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Climate Hustle

BEST Results Consistent with Human-Caused Global Warming

Posted on 3 August 2012 by dana1981

Richard Muller is the head of the Berkeley Earth Surface Temperature (BEST) project, which has just made available a preliminary paper (not yet having passed the peer-review process) regarding the causes of the recent global warming. 

Muller started out very skeptical about the accuracy of the surface temperature record and the causes of global warming.  For example, see these collections of his skeptical quotes and articles.  Muller formed the BEST team to investigate his climate-related skepticism independently, even obtaining funding from the Koch Foundation, whose wealth is primarily derived from fossil fuel interests. 

Now despite his prior criticisms of the climate science community (i.e. see our previous Muller posts), Muller and BEST have independently confirmed the accuracy of some of the main components of the body of climate science research.  As Muller wrote in an editorial published in the NY Times,

"Call me a converted skeptic. Three years ago I identified problems in previous climate studies that, in my mind, threw doubt on the very existence of global warming. Last year, following an intensive research effort involving a dozen scientists, I concluded that global warming was real and that the prior estimates of the rate of warming were correct. I’m now going a step further: Humans are almost entirely the cause."

As Muller notes, the original BEST results confirmed the accuracy of the surface temperture record, finding 0.87°C global surface warming over land during the past 50 years (Figure 1).  The BEST team data and methodology have also been made available to the public for maximum transparency so that anyone can check and attempt to replicate or find flaws therein.

BEST results

Figure 1: The BEST decadal land-surface average temperature using a 10-year moving average of surface temperatures over land.  Anomalies are relative to the Jan 1950 - December 1979 mean. The grey band indicates 95% statistical and spatial uncertainty interval.  Click on the graph to also see the 12-month moving average.

Now as Muller notes, the BEST team has weighed in on the causes of that global warming, finding that as the rest of the climate science community had already demonstrated, it is almost entirely due to humans.  In response to the BEST announcement, Michael Mann noted:

"Muller's announcement last year that the Earth is indeed warming brought him up to date w/ where the scientific community was in the 1980s. His announcement this week that the warming can only be explained by human influences, brings him up to date with where the science was in the mid 1990s."

Ken Caldeira told Climate Progress:

"The basic scientific results have been established for a long time now, so I do not see the results of Muller et al as being scientifically important.  However, their result may be politically important.  It shows that even people who suspect climate scientists of being charlatans, when they take a hard look at the data, see that the climate scientists have been right all along."

The BEST approach in determining the attribution of the observed warming was a simple one, examining the correlations between the various radiative forcings and the temperature data.  The BEST team found that greenhouse gases and volcanic eruptions could account for most of the observed temperature change, and suggest that the remainder of the variability is fairly consistent with the Atlantic Multidecadal Oscillation (AMO), an ocean cycle, and very little contribution from changes in solar activity (Figure 2).  Note that while the BEST approach is based on correlations, they are correlations of variables with known causal relationships (i.e. an increased greenhouse effect is known to cause global warming), although they do not appear to have considered some important influences like human aerosol emissions or the El Niño Southern Oscillation.  Tamino also provides a good critique of the BEST approach.

BEST attribution

Figure 2: The decadal land surface temperature from the BEST average (black), compared to a linear combination of volcanic sulfate emissions and the natural logarithm of CO2 (red). Inclusion of a proxy for solar activity did not significantly improve the fit. The grey area is the 95% confidence interval.

However, there is a great deal more evidence for human-caused global warming, using much more robust methodologies than in the new BEST paper.  This post, in the Skeptical Science tradition, will look at the full body of scientific evidence regarding the attribution of global warming discussed by Mann and Calderia - how we know humans are the cause:

1) Basic physics - human fossil fuel combustion has increased the greenhouse effect, causing a global energy imbalance, which the planet responds to by warming.  Over the past several centuries, human greenhouse gas emissions have caused by far the largest radiative forcing (energy imbalance), and thus must be the driver of any observed long-term global warming.

2) Human fingerprints - there are a number of climate changes we expect to see in response to an increased greenhouse effect.  We have indeed observed these changes, which are 'fingerprints' of human-caused global warming.

3) Attribution studies - many studies have been performed to try and determine the causes of the observed global warming, and every such study has been consistent in concluding that humans are the driving force.

1) Basic Physics

For starters, a long-term increase in the average global temperature must be caused by a global energy imbalance - an external radiative forcing.  We have observed an increased greenhouse effect with more radiation reaching the surface and less leaving the atmosphere.  Scientists have quantified the energy imbalance caused by this increased greenhouse effect, and the radiative forcings associated with various other effects like increasing solar radiation.  Overall, they find that by far the largest radiative forcing over the past 250 years comes from the increased greenhouse effect, which we also know is due to human fossil fuel combustion (Figure 3).

forcings

Figure 3: Global average radiative forcing in 2005 (best estimates and 5 to 95% uncertainty ranges) with respect to 1750 (IPCC AR4).

