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What we know and what we don't know

Posted on 12 July 2011 by Verity

This is a cross-post from the Carbon Brief.

“...The science of global warming is far from settled”
Nigel Lawson, “An appeal to reason: a cool look at global warming”, 2008.

Climate skeptics often claim that although increasing levels of carbon dioxide may be causing global temperatures to rise, there are many uncertainties in climate science - with the implication that it would be unwise to put in place potentially expensive or disruptive measures to reduce emissions.

For those not actively working within the field of climate science it can be difficult to determine just how sure scientists are of what they are saying.

In order to do so it is important to understand the method by which science proceeds. Science progresses by testing theories, examining results, repeating the tests and extending the theories. It's this process that allows valid results to be confirmed, and disproven theories to be abandoned. Over time, as a large supporting body of evidence is built and attempts to disprove a theory have failed, that theory can be considered sound. Although we can never be absolutely certain that a theory is true, we can be confident in it given a large volume of supporting evidence and numerous failed attempts to disprove it.

(Well, that's the theory. In practice, the process is usually a bit messier). 

So here’s a brief article summarising what bits of climate science we have strong evidence for, and what we are less sure about.

What we have strong evidence for:

Greenhouse gases, including carbon dioxide, warm the planet – the theory that gases including carbon dioxide, methane, nitrous oxide and water vapour retain heat in the atmosphere was first suggested 150 years ago. Svante Arrhenius went on to calculate the potential effect of changing CO2 on climate in 1896. That was followed by over a century of discussion, testing, and refinement of the theory, a process which provided a wealth of supporting evidence.

Other researchers initially argued against the theory, but they were unable to disprove it. The warming effect of carbon dioxide can in fact be demonstrated in the laboratory. As Richard Somerville, climate scientist and distinguished Professor Emeritus at Scripps Institution of Oceanography puts it:

“The greenhouse effect is well understood. It is as real as gravity.”

Atmospheric CO2 is increasing, and has been since the industrial revolution. This is shown by direct measurements from ice-cores and the atmosphere. Levels of the greenhouse gases methane and nitrous oxide have also risen markedly over the same period.

Human activities are causing that rise in CO2. We know that burning fossil fuels and deforestation releases carbon dioxide. Scientists have demonstrated that much of the increase in CO2 in the atmosphere comes as a result of human activities by studying its isotopic composition. CO2 which comes from burning fossil fuels has a distinct manmade signal (explained further here). The proportion of CO2 in the atmosphere that has this “human fingerprint” is rising. The rise in other greenhouse gases such as methane and nitrous oxide can also be attributed to human activities including agriculture and fossil fuel use.

The average global temperature is rising at the surface of the planet (atmospheric and sea surface temperatures). Since it is near impossible to distinguish temperature trends over the short term from ‘noise’ in the data, climate scientists prefer to consider the longer-term temperature trend. This shows an increase of around 0.75˚C since the beginning of the 20th century. A mass of independent evidence - for example the rising temperature of the oceans, rising humidity, rising sea level and melting sea ice - from many different sources also indicate that the world is warming.

Skeptics frequently cite solar activity or other natural climate variation to explain the warming trend. All of these natural elements have been thoroughly investigated by climate scientists, and have been ruled out as the dominant cause of warming.

These fundamental principals, added to the fact that there are no plausible competing theories to explain the observed warming trend, have convinced 97% of active climate scientists that humans are a significant contributing factor to global warming. The IPCC concluded in its most recent report that there is a 90% likelihood that human activities have led to overall warming since pre-industrial times.

What is still under discussion:

What our future emissions will be. Future emissions are likely to depend on several key factors, including global population, energy resource availability, technology, and policy. The IPCC have developed a series of potential greenhouse gas emissions scenarios, based on different global development storylines. These are what are used for the IPCC’s climate projections for the 21st century.

How much temperatures will rise from any given emissions pathway - There are significant uncertainties in assessing how much temperatures will rise because of the difficulties inherent in modelling a system as complex as the climate.

