Of Particular Significance

Humans, Carbon Dioxide and Climate

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 07/31/2012

Professor Richard Muller of UC Berkeley isn’t the first scientist to be converted to the idea that humans are causing a change in the climate through carbon dioxide emissions.  Nor is he, by a long shot, the most expert among them.  But he’s one of the most famous, now, because he was also a loud skeptic not long in the past. He’s described the reasons for his conversion, based on a scientific study that he organized and helped lead, in a recent op-ed post in the New York Times.  It’s a little self-serving at best, but makes for interesting reading.

Immediately, of course, he’s being lambasted for everything he’s done, on all conceivable grounds.  Discredit him as fast as possible, is the approach — instead of let’s look at the study carefully and see if it does or does not have flaws. Well, I’m sure most of those attacking him right now haven’t had time to read his study yet, because it was just posted.  Let’s wait a few days and see if anyone makes more intelligent remarks about its limitations.

One interesting question here is Judith Curry, who disagreed with the majority view on Muller’s panel.  I’d like to understand her point of view more clearly, though honestly she didn’t make a good impression on me with her objections last November, which seemed thin and statistically flawed.  My impression is that this time she views the approach to the data used in the most recent Muller et al. paper as disturbingly simplistic.   Maybe it is.  The data is open for any expert to use, so this is an objection that I would think could be settled.  If she’s right, more complex and complete models applied to the data should give qualitatively different results; let’s see if they do.

Unlike many bloggers, I’m not willing to pontificate on a subject in which I’m not expert.  But personally, I think this whole debate is missing the point anyway.  What we are doing, folks, in dumping all of this carbon dioxide into our atmosphere is an uncontrolled and difficult-to-reverse scientific experiment on our planet… the only one we’ve got.  (Hmmm…  let’s see what happens to the Earth if we turn up the CO2! Gosh, won’t that be interesting to watch!) Would you do an uncontrolled scientific experiment inside your own home?  You probably wouldn’t think it very smart to do that.  And if a bunch of apparently intelligent people started warning you this might turn out disastrously — even if other people who are apparently intelligent disagreed with them — you might consider that given the uncertainty, the question might turn on an issue of prudence.  Perhaps it would be wise to get control of this experiment before it has a chance to take control of us.

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49 Responses

  1. Mr. Matt Strassler:

    [I tried to post this yesterday but my comment didn’t appear. Maybe some glitch?]

    Have you seen the response to your brief (but totally sensate) article at the Lubos Motl website?

    I can just say that Lubos Motl make very readable and interesting analysis about high energy physics (when he talks about SUSY, dark matter and the LHC, he is very optimistic when a lot of people had already lost hope, for example) but when he talks about climate, he just insults everyone that believes in man-made global warming.

    I commented in his blog, and the only response I received was aggression and insults.

    I do not know what to think.

    1. Lubos is a very brilliant man; he is also extreme in his views on just about everything. I don’t find his opinions interesting, unless he’s talking about formal aspects of physics and math, where he has many interesting insights.

  2. Just like Trevor has pointed out, the scientific evidence strongly indicates that the earth has been experiencing a persistent increase on the average temperature, just as the report from Richard Muller shows:


    This report has only studied in some detail the evolution of average land temperature over time.

    The data sets and their graphics are very clear and simple to understand what they imply: the earth has been warming up for quite a while, now (for at least the last 250 years!)

    It has also studied the evolution over time of the average concentration of CO2 in the atmosphere, and has found a very good fit of both evolutions, which indicates some kind of correlation between both effects.

    It may require some more detailed experiments to clearly determine a cause-effect relationship behind such a correlation.

