Greenhouse focus confirms humans’ warming role

Reto Knutti, from the Institute for Atmospheric and Climate Science at the Swiss Federal Institute of Technology Zurich, and his colleague Markus Huber, have developed a new model to demonstrate humans' responsibility for recent warming. Credit: Swiss Federal Institute of Technology Zurich

Reto Knutti, from the Institute for Atmospheric and Climate Science at the Swiss Federal Institute of Technology Zurich, and his colleague Markus Huber, have developed a new model to demonstrate humans' responsibility for recent warming. Credit: Swiss Federal Institute of Technology Zurich

At least three-quarters of the climate warming observed since the mid-twentieth century is extremely likely to be caused by human activities. That’s what Reto Knutti and Markus Huber from the Swiss Federal Institute of Technology, Zurich, said last week, confirming previous similar conclusions made using a different method. They say that it is “extremely unlikely” that the temperature changes we have seen are caused by natural variation, even if that variation is much stronger than current models suggest.

The Swiss researchers are clearly not the first to find humans are very likely to be responsible for global temperature rises. However, as a contributor to previous reports by the UN Intergovernmental Panel on Climate Change (IPCC), Knutti felt that the methods used to establish responsibility could be better. “Attribution of past changes was largely presented as a result of “optimal fingerprinting”, and that is a black box for most people,” he told Simple Climate. “It’s statistically complex, makes a number of assumptions and is not physically intuitive.”

The optimal fingerprinting method that previous studies used looks at different measured “forcings” that alter energy flows in Earth’s climate using complex computer models. First, the models simulate patterns caused by energy trapped in the atmosphere by greenhouse gases, for example. Then they go on to simulate patterns caused by other forcings, like the energy reaching the Earth from the Sun.

When each forcing has been considered, all the simulated patterns are then combined to match patterns seen in real life using a statistical technique called regression analysis. This effectively adds the patterns together, after multiplying each by a number known as a scaling factor. The size of the different scaling factors can be used to work out how much of the changes that are seen comes from each forcing. However, this approach relies on models’ ability to accurately simulate warming patterns through time and space. It also does not automatically provide a balance of energy flows that matches reality.

Energy conservation

Simulated contributions from human caused, or anthropogenic, and natural forcing agents to the total observed global temperature change relative to the 1850-1900 average. Short term variations are a result of natural climate fluctuations (e.g., El Niño) and are not explained by external forcings. Credit: Reto Knutti

Simulated contributions from human caused, or anthropogenic, and natural forcing agents to the total observed global temperature change relative to the 1850-1900 average. Short term variations are a result of natural climate fluctuations (e.g., El Niño) and are not explained by external forcings. Credit: Reto Knutti

Knutti and Huber’s method, by contrast, is based on running a much simpler model thousands of times with slightly different settings, or parameters. “Then we compare these with the observed warming and ocean heat uptake, and keep the models that are consistent with what’s actually seen,” Knutti said. “We can then run the model with each of those parameter sets for each forcing individually, for example looking at CO2. That gives us a best estimate and uncertainty for the CO2 contribution, and with the other forcings.”

In the models they kept, CO2 and other greenhouse gases in the atmosphere strongly drove temperature increases. However, there was also added cooling from solid and liquid particles in the atmosphere, known as aerosols, which include clouds and sulphur coming from human pollution and volcanoes. “Greenhouse gases alone would have warmed the Earth’s surface more than was observed, and are partly offset by aerosols,” Knutti said. Greenhouse gases contributed 0.85ºC of warming, and aerosols reduced this to give the 0.56ºC increase in average temperature seen since 1950, the scientists found.

Separately, Knutti and Huber could work out how much of the temperature increase we’ve seen is down to natural variability by using simulations of a set of more complex models with no extra forcing. They found less that a one-in-twenty chance that it contributed more than a quarter of the warming since 1950, or more than a fifth of the warming since 1900. In a paper in research journal Nature Geoscience published last week, they wrote that even if natural variability were three times larger than their models said, it would still be extremely unlikely to cause the temperature rises seen.

Eliminating models that didn’t match measured warming and ocean heat means that their approach represents real energy flows much more accurately. As Knutti explained, that’s exactly what he wanted to do. “The fact that we have observed significant changes in both the forcing and surface and ocean response suggested that the energy balance would tell us a lot about the causes of past warming,” he said. “At least to a physicist, conservation of energy is fundamental.”

