energy neutrons that can cause more fission.  It is a runaway process, it is dangerous and unstable.  We should be happy there are not more positive feedback processes on our planet.

Since negative feedback processes are much more common, and since positive feedback processes almost never yield a stable system, scientists assume that processes they meet are negative feedback until proven otherwise.  Except in climate, it seems, where everyone assumes positive feedback is common.

Back to the climate question.  The anthropogenic guys are saying that when the earth heated, it caused CO2 to outgas from the oceans, which in turn caused more warming, which causes more outgassing, etc.  But where does it stop?  If this is really how things work, why isn't the Earth more like Venus?  If you are going to posit such a runaway process, you have to also posit what stops it.  So far, the only thing I can think of is that the process would stop when the all bands of light that are absorbable by CO2 are fully saturated.

But the feedback is worse than this.  I won't go into it now, but as you can see from this post, or from section 8.6 of the 2007 IPCC report, the current climate models assume that warming from CO2 itself yields further positive feedback effects (e.g. more humidity) that further accelerate warming, acting as a multiplier as great as 3-times on CO2 effects alone.

So here is the RealClimate view of the world:  Any small warming from some outside source (think Mr. Sun) is accelerated by outgassing CO2 which is in turn accelerated by these other effects in their climate models.  In other words, global temperature is a ball sitting perched on the top of a mountain, and the smallest nudge causes it to accelerate away.  This is the point at which, despite having only limited knowledge about the climate, I have to call bullshit!  There is just no way our planet's climate could be as stable as it has been long-term and be built on such positive feedback loops.  No way.  Either these folks are over-estimating the positive feedback or ignoring negative feedbacks or both.  (and yes, I know we have had ice ages and such but against the backdrop of the range of temperatures the Earth theoretically could have in different situations, our climate variation has been small).

Postscript:  The other day I mentioned that it was funny a group studying solar output felt the need to put in a statement validating anthropogenic global warming despite the fact that nothing in their research said any such thing.  Motl points to a similar thing in the ice core studies:

Well, the website tells us that the paper that reported the lag contained the following sentence:

  • ...
    is still in full agreement with the idea that CO2 plays, through its
    greenhouse effect, a key role in amplifying the initial orbital forcing

Again, this statement was included despite the fact that their study pretty clearly refutes some key premises in anthropogenic global warming theory.  It's become a phrase like "no animal was hurt in the filming of this movie" that you have to append to every climate study.  Or, probably a better analogy, it is like Copernicus spending a few chapters assuring everyone he still believes in God and the Bible before he lays out his heliocentric view of the solar system. 

Update: All this is not to say that there are not positive feedback loops in climate.  Ice albedo is probably one -- as temperatures rise, ice melts and less sunlight is reflected back into space by the ice so the world warms more.  My point is that it does not make any sense to say that positive feedback processes dominate.

Correction: Like a moron, I have been using anthropomorphic rather than anthropogenic to refer to man-made climate effects.  Oops.  Thanks to my reader who corrected me.  I have fixed this article but am too lazy to go back and edit the past.

Further Update:  The irony of my correction above juxtaposed against the title of the previous post is not lost on me.

Update to the Postscript: Oh my god, here it is again.  An NOAA-funded study comes to the conclusion that global warming might actually reduce hurricane strength and frequency.  Nowhere in the study did the researchers touch any topic related to anthropogenic warming -- they just studied what might happen to hurricanes if the world warms for any reason.  But here is that disclaimer again:

"This study does not, in any way, undermine the widespread consensus in the scientific community about the reality of global warming," said co-author Brian Soden, Rosenstiel School associate professor of meteorology and physical oceanography whose research is partly funded by NOAA.

Does the NOAA and other funding bodies actually require that this boilerplate be added to every study?


  1. Monsyne Dragon:

    Or, in short, since it only takes a small perturbation to force a system out of a unstable equilibrium (that is, a state that has a positive feedback), you are vastly less likely to find something in an unstable equilibrium, as opposed to a stable one (namely a state with a negative feedback).

    BTW, minor nit: the term is anthropoGENIC, not anthropomorphic.

  2. tsiroth:

    Whew, thanks Monsyne, that's been bugging me, too.

