August 09, 2012

Climate Distortion

This week, with great fanfare,  NASA scientist James Hansen and associates released a paper "The Perception of Climate Change"  in the journal PNAS that claims that recent heat waves and droughts were caused by human-induced climate change.  To quote their abstract:

" It follows that we can state, with a high degree of confidence, that extreme anomalies such as those in Texas and Oklahoma in 2011 and Moscow in 2010 were a consequence of global warming because their likelihood in the absence of global warming was exceedingly small."

This paper (found here) has been quoted in hundreds, if not thousands, of media outlets and newspapers and has garnered the praise of many environmental advocacy groups.

The problem?  Their conclusions are demonstrably false and their characterization of the science and statistics are deceptive at best. 

And the problem goes beyond this unfortunate paper.  It extends to the way the media has misunderstood and miscommunicated our current state of knowledge of climate change.  No wonder the public is confused, skeptic/denier groups hold on to wacky/unscientific theories, and our leaders dither on climate change.  And let me repeat something I have said several times....I believe that human-induced global warming is both observed, real, and a serious problem for mankind.  So if anyone wants to call me a denier or some other ad hominem name, please refrain from such remarks.

Well, lets start with a little test.

The heat waves/droughts in the mid-section of the U.S. during past two years were caused by:

a.  90% natural variability and 10% human-induced global warming
b.  50% natural variability and 50% human-induced global warming
c.  10% natural variability and 90% human-induced global warming

Time is up!  Write down your answer.  As I will try to demonstrate, the correct answer is probably very close to (a).  90% of the temperature anomaly this and last summer is the result of natural variability with a minor assist from global warming.

Really different than the impression you are getting from Dr. Hansen and the media, right?  But it is the truth.

Let me prove to you now that Dr. Hansen's claims are  deceptive.  Consider the heat wave in  Texas/Oklahoma last year.  Below you will find the mean temperatures for July and August over the U.S. (top panels), while below are the differences (anomalies) from normal (or climatology).  The anomalies were over 8F in July and over 7F in August.

How big could the global warming signal be?  And particularly the warming due to mankind's emission of greenhouse gases?  The IPCC is the world scientific body that has examined such questions.  They note that human influence should have become significant somewhere in the mid-70s and the generally accepted estimated of the warming of the Northern Hemisphere since then is roughly 1F or  C (see IPCC graphic below).

Now this warming could well include some component of natural warming (particularly since there had been warming since the end of the 1800s).   But lets assume it is all due to human-emitted greenhouse gases. The full one degree F.

But what about Texas and Oklahoma?  The hemispheric value includes the Arctic over when the IPCC has shown the warming is far larger than anywhere else (due to melting sea ice for one reason).   Here are the temperature changes over all of Texas for June to August.   A big spike in 2011...but what about the long-term trend?   ...that would be the trend associated with global warming.  Nearly flat, but perhaps we can convince ourselves there was a small upward trend since 1970 of perhaps .5-1F.   And remember these observations are contaminated by urban heat island effects.

So I think you can see that the global warming signal due to human-emitted gases could not possibly be more than 1F, and is probably much less.  Yet the heat wave last summer, expressed as monthly anomalies, reached 7-8F over large portions of Texas and Oklahoma.

What can you conclude?  Something other than global warming produced the lion's share of the heat wave...and we know what it was:  a major change in the circulation over the U.S. last summer.  A big area of high pressure and high heights over the center of the U.S. The graphic below shows the differences of the upper level (500hPa) heights from normal over the U.S.  for last summer.  Green indicates above normal heights (a ridge) and blues indicate lower heights (trough).   So last summer we had a persistent pattern of mid-continental ridging and troughing on the coast.  This summer has been the same.  The upper level flow pattern has amplified in a wave-like way.

And there is no reason to think, based on theoretical or observational research that this is anything but natural variability. 
To put it another way: in July of last year, at least 7/8th (87%) of the warming was due to natural processes, and the truth surely was well over 90%.  It is funny that Dr. Hansen and others exaggerating the effects of human emissions don't say it this way.  The correct way.
The media, repeating this stuff, provides deceptive storiesy to their readers.  And the damage to the credibility of my profession is huge.

As an aside, the journal that this article was published in...the Proceedings of the National Academy of Sciences (PNAS)...allows members of the National Academy (like Dr. Hansen) to publish articles with essentially no peer review.  Until 2010 they could publish anything, with no peer review, and most recently the submission review is "supervised" by the submitting academy member WHO GETS TO SELECT THE REVIEWERS. Folks, this is really unfortunate for an entity that claims to be national journal of some reputation.  The result has been a lot of very bad papers in PNAS that would never have been accepted in real journals,with a real peer review process.  One could use stronger words, but this is a family blog.

So you think these exaggerations of Hansen and his fellow-travelers is bad enough?  It is much worse than that.   They spend a lot of time talking about statistics (bell curves) and how warming is producing more extremes.  But they don't give folks the straight story...let me explain.

Many atmospheric and other variables follow a bell curve (a.k.a. a Gaussian) in which most observations are near the mean and then the frequency drops away towards extremes on both sides (see graphic).  So the probability is highest that the observation is near the mean and probabilities drop for higher and lower values.  An important aspect of the bell curve is the standard deviation (indicated by Greek letter sigma).  You can calculate this number from the observations (I won't go into that here, but it is straightforward and in all statistics texts).  Turns out the that if the observation type is well described by a bell curve (and temperature generally is), 68% of the observations should fall within one standard deviation (one sigma) of the mean (both above and below).  The graphic shows this with the dark blue color.  Roughly 95% should fall within two sigma of the mean (dark plus medium blue), and roughly 99% within 3 sigma.  So very few observations..the most extreme should fall more than 3 standard deviations from the mean.

 Now as the earth warms up the temperature variations shown remain like the bell curve...or Gaussian, but the mean should shift to warmer temperatures (see the figure below). The result is that you get more warm extremes and less cold extremes (less cold extremes are not mentioned very often for some reason).

So the result is that you seem more warm temperature records and less cold temperature records.   We are in fact seeing this.  The earth is warming and there are more maximum temperature records than cold ones.  Hansen and friends make a big deal about this.