The range of emissions scenarios project that temperatures will increase by between 1.8˚C and around 4˚C by the end of this century. We cannot yet tell which of these emissions scenarios is the most likely to happen - although it has been suggested that our current emissions could put us on track for a temperature rise of 4˚C or more.

We cannot know precisely what the effects of temperature rise will be. Where, when and how severe will the physical impacts be? How will societies respond? Making these kind of predictions is particularly difficult when it comes down to the regional level. When the IPCC assessed the mass of evidence it was found that the impacts of warming are likely to be predominantly negative, particularly at the higher projected temperatures. For example, at a temperature rise of 3 - 4°C above pre-industrial levels we could see:

  • Increased water stress for around one sixth of the world’s population
  • 20 - 30% of plant and animal species at increased risk of extinction
  • Increased coastal damage from floods and storms
  • Oceans acidification and coral mortality
  • Diminished net carbon uptake by ocean and land sinks
  • Decreased cereal production at low latitudes and in some high latitude regions
  • Increased injury and mortality from heat waves, floods and droughts - increased burden on health services

Overall, the issue is not "are we having an effect on our planet?" but "what is the scale and timing of the effect we are having on our planet?". Uncertainty in one area of climate science (for example in future projections from climate models) does not mean other areas (for example the evidence that temperature is currently rising) are any less robust.

Thanks to PIRC for the concept and some of the words!

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Comments

Comments 1 to 44:

  1. Very good analysis of what we do know, and the contentions that a majority of scientists believe that humans have contributed.

    The unknowns need to be assessed for what they are. We do not know what lies in the future for CO2 emission, nor do we know how much warming will be caused. Other contributors and feedbakcs are still being assessed. Lastly, we can only speculate on future effects based on observed effects.
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  2. Eric the Red We do know something very important about what lies in the future for CO2 emissions, which is that it is almost entirely in or own hands; if we want atmospheric CO2 to fall, we can make it happen; if we want it to stabilise we can make that happen too; if we are stupid enough to continue the exponential rise all we have to do is carry on with "business as usual".

    As regards climate sensitivity etc., the fact that we don't know anything for certain doesn't mean we don't know anything; not all theories that have yet to be refuted have equal support from the observations. Some theories are more plausible than others, and there is a well understood mechanism for determining the best course of action under uncertainty - namely statistical decision theory. So lack of certainty is not a good reason for not taking any action and waiting to see what will happen.
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  3. Dikran,

    The CO2 rise was only exponential when you start from preindustrial levels. The rise has been fairly linear since 1975. Change is the only constant in our civilization, and no one could foresee the changes today 90 years ago, and we cannot foresee the changes 90 years from now. I do not think many people expect a contiued rise to 550 ppm by 2100.

    I do not think the point of this article to claim that we do not know anything at all, but rather what is certain, and what is uncertain. Nor do I think this article advocated not taking any action.
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  4. Eric the Red an exponential with a low rate constant can look "fairly linear", but it is still exponential. If you can show me an anlysis that robustly demonstrates that it is linear (rather than there just isn;'t enough data over shuch a short time span to distinguish between linear and exponential with statistical significance) then I am happy to stand corrected.

    The rise in CO2 is unaffected by our expectations, it is affected by our actions. As Niels Bhor said "Prediction is very difficult, especially about the future" - in the 70s they though we would all be flying around in our hovercars and would have a domestic robot doing our chores by now, but it hasnt happened. IMHO it is extremely rash to decide the action we should take now on the basis of what technological solutions the future may offer. There is an appreciable probability that such solutions will not be made available, or if they are they will be available too late. The advantage of predictions based on a continuation of what has gone before is that we know it is plausible a-priori.
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  5. Yes Dikran,

    An exponential with a zero exponent is linear, so there is essential no different between the two.

    Using a continuation of past data works for the short term. At some point, the trend will change. We just do not know in which direction, how fast, or for how long. An example uses the 1970s prediction of mass starvation based on the exponential population increase and linearly rising food production.