  3. ArtD0dger:

    As a side-note, if climate really were driven by these hair-trigger positive feedback processes, then the proposed method of reacting to climate change by reducing CO2 emissions would be inadequate to the control task. I'm too rusty/lazy in control systems theory to describe it quantitatively, but basically controlling an unstable plant requires an aggressively high-gain, anticipatory feedback compensator fed by accurate information. It would be like flying one of those forward swept-wing experimental airplanes where the computer has to adjust the control surfaces every millisecond to keep it flying straight. Reacting in the right direction with the wrong phase lag can actually INCREASE the instability.

    -- I'm not sure Warren actually reads these comments. People have been bugging him about his use of "anthropomorphic" for months.

  4. Richard Nikoley:


    Anthropomorphic means: man-like
    Anthropogenic means: caused by man

  5. Max:

    So, they assume that the positive feedbacks are dominant? Wouldn't the Earth climate system be an extremly unstable system? I mean, we had big temperature swings in the past, if the Earth really were a system with dominant positive feedbacks, we would have had several system failures during the past. However, instead we had climate swings from cold to warm and back, which is more of a stable self-regulating system.

    Given, my knowledge on models and systems is limited to engineering application, since I have only basic knowledge on measuring and control technology. But ultimately climate models aren't much different to complex modelling of mechanical, fluid mechanical or electrical systems.
    The question is when dominate negative and when positive feedbacks, where is the top of the hill after the valley?

  6. eddie:

    Well, looks like Warren reads his comments sometimes. I guess he usually has better things to do, like write more blog posts that we can comment on. :)

    I wonder if he'll ever check his spellchecker for "ammendment" vs "amendment".

  7. RobC:

    Besides positive feedback, there's also a saturation effect. Don't be misled into thinking I know something about it, but it's something like this: since most of the IR radiation is already trapped in the atmosphere by greenhouse gases, it takes a lot more greenhouse gas to get a little more global warming effect. So, it appears, there are two things going on (along with 2 million other things) and we can say one compounds the effect and the other moderates it. I think that's why you have to use computer models to figure out what the end result will be, and there's only one way to check the computer models. This is where the precautionary principle comes in.

  8. dearieme:

    But use of the Precautionary Principle violates the Precautionary Principle.

  9. Reasic:

    Hello, all. Just curious. Did you read my response to Motl?

  10. Reasic:

    Hello, all. Just curious. Did you read my response to Motl?

  11. Reasic:

    Sorry about the double post. I got distracted.

  12. Mesa EconoGuy:

    I’m in the weird position of having 1) a hard science background, 2) a statistical modeling background, and 3) an economics (capital markets) background and current experience.

    I have not seen either Gore’s mess or this counterargument (possible mess, though my science background tells me the solar activity correlation is probably more likely).

    I once built a statistical pricing model (one of the most seemingly random events) for old corrugated containers – basically used cardboard boxes – which, once I incorporated what I thought were the right input variables, I fit almost perfectly with past price behavior, my own “hockey stick.” I used actual measurable data, which many of these models do not, but I got it to look really, really good using accurate pricing parameters.

    Guess what happened when we plugged in the predictive values? It went to hell, and quickly. So I re-tooled the model, and that crapped out, too.

    You nailed the root problem with this statement: “If you are going to posit such a runaway process, you have to also posit what stops it. “

    No one, not even Grammy-nominated scientist Cheryl Crow, can identify any discreet driving mechanism or process that is “causing” warming. But they are more than willing to impose draconian measures that will have far more detrimental economic effects than positive environmental impact, using what amount to basically scientific hunches.

    That’s unbelievably arrogant and dangerous.

  13. Mesa EconoGuy:

    And, sorry for the full length, but the economically ignorant UN is about to re-market global warming as an economic event:

    -- Re-brand global warming as economic woe-UN draft --
    By Alister Doyle, Environment Correspondent
    OSLO, April 12 (Reuters) - A fight against global warming
    could work better if viewed as part of the world's economic
    problems and not a purely environmental headache, a draft United
    Nations report says.
    The report, due for release in Bangkok on May 4, says
    economic policies for everything from forestry to insurance can
    have big spinoffs in limiting greenhouse gas emissions.
    "Framing the debate as a development problem rather than an
    environmental one may better address the immediate goals of all
    countries, and particularly developing countries and their
    special vulnerability to climate change," the draft says.
    Efforts to curb use of fossil fuels, for instance, can cut
    emissions of greenhouse gases blamed for stoking global warming.
    At the same time, such measures curb air pollution and improve
    energy security by reducing dependence on energy imports.
    The study says developing nations -- such as China, India,
    Mexico and Brazil -- have cut the growth of their greenhouse
    emissions in the past 30 years by 500 million tonnes a year, for
    reasons other than climate.
    "Many of these efforts are motivated by economic development
    and poverty alleviation, energy security, and local
    environmental protection," it says.
    Those cuts are more than those required by the Kyoto
    Protocol, the main U.N. plan for fighting global warming that
    binds 35 developed nations to cut emissions by 5 percent below
    1990 levels by 2008-12, it says.
    "The most promising policy initiatives ... seem to be those
    that capitalise on natural synergies between climate protection
    and development priorities to simultaneously advance both," it
    The 101-page draft technical summary, obtained by Reuters,
    is part of an authoritative U.N. series about global warming
    that will guide policymakers in coming years. It also concludes
    that measures to fight climate change can be inexpensive.
    Insurers, for instance, could help by charging lower
    premiums for buildings away from areas at risk of floods,
    erosion, melting permafrost or rising seas. And protecting
    forests can help soak up greenhouse gases and slow erosion.
    "In industrialised countries, climate change continues to be
    regarded mainly as a separate, environmental problem that is to
    be addressed through specific climate change policies," it says.
    It says a broad discussion about economic development and
    climate change had not seriously been initiated in rich states.
    Government negotiations on ways to fight climate change
    after a first period of Kyoto ends in 2012 are stalled, with
    disputes about how far rich nations should cut emissions and to
    what extent developing states should brake emissions growth.
    President George W. Bush pulled the United States out of
    Kyoto in 2001, arguing emissions caps would damage the U.S.
    economy and developing nations are wrongly excluded until 2012.

  14. Ian Random:

    I was poking around Realclimate awhile back and noticed a talk by Prof. Mann from 2000. It showed solar radiation increasing by 1 watt/m^2 in the 90's. Then I remembered that Junkscience showed an IPCC graph that claims 1 watt/m^2 is the discrepancy that is causing everything to go to hell. Of course, if you say all this is irrelevant since an ice age is gonna happen, Realclimate says the thermohaline circulation is going to stop and cause a runaway effect. But then again Realclimate can't explain anything, other than when the heating agrees with their estimates that proves everything and to ignore it when it doesn't agree even though they can't explain it. After that, I dropped it from the linklist.

  15. Reasic:

    Ian, 1 W/m^2 is how much the solar cycles vary per cycle. They go up that amount but then back down that amount every 11 years. Is that what Mann was talking about? It helps to have links to be able to see what you're talking about.

  16. Reasic:


    I haven't seen Gore's movie either. I don't need to. I've been convinced of AGW by the science. I don't turn to Gore for answers any more than I would Cheryl Crow or my little brother. I look at the peer-reviewed research. It's been my experience that there are many more answers there than skeptics would have you believe.

    No one, not even Grammy-nominated scientist Cheryl Crow, can identify any discreet driving mechanism or process that is “causing” warming.

    As far as Cheryl Crow, she's obviously not a scientist. She, like many others, simply trusts the scientific process.

    There is no one driving mechanism. There are many factors that influence our climate. If you look at page 4 of the first SPM for AR4, you'll see a chart of "Radiative Forcing Components". Through extensive research, scientists have been able to quantify the contribution of each component to warming or cooling. CO2 comes out on top with 1.66 W/m^2.


    An very inconvenient fact for the GW theorists is that if you go to the NOAA site and download then cross correlate the data, you will see that the O18 changes lead both CO2 and CH4 data by several thousand years, not just a few hundred. Even more interesting is that the CH4 and CO2 data are much more strongly correlated than the O18 data, and in sync, strongly suggesting they are both caused by the same thing, for example release of methane hydrates by warmer oceans. Whatever the explanation, the data clearly say that CO2/methane changes are coupled and follow the O18 data in time, not lead. And yes, both methane and CO2 are currently rising, not just CO2.

    It is bad enough to spend money fixing a non problem, but even worse to spend it on entirely the wrong thing.

  18. RobC:

    Allan, the temp/CO2 correlation is based on proxy data, so you can't take it literally. Having said that, it probably is true, because it merely shows what you'd expect: rising temperatures cause more greenhouse gas. However, an inescapable fact of physics is that greenhouse gases cause global warming. Otherwise Earth would be some 33 deg C colder than it is. That means we can have a compounding effect, where temperature drives greenhouse gas which drives temperature, etc, to the worst case. That is precisely what concerns people.