And having a way to assess climate change causes that is more firmly rooted in physical processes backs the conclusions of earlier efforts, Knutti added. “The fact that our results are entirely consistent with the optimal fingerprinting, but based on a different method, model and type of observation, is an argument for even higher confidence in human induced climate change,” he said. “If optimal fingerprinting tells us that human influence is strong, that is OK, but if we can understand that in terms of physical processes, the greenhouse effect, and if it is measurably consistent with the external forcing and observed energy balance response, that makes a much stronger argument.”

12 Responses to “Greenhouse focus confirms humans’ warming role”

  1. rogerthesurf Says:

    Andy
    “Greenhouse focus confirms humans’ warming role”

    I don’t think so!

    The thing is, if I or any scientist had any trust in models in predicting future climate etc, we would all be thoroughly convinced by now and we would most certainly have that consensus that you and people like you are always trumpeting about.

    However I am familiar with mathematical modeling through my humble studies of economics and most scientists would not rely on modeling to confidently predict the future.

    You see, a model is in itself a hypothesis, or the result of the integration/incorporation of a number of hypothesis.
    The modeler includes parameters that follow his current hypothesis. To simplify for purposes of explanation, in the case of the yet to be proven “Anthropogenic CO2 causes Global Warming” hypothesis, he may include a parameter that calculates how much warming from a certain amount of CO2 and perhaps includes the positive relationship between this and water vapour. When the model is run it then comes up with a result given current temperatures (whatever they are) and the CO2 predicted to be present some time in the future.
    Sounds sensible, but considering that even the relationship between CO2 and water vapour is not proven, let alone whether CO2 has any significant effect by itself, so the final result, based on these unproven hypothesis such as these, is no doubt interesting but meaningless – unless they can be verified by other means such as empirical, statistical or elimination of competing hypothesis.

    Without these “other means” no scientist in their right mind would call any model results proof and considering that we are contemplating ruining our civilisation in order to halt this global warming, we do need very good proof indeed.

    If such a proof existed for the “anthropogenic CO2 causes Global Warming” hypothesis one needs to demand ACADEMIC, PUBLISHED AND PEER REVIEWED papers that give a reasonable scientific proof.

    One would expect an authorative academic paper to use at least one of the following methods.

    1 Empirical proof that shows the causation factor of CO2 with respect of Global Warming.

    2. Statistical proof of Anthropogenic CO2. In case you dont know it, correlations are never proof.

    3. Evidence for the “Anthropogenic CO2 causes Global Warming” hypothesis to be adopted over the null hypothesis.

    Now you may need a little reading to understand what these things are. Here is a site which describes what is needed for #3 which might help. http://www.experiment-resources.com/null-hypothesis.html

    When we can point to at least one scientific, peer reviewed publication that shows at least one of the above, only then will we be in a position to recommend destroying society as we know it, seeing our families starve and carrying out all the other things that will be required to actually decrease the CO2 in the atmosphere.

    Cheers

    Roger
    http://www.rogerfromnewzealand.wordpress.com

    • andyextance Says:

      Just another quick comment.

      Your three numbered points seem a bit confusing. How are they methods? They seem a bit like underlying assumptions you’re questioning. If they are methods, could you please explain how they could be used in this paper?

      Even if they are assumptions you’re challenging the authors to prove, it’s still all a bit murky. What do you mean by “the causation factor of CO2 with respect of Global Warming”? Do you want evidence that CO2 is causing global warming? What does “Statistical proof of Anthropogenic CO2” mean? You want evidence that humans are producing CO2? This is something it’s fairly easy to add up from the amount of fossil fuels we burn, and scientists do a tally several times a year. Here’s a story about 2010’s emissions:

      http://environmentalresearchweb.org/cws/article/news/48196

      I do at least understand what you mean “Evidence for the “Anthropogenic CO2 causes Global Warming” hypothesis to be adopted over the null hypothesis.”

      And I would point out that there are plenty of peer-reviewed studies support these assumptions. I expect you’ll try to discredit the IPCC (though I’d be pleased if you proved me wrong) but the fact stands that its reports are authored by the world’s leading climate scientists, and to try and claim otherwise would be dishonest. Within the fourth assessment report, published in 2007, there is plenty of information that gives good reason to make these assumptions. Read it for yourself:

      http://www.ipcc.ch/publications_and_data/ar4/syr/en/spms2.html

  2. andyextance Says:

    Thanks for the comments Roger. These findings are from an “ACADEMIC, PUBLISHED AND PEER REVIEWED paper”, as indicated in the text. To be clear, you can get access to it at the link below (though you have to pay):

    http://www.nature.com/ngeo/journal/v5/n1/full/ngeo1327.html

    It’s worth a careful read.