    Nice quote. I need to remember that.
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  6. Eric the Red O.K. I see that you are merely trolling, as exemplified by the fact that rather than produce some evidence that the rise in CO2 is linear rather than exponential, or admit that you have no such evidence, you point out that linear is a special case of exponential as if that somehow made your point (rather than mine). Sorry Eric, life is too short.

    The idea that there is no essential difference between linear and exponential I'm sure will revolutionise the field of control theory! ;o)
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  7. Actually, the rate at which the atmospheric CO2 concentration is increasing... is itself increasing;

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    Response:

    [DB] As supported by this Wood For Trees graphic:

    WFT

    [Source]

    Yup, greater than linear.

  8. Yes CB, that was our point. The rate of CO2 increase was increasing as your graph shows, but is now averaging about 1.8 ppm/yr.

    http://www.esrl.noaa.gov/gmd/ccgg/trends/
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    Response:

    [DB] Looking at all of the data instead of the standard dissemblers cherry-picked start dates:

    AGR

    year  ppm/yr
    1959   0.94
    1960   0.54
    1961   0.95
    1962   0.64
    1963   0.71
    1964   0.28
    1965   1.02
    1966   1.24
    1967   0.74
    1968   1.03
    1969   1.31
    1970   1.06
    1971   0.85
    1972   1.69
    1973   1.21
    1974   0.77
    1975   1.13
    1976   0.84
    1977   2.10
    1978   1.29
    1979   1.75
    1980   1.73
    1981   1.43
    1982   0.74
    1983   2.17
    1984   1.37
    1985   1.27
    1986   1.45
    1987   2.33
    1988   2.12
    1989   1.31
    1990   1.28
    1991   0.98
    1992   0.46
    1993   1.36
    1994   1.93
    1995   1.93
    1996   1.23
    1997   1.92
    1998   2.98
    1999   0.90
    2000   1.76
    2001   1.57
    2002   2.60
    2003   2.30
    2004   1.55
    2005   2.50
    2006   1.73
    2007   2.24
    2008   1.63
    2009   1.89
    2010   2.42

    [Source]

     


    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.  This also includes playing rhetorical games.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  9. Eric the Red I like the "our point", most amusing. CBDunkerson's plot directly refutes your assertion that "The rise has been fairly linear since 1975.". That assertion is clearly incorrect, has been challenged, the challenge ducked and now you are trying to suggest that we had been making the same point! Your chutzpah is beyond belief!
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  10. Eric, I wrote:

    "If you can show me an anlysis that robustly demonstrates that it is linear (rather than there just isn't enough data over shuch a short time span to distinguish between linear and exponential with statistical significance) then I am happy to stand corrected."

    You failed to do so, you still have failed to do so. Now I've had enough of this nonsense, TTFN.
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  11. Let's examine a 10 year running average;

    1961-1970: 0.898
    1971-1980: 1.336 (+0.438)
    1981-1990: 1.547 (+0.209)
    1991-2000: 1.545 (-0.002)
    2001-2010: 2.043 (+0.498)

    From this we can see that there was a 'leveling off' in the 90s (mostly due to 1992 having the second lowest increase on record), but then increases accelerated in the 2000s.

    Note again that these are increases in the rate of increase... a linear rise would have these values staying steady. Instead, the most recent ten years show the largest increase in the series.
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  12. I sense something Monckton'esq going on here, and more strawmen arguments from contrarians to distract us from inconvenient truths...darn it I should be doing other stuff.

    Tamino has addressed this silliness here and here. He concludes:

    "CO2 has increased faster than exponential. Even using the shorter NOAA global dataset. And yes, the result is statisically significant."

    EOS.
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  13. Eric the Red. You have got the situation 180 degrees the wrong way round. The reason we have statistics is because we are able to see in noisy data pretty much anything we wish to see. However being able to see some pattern in the data doesn't mean that it is meaningful rather than an artifact of the noise. Statistical hypothesis testing is one way in which we can guard against jumping to such conclusions. Your analysis did nothing to suggest that the hypothesised departure from exponential is anything other than an artifact of the noise.