  19. Mesa EconoGuy:

    I’m not going to wade into the weeds too deep here, but p. 4 of the report tells me (and you) practically nothing.

    This is particularly troubling:
    LOSU – Level of scientific understanding: High? Excuse me? These people can’t get the 5 day forecast right. I call bullshit here. They have no idea what the processes are, only that they have measured and observed certain component interactions within what is an unbelievably complex system. It sure is a pretty chart though.

    That brings up the (non) predictive value of current models – many are deliberately loaded with 2 to 3 times observed CO2 values, and other statistical mistakes, in order to get the outcome desired. This is nothing short of scientifically lying.

    Economically speaking, basing a course of policy action on biased predictive models and self-described “high LOSU” of partially understood systems is incredibly reckless, particularly given the mechanism of choice to do so – massive government intervention (Kyoto). This non-market intervention will fail, and will have many negative side-effects, such as stunting economic growth of many developing nations, and distorting economic interactions.

    It will also foster myriad ways around such restrictions.

    Currently, this isn’t a scientific process at all. It is a politically-driven scientific race to a conclusion that may or may not be correct, but offers many rent-seekers many potential possibilities, not the least of which is increased government regulation.

    People like Cheryl Crow 1) aren’t scientifically trained, and 2) lack the intellectual capacity for skeptical analysis. I’m glad she’s on the GW side.

    This debate isn’t over – it’s just getting started.

  20. Allan Ames:

    RobC - Your caution about proxy data is appropriate and well taken. However, I think the roles of various GHGs needs debate. What I see here in Central NH is that on clear nights when radiation is limiting temperatures approach the dew point. If I want to predict tomorrows temperature, I use the evening dew point not the CO2/NH4 concentration. Point is, the main effect by far is from water.

  21. John Lang:

    Thought I would add that not only does CO2 lag the temperature changes, but the change in CO2 can only explain a small part of the temperature changes during the ice age.

    C02 increases from 180 ppm to 280 ppm through a glacial cycle. The CO2 changes (55%) could only explain between 0.8C to 2.4C of the temperature changes in a glacial cycle.

    The temperature changes are in the order of 5C globally in a glacial cycle so add the 800 year lag to the 16% to 48% explanability of the temperature change and you get ...

    ... CO2 is a minor greenhouse gas and does not drive the climate.

  22. Jeremy Kenyon:

    There seems to be an assumption in this thread that a positive feedback is just that - a positive feedback that keeps on forever being positive.

    There are many examples in nature of positive feedbacks that die out.

    - Set fire to a forest. It starts from a cold forest, then add a small flame, it grows to a huge forest fire, burns out, goes out, goes cold. Few years later the whole thing repeats.

    - Population growth - algae blooms - they start small, they grow almost exponentially, run out of food, die off.

    - Spread of a disease in a population - the more people have it, the more they infect, until it burns itself out.

    The same thing happens with CO2 and temperature. The positive feedback starts up, gets worse, until eventually it hits a stabilisation.

    In the case of our climate it could be as simple as it is only very marginally positive, so our extra help is enough to put it into a growth mode when combined with the increase in solar influx. Take away either and that is enough to kill the positive feedback.

    Or it could be that eventually it gets so hot that we become a shiny ball of cloud which cools down rapidly.

    The whole of the last several million years has been a classic two state climate, oscillating between ice ages and warm periods, with sudden changes between the two. That is undisputed by anyone on any side of the debate. That is exactly the sort of situation that would be caused by having positive feedback to switch from cold to warm, and eventually a negative feedback to switch fom warm to cold.

    In geological time, the balance of the system has changed several times, and just like any system can have a resonance at certain points, the climate can reach a resonant point where it is teetering between two states (our current 100,000 year ice age warm period cycle). Eventually the contintents shift or the sun changes and things settle down into a long warm or cold period.