    • rogerthesurf Says:

      Andy,
      Thanks for your reply,

      I looked at the link and the first thing I read is :-

      “Based on a massive ensemble of simulations with an intermediate-complexity climate model we demonstrate……. “

      Sorry old son but perhaps you should read my comment above a little more carefully.
      Like I and every real scientist will affirm you simply cannot prove anything using a model or a simulation.

      Cheers

      Roger

      http://www.rogerfromnewzealand.wordpress.com

      • andyextance Says:

        I disagree – there are things you can prove using a model or simulation. Let’s take the original invention of the Monte Carlo simulation method by Stanislaw Ulam, documented in Wikipedia:

        http://en.wikipedia.org/wiki/Monte_Carlo_method

        He developed it because he wanted to work out probabilities associated with a card game. But he realised that just playing the game many times might give him an answer just as readily as trying to work it out from basic probability laws, and that computers could help him do this. So, in this way modelling could help prove that the probabilities derived mathematically were correct – or otherwise.

        This work is somewhat similar to that. Previously scientists have previously assessed humans’ role in warming using optimal fingerprinting – one type of modelling. Knutti and Huber have used a completely different type of modelling to come up with the same result. Because the same answer has been achieved different ways, that offers independent proof of the original conclusion.

        In physical science models are more than hypotheses. They are built on established theory and observations. They are also often widely used once developed. It should soon become obvious as different people use them whether any inappropriate parameters have been included. To include such parameters would be to effectively throw away professional credibility.

        If you rule out models, how do you propose getting the proof that you require for global warming? We cannot compare an Earth with the amount of CO2 we currently have in the atmosphere to another one that just happens to be nearby that has less. We can look to history, but in terms of exploring other scenarios models are about as good as it gets.

        Finally, as an economist, I assume that you are in favour of the principles of the free market. Whether that’s true or not, perhaps you might stop and consider for a while what would happen if you tried to apply your objections to the science behind global warming to those principles? As an experienced practitioner in this area, I hope that you would be able lay out a cast-iron case proving the benefit of a free market – and, as you’re so skeptical of models, one that doesn’t rely on them.

      • andyextance Says:

        As a follow up, I coincidentally came across a good, clear, open-access paper explaining how optimal fingerprinting attributes warming to human actions. Though it does rely largely on models it does make a pertinent comment:

        “A key reason for having high confidence in the results of fingerprinting studies is that they do not depend on the climate models simulating the amplitude of the fingerprints correctly; instead they estimate the exact amplitude from observations. Attribution estimates are thus not predicated on knowing with absolute precision the magnitude of a forcing, or whether climate models respond to a forcing with the correct amplitude. For example, if the true observed response were due to a smaller aerosol signal, balanced by a smaller greenhouse gas signal than that derived from the models, then the results from fingerprint methods would include these possibilities within their uncertainty ranges. Thus, for attribution studies it does not really matter if climate model simulations of the 20th century do not fully explore the uncertainty in the magnitude of both. Similarly, some optimal fingerprinting results using a separate solar signal allow for the possibility that the climate system may have a stronger response to solar forcing than obtained in models. Thus, results from fingerprint methods are more robust and account for uncertainties in forcing and response more completely than the simple comparisons of model simulated and observed changes.”

        Check out the original at:
        http://iopscience.iop.org/1748-9326/6/4/044025/fulltext/

  3. rogerthesurf Says:

    Andy,

    Sorry for the time taken to reply. I have been away.

    The Monte Carlo simulation is not exactly a model as are being used to try and forecast climate change etc. There are a lot more facts, such as normal distributions, (which are mathematically proven by the way), being used here.

    It all depends on the inputs. Like I said, not only the inputs for climate change models hypotheses in themselves, (for instance forecast base conditions), but the algorithims are also hypotheses’. If these inputs and algorithims were based on absolute proven facts, like the inputs and simulation described in your link, of course we could be sure that the climate change models were giving us useable results. But the fact is they simply are not using reliable inputs and any results are equally unreliable, strangely enough tending to reflect the beliefs of the researchers whose assumptions and hypothesis’ have been fed into the model anyway..

    Actually I have written plenty of software over the years that do very similar things as your link describes.