But what they are not telling you is that the very warm anomalies we are seeing today would have been nearly as large if global warming had never occurred.  In his paper he makes a big deal about large (three sigma) anomalies from climatology.   Well, without any global warming the anomalies might have been say 2.8 sigma.   Or in terms of terms, heat waves of 10F might have been only 9F if global warming had not occurred.  To say it differently, the impact of global warming due to greenhouse gases is still small compared to natural processes, and the impacts to society would have been pretty much the same.  But you never hear it this way.   Those exaggerating the global warming signal imply that we are going from normal conditions to extremes due to global warming.  In reality, we go from naturally induced extremes, to a bit stronger extremes due to global warming.

Let me say it am alternative way. You can see from the bell curve that the probability of a certain temperature changes rapidly when you are on the sides of the bell curve.  So if the bell curve shifts warmer, you get a big change in the probabilities of high temperatures.  So you get a lot more records even if the warming...and the impacts of the warming...are not that large.

Lets be clear here.  Although the global warming signal is relatively weak today in most of the planet (outside of the Arctic), our best science indicates that the warming will greatly increase by the end of the century.  At this point, the human-induced warming will be much more comparable to the natural variability and our climate will truly be different.

Unfortunately, a very limited, but highly visible, group of scientists like Hansen are choosing to tell a story that is not supported by the facts, with a media that is happy to amplify such claims.  Global warming due to greenhouse gas emissions of mankind is a very serious which our civilization is not dealing with in an effective way.  But scientists must give society the straight facts and not shade or exaggerate the facts based on our personal views on what should be done.

Announcement: Columbus Day Storm 50th Anniversary Gala at the UW: Oct. 11, 7:30 PM

On Thursday evening, October 11 at 7:30 PM, the UW will host a gathering to review and remember the 1962 Columbus Day Storm (October 12th will be the 50th anniversary).  I will discuss the major aspects of the storm and windstorm chronicler Wolf Reed will tell even more.  The Mt. Hebo radar dome broke apart that night as winds gusted above 150 mph, and we will have an eye witness account.  And there will be time for your comments, questions, or stories.  Steve Pool of KOMO TV will MC.  This meeting should be great fun will take place in Kane 120 on the UW Seattle campus.  You need to register for this if you want to go, since I expect it to fill.  To do so, go here.  The gathering is free, but the expenses are being covered by my research fund, so any contributions to offset the costs are very welcome. 


  1. Cliff - my understanding of the linkage here is that anthropogenic warming is contributing to climate instability, resulting in more local extreme weather, I.e., higher highs and lower lows IN CERTAIN PLACES. Obviously one degree is less than eight degrees, but man made heat is not injected into the environment uniformly, so averaging out the contribution to a global one degree may not be valid.

    I'm not a climate scientist, just trying to make sense of all the competing claims on this issue. From a lay perspective, one does pause when a local university prof calls BS on NASA and its associated resources. Are you really smarter than all the climate people NASA is relying on, are you off your rocker, or has politics poisoned the message? See what I'm saying?

    I believe that global warming is real; beyond that, I don't believe much of anything anybody points to in terms of concrete examples of warming effects. "Hottest July ever" is meaningless, other than that something is going on, but too many arbitrary numbers are being plugged into generalised best guess equations for us to have more than a rudimentary inkling that something is up.

    Thanks for a thought-provoking post!

  2. So, one problem I have with being extremely cautious about declaring whether observed weather conditions are the result of human caused climate change is the same as I have over waiting for an official statement that an economy is in recession. It is all based on backward looking data, and a clear declaration only comes well after it is totally clear to everyone that it has happened.

    Example is a recession in the US, which happens after the US economy has contracted for 2 consecutive quarters, and the measurements are not finalized for at least 3 months. So we have economists saying "we are in a recession" well after everyone else can see it. The formal definition makes it impossible to announce when one has started, and can only be confirmed well after the fact.

    I guess I see the same thing here. Yes, I understand what you are saying regarding the statistical nature of the weather anomalies we've seen. The # 1 driver is most likely natural variability. And yet these anomalies also conform to many of the major climate projection models. So when people see weather that conforms to those predictions, they see a connection. And I’m not sure that means they are wrong….they just can’t prove single event causality.

    But I do have to say that we could be well on the way to a warmer planet before I see complete agreement that we are seeing cause and effect.

  3. I haven't read the paper but it seems conceivable that global warming could increase the standard deviation in addition to shifting the curve. If not uniformely than definitely in some places (some places could instead come into more regular marine influence, for instance, and have their std dev decrease). I remember you were studying the effect of climate change on blocking patterns, but what about amplitude or strength of the jet stream? A more vigorous jet stream would seem to lead to more extremes (on both ends, but more likely on the hot side due to the sliding curve). I don't think it's a slam dunk case that climate change is "responsible" for recent high-profile weather events, but I don't think it's a slam dunk case that it's not either.

  4. I applaud your expose of the subterfuge of Hansen et al! However, I'm surprised at your belief "...that human-induced global warming is both observed, real, and a serious problem for mankind." This belief will remain untestable and thus unscientific until the statistical population underlying the model by which one reaches this belief is identified. So far as I've been able to determine, the idea of a statistical population is foreign to the field of climatology. The climatologists of IPCC Working Group 1, for example, reference no statistical population in reaching their conclusions.

  5. Cliff, I believe your view of climate change is overly simplistic. You yourself say the Arctic is warming much faster than the lower latitudes. Do you really think this significant change in N-S temperature gradient will not have a significant effect on weather patterns? The current science, as I understand it, is that it does. It results in a slowing of the mean W-E jet speeds (which makes sense) making for more amplified, stagnant patterns. These cause more extremes (records), and more persistent blocking patterns (droughts, floods). Statistically, this means not just a simple 1F shift of the temperature distribution, but a stretching of the bell curve, leading to even more extremes. Further, when you change the far ends of the bell curve, you make huge changes to the statistics. It makes *unprecedented* heatwaves, like the ones we've been seeing, into 1 in 30yr events instead of 1 in 3000yr events. So while pushing the extremes out "a bit" further might not sound like a big deal, it is. Especially when your infrastructure that is engineered for 1 in 100 yr events, is now seeing 1 in 1000 or 10,000yr events. This shifting and stretching of the bell curve is not just in the models, but also in the observations: (you'll love me for posting a [presumably] unreviewed Hansen paper, but it's the best I could come up with in a few minutes, see figure 4).

  6. Cliff,

    I think it's a little disingenuous to use a blog to combat Hansen's paper - it is after all a peer-reviewed research paper. One of the big problems with the 'denialist' side is that they refuse to release peer-reviewed papers and instead proceed to do 'blog' research.