It's just fundamental physics that this large radiative forcing must result in global warming until the Earth reaches a new energy equilibrium at a higher temperature.  For 'skeptics' to make a convincing argument that humans are not causing global warming, they must both explain where this large greenhouse gas radiative forcing has gone, and find an even larger 'natural' radiative forcing which nobody has yet identified.  Until the 'skeptics' can explain this, the evidence clearly indicates that humans are driving global warming.

2) Human Fingerprints

There are also a number of 'fingerprints' which are either indicative of or consistent with what we expect from global warming caused by an increased greenhouse effect.  For example, we expect to see the lower atmosphere warm and the upper atmosphere cool, because greenhouse gases are primarily located in the lower atmosphere, and effectively trap heat there.  More radiation is directed back towards the surface, less makes it up into the upper atmosphere.  There are many other examples of human global warming 'fingerprints' (Figure 4).

fingerprints

Figure 4: Fingerprints of human-caused global warming.

3) Attribution Studies

As we have previously discussed, there have been a great many studies using various different approaches to determine the causes of the observed global warming.  Every such attribution study has been consistent in concluding that humans are driving global warming (Figure 5), with greenhouse gases causing more than 100% of the observed warming because much of that is offset by the cooling effects of human aerosol emissions, which block sunlight (Figure 6).

HvA 50 years

Figure 5: Net human and natural percent contributions to the observed global surface warming over the past 50-65 years according to Tett et al. 2000 (T00, dark blue), Meehl et al. 2004 (M04, red), Stone et al. 2007 (S07, green), Lean and Rind 2008 (LR08, purple), Huber and Knutti 2011 (HK11, light blue), and Gillett et al. 2012 (G12, orange).

50-65 years

Figure 6: Percent contributions of various effects to the observed global surface warming over the past 50-65 years according to Tett et al. 2000 (T00, dark blue), Meehl et al. 2004 (M04, red), Stone et al. 2007 (S07, green), Lean and Rind 2008 (LR08, purple), Huber and Knutti 2011 (HK11, light blue), and Gillett et al. 2012 (G12, orange).

All of these studies find that humans are responsible for close to 100% of the observed global warming over the past 50 years, and human greenhouse gas emissions are responsible for close to 150% of the observed warming, with human aerosol (sulfur dioxide - SO2) emissions offsetting approximately one-third to one-half of that greenhouse warming.

As Michael Mann noted, this is not a new conclusion.  In fact, climate scientists first reached a consensus that the human influence on climate change was observable way back in 1995 in the IPCC Second Assessment Report, which concluded:

"The balance of evidence suggests a discernible human influence on global climate"

This conclusion became stronger in the 2001 IPCC Third Assessment Report, which concluded:

"most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations"

"Likely" corresponds to greater than 66% probability. In the 2007 IPCC Fourth Assessment Report, confidence in this statement grew even stronger to "very likely", which corresponds to greater than 90% probability.

Long Story Short, We're Causing Global Warming

On top of these many lines of evidence which mostly focused on global warming at the surface, Gleckler et al. (2012) also confirmed that the warming of the oceans has been caused by humans.  While it's nice that Muller and the BEST team have confirmed human-caused global warming to their own satisfaction, it is not a new result by any stretch of the imagination, and there have been a number of studies with far more robust methodology arriving at the same conclusion.

The BEST team also found that the observed warming is consistent with an equilibrium climate sensitivity of 3.1 ± 0.3°C for CO2 doubling, in line with the IPCC climate sensitivity range, and demonstrates once again that contrary to the persistent claims of Richard Lindzen, the Earth has warmed as much as we expect given a relatively high climate sensitivity.

The bottom line is that humans are the driving force behind the current global warming.  Muller and the BEST team are good scientists, so it was inevitable that they would eventually agree with the body of scientific literature on this issue.

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Comments

Comments 1 to 35:

  1. An interesting interview with Muller (in particular, I thought the discussion about the Koch brothers was interesting)...

    http://hereandnow.wbur.org/2012/08/02/climate-change-skeptic
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  2. I think this is the appropriate topic to remind everyone that Anthony Watts once
    endorsed
    Richard Muller's BEST project

    Some excerpts from the article:

    But here’s the thing: I have no certainty nor expectations in the results. Like them, I have no idea whether it will show more warming, about the same, no change, or cooling in the land surface temperature record they are analyzing. Neither do they, as they have not run the full data set, only small test runs on certain areas to evaluate the code. However, I can say that having examined the method, on the surface it seems to be a novel approach that handles many of the issues that have been raised.


    So he claims to have looked at Muller's methods and approves. Next:

    And, I’m prepared to accept whatever result they produce, even if it proves my premise wrong. I’m taking this bold step because the method has promise.


    Caught in the net of his own weaving. Poetic.
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  3. Trent @2 - indeed Watts is backtracking, claiming that he's not backtracking because he says based on the method BEST used, their results were right, but he believes the new station classification system he's using has changed the results.

    Problem is as we noted in the previous post, Watts et al. messed up the analysis. So now the questions are (1) will Watts admit that their analysis is wrong? and (2) will Watts then live up to his word and finally accept the BEST results, that the surface temperature record is reliable?