    In short, you can do "more than that", you can devise some test that demonstrates that there is statistically significant evidence for your hypothesis.
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  14. CB,

    Best to look at a moving average. I used a 5-year moving average, which has changed very little in 13 years; 2.00 in 1996, 1.98 in 2008, ranging from 1.74 to 2.14. The low values during the 1990s yield a misleading spike in the 2000s. This is the problem with cherry-picking values.
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  15. Eric the Red You do realise the 1975 start date is a cherry pick? You have obviously chosen the start point to maximise the evidence for your hypothesis.

    Can I suggest that we abandon this topic of conversation. Eric seems to have quite neatly derailed the discussion of the topic of the article with pointless quibbling about whether the growth of atmospheric CO2 is exponential or linear, despite the fact that Tamino has already covered this with a much more solid analysis than Eric's (it even includes a test for statistical significance - take note Eric).
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  16. Eric the Red @15, the last few years have shown a lower than usual growth in CO2 content because:

    1) There was a decline in emissions in 2008 related to the Global Financial Crisis:



    2) There was an increase in oceanic absorption of CO2, particularly in 2008, because of a strong La Nina.


    Despite this the trend in the growth of CO2 concentration was positive over the period 2005-2009 (the last year in Tamino's analysis):



    Let me emphasise that, even with the Global Financial Crisis and the coolest global temperatures in a decade, growth in CO2 concentrations was greater than linear. So unless you are projecting the GFK as the new economic norm, and 2008 temperatures or less as a constant feature for the coming decades, the last few years have had unusually low growth in CO2 concentrations relative to normal conditions.

    If, instead of cherry picking aberrant conditions for your projections, you take the whole of the data, we can expect continued faster than exponential growth unless serious measures are taken to restrict emissions.
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  17. Tom,

    Based on your previous post, would you expect less than linear growth this year due to the strong La Nina? Even with the strong increase in emissions, the rate of CO2 increase is decelerating.

    I am looking at the whole data, that is why I can see the changes. People here have been ignoring that which is inconvenient. Look at your last plot. Would you choose 1998 as your starting point? No, that would be obviously cherry picking. Looking at the plot as a whole, the declining slope in the CO2 increase becomes evident.
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    Moderator Response: [Dikran Marsupial] I am going to drop out of this discussion at this point. Albatross has provided you with links to analyses performed by Tamino that show statistically significant evidence that the rise is non linear. Please go and review the evidence that Tamino has provided; and if you can find a methodological fault in his work then do tell us about it. However, unless you can do that, I suggest this minor issue be considered off-topic for this particular article.
  18. Eric the Red - I strongly suggest you take this up with Tamino (links here, from Albatross). He has rigorously demonstrated a statistically significant greater than exponential growth in CO2. Cherry-picking single years, as you suggest, isn't science - it's denial.

    I will note that Tamino is somewhat, er, less accommodating of unacknowledged dyscalculia than most people here.
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  19. ETR#17: "I am looking at the whole data, that is why I can see the changes."

    That's interesting; perhaps you have some graphics of the 'whole data' you'd like to share. Do you take MLO all the way back to 1958? Have you included other long life monitoring locations, such as Barrow or Summit? Have you observed how well 'excess' CO2 concentrations (measured ppm above the global average) correlates with local human activity (traffic, seasonal heating, etc) down to the weekly time scale? Oh, and for the 'whole data,' do you include Law Dome CO2?

    "People here have been ignoring that which is inconvenient."

    That's just flat incorrect, almost to the point of being funny. Anything with the word 'inconvenient' in it these days is always a good laugh line.

    "Looking at the plot as a whole, the declining slope in the CO2 increase becomes evident."