    Kind regards, GEN

  3. Lino,
    Focussing on the physics, you have to explain how the temperature of the Earth has remained remarkably constant, especially given that the heat emitted by the Sun has increased greatly over the past several billion years. One of the initial achievements of climate science was to recognise that the increasing strength of the Sun was being matched by falling levels of carbon dioxide; that two great independent variables were cancelling one another out.
    If you examine the other climate variables, you recognise that that they are either relatively constant over time (you keep mentioning magma, which I don’t believe to be a significant heat source, but anyway the heat from the Earth’s core is relatively constant, and I understood that the Earth’s core is cooling, not heating up);
    Or their effect is ephemeral (volcanic activity injects coolants into the atmosphere, but these are rained out relatively quickly).
    Or they are dependent variables (the amount of water vapour is dependent on the Earth’s temperature, so water vapour merely provides a feedback mechanism).
    Or they are long term, or not of sufficient strength, or are not biased to either heating or cooling (the geometry of the Earth’s continents and resulting ocean currents).
    But you are correct in that these and other variables can have a significant short term effect. Therefore you can’t look at a short time period and always expect to see a clear trend, especially in time periods when the increase in carbon dioxide levels is relatively muted.

    The conclusion is that global warming is real, serious, and being driven primarily by increases in carbon dioxide levels.
    Methane is also a potentially serious threat, but avoided in the interests of brevity.

  4. Correlations of average temperature of the atmosphere with the increase in concentration of certain gases over time are complex (a rather thorny issue to tackle, actually), as there are many different effects that cause a rise of the average temperature of the air.

    For instance, we may consider how the specific heat capacity of air changes with the increase in average concentration of greenhouse gases (the specific heat capacity of a material like air determines the ability of that material to retain heat, with a higher specific heat capacity meaning a higher ability of the material to retain heat). In this case, water vapor is an important factor.

    We may also consider how the transmission of radiative energy from the earth back to space changes with the increase in average concentration of greenhouse gases (this is the main effect taken into consideration with greenhouse gases and the reason why they are collectively called “greenhouse” gases). In this case, CO2, CH4 and H2O are important factors.

    CH4 is 21 times more effective by weight than CO2 as infrared absorber, but while the average lifetime of CH4 in the atmosphere is about 12 years, the average lifetime of CO2 in the atmosphere is about 100 years.

    But in a planet like the earth, weather patterns are mainly affected by the larger water masses, like the oceans (that is one of the reasons why so many climate scientists are physical oceanographers!).

    Marine currents in the oceans work as conveyor belts transporting and redistributing heat (or cold). These marine currents work on a delicate equilibrium based on many factors, and one of them is salinity.

    There are very complex effects that link global warming affecting the level of salinity, which in turn affect certain marine currents, which affect the average temperature of continents.

    For instance, the melting of the polar ice cap is diluting the salinity of the Gulf Stream, which slows it down a bit, which means that the Gulf Stream is not sending enough heat from the Equator to northern Europe (including England), and that could explain why England has become a little more chilly in the last decade or so.

    At the same time, global warming has pumped a increase on the average strength of hurricanes, tropical storms, typhoons and tornados, as well as it has increased the average duration and average strength of El Niño and La Niña.

    Just as I said earlier, there are some very complex correlations.

    Kind regards, GEN

  5. Eric:

    Thank you for your detailed examination of atmospheric processes. However, I note that per your argument, CO2 is present at higher altitudes, and it is CO2 which can radiate out into space earth’s radiant heat. Hence, it would seem that CO2 at higher concentrations, per your argument, would increase the amount of energy being radiated back out into space. So where’s the problem then with CO2? I’m confused.

    As to water vapor, and it’s condensation, no matter whatever equilibrium value it returns to, if the temperature increases, then it would seem surely cause that equilibrium level to rise.

    I live on the West coast. On the East coast they have wonderful outdoor parties until 2:00 in the morning, something we don’t have out here in the West. Why? Because our lack of humidity (water vapor) means nighttime temperatures plummet. So, the water vapor retains the heat. Now, if ocean currents warm up a little, causing water vapor levels to rise, it would seem that nighttime temperatures measured on the East coast would have to rise. This can skew temperatures as more areas of the East expand their housing, and more thermometers are placed and read.