    This will be a good test of Watts' purported skepticism. Grab some popcorn and enjoy the show.
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  4. I find it quite interesting that the BEST averaging method (no metadata used, other than periods >= one year where stations were not operational), just identifying outlier breaks in data due to inhomogeneities with nearby stations and splitting records at those points, ends up consistent with the USHCN temperatures which use multiple types of metadata to directly correct for station moves, equipment changes, time-of-observation shifts, etc.

    This is also relevant to the recent thread on the draft paper by Watts, as the consistency/consilience of the results using two quite different methods of correction indicate robust data - which calls into question Watt's insistence that adjustments such as time-of-observation are biased.

    While I agree with Dr. Mann that it's nice to see the BEST attribution work finally reach the 1980's, the averaging methods they present are extremely useful work.
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  5. KR - agreed that the BEST analysis of the surface temperature record is a very useful contribution. And agreed that the fact that their methodology yields a result consistent with the other groups' methodologies is really strong evidence that the surface temperature record is accurate. That's a really important point, as is the fact that when you compare raw and adjusted data globally, there is very little difference. Frankly it's exceptionally implausible that the Watts conclusion (of a spurious doubling of the temperature trend) is even remotely close to being accurate.

    Regarding the BEST attribution result, as discussed in the post, it's not really noteworthy, because their methodology was very simple and their results are just consistent with every other study. At least with their temperature record, while their results were also consistent with every other study, their methodology was a new and interesting approach.
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  6. Joshua @1. I heard that PBS radio interview today too and agree with you that it was interesting. The interviewer did a very good job pressing Muller regarding his rationale for being "skeptical" of previous work that arrived at essentially the same conclusions as BEST. As Joshua@1 notes, Muller's comments on the Kochs and the Koch Foundation response to BEST's conclusions were the most interesting aspect. Muller said the Kochs were fine with his conclusions, and they just want the best science, which we now have, thanks to BEST (according to Muller). Muller would not accept that the Kochs did or even attempted to discount pre-BEST climate science. He was adamant on this. It seems a new page may have turned in the playbook of those that want no CO2 reduction schemes: That being that only now, finally, it is logical to accept that warming is occurring due to fossil fuels, but (as Muller indicated in the interview)it would only make sense for the US to reduce emissions after the US is satisfied that China also will do so at the same time. Seems like a good way to not look obstructionist, not deny the science, while hoping for business as usual.
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  7. "For 'skeptics' to make a convincing argument that humans are not causing global warming"

    Whilst posting here is probably a bad idea, I do just want to point out that "serious" sceptics are not trying to say 'that humans are not causing global warming'.

    "Serious" sceptics (in fact most sceptics from my experience) agree that global warming is occurring and humans are exacerbating the issue through GHG emissions. What "serious" sceptics are saying is that the sole/majority attribution of warming to human emissions isn't correct and there's other things at play.

    This "global warming debate" is NOT about whether it's occurring or not, or even if humans are exacerbating the issue or not. The debate is quite simply about attribution calculation, or in scientific terms, climate sensitivity.

    Essentially, the results of both sides will be either rushed upheaval change, or slow planned change. There's no argument that we need to change.
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    Moderator Response: [DB] As for "debate", see here.
  8. In an interview with Rachael Maddow the other day Muller said that we need to do two things to combat Co2: Conservation,and getting the third world and developing nations to replace coal with natural gas...
    No mention of renewable technologies at all.
    I will let you draw your own conclusions.
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  9. Dale #7-Why would it be a bad idea to post here?
    What is a bad idea,is not taking advantage of the huge resource here to answer the very questions that you pose.
    Hint:Asked,and answered many times over.Don't believe me?
    Just look for yourself.
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  10. Dale @7 - I very much disagree that "serious skeptics" dispute attribution. As this post shows, there is simply no serious case to be made that humans aren't the dominant cause of the global warming over the past 50+ years. And frankly the case for low climate sensitivity isn't much less weak.
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  11. tmac @9:
    I do read here regularly..... as well as a number of other sites (consolidation sites such as this one plus scientist blogs among them).

    tmac & dana:
    My point is that the "serious" sceptics are the ones discussing attribution. No "serious" sceptic questions whether warming has occurred or not, or that human emissions have influenced that warming to some degree. Hence the comment I quoted in 7 is technically not right and acts as a purely polarising comment rather than a scientific observational comment. Isn't the entire point of being sceptical in the scientific sense to question these things? To not question is to not be sceptical.

    Personally, I'd rather see questioning of results in science rather than acceptance. Regardless of what consensus says. There's plenty of examples where consensus was questioned only to find out something new about that topic. That's how science advances.
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    Moderator Response: [DB] Please return to the topic of this thread, BEST Results Consistent with Human-Caused Global Warming.
  12. Dale - the issue is that there is a difference between questioning and denying. It's not that the 'skeptics' say "I'm not sure climate sensitivity is as high as 3°C", for example, it's that they say "climate sensitivity is less than 1°C".