    No, go back to the graph DB posted at #7 and let's play 'find the declining slope.' The game starts when you fit lines with slopes of 0.5 ppm/yr, 0.75 ppm/yr, 1 ppm/yr, 1.25 ppm/yr, 1.5 ppm/yr, etc. beginning at 315 ppm in 1958. Then let's talk about 'declining slopes.'
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  20. Back on-topic: I've used just this approach when arguing climate change with some denier friends. Lay out the incontrovertible scientific facts (i.e. that which is know to a very high degree of certainty), and let them draw their own conclusions.
    While I'm not sure they've entirely abandoned their denier ways, they at least don't try to persuade me that I'm wrong about the basics of climate change any more... :-)
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  21. Begging the moderators indulgence.

    Eric the Red @17,

    In 1986 the economic system of the Soviet Union collapsed, leading to a very sharp contraction in Soviet emissions, and a contraction in world emissions. This was reinforced by similar collapses in production in former Soviet satellites, including East Germany. The contraction was sufficiently rapid to more than offset China's rapid growth in emissions in the period. The effect was reinforced by a sharp reduction in global temperatures due to Mount Pinatubo. Note that while the combined emissions of the US, the former USSR, and China contracted (entirely due to the former USSR as US and Chinese emissions continued to grow) in this period, world emissions continued to rise, as did CO2 concentrations.

    Former Soviet Union (now the Commonwealth of Independent States) stabilised their economies and hence emissions around 1996, allowing the underlying growth in world emissions to reassert itself again. This was reinforced by the 1997/98 El Nino.

    Around 1999 Chinese emissions took a sharp turn upwards, doubling in around 10 years (which requires around a 7% per annum growth rate). That rapid growth in Chinese emissions is ongoing.



    So, unless you are predicting a similar collapse to industrial output in Europe or the US to that which occured in former Soviet states during the collapse of the Soviet Union in the next decade, and another collapse for whichever did not collapse in the following decade, the reduction in the growth rate of CO2 concentrations in the 1990s is an aberration and not projectable.

    If we consider the 1970's and 1980s, they exhibit more than exponential growth. If we consider the 2000's, they exhibit more than exponential growth. If we consider the pattern over the whole period, 1975 to 2010, it exhibits more than exponential growth. The only way you are able to see merely exponential growth in the curve is to focus on two highly unusual, and very sharp economic contractions.

    Given that, and given that emissions growth is currently tracking the A1 and B2 range, the sensible projection, given no radical changes of policy are either the A1B scenario (if China follows through with its policy of reducing emissions intensity, and India, Brazil and/or Africa do not experience a similar economic renaissance), or the A2 scenario if China does not follow through.



    There have been several comments on SS lately about the futility of "chartism" (normally using Tamino's less polite term), ie, of trying to predict trends without understanding of the underlying causes. I think "chartism" is exactly what you are indulging in. As can be seen, if underlying causes are looked at chartism about CO2 increases is revealed for the nonsense it always is.

    As an (IMO) irrelevant addendum, and only because you asked:
    Based on my last post and the evidence, I would expect stronger than linear growth, and stronger than the best fit trend growth for 2010 because of the recovery from the GFC, and a strong El Nino. That is, I would expect a sharp up tick for the next datum on Tamino's graph (the second) above. If no strong El Nino develops in the last months of 2011, I would expect the ongoing recovery plus the strong La Nina to result in a lower growth than 2010 but higher than in 2009, resulting approximately in an ongoing linear trend in the growth of the growth rate for the period 2007-2011, and hence exponential growth in concentration. Continued warming in 2012 will result in that becoming faster than exponential growth in concentration from 2012.

    Having said that, the recovery is on very shaky legs in Europe and the US at the moment (for different reasons), and a strong tropical could erupt tomorrow. Predicting short term trends beyond continuing growth is a mugs game. Medium term, all the evidence suggests continued faster than exponential growth. Long term is up to us.

    As noted, I consider this discussion of short term predictions irrelevant for reasons given, and will not indulge it any further in later comments.
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  22. We also know that a warmer temperature will result in a larger capacity of the atmosphere to hold water. If the actual amount of water held in the atmosphere changes at a similar rate to the change in capacity then we have positive water vapour feedback.