    I'm a big fan of your blog but I just want to make sure the same things done by those on the anti-science side are not done here. Laymen such as myself see a blog on side (albeit from a very respected source!) and a peer-reveiwed research paper getting a lot of traction among big names like NOAA, and Hansen has contributed a lot to the field.

    I guess I could say my concerns are, with a peer-reviewed paper, you would expect them to have taken into account the concerns you quickly bring up, concerns that seem to be pretty glaring if true.

  7. There are a number of fundemental flaws in your reasoning here. You base your argument on the notional model that events can be linearly decomposed as 'global warming' + 'weather' and that weather is unchanging and that all that matters is the ratio of the GW part and the weather part with respect to some baseline.

    The last part of this is your value judgement and is neither universally shared nor the subject of Hansen's paper, and for the initial science statement, you mischaracterise what the expected GW signal is and ignore the fact that extremes may have non-linear behaviours.

    Starting with the expected GW signal - this cannot be derived from the observed (noisy) data directly. Any specific data series is a combination of the stochastic 'weather' and climate change (though you cannot assume they are independent). Thus any trend through this data is affected by the signal to noise ratio. The climate change trends will be hardest to see in noisy environments and will have large error bars depending on the statistical structure of the noise. At larger scales, the weather tends to cancel out more and the signal (for instance at the global, hemispheric or continental scale) will be more robust. Additionally, estimates of what the ratio of the Texan GW signal is expected to be relative to the global mean change will involve the land-ocean contrast and the amplification in mid to high latitudes with respect to the topics. Judging from IPCC AR4, summer temperatures in Texas should rise at about 50% more than the global value (eyeballing from chp 10 in AR4).

    Secondly, you completely neglect the possibility that there are non-linear feedbacks at play - via soil moisture, aerosols, and conceivably, fires etc. - that amplify the strongest heat waves. In which case a shift of the mean produces more than an expected change at the extremes.

    Thirdly, you mischaracterise what is being claimed. Hansen's analysis is related to the frequency of 3sigma+ events across the hemisphere, for which he provides compelling evidence that they have greatly increased over the last few decades. It then follows that any specific event (whether in Texas or elsewhere) is far more likely than it would have been. The area ratio of affected regions appears to be about 30 - though the exact ratio for specific kinds of events depends a little on what you define as an independent event. Thus claims of causation are being based on a threshold. Your objection to this is based not on a critique of the calculation, but rather a redefinition of what matters.

    Jumping to an analogy for a minute, I think your definition of causality based on the ratio of the GW to weather temperature anomalies over a baseline, would be totally fine if the importance of the event went like the integrated sum of these anomalies. An example that would fit this model would be someone collecting marbles or some other countable thing. However, the impact of extremes is not linear like this - 20 days at 85 deg F when climatology is 80 deg F, does not have anything like the same affect as 4 days at 105 deg F, or 2 days at 130 deg F! And this goes for crops, water supplies, human health, power supplies etc.

    Thus threshold definitions are far more of a natural fit to this problem, and the analysis from Hansen is perfectly valid. You cannot argue he is misleading because you choose to only care about a metric he doesn't address.

  8. Still not sure why we should be more afraid of another MWP than an LIA. So heat waves reduce economic output. How about cold spells? Any studies there? Or are we still waiting for one? If we've prevented them, then jolly good!

  9. Is studying and making findings on a one year or 100 year trend in a 6 - 8 billion year variable system not questionable on the false premise of trends?

  10. To Branden: Hansen's paper wasn't peer-reviewed in any strict sense and to label it such is to all but entirely gut the notion of peer review.

    To Cliff: I applaud your post, disagree with some of your notions, but that's fine. I was disappointed to see you write that the IPCC is a "scientific body." The IPCC is composed of roughly 1600 (number goes up and down) people, most of whom are highly paid bureaucratic hacks with no science credentials. Last I knew was that there were 63 actual scientists on board, not enough to lay valid claim to being a scientific body. Check it out if you don't believe me. The IPCC is about nothing if not politics, especially if you look back on its intellectually checkered history.

  11. The truth or YOUR truth, along with BP, Texaco or which other one YOU prefer?
    I understand Gov.s not wanting to go against petrodollars and that a lot of wise men give their "disinterested" help to maintain the petrodollar idea in place.
    Sorry, but I don't agree with you.
    I just read that this has to be approved by you, so I know it will not appear on your page.

  12. "I believe that human-induced global warming is both observed, real, and a serious problem for mankind."

    "The IPCC is the world scientific body that has examined such questions. They note that human influence should have become significant somewhere in the mid-70s and the generally accepted estimated of the warming of the Northern Hemisphere since then is roughly 1F or C (see IPCC graphic below)."

    Thank you for highlighting the corruption of Hansen et al. They are as shameful as the MSM are critically delinquent.

    Nevertheless, you state you 'believe' in AGW. If you mean 0.155C/decade (Watts et al. awaiting publication) please explain what empirical evidence demonstrates the anthropogenic signature, and what you 'believe' the value of climate sensitivity to be?

    You state that the IPCC is a scientific body. It is not and never has been. In its own words and by the admission of its Chairman, it is a political body - always has been, always will be. Science by politics and consensus is not science.

    In my view, Hansens' article is simply about weather - not climate. From Someone who tried to re-write climate history (eradicate the historical warm periods) to amplify the appearance of present day warming, which is indistinguishable from previous warming periods, has confirmed their corruption and intellectual bankruptcy.

  13. The true scientist does two very important things missing from a lot of AGW papers:
    * he strives as much as possible to be indifferent to the implications of his conclusions, because such thinking tends to become tainted by emotional concerns
    * he tries to DISPROVE his hypotheses, not prove them.

    The problem with a number of AGW climate workers is that their mindset is not truly scientific -- it is advocacy and policy oriented. Some amateur AGW scientists have outright admitted that the scientific community should "dumb down" the science to make it easier to use to motivate the public to push for political change.

    And that's exactly how I would characterize the way Hansen's paper was sold by the media. So, extreme events are now "more likely"? How much more extreme? How much more likely?

  14. Could it be possible that some natural climate events like El Nino, La Nina, etc be magnified or lessened due to anthropogenic warming over time? If so, how long would you need data for to see those anthropogenic warming influences on natural climate events?

  15. George: "research paper published Monday in the Proceedings of the National Academy of Sciences."

    Is that not a peer-reviewed journal? If not then I retract that part of my comment.

    Fred - citing Watts. You should know better (and if not, then read up a little).