    It is in the nature of scientific inquiry to be skeptical. Scientists who accept the body of evidence are still open-minded skeptics. But most of the people who proclaim to be 'skeptical' about climate sensitivity, for example, are not actual skeptics. Their minds are made up that climate sensitivity must somehow be low.
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  13. Dale -

    I've been hanging out in the "skeptical" blogsphere for a while, and while I'm going to stay away from a discussion of how to differentiate a "serious skeptic" from a
    "nonserious? skeptic," I disagree with your statement of the distribution of what "skeptics" tend to believe.

    First, I see quite a number of "skeptics" who either outright reject that CO2 is a GHG or who argue that as a trace gas, ACO2 could never influence global temperatures to any significant extent. Further, there are many "skeptics" who say that they don't doubt that the Earth is warming, and that ACO2 plays a role, but they systematically reject any scientific method for measuring and/or establishing a rise in global mean temperatures or attribution of any rise to ACO2 - so I think that their statement of what they believe is internally incoherent.

    Finally, FWIW, I have often been told by "skeptics" that the belief of "skeptics" is not monolithic, and therefore can't be easily categorized, only to turn around and read blog post after blog post where "skeptics" categorize what most "skeptics" believe.
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    Moderator Response: [DB] Attempted thread-jacking aside, let us return to the topic of this thread, BEST Results Consistent with Human-Caused Global Warming.
  14. Dale: it might help your case if you give a name of someone that you consider to be a "serious" skeptic. That will avoid having the discussion bog down in differences of opinion that are based on observations of different groups of "skeptics".

    Every good scientist is a skeptic, and raises questions about others' research. The set of self-styled "skeptics" (in the climate area) that are good scientists and true skeptics is very, very small (IMHO).

    Asking questions that have been answered many times (and where the answers are well-established and accepted by nearly all the scientists in the discipline), and asking them again and again because you don't like the answers is not skepticism.

    Muller and the BEST group had "skepticism" that was ignorant (or unaccepting) of well-established knowledge in climate science. Their results appear to have been a surprise to two groups:

    - a few of them that have now decided the mainstream climate science had it right

    - a few more of them that cannot accept the results, because they were never "serious" skeptics in the first place.

    The vast majority of climate scientists are not surprised.
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    Moderator Response: [DB] Please let us return to the OP of this thread; enough chasing after shadows.
  15. Mod:
    Apologies, but I thought a discussion on scepticism over attribution was appropriate for the thread considering Muller himself was originally sceptical of attribution and through this study changed.
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  16. Good post and graphics, thankyou Dana.

    With the comments above, lead to some thoughts and questions, hope that is ok.

    "Call me a converted skeptic. Three years ago I identified problems in previous climate studies that, in my mind, threw doubt on the very existence of global warming. Last year, following an intensive research effort involving a dozen scientists, I concluded that global warming was real and that the prior estimates of the rate of warming were correct. I’m now going a step further: Humans are almost entirely the cause."

    To establish skeptical view or "denial driven view", is very difficult but it strikes me there are many who fully recognise global warming, but are skeptical of the size for the issue, this can range from a healthy skepticism as part of scientific method to denial in disguise.

    I find that people that say things like "CO2 isn't even a warming agent", "its all volcanoes" are normally not "skeptics" (whatever that this) as such, more just not prepared to even look for fear of the possibility, for whatever reason.

    For those who are not skeptical about environmental change what does all this actually mean?

    "The BEST team also found that the observed warming is consistent with an equilibrium climate sensitivity of 3.1 ± 0.3°C for CO2 doubling, in line with the IPCC climate sensitivity range, and demonstrates once again that contrary to the persistent claims of Richard Lindzen, the Earth has warmed as much as we expect given a relatively high climate sensitivity."

    For me this is could be slightly skeptical view, for to say that a CS of 3.1C is relatively high, is slightly underestimating the higher potential of CS, for a CS of 3.1C for me is a middle of road potential possibility of climate sensitivity, and there is a ~50% chance it could be higher. A relatively high CS would be 3.75C-4C, with a 3C mean and 95% range 1.5C-4.5C, SD 0.75C.

    And with that middle of the road potential Hansen is still calling for 350ppm by 2100.

    The higher ppm we get to the harder returning to 350ppm becomes and it makes sense that the higher the heating imbalance or the larger the effective heater the faster things will proceed.

    So my questions are, considering the BEST results confirmations of warming and the size of the CO2 problem.

    What is a safe peak ppm?

    a) 400-410ppm
    b) 410-420ppm
    c) 420-450ppm
    d) 450-500ppm
    e) 500-550ppm

    What is most likely CO2 peak, all things considered?

    Just wondering what people think?
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  17. Regarding 'nights warm faster than days' on your Fingerprints infographic: though commonly stated (it's mentioned in the new BEST paper) this is not really a fingerprint of anthropogenic warming.