    But what is the source of this increased water temperature? The amount of heat from magma might pale in comparison with that which comes from the sun, but how much of that heat is radiated out into space? Any heat coming from underwater volcanoes and such—including the mid-Atlantic ridge, has to remain in the ocean, and then radiated out into the atmosphere, perhaps taking some water vapor along with it.

    So this is a complicated matter. And I invoke volcanic activity simply as a way of explaining why this current heating phase started back in the 1800’s. If you go to the wikipedia page linked above, you’ll see that the temperature begins rising rapidly in the early 1800’s. The small graph to the side also shows that during the 1940’s temperature went sideways, almost declining. And yet this is the time when the world is at war, with factories humming to produce all manner of military goods, a war followed by an explosion in the number of cars that were produced—but the temperatures stay flat, just like in the early 2000’s. Where is the correlation here between CO2 and temperature?

    These are weighty matters, with the welfare of the world’s neediest in the balance. Why the alarm?

    I just saw a video at Lubos Motl’s blog, with a climate scientist showing a graph of what computer models predicted, and what actual temperatures followed. No correlation whatsoever. What’s driving this frenzy? Is it greed? I think so. Al Gore wasn’t a multi-millionare when he was VP. Why is he now? That’s an angle that needs exploring.

    But, let the Climate Wars be fought somewhere else. Here we focus on physics.

  6. Water vapor works more like a buffer, avoiding large fluctuations of air temperature.

    As the air gets hotter, with a higher temperature comes a higher limit of water vapor saturation, which means that the air is capable of containing a larger share of water vapor (air works a solvent, with water vapor diluted in such a solution).

    With a larger amount of vapor, the air can contain more and larger clouds, that will cover the earth from the sun, which will eventually produce a reduction of air temperature, which will force some of the vapor to condense , and the cycle starts all over again.

    So, we have that water vapor is the least problematic of the three greenhouse gases (it brings along some important benefits, besides its greenhouse effect), methane is the most problematic (bovine herds are a major source of methane!), and CO2 is somewhere in the middle.

    Kind regards, GEN

    1. Methane has a greater warming potential per molecule than CO2 in the current atmosphere because there is so little of it relative to CO2, not because methane is a better absorber of IR (it isn’t). Greenhouse warming is roughly logarithmic in the concentration of the gas and since there is less than 2ppm of methane and 400ppm of CO2, an additional molecule of methane has a larger impact than an additional molecule of CO2. At present levels, the warming effect of CO2 is much larger than methane and given current emissions CO2 will cause much more warming for the near future. Methane could become a big problem though.

  7. Regarding the main greenhouse gases, CO2, water vapor and methane, it is methane the most problematic of the three, by a long shot.

    Water vapor has a very different (and dynamic) behavior than CO2 and methane. The is a saturation limit for the amount of water vapor that can be contained by air (that saturation limit is a function of temperature and pressure), but CO2 and methane do not exhibit a similar saturation limit.

    Getting back to methane (CH4) as the most problematic greenhouse gas, here is some summary info on CH4 by the EPA:


  8. Trevor:

    I’m sure CO2 absorbs at the infrared, or else no one would even be talking about it. But, again, it is water vapor that makes hothouses hot, not CO2. And a warming ocean, whether by: (a) magma intrusions at above normal levels, or (b) by increased solar radiation, or (c) reduced cloud covering over the oceans, increases the amount of water vapor in the atmosphere.

    You say to not confuse a symptom with a cause. And yet, it is a well-established fact that rising CO2 levels lags behind rises in global temperatures by as much as 400 years. So, shouldn’t this be advice you ought to consider?

    As to food shortages: have you ever heard of droughts? We’re experiencing one of the worst droughts on record. How will that effect crop production? Do you have a way of ending the drought?

    It is one thing to be concerned about the environment, and another to play God. The people of North Korea are absolutely starving to death. Is it the weather? Maybe it’s here that political involvement would be good.

    And, I’m afraid, you’ve skirted the whole issue of computer models and their predictions: how do they match up? Or is it easier to change the subject?

    I’m not interested in debate, Trevor. But when the standard of living of the entire world is at stake, and that of the most impoverished the greatest of all, then caution is clearly in order.