  16. Cliff, I have to say that your points here are missing a critical concepts with regards to statistics and climate variability. These points you have missed are actually clearly explained in Hansens paper and I would suggest that you read the paper before attempting to dismantle it. The paper is available at:

    First, one key point that you have missed has to do with probability and normal distributions. I take directly from Hansen's paper, "The tails of the normal distribution (which we illustrate below) decrease quite rapidly so there is only a 2.3% chance of the temperature exceeding +2σ, where σ is the standard deviation, and a 2.3% chance of being colder than −2σ. The chance of exceeding +3σ is only 0.13% for a normal distribution of variability, with the same chance of a negative anomaly exceeding −3σ."

    Second, as has been pointed out by other comments, with global warming are seeing not only a upwards shift in the mean of the distribution but also an increase in variability and thus the width of the distribution. Taken from Hansens paper, "The global mean of the local standard deviation of June–July– August surface temperature increases from 0.50 °C for 1951–980 data to 0.58 °C for 1981–2010 data." We can see this widening clearly in Hansen's figure 4.

    Please look at Hansens figure 4. Hansen explains, "The probability distribution shifts to the right in each successive decade in the past 30 y and the distribution becomes broader, with the broadening adding to the increase of hot anomalies. Occurrence of 3σ, 4σ, and 5σ anomalies, practically absent in 1951–1980, is substantial in the past decade, consistent with the large brown areas in Fig. 3."

    If you put these two points together and simply look at figure 4 and figure 3, the probability of these extreme events occurring is far less than 0.013 without global warming. But with global warming, these events are now not extraordinary at all.

    Hansen concludes, "One implication of this shift is that the extreme summer climate anomalies in Texas in 2011, in Moscow in 2010, and in France in 2003 almost certainly would not have occurred in the absence of global warming with its resulting shift of the anomaly distribution. In other words, we can say with high confidence that such extreme anomalies would not have occurred in the absence of global warming."

    Overall, Cliff, it seems that you understand many of the fundamentals. But remember that your words posted here are available to all including those who don't have the background to understand your points and thus can easily be misled. Some of the comments already posted here have sensationalized your own statements, beyond what I think you may have intended. I think if you do some more reading and educate yourself further before posting on these topics, you will avoid lessening public concern when in fact, Hansen's points are very valid and quite frightening.


  17. I buy your argument that "a major change in the circulation over the U.S. last summer" was the primary cause of the heat anomalies. However, like others, I wonder if AGW would have an influence of some sort on that circulation, increasing the likelihood in some places like Texas of further heat waves like what was observed.

  18. NAS member don't have to pass peer review when publishing in PNAS, and Hansen's paper wasn't. It's being widely criticized by both sides of the debate.

  19. 1) "The heat waves/droughts in the mid-section of the U.S. during past two years were caused by ..."

    My immediate reaction was, wrong question. It is absurd to try to divy up responsibility in this way. Weather is chaotic. Famously, the flap of a butterfly's wing of the coast of Hong Kong can cause a hurricane of the coast of California (except cause is the wrong word there too). If we could run a parallel world experiment, one with global warming and one without, both would experience droughts and floods etc, but they would not experience them at the same time and place except coincidentally. The correct question is, has global warming changes the return interval of certain types of events, and events of a certain intensity. No other approach to the question of extreme events is, or even could be, scientific because of the stochastic nature of weather. Curiously, that is exactly the approach Hansen takes.

    2) "So I think you can see that the global warming signal due to human-emitted gases could not possibly be more than 1F ..."

    Cliff Mass needs to learn the meaning of the word "mean". The mean temperature increase in Texas is about 0.5 C, but the mean is the average. The mean summer increase is different from the mean winter increase, both being different from the mean annual increase. Likewise, the mean nighttime increase differs from the mean daytime increase. It is certainly possible that the mean increase for different types of weather events also difer from each other, and from the mean annual increase. Quoting the mean cannot tell you that. Cliff Mass does not appear to even grasp this possibility, let alone present evidence for it. If the average increase of temperature during blocking events was 2 C in Texas, while the average durring all other types of weather was lower than 0.5 C, so that given the frequency of blocking events the average increase was 0.5 C, then in a blocking event caused heat wave with tempeatures 4 C above the mean, global warming would have been responsible for 50% of the additional heat, not 10% as claimed by Cliff Mass.

    In essence, Mass's entire argument is bases on the assumption that the variance in temperature increase across weather patterns is zero - an extraordinary claim for which he provides no evidence.

    3) On a related point, it would certainly be possible to determine the mean temperature increase in Texas for blocking events for the period of climatology. If Mass's argument had any validity, it would be perfectly acceptable to deduct this value from the temperature increases for Texas 2011, and assign the difference to global warming. The result would not by to assign only 10% of the increase to global warming. (Of course this would also be a bad argument for the same reason.)

    4) "[T]he impact of global warming due to greenhouse gases is still small compared to natural processes, and the impacts to society would have been pretty much the same."

    An increase of 1 degree C from 26 to 27 C is barely noticable for a resident of Brisbane. An increase from 29 to 30 C, however, results in an appreciable increase in discomfort. An increase from 34 to 35 C has an even greater impact on comfort. The closer the temperature comes to the core body temperature, the greater the impact of each degree C on our ability to cool ourselves and we progress from taking slightly less strenuous efforts to keep cool to, in the end, requiring the entire devotion of our day (or massive expenditure on electricity if we have air conditioning) to keeping cool simply so we will survive the day. A 0.6 C increase in temperature can make the difference between a hot spell and a heat wave; and between a heat wave and a heat wave that is likely to cause a significant number of deaths.

    In this regard, Hansen's classification in terms of extreme events is far more usefull than Mass's attempt to downplay the increase.

  20. Cliff Mass
    Compliments on restoring integrity in climate science.

    To further your argument, I recommend addressing climate persistence as quantified by Hurst-Kolmogorov dynamics.
    e.g., K. Koutsoyiannis and Montanari 2006 found that natural variance quantified by HK dynamics is about twice as large as estimated by conventional statistics.

    See slide 10 in Hurst Kolmogorov Dynamics in Paleoclimate reconstructions 2010
    e.g. for Vostok 2.62 vs 5.80

    See further papers on Hurst Kolmogorov Dynamics

  21. Cliff Mass has made the assumption that the spread in temperatures would not change, in his argument that an increase of 1F in the Temperature anomaly could not be a significant factor in the recent US heat wave which saw an anomaly of 7-8F.