    To avoid water vapour feedback we require that the relative humditity of the atmosphere goes down as temperature increases, and therefore goes up as temperature increases.

    Although there is not obvious reason this cannot happen for small changes in temperature, for large enough changes in temperature this will eventually require that the atmosphere either store more than its total possible capacity, or that the relative humidity drops to values lower than the driest desert observed on earth today.

    It would seem impossible for water vapour feedback to be negative over large enough changes of temperature, and only possible over a restricted range. For a negative feedback to be possible we require that such a range exists, and that we are lucky enough that this range overlaps the temperature change we are now undergoing.
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  23. This succinct summary is useful...the more succinct the better, I find, because in face-to-face conversations, people taking the so-called "skeptic" position often change the topic frequently.

    This type of info seems to be best suited for people who are willing to modify their opinions in light of established facts. But as we know, not everyone is like that. I'm not sure what the proper approach is to those who aren't. But I think it's best to extend people the benefit of the doubt for as long as possible.

    For example, ETR's assertion that looking at all the data, CO2 rise is decelerating may seem like an unwillingness to accepts the facts plainly presented. But I wonder if perhaps he is reading the graphs of rate of CO2 increase presented here as graphs of CO2 level (instead of rate of increase). In that case graphs like the one from Tamino that Tom presents @ 16 would indeed *look* like there was a deceleration, and ETR would think *we* are the ones in denial.

    But of course, it is in fact a graph of *rate* of increase, and any curvature is not acceleration but acceleration of acceleration (or "jerk").

    I think extending the benefit of the doubt feels better and has a better impact on lurkers than branding someone a denialist...even if they probably are. And I choose to believe that ETR is misreading the y-axis but being otherwise reasonable.

    Mods, I realize that most of this crosses into territory that's been declared off-topic, and I certainly won't be offended if this comment is deleted because of that. I just thought it was worth noting that in this particular case, what looks at a glance like trolling could be an honest mistake. I don't participate here often, so I don't really know the cast of regular characters....
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  24. kevin s, I greatly appreciate the sentiment and comments, but let me assure you that Eric the Red is one of the regular cast of characters here, and is very unlikely to be misreading the graph in the way you suggest.
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  25. Kevin,

    Tom is correct in that I am not misreading the graph. If the CO2 increase was exponential, the rate of increase (Tom @16) would show a linear rise. Since 1900, atmospheric CO2 showed a near linear rise until WWII, then an exponential rise. As shown in @8 and @16, the rate of increase is decelerating. In an exponential, it would be constant, and if it were faster than exponential, it should be accelerating.

    I am not discounting Tom's analysis, as it may accurately portray the causes. However, the increase started deviating from an exponential growth in the 1960s, and is approaching a linear increase (has been linear for the past 13 years). In fact, had we continued growing exponentially, the rate of increase would be over 3ppm/yr, not the 2 that we have measured recently. The exponential growth was during a time of exponentially rising population and economic growth. Neither of these appear to be happening today.
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  26. I would suggest taking the (off topic) discussion on CO2 growth rates to the An exponential increase in CO2 will result in a linear increase in temperature thread. Or better yet, Eric the Red, go discuss this with Tamino, who has rigorously shown the greater than exponential growth of CO2.
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  27. Commenters may have noticed this is a cross-post from 'The Carbon Brief' (link provided above at the top of this article). A number of sceptics are making comments on there which some of you more clued-up posters might like to address.