    No one has still answered the question: why, in the early 1800’s, without cars, without a huge number of factories, without electrical-generation stations, without airplanes, without that many railroads, did the temperature start to go up? If you can’t answer that simple question, then how much is it that you really know?

    One last thing: how much money has GE spent hoping to position themselves to be at the receiving end of all this government money that will be spent (and, otherwise, not go to helping the needy)? It seems clear to me that there are many, many rich corporations who stand ready to benefit from off-sets and other such things. Do you really think that after spending billions upon billions of dollars getting ready for the government-handouts that they are not going to exert influence on politicians and journalists, AND scientists? To think so would be naive.

    I’ve said all I have to say.

    1. How many sigmas are there in that early 1800s rise? How many are there in the later rise? When I look at graphs like this one: http://en.wikipedia.org/wiki/File:1000_Year_Temperature_Comparison.png I don’t see an unambiguous rise in the early 1800s. Am I looking at the wrong graph?

      Also, I’m pretty sure there are a lot more powerful corporations that stand to lose from going to a different power source than those that stand to gain from it, hence the reason corporate America has been fighting this.

    2. Lino, there seems to be some misunderstanding about how the greenhouse effect works and the roles that water vapor and CO2 play.
      The earth’s surface temperature is determined by energy balance: an excess of energy in over energy out makes the temperature go up and vise versa. The dominant source of incoming energy is solar radiation. Other sources such as heat transfer from the interior of the earth are tiny in comparison (the earth’s mantle is a really good insulator). The energy transferred by magma flow is also tiny compared to incoming solar radiation.The earth cools by radiating into space. Other energy losses such as from diffusion from the outer edge of the atmosphere are tiny in comparison. So, the earth’s surface temperature is determined predominantly by the balance of incoming and outgoing radiation.
      The amount of outgoing radiation is a strong function of the temperature of the radiating substance (T^4). If the temperature goes up/down, then the outgoing radiation will increase/decrease until a new equilibrium is established. When the outgoing radiation is absorbed by a greenhouse gas, water vapor, CO2, etc., the energy is quickly converted into kinetic energy and distributed among neighboring molecules. This, by itself, is not sufficient to produce the greenhouse effect. In order for the earth to shed energy, a radiated photon has to escape the atmosphere. The mean free path of photons in the absorption bands is a small fraction of the height of the atmosphere. This means that radiation in the absorption bands occurs at high altitude. It is colder at higher altitude which means that it is less efficient at radiating. So in order to establish a new radiation equilibrium, the temperature of the atmosphere must increase. Basically, the greenhouse effect elevates the effective height in the atmosphere where the outgoing radiation is produced. The stratosphere contains almost zero water vapor but is chock full of CO2. This means that CO2 plays a very fundamental role in the outgoing radiation.
      Water vapor also behaves very differently from CO2 because (at earth’s present conditions) water condenses but CO2 does not. Because of this, the amount of water vapor is determined by temperature according to the Clausius-Claperyon equation.
      If one were to suddenly double the amount of water vapor in the atmosphere (twice it’s equilibrium amount), it would return to its equilibrium amount after several days. On the other hand, if one were to double the amount of CO2 in the atmosphere, it would return to its equilibrium value after hundreds of years. This is why CO2 is a climate forcing and water vapor is a feedback in this case.

      So what about CO2 lagging temperature? Yes, this can be the case. For example, the transition out of an ice age is initiated by changes in incoming solar radiation due to orbital changes. This by itself would not induce much of a change, however, the small temperature increase causes more CO2 to be removed from the ocean which increases the greenhouse effect which increases the temperature which results in more CO2 in the atmosphere. This constitutes a feedback with CO2 concentration lagging temperature. The transition takes thousands of years.

      As far as warming starting in 1800, this is simply wrong. The average global temperature from 1800 to 1900 is pretty flat. Warming started after about 1920.