    Direct CO2 forcing is not considered to have anything other than a negligable effect on diurnal temperature range (DTR). In terms of forcing, the primary anthropogenic cause of decreased DTR (nights warming faster than days) is aerosols, which reflect or absorb solar radiation, holding back Tmax while both Tmax and Tmin warm due to an increasing greenhouse effect. So, looking just at forcings, decreased DTR would actually be a fingerprint of anthropogenic cooling.

    However, some of the main factors involved in decreasing DTR are likely to be feedbacks - water vapour (the primary effect is absorption of solar radiation reducing Tmax, and not the greenhouse effect increasing Tmin), clouds and soil moisture. Unless it could be shown that the specifics of these feedbacks are unique to greenhouse warming, I don't think they could be regarded as fingerprints of anthropogenic effects.

    On the other hand, I assume that solar-induced warming would have an effect on DTR (make days warm faster than nights), at least at first order, so perhaps it could be considered a fingerprint for distinguishing solar and greenhouse warming.

    Refs:
    Stenchikov and Robock (1995)

    Stone and Weaver (2003)

    Zhou et al. (2010)
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  18. Dana

    great post. I have a question regards the labeling of figure 5. If these are contributors to "global warming" shouldn't they add to 100%, i.e., human (sum of warming and cooling forcings) and natural (sum of warming and cooling forcings) influences? I don't know if I'm describing my confusion clearly.

    Thanks again

    Tony
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  19. George Marshall (of the British Climate Outreach and Information Network, not of George C. Marshall Inst.) identifies in his Irresistible Story of Richard Muller post that Dr. Muller's change of heart is a cultural transformation, not a scientific one, dispite what Dr. Muller writes.
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  20. Ranyl,
    You ask what a "safe" maximum ppm of CO2 is. Safe for who? I live at 70 feet above sea level. I would be safe at a much higher level than millions of people in Bangladesh. Many of them have already been forced from their homes by sea level rise. Ask the farmers in Oklahoma what level of drought and heat they can stand. Can you define what you mean by "safe"? Or do you mean "less than a catastrophe for the USA"?
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  21. Lots of good comments here.

    ranly @16 - I agree that 3°C sensitivity is middle of the road. I tried to be careful to call it "relatively" high, that being relative to the climate contrarian claims of climate sensitivity < 1°C. I didn't want to say "not low", though middle of the road may have been a better choice of words.

    As for what CO2 concentration is safe, we can't really answer that question. For one thing it depends on your definition of "safe", i.e. how much damage are you willing to accept. I'd say 350 ppm is a good conservatively safe value, but I'd be reasonably happy with 450 ppm, since I think that's the best we could possibly achieve at this point.

    As to where we'll most likely peak, my guess is somewhere around 550 ppm, but it could easily be much higher. A lot depends on how long the natural carbon sinks can continue to keep up with our rising emissions. So far they've been up to the task, but we can't expect that to continue forever.
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  22. pauls @17 - yes, the nights warming faster than days is one of those 'fingerprints' that is consistent with AGW, but not necessarily indicative only of AGW. There are a number of those 'fingerprints' that could hypothetically be explained by other effects, but when you consider them all together, the fact that they're all consistent with what we expect to see from AGW is what's really convincing.

    Tony @ 18 - most of the studies illustrated in Figure 5 are model-based. So they generally perform model runs to try and match the observed temperature increase, and then determine how much of the modeled increase is due to each factor. But the models don't perfectly match the observations, so for example if they show 10% less warming than observed, the numbers will add up to ~90%. The graphics show what percentage of the observed warming was attributed to each factor. If it showed how much modeled warming was attributed, then they would add up to 100%, but I think that would be less informative.
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  23. Micheal and Dana,

    What is safe? and over what time period?

    Crux questions I suppose.

    Maybe safe is the amount that means that we can adapt enough to prevent civilization chaos.

    2C above pre-industrial seems the highest limit of safety for me due to complex interactions of everything, e.g. Bangladesh has ~100 million people, they will have go somewhere as sea level rises, deluge flooding increases and glacial melt flooding, make it irrational to stay, and so the knock effects go on. Not because of the possibility of inducing tipping points, they are wild cards that become more likely over 2C, but sudden 2C transition isn't looking that pretty in itself if 0.8C can induce these weather extremes being experienced, and we have been that hot for long (what will a natural 1:200 year event amplified by this warming be like?)

    Lots of ill-health and deaths occur after the acute flood and are rarely recorded, people from Pakistan are still not in permenant shelter after the floods, even here in the UK after the 2010 floods people are still displaced. And then of course there is all the costs of clear up, all the additional white goods to be made (positive feedback on CO2 emissions due to embodied energy and waste disposal), and the huge insurance costs, all picking away at fincancial security which isn't exactly that secure at present. And then there is the lack of water security after a flood, loss of crops, etc, etc...

    Is safe a level where food and water security can be maintained to a level that doesn't induce civilizations breakdown generally, although that is already in some areas.

    350ppm however doesn't seem conservative safe to me, it seems at the edge of the safety, and still below the 95% safe that any medical practioner would accept as acceptably safe for the treatment of a patient.