    If you look at our climate, and compare it to a machine that has a vibration problem, you hear the vibration build up and then die away, build up and die away - the big build up and die away is the hundreds of millions of years climate shift, and the individual vibrations that make up the fine grain are the 100k year switches between ice age and warm spell. (Of course, in the climate case, the whole thing is bounded by the creation of the solar system and the sun going poof and is definitely not cyclic in the billions of years timescale)

    What we have right now (in my view) is an opportunity to actually control things and prevent both the positive feedback being enough to lead to rapid temperature growth, and the negative feedback being enough to cause an ice age. At least for the time being, when the continents, orbits and solar situation mean it is so finely balanced. In longer timescales, we will have to adapt, but for the next few million years its finely balanced and we can keep it just where we want it.

    If people would stop bickering about it and misrepresenting the situation in either direction and look at the bigger picture then we might actually start constructively planning the climate for our future.

  23. Harry N:

    Obviously, there are several feedbacks involved in deglaciation, like ice albedo, CO2, and water vapor, but it does seem that in the current situation, CO2 is the primary forcing, and that the relatively rapid accumulation is clearly linked with human activity. So during this anomalous trend in a relatively stable interglacial, what are all the negative feedbacks that will come to our rescue? Clouds don't seem to be a good bet anytime soon, considering an increase in heat-trapping upper-level cloud cover may be countering any cooling effect from thick, lower-level clouds. And strong warming events in prehistory weren't prevented by cloud feedback. Reflective ice cover is declining, tundra containing methane and organic matter is thawing, the atmospheric capacity for holding more uncondensed water vapor is rising with temperature, CO2-releasing wildfires are on the increase... But where are all the peer-reviewed studies suggesting negative feedbacks will quickly gain the upper hand and bring things under control?

    It seems that with a sufficient long-term forcing, amplifying feedbacks will dominate on timescales that are important to humans. So if we allow warming to progress and the number and strength of positive feedbacks to grow, this trend may have quite a ways to run before it slows and relaxes toward something resembling equilibrium.

    If we're still be in the early stages of this process and reasonable steps can be taken against uncontrolled warming without the economic devastation predicted by "alarmists" on the contrarian side, based on ECONOMIC MODELS at best, I would prefer to err on the side of caution. We are, after all, dealing with a system with the capacity for disruptive swings given enough of a push.

    And to quote J. Willard Rabett:

    1. Adaptation responds to current losses.
    2. Mitigation responds to future losses.
    3. Adaptation plus future costs is more expensive than mitigation.
    4. Adaptation without mitigation drives procrastination penalties to infinity.

  24. Alex:

    Although, Harry, we dare not ask how firmly rooted in physical reality those economic models are, or what kind of validation record they have, even for macro-economic events. :-)

  25. Mark:

    "But where does it stop? If this is really how things work, why isn't the Earth more like Venus? If you are going to posit such a runaway process, you have to also posit what stops it. So far, the only thing I can think of is that the process would stop when the all bands of light that are absorbable by CO2 are fully saturated."

    This makes no sense. If the greenhouse effect of CO2 maxed out at the levels seen in the ice core samples, then why are we worried about adding more carbon now? We're already well beyond the levels in the ice core, so by your explaination, already saturated.

    I am so frustrated that I cannot find a good answer to this question even at realclimate. They talk about the positive feedback, but don't explain what halts it.

  26. Mark:

    I just noticed a post in response to this blog entry on realclimate (

    He points out that other positive feedback systems have a mechanisms that limits them. But he does not offer on this case!

    The other obvious candidate is that CO2 gets sufficiently depleted out of the ocean so that no more comes out. But then you would expect the temperature and C02 to peak at the same time, not CO2 still rising for 100's of years after temp peak.

    It seems a bit absurd that something this important to the climate change hypothesis does not have an easy to find explanation.

  27. Mark S:

    "So far, the only thing I can think of is that the process would stop when the all bands of light that are absorbable by CO2 are fully saturated."

    I was asking a scientist friend about this because it was really bugging me. He pointed out that the energy emitted from the earth as black body radiation increases as the fourth power of the absolute temperature of the earth. The increased forcing from CO2 only goes up logarithmically with CO2 concentration. This means that even though as CO2 is released from the ocean, causing increased greenhouse forcing and thus increasing temperature, this is counteracted by the increased black body heat radiated from the earth. This is likely what puts the upper limit on this positive feedback, allowing a new equilibrium to be found rather than becoming an out of control feedback loop.


  28. Burke:

    I just read an article in the New York Post offering the opinion that AGWists are making a mistake. He says that the main stabilizing effect is caused by precipitation.