  9. That increased levels of carbon dioxide cause an increase in a planet’s temperature is a scientific fact; theoretically (it absorbs infra red radiation); laboratory tests (absorption and retention of heat by different atmospheres); by observation (in the Earth’s climatic record); and astronomy (Venus).
    Here is my attempt at an illustration, apologies for the errors it undoubtedly contains! The current concentration of carbon dioxide in the Earth’s atmosphere is some 400 ppm by volume, and is currently rising by some 2 ppm per year. If fossil fuels can be exploited at the current rate for the next hundred years (after which they could be close to economic exhaustion) that would imply a concentration of 600 ppm; close to a level which, if sustained, might be able to melt Antartica’s ice cap. But after that humanity has, presumably, shot its bolt and, assuming no catastrophic release of methane (a big assumption), we should be safe.
    The value of climate scientists, continually checking and testing their data and models, is that they can offer an accurate quantitative calculation, with a full and precise analysis. But I do worry that, in their efforts to avoid making a statement that cannot be 100% supported, they are failing to deliver a clear and timely message. Contrast that with my illustration; probably wrong but an attention grabber!
    But never confuse a symptom with a cause. The driver of climate change is the growth in the numbers and affluence of the human population.
    Jeremy Grantham has just posted on GMO’s website an essay titled “Welcome to Dystopia!” in which he analyses the current food crisis, on the basis that we are about 5 years into a chronic global food crisis that will be both long term and politically dangerous.
    Whether or not you accept his gloomy prognosis as it relates to the human population, these future challenges can only worsen the already huge damage inflicted on our environment.
    So climate change is not a problem that can be left to scientists. But it would be helpful if they could give a clearer message, placed in a proper context.

  10. Isn’t “Global Warming” also known as the “hothouse effect”? One question: when you enter a “hothouse”, do you cough, or do you sweat?

    Water vapor is a much stronger causative agent for “hothouse” effects; and if the sun becomes more active, or if cosmic rays are reduced—causing fewer clouds to be seeded, or if the earth’s magma layer inches closer to the ocean bottom, any, or all, of these can cause an overall rise in ocean temperature, releasing condensed CO2, as well as water vapor, and marginally increasing atmospheric temperatures.

    This latest bout of warming began in the early 1800’s. What was the causative agent back then?

    Computer models have been around for years—what 20 years, at least: well, how do their projections track with actual temperatures?

    Even the most committed global warming activist admits that temperature has not increased for the last 10 or 12 years. Based on the huge difference in effect between water and CO2, we can account for why temperatures have not gone up despite the continual output of human-made CO2; i.e., water vapor content has stayed the same while CO2 continues to rise.

    When underdeveloped countries can’t build electrical generating power stations because of putative anthropogenic GW, then we better be darn sure we’ve got all of this science nailed–it’s our moral obligation.

  11. Since climate scientists commenting on this seem to agree with that Muller is self serving (say, Curry and those climatologist blogger that has quoted her), what is the use of rewarding him further?

  12. In response to the “conducting a science experiment in your home” argument: I don’t think that’s a very good analogy. The use of fossil fuels to power our civilization is hardly similar in motivation to some experiment to gather knowledge. Energy and economics are serious things. Discontinuing use of fossil fuels in favor of other energy sources could produce the biggest sudden drop in the standard of living of human beings since the Great Depression. Turning off the flood of cheap power that makes modern life possible is a huge decision that needs more justification than just “let’s err on the side of caution”.

    I usually make the argument that, for the lack of any deeper understanding, the best I can do is to offer a sort of first-order guess. To first order, I would sure expect that increasing the amount of a highly infrared-absorbing gas in the atmosphere would increase the average temperature of that atmosphere. This first-order guess doesn’t prove anything, but it demonstrates to my satisfaction that no one with only a first-order knowledge can rationally justify leaving the world’s power switch on without further study. So, at the very least, you have to know more than I do to take Lubos’ position. This approach lets you argue with people who know as much as you do or less. Since you have no hope of arguing with people who know more than you, that’s the best you can do.