    Why?

    Well as the Pliocene had CO2 about 350ppm, and was 3-5C hotter, all things being equal that is were we will end up with 350ppm, and although that will 1000years or so, about 60-80% is meant to occur in 100years, which seems reasonable as any heating event has a linear rise followed an expotential decay. Therefore 350ppm by 2100 induces 1.8C to 3C warming in a 100years, if GHG CS and Ice melt CS included.

    Although the carbon sinks are keeping at present as just reported in Nature, most feel this won't continue much longer and several sink areas are looking dodgey, like the Canadian Boreal forest seems to be source at present due fires and Pine beetle problems, and ofcourse there is the general fact that CO2 increases naturally by ~14-20ppm per 1C of warming and permaforst and permaice on the Arctic ice shelf are melting.

    450ppm for me is really not safe in anyway, that is CO2 levels not seen for 20-40million years and means >2C for definant eventually and 2C by 2100 very likely indeed and >1.8C a certainity and 100ppm is a lot of CO2 to remove as 350ppm looks more appealign as events continue to occur.

    And it is all about the rate of change for eco-systems and crop growing potential, faster we go the less chance things can adapt or move and when looking at the fishery changes for PDO and Nina changes, eco-systems acutely react poorly to sudden changes in the prevailing regime. The desert regions will shift and are already, wet areas will become drier and so on.

    Then weather extremes which have a far deeper effect than just the acute event as highlighted above. How frequent to 1:100 events need to become for them to impinge on safety all round?

    Presuming the potential extreme events (flooding, heat waves, droughts) track the shift in temperature mean, a shift of another 0.8C, may be very significant indeed.

    How many SD from the mean is a 0.8C shift and what will that mean for severe events?

    Very hard to say as for the last 2000 years the mean has been shifting up and down, from the MWE, the Roman period and the LIA. But we are currently hotter than all these, indeed Hansen says hotter than the Holocene Thermal maximum, and the general noise arround the shifting mean for the last 2000yeas is about ~+/- 0.4C 95% range. So taking the 1900-2000 as a mean we have shifted from, we have shifted ~1.5-2 SD's...USA has only just shifted in the last 10 years due to the 1930-40's heat periods an dwhy the droughts are just becoming as severe as then now (Texas 2011, now 2012). So another 0.8C is lots of SD above, ~4 to 5, and intuitively doesn't that mean that 100 year heating events will basically be cold events and 1:1000, events occur every 10 years or so, and those sort of extremes do directly impinge of water and food security everywhere. Shift the mean by 2SD and doesn't that mean that the previous mean is now a cold extreme at the 95% range and the previous 95% hot limit is the new mean and thus the new 95% range (1:20 year events) include events that were basically 4SD from the mean previously or 1:500 events and 1:100 events become very extreme compared to now?

    Look at the mega droughts of Medeival Warm Event in the western USA, can these return as we warm, or were they due to more persistent La Nina periodicals due to increased equatorial solar irradation at the time?

    How will the changing Arctic sea ice effect weather events?

    Sudden out pourings of cold in winter and heat in summer due to blocking events seem to be already occuring more often and the irregularity of this is not helping, very warm March UK, cold wet April with frost, and the fruit tree crop was impacted severely.

    The American crop this year must be hard to predict at least, with the drought and the storms, the recent Austrailian drought and 2011 floods must have impacted things.

    What is safe?

    Well impossible to say for sure, but we are about to find out?

    The El-Nino is building, sunspots are rising, sulphur emissions are just about starting fall globally, and Arctic sea ice loss is racing away, all meaning the this next twleve months - 24 months should be hot?

    I don't really feel that safe at the 390ppm of now to be honest, these weather events are clearly extreme, and it is quite hard to break an extreme in a long record and gets harder with every year and there is clearly more heating to come, suggestive that these extremes will become more severe and more frequent.

    And what about all the heat of the last 30years that has been subducted to the middle depths of Atlantic in the last 30 years, when does that find its way to Antartica peninsula, the bottom warm water on the Antartic shelf is already heating significantly, if that heat returns to surface how sensitive will the CS be then?

    It takes ~30years for the Argus current heat to reach the North Atlantic so by push and shove thinking (push it in one end at a certian rate and it has flow somewhere else the North Atlantic sea level would rise and it has out of the other at a similiar rate), what is the transit for the heat accumulation of heat in the THC from the Indian Ocean, Southern Atlantic, Tropcial Atlantic and North Atlantic back to the Southern ocean upwelling?

    Would heat returning to the surface would turn the heating up rate or just get lost in the latent heat of undermelting the WAIS under Pine Island?

    What is safe?

    Not a lot for as Dana says 550ppm is looking almost inevitable unless things change, and no one can let go of our addiction to power despite the carbon costs of all power generation even wind turbines have a large carbon cost when you have a budget as tight as that needed to actually get to 350ppm.

    Could go on and on about what is safe, however for me it is wha tis safe for everyone, and therefore 350ppm is not really that safe but the best we even dream about.
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  24. C02 at near 400ppm is totally not acceptable- and we are near that now- though the effects of this are 25 years away- what we are seeing now is C02 just past 350ppm.