    It seems Mass has neglected the data in figure 4 of Hansen's paper. Hansen shows curves of local temperature anomaly distribution for each decade since 1951, measure in units of the local grid's standard deviation for various time periods including the 30 year base period between 1951-1980.

    The reduction in peak height between the first decade 1951-61, and the last decade shows how the peak occurances have declined and the number of occurences of extreme heat have increased. The result is that the extent of local regions affected by extreme heat has increased enormously with time as the climate has warmed. The increase in the area of the globe experiencing extreme heat is an important phenomenon, and will impact humans through its effect on crops, and the survival of pests.

    Hansen's paper shows that Cliff Mass's assumption is wrong and his argument that Global warming cannot have a significant effect on extreme temperature fails.

  22. Well after we are all dead, it will probably be accepted that human activity caused significant global warming.

    The situation is hopeless.

    Many people do not believe it, don't want to believe it, or could care less.

    The human race will not take significant action to prevent global warming.

    It will not happen.

    Even those who accept the theory are bad-mouthing others who accept the theory.

    What a sad joke.

  23. This article correctly points out that the natural variations in climate are huge.
    The implication is that we cannot know with any degree of certainty that we have caused a big warm up, until it is very late in the game.
    This is a great dilemma for scientists who are taught to be skeptics regarding data analysis- and drawing conclusions from limited data points.
    In essence, the general populace is hoping scientists will take a guess, from which policy can be prescribed.
    That threatens scientific credibility, and is really not the role for science.
    Playing with fire, literally, we are.

  24. Eadler...take a look at Hansen's Figure 2. The summer standard deviations hardly change...particularly over the midlatitudes. Those Gaussians he shows seems inconsistent with Figure 2.

    A lot of comments...when I have some time I will try to answer more..cliff

  25. The recent high temperatures weren't even as high as they were in the '30s

  26. We don't have a statistical population of planets to experiment with, but some of us have grandchildren who we care about.

  27. AfterMr.Hansen appeared on the PBS News Hour the following comment was posted:

    While parts of Europe, Scandinavia and the UK are experiencing a wetter,cooler summer and parts of Europe suffered a brutally cold 2011-2012 winter, Mr.Hansen is given the time to talk about weather, not climate, and present the current hot conditions in the USA as if it is a world wide warming trend.
    The idea that there is a global temperature reporting system is a pipe dream as the number of world wide reporting stations has decreased dramatically over the years.
    "The University of Delaware has an animated movie of station locations over time [].
    There is a very limited number of reporting station in the Southern Hemisphere covering South America and Africa and few in the Arctic and Antarctic areas.

    The bulk of the reporting stations are in the Northern Hemisphere centered in the US and Europe and are in the hands of government entities NASA/NOAA/GISS in the US and the CRU in the UK.
    Both use unspecified methodology to correct, massage or manipulate the measured temperatures both current as well as past data. AGW is truly man made in government facilities.
    As Einstein is reported to have said "If the facts don't fit the theory, change the facts."

    Also Mr.Hansen ignores a recent study that concludes that global cooling has been occurring for millennia.
    Orbital forcing of tree-ring data.
    Nature Published online 08 July 2012.
    "Here, we present new evidence based on maximum latewood density data from northern Scandinavia, indicating that this cooling trend was stronger (−0.31°C per 1,000years, ±0.03°C) than previously reported, and demonstrate that this signature is missing in published tree-ring proxy records. The long-term trend now revealed in maximum latewood density data is in line with coupled general circulation models7, 8 indicating albedo-driven feedback mechanisms and substantial summer cooling over the past two millennia in northern boreal and Arctic latitudes. These findings, together with the missing orbital signature in published dendrochronological records, suggest that large-scale near-surface air-temperature reconstructions9, 10, 11, 12, 13 relying on tree-ring data may underestimate pre-instrumental temperatures including warmth during Medieval and Roman times."

    The temperature reconstruction chart is found here:
    Perhaps the Newshour could have a reputable non-government employee or
    non- government funded academic present the case for natural occurring hot, dry weather in the US similar to the 1930s Dust Bowl.

  28. Cliff, I will take issue with your last graph. You can have a shift in the average temperature to being warmer WITHOUT it getting hotter at the right side simply by having the bell curve narrower. That is, shift to short mild winters, but leaving the summers the same. In fact, in Canada that is exactly what is happening. Deep cold winters are rarer today than in 1900. Yet the number of hot days (over 30c) has been reduced by 1/3 since 1930. That's what the data from Environment Canada shows.

  29. " global warming could increase the standard deviation"

    In the last graph no. Standard Deviation is the measure of the width of the bell curve. The higher the SD the wider the bell curve. If the bell curve does not change in shape but shifts left of right, there is no change in the SD. However, if anything a warming world would have a narrower bell curve, lower SD.

  30. Cliff, thanks for a sober account of facts.

    The climate shift figure is widely used, so I decided to make one with the real shape of a 3°C shift, as it happens reality is not that scary:

  31. Jack, not true. PNAS says:
    The standard mode of transmitting manuscripts is for authors to use Direct Submission. Authors must recommend three appropriate Editorial Board members, three NAS members who are expert in the paper's scientific area, and five qualified reviewers. The Board may choose someone who is or is not on that list or may reject the paper without further review. Authors are encouraged to indicate why their suggested editors are well qualified to handle the paper. A directory of PNAS member editors and their research interests is available at The editor may obtain reviews of the paper from at least two qualified reviewers, each from a different institution and not from the authors' institutions. For Direct Submission papers, the PNAS Office will invite the reviewers, secure the reviews, and forward them to the editor. The PNAS Office will also secure any revisions and subsequent reviews. The name of the editor, who is to remain anonymous to the author until the paper is accepted, will be published in PNAS as editor of the article. Direct Submissions are published as “Edited by” the responsible editor and have an identifying footnote.

  32. Its a pretty sad science if you have to make a declaration of faith on global warming before you can critique. Are you suggesting criticism isn't valid if you couldn't make that declaration?