  13. Muller was always opportunistic; he did psychophysics when that was fashionable, then the “Nemesis” star (the invisible twin of the sun dumping comets on us periodically). Then he became a CO2 skeptic, handsomely financed by fossil fuel plutocrats (Koch brothers).

    Many of the scientists who deny the rising CO2 curve means anything are just paid by the fossil fuel companies: watch the Nobel class warming skeptics in France, Allegre and Courtillot (they will not get the Nobel, as they are geophysicists) . They were directors of the Institut de Physique du Globe in Paris, which depends on fossil fuel funding.

    Acidification of oceans cannot be denied. Nor the rise of temperatures in ocean and soils. Neither can the parts per million of CO2 plus man made CO2 equivalent gases. That is 395 ppm from CO2 plus at least 60 ppm of CO2 equivalent gases, for a total of above 450 ppm. The long term density had been 280 ppm. Some evaluations show that Antarctica is unstable at 440 ppm.

    Massive glaciations have existed on Earth for four million years. There were none for dozens of decades before that, so we must expect a brutal shock to the entire biosphere. Differently from changes in the last 65 million years, this change is too fast for biological evolution to adapt.

    We are facing a biosphere collapse. And the holocaust that will accompany it. I was just back in Alaska, 30 years since my last visit, and was stunned that entire glaciers had completely disappeared, entirely replaced by… lakes, as far as the eye can see.

  14. IMHO, what Dr Richard Muller has done is following just basic principles of science, and the point is not whether or not he proves to be right. The major point is what truth his research may bring forward, no matter how unexpected that truth may turn out to be.

    The scientific process (what we could call “business as usual” in the scientific professions) will take care of the proper outcome to come forward (eventually).

    Kind regards, Gastón E. Nusimovich

  15. Climate change is either occurring or not. If it is, it will be either beneficial to humanity, neutral, or detrimental. If it is detrimental, then it is to our benefit to attempt to create a neutral or beneficial change instead.
    It is quite clear that climate change is occurring. It is clear that continued change will be detrimental.
    If continued change would likely cause a certain amount of damage, then it is sensible to spend up to (but no more than) that amount to stop the change.
    The potential for damage is very, very high. Thus, CO2 regulation (which is expensive) will in the long term likely be the cheaper solution than attempting to move a bunch of costal cities, etc.
    Note that the cause of the climate change is irrelevant to the argument. Knowing what causes it is needed to form proper mitigation strategies, but isn’t needed to determine if mitigation should be attempted or not.

  16. Mike Anthis: “Consider the brou-ha-ha over superlumino neutrinos. Millions got excited over an outlaw experiment that they really knew nothing about”.

    Mr. Anthis, you are optimistic regarding to the people that fully understood the issue, to be a reader does not mean to know the matter properly. I would say that only few keep up wandering.

  17. Matt, you wrote:

    “Unlike many bloggers, I’m not willing to pontificate on a subject in which I’m not expert.”

    Thank god for that!
    I love this blog and for a moment there, I thought you had decided to balance Lubos Motl’s anti-climate-change stance blog with your very own pro-climate-change one.

    Something must happen to the brains of some scientists as they get older, such as the development of a belief that their current knowledge in science somehow automatically carries over into other scientific disciplines and they don’t have to bother to study as they did in their early 20s, late teens for hours a day. Hence you get retired engineers trying to prove Einstein was wrong, elderly physicists ignorantly criticizing string theory, and competent middle-aged physicists criticizing climate change.

    Yes, let’s leave climate change to the experts who’ve devoted their lives to this subject such as those at Oxford: http://www.ox.ac.uk/media/news_releases_for_journalists/ccexperts.html

    And of course, a highly regarded institution such as Rutgers will have one:

  18. “Perhaps it would be wise to get control of this [CO2] experiment”. Perhaps let’s start at CERN. How much power does LHC consume? Better ideas, anybody?