    A common simpler model I often see being used it the forcast budget in accounting software. The results are never correct, because first of all the major input is sales for the coming year. No one knows what the sales are going to be, but the budget does give a guide to what could happen. If we knew exactly the sales and exactly the costs to be incurred, we would know exactly our profit or loss.

    Here is a meteorological model at work in my home city.

    http://www.metservice.com/national/maps-rain-radar/rain-radar-forecasts/rain-forecast-3-day

    Because I am a yachtsman and skier, I consult it often. As these things go, its fairly accurate in that its about 50% correct, but they also cheat and update it as needed to make it fit in with the observed (factual) conditions.
    In fact I would not plan a barbeque on information from this model alone.:)

    “If you rule out models, how do you propose getting the proof that you require for global warming? We cannot compare an Earth with the amount of CO2 we currently have in the atmosphere to another one that just happens to be nearby that has less. We can look to history, but in terms of exploring other scenarios models are about as good as it gets. “

    Quite true, the job to find proper reliable proof is very difficult indeed. I think every honest scientist would agree with that.

    “It should soon become obvious as different people use them whether any inappropriate parameters have been included. To include such parameters would be to effectively throw away professional credibility. “

    Correct again, perhaps this accounts for the uproar in the scientific community over the abuse of scientific methods.

    “Finally, as an economist, I assume that you are in favour of the principles of the free market. Whether that’s true or not, perhaps you might stop and consider for a while what would happen if you tried to apply your objections to the science behind global warming to those principles?”

    You bet I am in favour. There is ample evidence in history to help me there.

    Repeated correlations suggest that any restriction on free trade will decrease economic well being.
    For instance, Soviet Russia, Eastern Europe, Peoples Republic of China are obvious examples. So many extreme correlations here that its obvious that communism causes poverty and starvation is factual. (Estimated 60 million died of starvation in PRC in 1960 alone).
    Coming to the present day where we see PRC adopting the free market and becoming a world economic power within 30 years (and they have only just started), while Europe, USA and most other western countries are sliding left into socialism. Notice that financial crises in the EC including Spain, Greece, Portugal and latterly Italy are caused by increasingly excessive taxation and government spending, (much of it on Global Warming and “sustainability” measures”.
    My country and the US are not that far behind.
    Any first year student of economics can see these crises coming.

    Your Second Comment

    “Your three numbered points seem a bit confusing. How are they methods? They seem a bit like underlying assumptions you’re questioning. If they are methods, could you please explain how they could be used in this paper?”

    Of course they question underlying assumptions. If you want proof there must be no assumptions at all

    The methods I describe are a simple explanation how one may prove that a hypothesis should be regarded as a fact.

    “What does “Statistical proof of Anthropogenic CO2″ mean?”

    My apologies, that should read “Statistical proof that Anthropogenic CO2 causes Global Warming”

    The point is here that at the moment, all we have is a correlation that temperatures appear to be rising and measure CO2 is rising. What is missing is any proof that the two are related. In other words, correlations may suggest and are a necessary condition for a proof – but never constitute a proof.( Quote from my freshman statistics tutor)

    “Within the fourth assessment report, published in 2007, there is plenty of information that gives good reason to make these assumptions”.

    Yes there are plenty of assumptions, I will repeat, in order to jeapodise our way of life and condemn us all to poverty, do you not think it is reasonable to have scientific facts to guide us in this very serious decision. This is what I have been saying all along.

    If you think the IPCC is reliable, well for a start, you haven’t read Lambrosie’s book yet.

    “I do at least understand what you mean “Evidence for the “Anthropogenic CO2 causes Global Warming” hypothesis to be adopted over the null hypothesis.”
    “And I would point out that there are plenty of peer-reviewed studies support these assumptions.”

    Really? Show me a peer reviewed scientific paper that shows that the Anthropogenic CO2 causes Global Warming” hypothesis should be adopted over the null hypothesis.

    You realise that to prove this, a paper would have to find factual evidence showing the causation all the previous warmings (and there are at least three in historical times), which occurred when there was no anthropogenic CO2, – and then show that the current warming is not caused by any of the same factors.

    Your final link, Try checking how many times and in which context they use the word suggest.

    Andy, I hope I have covered all the points that you raise in your replies. Yes the credibility of the IPCC is definitely worse than questionable, commentators who exaggerate the excesses of the IPCC assertions sink to an even lower level.