  33. The Hansen, Sato and Ruedy paper provides intertesting stats on anomolies, but other than saying that the anomolies are related to global warming they leave out the mechanics of how the anomolies are produced. They simply presented the anomolies. I am not sure how overall helpful this paper is other saying yes there have been more hot anomolies compared to the base period they used.
    However, others have suggested that these anomolies are more related to global warming impacting circulation and the development of more and longer lasting blocking events and have presented very plausible mechanics in how such paterns develop with a warmed Arctic(Francis and Vavrus,2012).
    I think it is worthwhile to attempt to improve the public's understanding of blocking events leading to extreme weather. Indeed, the media has that is being so often maligned has presented the ide that there will be winners and losers with parts of the globe impacted more severely than others
    Here is my question Cliff: Is acceptable to suggest that the freuency of these types of blocking events and severity may already be influenced by the overall minor global warming? And Is it reasonable based on global warming modles to expect that these types of long lasting blocking events will increase as the Arctic regions go through major changes due to ice melt?

  34. Thank you, Dr. Mass, for another informative and detailed post. Having worked (in the past) in a job where we studied past climates, I really enjoy reading this stuff.

    I am afraid, though, that many people are more interested in being strident than in being factually correct. And, unfortunately, that doesn't seem to be limited to one side of the political aisle or the other.

    Keep fighting the good fight!

  35. Unknown will probably say that Hansen's radically false paper is good because it heightens awareness. The sane amongst us agree with Cliff. It's much better to simply pursue the real science and let that guide policy. Claims that it is too late are complete bunk. Climate is only one of dozens of serious problems that confront humanity. Everything must be put in to perspective and scarce resources balanced appropriately.

    Chicken Little should be grilled and served up in sandwiches.

  36. The air-ocean climate models generally have a consensus of higher variability around whatever average temperatures occur as a feature of the warming. This means that the warmer extremes will be more significant. Larger swings around the higher average are consistent with that.

    Second, even a 1 or 2 degree C contribution to the mean warming of the Northern Hemisphere implies much larger effects in the middle and upper latitudes. I'm not disagreeing with the general tenor of the entry, though, which is that too much "overinterpretation" is occurring this summer.

    But this would mean that the meteorological/climatological patterns responsible for the temperatures should be such that meteorologists would be able to identify them as "warm patterns." That was poorly put, but to express it another way, the decrease in pole to equator temperature gradients should yield more "low index" (highly meridional) patterns...similar to the fixed pattern this summer that resulted in the ridging over Greenland and the East Coast.

    While any one pattern or anomaly certainly cannot be used to cry "...see, this is global warming...", I think the pattern we had this summer is consistent with what climatologists expect to occur. Of course, we will all be long dead to prove this.

    Finally, I am looking all over for the journal article that had the consensus of the climatological models that had essentially no natural increase in mean temperatures (and variability) from the early 20th century on....and then inclusion of the impact of Greenhouse gases essentially produced curves that look very much like the temperatures that have occurred.

    I'm not disagreeing with the general tenor of Cliff's posting here....but think that there is more to this warm event this past summer than meets the eye.

  37. There seems to be some confusion about whether the Hansen paper is peer-reviewed.

    Above, Schoedinger quoted the PNAS review method for Direct Submissions. The direct submission method is a normal peer review. But Hansen's paper appears,to be a Contributed Paper. See The section "contributed submissions" at .

    The PNAS member/author himself selects two reviewers and provides their comments to PNAS. The only apparent limits on this "pal review" is that the two reviewers chosen by the author cannot have collaborated with the author of the contributed paper within the last 24 months.

    If the paper is, as it appears, a contributed paper then it is NOT peer-reviewed in the normal sense.

  38. 43Overall, I endorse the notion that only some relatively small fraction of the anomalies can be attributed to AGW - it should be evident that assigning numbers to that is ... complicated. It seems difficult to find ground upon which most can agree. From my perspective, one year's worth of weather doesn't allow us to say much about how AGW contributed - many of us have been battling the deniers on this very point, so it would be hypocritical to do similar things. On the other hand, when we begin to accumulate year after year of record-breaking heat, it seems evident that some signal is evidently emerging from the large variability.

    Whatever else one might think about his blog, Prof. Mass has surely provided some thought-provoking perspective. It's not evident to me that dropping media bombs in some sort of 'shock and awe' campaign is doing the cause of seeking mediation of AGW much good.

  39. Hi Cliff, I read the Hansen et al. paper today. One of the main points they make is that *sigma* is increasing with time (the bell curve is getting wider). It is more than just the shift. You don't seem to address this in your blog.

    Your points about the PNAS peer-review process are sobering.

  40. Gary...look at his figure 2 (which shows the standard deviations) and tell me whether it looks like the standard deviation over the U.S.--or over most of the U.S. is changing...doesn't look that way to me. The Gaussians they show are for the whole hemisphere...and they look funny. This is something that would have been caught BEFORE publication if the paper was properly reviewed...which it obviously wasn't...cliff

  41. Cliff, There is some increase even in the global sigma (0.5 to 0.58), but the lower set of panels in Fig. 4 show the analysis just using NH land data (due to data issues over water). The frequency distributions grow wider with time by decade in Fig. 4.

  42. A few things need repeating:
    1. Hansen's paper was NOT peer-reviewed.
    2. Cliff is not the only scholar questioning the attribution of extreme weather to anthropogenic global warming. Many articles question such a link. E.g.:
    Kenneth E. Kunkel et al., Monitoring and Understanding Trends in Extreme Storms: State of Knowledge
    The authors find no significant trends in severe thunderstorms, overall ice storms, or change in the percentage of the contiguous US impacted by extreme snowfall; trends in tropical cyclones are controversial and indeterminate. The authors state that "attribution of trends to anthropogenic forcing [man-made global warming] remains controversial."

    In fact, the claim that extreme weather is on the increase is actually not borne out by facts, if one takes the trouble to look at the historical record. E.g., a paper in the Geophysical Research Letters finds global cyclone activity at an historical low:
    Ryan N. Maue
    Recent historically low global tropical cyclone activity,
    "In the pentad since 2006, Northern Hemisphere and global tropical cyclone ACE (cyclone energy) has decreased dramatically to the lowest levels since the late 1970s. Additionally, the global frequency of tropical cyclones has reached a historical low." 

    The recent trend to talk up "extreme weather" seems to be an attempt to compensate for the lack of GLOBAL warming in the past decade. It may be warm or hot in the midwest US, but that's not much more than 1 or 2% of the planet. During the US hot spell, it's been very cold in the southern hemisphere (and rather cool in the Pacific Northwest).

    3. We have to keep in mind that the attribution of global warming to man-made causes is mostly the result of ideological and political machinations, not the expression of scientific research. See Bernie Lewin's detailed and eye-opening 3-part series on the wranglings about attribution in Madrid 1995 at Enthusiasm, Skepticism and Science.