  19. When I read this post I thought – how long will it take before Motl reacts on TRF? Not long indeed 🙂

    1. Haha! Yes, it almost seems like Prof.Strassler just wanted to throw the bait and wait for the Lubos’ attack! 😀

    1. Perhaps, but it’s far more likely that the birth of the universe is the real cause.

  20. it always seems to me it’s a case of prisoners dilemma and it’s game theory that drives up the CO2.

  21. Consider the brou-ha-ha over superlumino neutrinos. Millions got excited over an outlaw experiment that they really knew nothing about.

    Now, amplify that with huge doses of self-interest by multinationals that are larger than most countries.

    Reason stands about a comet’s chance in the chromosphere.

  22. …and everyone should remember that ocean acidification is much less-deniable (so to speak), in both its anthropogenic nature and its growingly immediate potential for negative social impact. By itself, ocean acidification is a good enough reason to decrease carbon emissions. Somehow, climate deniers get off the hook on ocean acidification, even after they admit that CO2 levels are anthropogenic.

    1. Now there’s a pivot worthy of a windmill salesman. Incapable of arguing in favor of Muller’s tripe, he gropes about in the dark and comes up with ocean acidification?
      Last I checked, the oceans are still saturated with salts washed down from land by the acidic rains, a process that has been on going since, for all intents and purposes, forever. Hopelessly and perpetually alkaline.

      Only a con man would invoke “ocean acidification” as a cause for government action. How can you tell when a climate scientist is lying to you?

      They’ll mention ocean acidification without irony or ridicule.

  23. I’m a research meteorologist, not a climatologist, so I’m no expert either, but there is enough overlap between the two fields that I feel I can say a few things with confidence at least:

    1) It’s very unlikely that statistical effects can explain away the observed trends in warming (and other related indicators, such as sea ice decline), and in fact very few people now argue that the globe is not warming. They mainly argue on how much, and the causes.

    2) It’s true that correlation between C02 rises and warming by themselves do not imply causation, but we have abundant evidence that C02 does in fact cause warming, so we have a strong physical connection here that cannot be ignored. It is certainly true that other effects are important and have been more important in Earth’s past, but we are talking about the short-term present here.

    3) Climate models that are run retrospectively for last century’s climate with a variety of uncertainty built into their physical parameterizations and initial conditions nevertheless fail (in an ensemble sense) to capture the *observed* warming of the latter half of the century *unless* they include anthropogenic C02 sources. When they do include those sources, the simulated temperature rises closely approximate the observed temperature rises. And, as a matter of fact, most of these models predicted a decline in temperatures toward the end of the century without the impact of anthropogenic sources. I work with atmospheric models on a daily basis that are very similar to these climate models, and while I know that they have many flaws and shortcomings, nevertheless it has become clear to me that they have the basic physics correct enough to capture the basic trends in global temperature, and they are improving all the time.

    I myself used to be a “scientific skeptic” as well, but I was convinced by following the evidence, that at least at this point in our planet’s history, anthropogenic effects are the cause of most of the recent warming, which is rather rapid when considering geologic timescales. We are indeed in the midst of a great experiment. How we respond to the consequences, whether they end up being milder or worse than expected, is up to us.

  24. humans will surely find a way out..here too.we’ll eventually develop better technique to manage our dear earth.

  25. I don’t think it’s beside the point at all. Given the enormous costs of reducing carbon emissions, most of all in the developing world, the argument for changing course should be made as strong as possible. The precautionary principle, while of course important here, seems to me like pretty weak tea compared to estimates of where climate change is likely to take us.

  26. More complex and complete models have in fact been applied to the data since the early nineties, consistently showing carbon dioxide being the main driver of the ongoing warming.

  27. Well it’s all just for show, he wasn’t an AGW skeptic to begin with, as he said himself last year in Huffington Post:
    “It is ironic if some people treat me as a traitor, since I was never a skeptic – only a scientific skeptic.”

    And it’s his fault for making a press release before his paper was available.

    Finally I didn’t read the paper (and don’t intend to) but he himself stated that his “proof” that humans are behind most of warming is the fact that co2 curve fits the warming trend best? How is that a proof of anything?Correlation…

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