    Cheers

    Roger

    http://www.rogerfromnewzealand.wordpress.com

    • andyextance Says:

      Well, this is definitely food for thought – thanks for that Roger.

      I agree that Monte Carlo simulations are not the same as models used to forecast climate change. But they do dispute your original assertion that “you cannot prove anything using a simulation”.

      Climate models are not the same as models used to create forecast budgets either. Or, for that matter, the model used in the classroom that Ian Pearson discusses. They’re models that are used by groups across the world and are often openly available – anyone can download them, for example:

      http://climate.uvic.ca/model/

      It would soon become obvious if they were being tweaked inappropriately. If they are being used so fraudulently, why hasn’t anyone debunked them, when it’s so easy to get access to the tools to do so? Pearson clearly found it pretty easy on his course.

      On your points about free market economics – all very well made – but do they conform to the requirements you laid out for climate change? You say “correlations suggest that any restriction on free trade will decrease economic well being”. But when you talk about global warming you say “correlations are never proof”. So you’re asking for non-correlation proof for an idea that you dispute – when you rely on correlations for an idea that you hold dear. I can see why you’d do this, but it hardly seems fair. The same can be said of your comments along the lines of “There must be no assumptions at all” – can free-market economics be said to satisfy this? And if it can’t – why isn’t it the subject of as much criticism as the science behind climate change?

      And on what constitutes evidence for the “Anthropogenic CO2 causes Global Warming Argument”, that evidence does not have to show what you suggest. Instead it can, and does, build a strong case based on scientific observations collected over more than three centuries. There’s lots of reading at this link:

      http://www.aip.org/history/climate/bibdate.htm

      Finally, I’ve recently been made aware of a good blog on this issue, called “All Models Are Wrong, (But Some Are Useful)” by Tamsin Edwards, a climate modeller at the University of Bristol. She’s only just started with it, but I’m interested to see what she comes up with. Probably something more illuminating than us! You can read it at:

      http://allmodelsarewrong.com

  4. rogerthesurf Says:

    PS,

    Here is a great blog that describes models and their shortcomings far more eloquently than I have been able to.

    Cheers

    Roger

    http://www.rogerfromnewzealand.wordpress.com

  5. rogerthesurf Says:

    Andy,

    Sorry for the lateness of my reply.

    With regard to your paragraph copied below;

    “On your points about free market economics – all very well made – but do they conform to the requirements you laid out for climate change? You say “correlations suggest that any restriction on free trade will decrease economic well being”. But when you talk about global warming you say “correlations are never proof”. So you’re asking for non-correlation proof for an idea that you dispute – when you rely on correlations for an idea that you hold dear. I can see why you’d do this, but it hardly seems fair. The same can be said of your comments along the lines of “There must be no assumptions at all” – can free-market economics be said to satisfy this? And if it can’t – why isn’t it the subject of as much criticism as the science behind climate change?”
    I must confess set you a little trap here and that I then held back to see if you could answer this question yourself.

    It is true that correlations are never proof, (but I have added many times “without an accompanying proof” and as you well know, thats all we have with the “Anthropogenic CO2 causes Global Warming Hypothesis”. A single correlation (maybe not even that) but assuming there is a correlation, what is absolutely certain that this is the ONLY correlation in history.

    If the Medieval Warm Period, the Roman Warming and the Holocene Maximum (just to name a few previous warmings), all happened in conjunction with a previous rise in CO2, we would be getting close to an empirical proof. In fact, if that was the case, we would not be having this conversation.

    Communism being always followed by economic poverty in a significant number of cases (with no exception as far as I know), makes us believe that communism will makes us all very poor.

    Empirical means “the record of one’s direct observations or experiences” (Thank you Wikipedia).

    You may not recall, but as an infant when you threw your toy from the high chair, and found it went down, you formulated a hypothesis that “Perhaps things dropped always go down”. By the time your mother picked your toy up for the third or fourth time, you decided that the hypothesis is correct and therefore it would also be unhealthy to fall from your chair etc. In other words you proved your hypothesis, made from the first time you noticed the correlation that when you dropped your toy and it went down, empirically.

    Hope this clarifys things for you.

    Cheers

    Roger

    http://www.rogerfromnewzealand.wordpress.com

  6. Butterfly effect limits climate models « Simple Climate Says:

    […] between different climate model predictions. When she told this to two fellow climate scientists, Reto Knutti, from the Swiss Federal Institute of Technology, Zurich and Massachusetts Institute of […]


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