    The weather extremes in years to come will become worse- far worse. How society is able to hold up to an increasing erratic climate is an unknown. But it is likely to be chaotic. Over the long haul we we are likely to see C02 near 650ppm- perhaps higher and at least 3.5 degrees C in warming over the PI era- we will not see 350ppm again for at least a thousand years- perhaps longer.
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  25. #23 ranyl pretty much speaks my mind. Human discontent, such as demonstrated by the Arab Spring, has already been connected to AGW.

    I once made a bumper sicker that read "Peace by 1927" because it sounded cool (I'd just read 1984, and like it's author, I reversed the current date.), and a history buff told me that it was about the right date to prevent WWII. So now, as a single issue voter, I might say "Peace with 350 ppm". At least this is something we can theoretically get back to. As it says in Deuteronomy "so that you and your children may live."
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  26. Excellent post. Should be a must read for anyone still open minded about the extent of human impact on the climate. And regarding that, the discussion of what levels of CO2 is "safe", related of course to prevent some catastrophic breakdown in the biosphere, atmosphere, and ocean systems supporting both humans and other creatures, what is absolutely critical here is a wholistic approach-- true Anthropocene Management. Increasing CO2 levels are just one of the many ways humans are altering this planet, and have been for many centuries. In a wholistic approach, we would look at not just CO2 but land uses, methane, the nitrogen cycle, water use, etc.

    Thus, while it might be good to pick a general target of CO2, at say 350 ppm, it should be part of an overall Anthropocene Management effort that looks at all the ways humans alter the planet of which controlling CO2 levels is just one aspect.

    My bigger fear related to this is that things will get out of control faster than most might imagine, leading to ever greater instability in governments and societies around the world. You might see reactionary governments come to power who have no interest in climate control or the instability might cause some to "go it alone" in terms of attempting to geoengineer the planet. We could have geoengineering efforts that end up doing more harm than good. It would be like having 10 different doctors independently treating a patient without any consultation with each other. This all could be very counter productive of course.
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  27. I just finished listening to the Diane Rehm show for Aug 14th on NPR titled New Consensus On Climate Change. It was very frustrating to listen to Dr. Muller undermining the importance of climate change,and the proposed solutions.I suspect that he will be back in another 10 years telling everyone why we need emergency and drastic action to reduce greenhouse gasses and why he was justified in downplaying the importance of that message in the record breaking summer of 2012.
    It seems as though Muller has not really learned his lesson yet.
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  28. From the standpoint of education, I think the BEST result is great because of the following:

    BEST:

    250 years time span with observed 1.5 degrees C temp increase.Then experimental 40% increase in CO2 since indust revolution,gives
    C2/C1 = 2^(t1/3) ~ 1.4 gives t1 ~ 1.5 degrees C indeed AND

    SINCE 1980:

    Since 1980 from Keeling curve, to present now different C2/C1 ~ 1.2 then

    C2/C1 = 1.2 = 2^(t2/3) gives t2 ~ 0.75 degrees C a little higher than observed for that time frame but not bad

    SO two different ranges of time and temperature change pretty consistent with same climate sensitivity of 3 degrees C and you can show a physics trained but "climate physics challenged" audience that climate sensitivity of 3 is a robust experimental result that does not depend on a simulation to be proven. Without Muller and BEST going back 250 years this argument is much less strong.
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  29. I will try this place to re - post comments I placed elsewhere. The moderator suggested a change of thread. I am interested in the optimum way to explain AGW to an audience with some scientific background but who are not in the climate field.

    In the BEST graph, "Global Land Surface Temperature 12 - Month Moving Average" there is a logarithmic curve fit to the data, with downward spikes associated with named volcanic eruptions.

    1. There is a deviation of the data that is a peak above the logarithmic fit, for the years around 1940. Does anyone have an opinion as to what this deviation is? Perhaps the Atlantic Multidecadel Oscillation, although it seems there is some question as to whether the AMO exists or not?

    2. If I take many points on this curve fit that are away from the volcano spikes and plot the temperature increase since 1750 against the log to the base two of the CO2 concentration ratio, I get a nice straight line with a climate sensitivity of 3 degrees C. For explaining AGW to a scientist who is a non climate specialist, I think this is wonderful because it experimentally shows the 3 degree C.S. and therefore the fiddling around with cloud physics as done by Lindzen and Spenser is irrelevant. A general audience will not understand a detailed critique of - say - Spencer's tweaking. But they would understand that you get the 3 degrees C.S. without worrying about the clouds at all.
    3. Because you get the 3.0 degrees C.S. experimentally, you do not depend on a simulation to argue the case. Again....the experts know the simulations are fine. But a non specialist, even with a scientific background, does NOT know this. The result directly from the BEST data gets around the "No one can trust a simulation ever" denialist argument, which is - to the scientifically trained but non climatologist individual usually the most difficult denialist argument to rebut.