    All contributions to the debate welcome!
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  28. Eric @ 25, Tom did not say you are not misreading the graph. He said you are not misreading it in the way I suggested (i.e. innocently). You most definitely are misreading the graph. (I'm referring here specifically to the graph from Tamino posted in comment 16 and your subsequent claim that CO2 increase is decelerating in recent years). That graph shows rate of increase of CO2. Any value larger than the one to its left indicates and *increase in rate of increase*, i.e. acceleration. Twelve of the most recent thirteen points on that graph are higher than those to their left. (also the trend across the whole data set is obviously positive, but that's beside the point for now)

    So there's no question at all that you're misreading the graph. I was suggesting that you might be doing so innocently, by accidentally mistaking the seemingly declining "jerk" (i.e. rate of change of acceleration)near the end of the record for deceleration. Tom simply told me he doubts you made this innocent mistake.
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  29. Kevin,

    There appears to be a slight confusion between graphs, and that may be partly my fault. The graph that Tom showed @16 does show accelerated warming. What must be understood is that this graph is a change in the rate of the 10-year moving average for growth rate, i.e. the rate for 2001-2010 is higher than the rate for 1991-2000.

    In an exponention growth curve, the CO2 increase rate would be rising linearly. Greater than exponential would be depicted as rising more rapidly, less than exponential as less rapidly.

    My statement about the previous 13 years concerns the actual CO2 data listed in @8, not the change in Taminos analysis. ut do not take my word for it, do the analysis yourself.
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  30. I think this adds to the what we don't know.

    Confirmation of an important unkown


    This also has an effect on Prof Trenbeths analysis.
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    Response:

    [DB] Please characterize and quantify what effect you believe that will have.

  31. Camburn - Understanding of cloud impacts has come a long way in the fourteen years since that was published.
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  32. Further to Eric: When you don't use the word "deceleration" your posts sound somewhat more reasonable, and when you say the rate has been "deviating from exponential" or "approaching linear" it's clear that even you don't *actually believe it's been decelerating (which would be a curve on the other side of linear on a CO2 concentration graph).

    But even in the more reasonable mode, I still think you come to wrong conclusions by ignoring statistical significance. You say the last 13 years has been linear...can you show how you come to that conclusion? Because looking at the error bars on Tamino's graph, I see acceleration with non-overlapping error bars--i.e. *statistically significant* non-linearity--within the last 13 years.
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  33. Camburn
    it refers to an old paper. Are you aware of any improvement since 15 years ago?
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  34. Yes Kevin, I should not have used the term "decelerate" to indicate a slowdown in the rate of increase.

    Once again, I am not using Tamino's graph because he is comparing recent measurements to those from 10 years prior. His value for 2010 is the average rate of increase for the past decade. In the post @8, you will see that the highest annual increase occurred in 1998, but in Tamino's graph, 1998 is the low point in the dip. The actual CO2 increase rate fell from 1987-1992, but in Tamino's graph, the change did not occur until 1992. When plotting a 10-year average, the most common practice is to center the average around the midpoint (2001-2010 would be plotting in 2005). Tamino is plotting them at the endpoint.

    The recent linearity will not become apparant by Tamino's method for several years. I am not saying that it will continue, possibly due to explanations presented by Tom @21, but you average over long timeframes, it takes similarly long timeframes for changes to occur.
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    Moderator Response: [Dikran Marsupial] Eric, can you show that the "linearisation" of the exponetial rise is statistically significant, i.e. that you can be sure it is not just an artifact of the noise. If you can't do that, then your argument is just an unupported hypothesis, and you are distracting from the discussion of more substantive issues.
  35. DSL, as if to illustrate my point, we have Camburn @30.

    I quote from the comments policy:

    "No link or pic only. Links to useful resources are welcome (see HTML tips below). However, comments containing only a link will be deleted. At least provide a short summary of the content of the webpage to facilitate discussion (and show you understand the page you're linking to). Similarly, images are very welcome as they can be very useful in explaining the science. But comments with pictures in isolation without explanation will be deleted."


    Clearly Camburn's post is in violation of the spirit of the policy if not the letter. Yet he would be the first to scream censorship if his inane and pointless post were deleted. And he also has been on Skeptical Science for a long time so their is no excuse for his casual disregard of comments policy.
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    Response:

    [DB] Please refrain from further discussion of the Comments Policy and moderation.  A return to the topic of this post is appreciated; thanks!