    4. In fact, attributing whatever warming has been going on to CO2, let alone human-produced CO2, ignores that fact that when the IPCC was created, its members were charged with investigating the effects CO2 on the climate, without considering the possibility that
    a) the observed warming might be due to natural causes, and that
    b) there are many factors other than CO2 that contribute to the climate.

    One interesting paper in this respect is Barnett et al, "Estimates of low frequency natural variability in near-surface air-temperature."

    Also interesting and encouraging is the fact that a report by the Research Council of Norway (“Norwegian Climate Research: An Evaluation), stresses that a good understanding of the climate system cannot be reached without a dedicated effort to understand the contribution of natural processes to climate change.

    5. When we talk about peer review, we have to keep in mind that it is actually quite often "pal review" instead, as clearly revealed by the Climategate emails (in fact "pal review" has unfortunately be documented to be quite common in disciplines other than climate studies). This has led Andrew Revkin to acknowledge that the work of some bloggers (e.g., Steve McIntyre) contributes much more to scientific rigor and integrity than the vaunted "peer review."

    Cliff is doing a service to science and to readers of his blog by raising objections to some mostly unsupported claims (unsupported and at odds with other scientific results which they ignore) which the media eagerly parrot and feed to an unsuspecting audience. I for one do want to keep my eyes open and refuse to be included in the parroting sequence. I can only do that with the help of people like Cliff Mass, Steve McIntyre and a few other well informed and qualified bloggers.

  43. Gary
    I understand...but look at figure 2...there the standard deviations don't seem to change...isn't something very wrong? Why are the two approaches to viewing the distributions so different?..cliff

  44. I have a problem with your use of global warming interchangeably with greenhouse warming. Greenhouse warming simply does not exist and all global warming, such as it is, is natural warming. Let me walk you through. Starting with the twentieth century, its first ten years saw cooling, not warming. It was followed by the early century warming that started suddenly in 1910 and stopped equally suddenly in 21940. There was no concurrent sudden increase of carbon dioxide in 1910 and by the laws of radiation physics this rules out greenhouse warming as a cause. There was no warming in the fifties, sixties, and seventies while carbon dioxide relentlessly increased. People were worried about the coming ice age and newspapers and magazined had articles about it. There is no satisfactory exolanation for the failure of increasing carbon dioxide to cause warming for thirty years. There are just contorted hypotheses to try to explain it away. One of them is smoke and aerosols from war production blocking out the sun. There was no warming in the eighties and nineties either while carbon dioxide kept going up. Don't forget Hansen testified in 1988 that global warming had started. He still remembers the very warm summer of 1988 which was nothing more than an El Nino. There were five of these in the eighties and nineties, each one followed by a cool La Nina, with the average temperature staying the same for twenty years. Real warming started with the super El Nino of 1998, twenty years after Hansen spoke. In four years global temperature rose by a third of a degree Celsius and then stopped. Since then there has been no more warming for more than ten years. A third of a degree is half of the entire warming that IPCC assign to the entire twentieth century and explains the very warm first decade of our century. As tomArctic warminbg, that one has nothing to do with carbon dioxide and is caused by Atlantic currents carrying warm Gulf Stream water into the Arctic Ocean. With that, we can say that there has been no greenhouse warming within the last 100 years. And all of Hansen's drought observations refer to the twenty-first century when the step warming brought to us by the super El Nino was controlling global temperature. To learn more, read "What Warming? Satellite view of global temperature change."

  45. All of this is making the huge assumption that the climate actually fits a gaussian model of variability. I strongly suggest people read Nassim Taleb's work - either the Black Swan or related papers - to understand that the applicability of these models to the natural world is highly questionable. The climate belongs to the "4th quadrant" where these models simply don't work. And, if fact, the models of climate change aren't working. The Economist recently ran an article showing how the temperature change is on the absolute edge of the predicted range, and that can't give us confidence in the use of these models.

    Another great site to understand the limits of climate models and statistics is called

  46. Cliff Mass Weather Blog said...
    "Eadler...take a look at Hansen's Figure 2. The summer standard deviations hardly change...particularly over the midlatitudes. Those Gaussians he shows seems inconsistent with Figure 2."

    I disagree. The standard deviations in figure 2 left versus center are for 30 year periods 30 years apart. It is possible to see that some regions have shifted colors upward. The change is bigger between left and right without detrending. The changes are not very visible in the global graph, because all significant shifts do not result in a visible color change in a particular grid.

    In figure 4 the each curve represents a single decade, not a 30 year period. Since the latest decade 2001-2011 is showing a much larger shift than 1991-2001 and 1981-1991, it is not easy to compare figure 4 and figure 2 by inspection and make the claim that you are making.

    You are being hasty in condemning Hansen and the peer review process, without having done a real calculation yourself.

  47. To my eye, it looks like their is more yellow and light blue/teal over the Northern Hemisphere in figure 2 for the last 30 years compared to the 30 years prior for June,July, and August, which does agree with figure 4.

  48. There seems to be a lot of interest in the standard deviations. Lets talk about this more. If you look at his results, the bell curve only widens for later decades when one uses the 1950-1980 base period. For a longer periods base periods, there is virtually no different. Why might this be true? Because 1950-1980 was a period with less warm extremes than periods BEFORE or AFTER it. This is not good. And AGAIN, you are hard pressed to see the increase in standard deviations in Figure 2. A lot of issues here folks.

  49. Cliff Mass says,

    "There seems to be a lot of interest in the standard deviations. Lets talk about this more. If you look at his results, the bell curve only widens for later decades when one uses the 1950-1980 base period. For a longer periods base periods, there is virtually no different. Why might this be true? Because 1950-1980 was a period with less warm extremes than periods BEFORE or AFTER it. This is not good. And AGAIN, you are hard pressed to see the increase in standard deviations in Figure 2. A lot of issues here folks."

    Cliff what you are saying is incorrect. No matter which base period you choose in figure 4 to use as the standard deviation to which you reference the temperature anomaly, the distribution widens for each decade as the date range increases by a decade beginning with 1951-1961.

    The earlier data is not in the paper, and you haven't shown it. It is not relevant your previous contention the statistics in figure 4 appeared obviously wrong simply by inspection of figure 2.

    If you have actually have analysed earlier data in the same way that Hansen did to produce figure 4, it would be interesting to see it. In fact the global average temperature in the years 1935-45 was actually warmer than 1951-1961. If warmer temperatures resulted in wider temperature distributions, it would be consistent with Hansen's contention that warmer temperatures produce relatively more extreme temperatures.