    I guess I am looking for comments because I have been invited to give an antidote presentation on AGW to people who have a technical background at a University where someone keeps inviting people like Monckton to present Heartland Institute misinformation. But what the heck....maybe the best thing to do is go ahead with it.
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  30. curiousd - Please take a look at the GISS model forcings, a combination of the best information on greenhouse gases, aerosols, and other influences. The net forcings are shown here.

    Note that the 1940's were the culmination of several decades of low volcanic activity, with anthropogenic aerosols increasing in the 1950's and volcanic activity ramping up in the 1960's. CO2 is not the only forcing - the climate response will be to the sum of all forcings, and a logarithmic, or linear, or pure polynomial curve would at best be only an approximate fit to the non-linear changes in those forcings.

    It is important to point out that the graph you pointed to:


    [Source]

    shows both the BEST data and a simple subset of forcings, "...a linear combination of volcanic sulfate emissions and the natural logarithm of CO2". I would consider that illustrative of overall trends, but again solar, anthropogenic aerosols, and other influences play a role too.

    Explain to your audience that there are multiple forcings in effect - but that as can be seen from the general trends, the anthropogenic influences are changing temperatures in ways that natural variation wouldn't.
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  31. Thank you KR. Your comments are most useful and encouraging.

    This website does an outstanding service in allowing scientifically trained non climate specialists to learn from experts in the field.
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  32. curiousd - I strongly suggest you look at the advanced version of "How sensitive is our climate". The instrumental record of very recent times is perhaps the least certain measure of climate sensitivity: if you include estimates based on paleo, volcanic, instrumental, last Glacial Maximum, etc., you have consilience for a 2-4.5C range, 3C most likely value. Consistent indications from multiple lines of investigation is very strong evidence. Show Knutti and Hegerl 2008 Figure 3 to your audience.

    Knutti and Hegerl 2008
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  33. Hi,

    I have taken all comments to heart and taken a step further. Indeed if I use the Best data from Fig. 1 above, starting from the time period when their data is plotted as well as land based GISS, Hadcru, and NOAA and simply determine the best linear fit to log base 2 of the corresponding CO2 concentration ratio versus temperature increase, I get a c.s. of 3 degrees C as BEST states they get.

    Now I have also considered the recent data from Foster and Rahmsdorf through 2011, which had the AGW isolated by multiple regression against indexes for ENSO, solar, volcanoes and which has a best straight line through the data drawn by those authors. Applied to that same straight line this simple analysis yields climate sensitivity of 1.94 degrees C, and it stands to reason it would be less than for the land based data from that BEST graph.

    The Arctic data shows a larger over all delta T than either world or land based from Best, but the Arctic data has a pronounced wiggle to it that makes it impossible to approximate with a simple model, IMO. I wonder if anyone is trying a multiple regression analysis for the Arctic data such as Foster and Rahmsdorf did for the global data?

    Finally, I presume the quantity I get by doing this simple procedure is called the "transient" C.S?
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  34. What am I to make about this guy Muller? To me he seems really inconsistent. Unless you take into account that he is often promoting natural gas and fracking. (before and after his 'conversion')

    He still uses his 'old ways' sometimes to diminish AGW, even after claiming that he is certain AGW is real. Why then is he still advocating the use of a fossil fuel? Even a method shown to be really devastating to earth's climate.

    One of the things that got me convinced that he is shady is his claim that 'hide the decline' is a reference to temperatures. This was a while after when the investigation of the scientists took place. It seems to me that he might be a covert shill for natural gas. The 'conversion' study was sponsored by Koch. He seems to be balancing on a tightrope.

    The study accomplished two things:

    1. Good for 'skeptical' public: there is a new independent study acknowledging antropogenic global warming. Deniers will have a hard time denying this. True skeptics in the general public will be more inclined to taking AGW serious.

    2. Good for Koch: there is a new 'trustworthy' scientist risen, who in order to curb global warming, is advocating the burning of Natural Gas and the 'clean' technique of fracking. Natural gas containing 80% methane. Methane: stays not as long in the atmosphere as CO2, but does have a greater greenhouse effect.

    What am I to make of this? Can someone explain why natural gas is a better solution than renewables. Muller seems to think it is the only real affordable option we have. Renewables are as of now too expensive. (what about nuclear energy?)

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  35. qinqo, my take on Muller is that he bought in to the whole 'climate change is a hoax' mythology hook line and sinker, but had enough integrity to acknowledge when his own research disproved (again, past research had done so before he ever started) one of those lies. Unfortunately, the same failures of logic and character which led him to buy into complete nonsense in the first place have also prevented him from thinking, 'Gee, I just made a fool of myself... maybe I should re-evaluate some of this stuff'... and thus he continues to make completely ridiculous claims on other aspects of the global warming 'debate'.

    Basically, if he has done research he'll go with what his data shows, but if he hasn't done the research he'll go with the 'skeptic' misinformation. It seems like he may think he is the only competent scientist on the planet... because he places the blog rantings of 'skeptics' above peer-reviewed research from the scientific community.

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