  36. Tom,

    I found the link interesting and informative, even though it is old. Yes, he probably should have included more details about the relevance of the cloud data in the link, but it is definitely useful and on topic for this thread.
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  37. Camburn - You present links for a reason, kindly state why when you post them. That's part of the Comments Policy for all participants here - when you fail to do so, you are in violation of that policy.

    Quite frankly, with some of the 'links only' posts (including yours) it's extremely difficult to determine what possible relevance they might have.
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    Response:

    [DB] Please refrain from further discussion of the Comments Policy and moderation.  A return to the topic of this post, What we know and what we don't know, is appreciated.  What I know (and what veteran habitues of SkS know as well) is that future off-topic conversation on this thread will be deleted, as will those already posted.  Thanks to all for your compliance in this matter.

  38. Readers following this sad thread,

    Nothing new here, to play on the title of the OP, this is what we know about this attempt to create faux debate-- the contrarians and 'skeptics' have no tenable or credible scientific case to make, so they resort to conspiracy theories, attempts to derail threads, and attempts to detract form the science. Repeat ad nauseum-- you know what contrarians, these antics are so transparent and only further undermine your credibility, not to mention being intellectually numbing.

    I interpret this behavior as implicit agreement with the salient points made in the points above. The only points that has been challenged by 'skeptics' (and it was a strawman argument at that) here is the rate of increase in CO2, and on that they have been shown repeatedly to be demonstrably wrong.
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  39. Sorry Daniel, we cross-posted; only saw your post after I submitted #48.
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    Response:

    [DB] No problem, Albatross.  Your conclusions are spot-on.

    I just played Lizzie Borden (a whack-whack here, a whack-whack there) to clean up the debris on this thread.

  40. For a layman such as myself, I see the 'take home' message of this post being that, thanks to the tireless research performed by climatologists and a wide variety of other [take your pick]-ologists, we know an awful lot about the Earth climate system, and we know increasingly more with each passing year.

    It may well be the case that there is more left to learn than there is learned about the behaviour of the Earth climate system. This does not diminish the sheer amount of accumulated knowledge already gathered.

    Certainly, from the perspective of public policy, it seems to me that we have enough knowledge to comfortably demand action on the matter.
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  41. Not quite sure what you mean by the strawman argument. But if you mean that those trying to show exponential CO2 growth have been demonstrably wrong, then I agree.

    In June, CO2 was 1.66 ppm higher than in 2010, and is averaging 1.62 ppm higher than 2010 throughtout the first six months of 2011. Most likely due to the strong La Nina and lower SST.

    http://co2now.org/
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    Moderator Response: [Dikran Marsupial] Eric, we are by now aware of your hypothesis that there has been a shift from exponential to linear growth in CO2. Now unless you can demonstrate that it isn't merely an artifact of the noise (i.e. a test of statistical significance) then there is nothing more that remains to be usefully said. The moderators have been very lenient with you so far, but this issue is now off-topic and it is unfair on other readers of SkS to allow the discussion to be derailed any further.

    Ironically, from the link you provide "What is the current trend? The concentrations of CO2 in the atmosphere are increasing at an accelerating rate from decade to decade. accelerating from decade to decade. The latest atmospheric CO2 data is consistent with a continuation of this long-standing trend."
  42. Composer @40,

    "Certainly, from the perspective of public policy, it seems to me that we have enough knowledge to comfortably demand action on the matter."

    Agreed!
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  43. Does the amount of water produced by the burning of fossil fuels significantly add to the worlds water supply?
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  44. cefarrar @43, in long chain polymers such as petrol, diesel oil, and jet fuel, approximately one molecule of water is produced for every molecule of CO2 in combustion. For natural gas (Methane), two molecules of water are produced for every molecule of CO2. Coal produces effectively no water.

    Given that the water vapour content of the atmosphere is greater than that of CO2, and the CO2 content has increased by only 0.1% of total atmospheric content, the amount of water vapour added is much less than that. It would have precipitated out and become fairly literally, just a drop in the ocean.
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