  50. "Because 1950-1980 was a period with less warm extremes than periods BEFORE or AFTER it."

    Correct. It is highly unscientific to use PART of a dataset as a base line, it skews the results. A baseline should be all available years, except the one you are comparing to. For example, if you want to see how hot 2012 has been you would use all available years, say from 1900 to 2011, and compare that to 2012. Makes one wonder what these people are trying to hide, doesn't it.

  51. Eadler2
    You are not correct. Look at his paper..he shows the distributions for other base periods and it supports what I say. Furthermore, if you look at plots of numbers of extremes for 100 years stations, the 1930s have far more extremes...a period he conveniently doesn't use in his base period standard deviations. This is simply disappointing science from someone who should know better...cliff

  52. A nice analysis of the standard deviation/variance issue, showing some of the problems with Hansen's analysis is found her:

  53. I think tamino skewered Hansen on this one. I was wondering when somebody would get around to posting that. ;-)

    It's a bad paper, it should never have been written and , Hansen surly must be fully aware of the problems with it, which is the really baffling part of this.

  54. Cliff Mass - your comments on the standard deviation problem go to the heart of this issue. I looked at Tamino's analysis and it brings out how contrived Hansen's presentation really is. But Hansen normalized the area under his curves in figure 9 to unity and aligned them so that you can compare the variance change from decade to decade. And if you also know what temperature was doing each decade this will give you an idea of what information these curves carry. First thing to note is that the normalized curves for the fifties, the sixties, and the seventies fall accurately on top of each other. Why is that? It's simple- there was no temperature change during these thirty years and their curves show no change in variance. Next, the curve for the eighties is slightly shifted to the right, and one would expect some temperature change to be involved. I attribute this to the great Pacific climate change of 1976 which raised global temperature between 1976 and 1980 by approximately 0.15 degrees. The next decade is the nineties and its distribution is more noticeably shifted to the right. It includes the very warm super El Nino of 1998 and its warmth must have had an influence on widening the distribution. Finally, the decade of the 2000-s is strongly broadened, indicating a sizable increase of global temperature during this decade. And this is what the record shows: the step warming initiated by the super El Nino of 1998 raised global temperature by a third of a degree Celsius by 2002 and then stopped. This is a substantial warming because IPCC gives only 0.6 degrees warming for the entire twentieth century. It was caused by the large mass of warm water the super El Nino had carried across the ocean and not by any imaginary greenhouse effect. It is this warmth that is responsible for the temperature records set during that decade. And all the Moscow, Texas and Oklahoma droughts that Hansen mentions by name also fall into this decade. Hansen is trying to say that there has been greenhouse warming during the entire period he includes but he is dead wrong. The only real warming within the last thirty years is the step warming brought to us by the super El Nino. His own data fit that interpretation well if you grant that they reflect statistics of warming events dependent upon global temperature.

  55. I agree that Tamino's explanation of why the decadal graphs in fig 4 diverge so much makes sense, and what we are seeing seems to be a result of the temperature increase rather than a increase in standard deviation.

    If Hansen had written out his procedure and conclusions in more detail, he might have caught this problem himself.

  56. Eadler2,
    This is what happens when a paper is not properly peer reviewed...and a real embarrassment for PNAS. Just because someone is a member of the NAS does not mean they should be able to publish papers without a real review. ...cliff

  57. Cliff, there are some faculty who feel they are beyond peer review. :-D

  58. Mr. Mass, my friend, Ed Hummel, a retired meteorologist, has tried to post a comment here, but finds he cannot as he has no gmail or google account. We exchanged emails about this post today, and I asked him if I could post a particular email of his. He said to go ahead.

    This is what he wrote this morning:

    If Mass feels so strongly about his views, let him publish them in a legitimate, peer-reviewed journal and then we'll see what happens! Hansen has been publishing his views in a variety of legitimate, peer-reviewed journals for decades, and they've all stood the test of time better than just about anybody else's!! To denigrate the National Academy of Sciences journal is just sour grapes in my opinion. Mass just seems to be another example of a meteorologist who thinks that climate science is only "stamp collecting" in Darwin's words. In doing so, he denigrates all the interdisciplinary research that ties everything that affects climate together. When he's had the volume of research and published work that Hansen has had for the last 50 years, then he can start knocking Hansen's work which as I said has certainly stood the test of time. In fact, as Hansen has himself pointed out, even he has underestimated the speed at which the changes are taking place. One of the quotes that really sticks in my mind in recent years was Richard Alley's statement a few years ago which maintained that the Arctic ice is disappearing a hundred years ahead of schedule. Mass can make all the statements he wants about agreeing with human induced climate change, but until he understands all the research that's been done on all the nonlinear changes that are occurring and will continue to occur at even faster rates, he should stick to watching the Chinese pollution float across the Pacific.

  59. Mr. Naumer,
    I wonder why your friend cannot comments himself (a gmail account only takes a minute)...but let me answer this.The key point is that Mr. Hansen's article DID NOT go through proper peer review. That is a key issue here! An academy member can select a few friends to send an article to and then makes the decision to publish themselves. A very strange procedure and one out of keeping with the reputation of the Academy.

    And I do plan on submitting a comments to a peer reviewed journal, as I have done for the snowpack issue a few years back.

    ..cliff mass

  60. To Cliff: As you admit, the planet is heating up. I live in South Carolina where the Division of Natural Resources reported a change is the shrimping season due to increased ocean temperatures. These increases are continuing over time and are just one of the many ways in which we observe a shifting climate. To name a few: cherries blooming in D.C. glaciers receding, changes in insect ranges. All one has to do to be convinced of climate change is to look.

    The danger of assuming that the climate change is limited is that it may not be. If the temperature gets too high, what happens to the deposits of methane? At some point we may no longer be able to slow it down or reverse it. For that reason, I think you are very short-sighted in your view.

    It looks like there can be a tipping point, beyond which nothing we can do will slow down the climate change. We need to act to prevent a tipping point.

  61. Something other than global warming produced the lion's share of the heat wave...and we know what it was: a major change in the circulation over the U.S. last summer. A big area of high pressure and high heights over the center of the U.S.

    Good thing you put the first half of that statement in bold, Dr. Mass, because otherwise your readers would have been thinking, "Gosh, I wonder what caused the high pressure and major change in circulation over the center of th US..."

    I mean, such blocking highs themselves just can't be a result of climate change, right?


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