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Research Links Extreme Summer Heat Events to Global Warming

Aug. 6, 2012

You may have already seen this reported.
"A new statistical analysis by NASA scientists has found that Earth's land areas have become much more likely to experience an extreme summer heat wave than they were in the middle of the 20th century."
The journal Proceedings of the National Academy of Sciences.

Earth's Northern Hemisphere over the past 30 years has seen more "hot" (orange), "very hot" (red) and "extremely hot" (brown) summers, compared to a base period defined in this study from 1951 to 1980. This visualization shows how the area experiencing "extremely hot" summers grows from nearly nonexistent during the base period to cover 12 percent of land in the Northern Hemisphere by 2011. Watch for the 2010 heat waves in the Middle East, Western Asia and Eastern Europe, or the 2011 heat waves in Texas, Oklahoma and Mexico. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

Recent years of extremely warm summers, including the Midwest this year, are quite likely due to global warming, according to lead author James Hansen of NASA's Goddard Institute for Space Studies (GISS) in New York.

"This summer people are seeing extreme heat and agricultural impacts," Hansen says. "We're asserting that this is causally connected to global warming, and in this paper we present the scientific evidence for that."
Summer temperatures since 1951 were studied. The odds have increased in recent decades for what they define as "hot," "very hot" and "extremely hot" summers.

The "extremely hot" summers occur more often. They define "extremely hot" as a mean summer temperature experienced by less than 1% of Earth's land area between 1951 and 1980. This 30 year span is the base period for the study. Since 2006, about 10% of land area across the Northern Hemisphere has experienced these "extremely hot" temperatures each summer.

The day after Hansen's publication, a follow-up analysis was posted August 7 in the Earth Observatory Blog called Earth Matters. Written by Adam Voiland, the blog post discusses the significance of the temperature extremes data profile when compared to the standard bell curve so many of us are familiar with from statistics studies. There is discussion of the standard deviation notation (σ) and how it is interpreted in this case of summer temperatures in the northern hemisphere.

Come below the fold for more of those details.

What is a Bell Curve and Standard Deviation?

Sigma (σ) is a letter of the Greek alphabet. It is used in statistics to represent standard deviation. It essentially describes how much data is spread out from the average, or mean. A plot of a normal distribution of data typically yields the familiar bell curve. Here are six examples of normal distributions with different standard deviations. Low standard deviation, in blue, says the data points are bunched up and close to the mean. High standard deviation, in yellow, says the data is more spread over a wider range.
Click image for source.

In a standard bell curve, 68% of the data points fall within one standard deviation (1σ) of the mean. While 95% are within two standard deviations (2σ). Three standard deviations (3σ) of the mean will contain 99.7% of the data. Very few points will lie beyond 3σ. Those are the characters that make up the extreme right wing and left wing fringe. The scientists reporting the finding of the Higgs Boson spoke of data within 3σ and how certain they were of it.

How is Temperature Related?

Now, substitute temperature variations from the mean, or anomalies, into a plot. The graph on the left shows how frequently summer temperature anomalies occurred in the 30-year base period 1951-1980, a time of stable global climate. The standard deviation σ was 0.6°C (1.1°F) in 1951-1980. Or, 68% of the variations measured were within 0.6˚C of the mean. By the next decade of 1981-1991, the peak of values shifted toward the right indicating warmer temperature anomalies. Each successive decade has shifted the curve more to the warmer end of the curve. In addition, there are many more temperature anomalies beyond the 3σ tail at the right end of the graph. And, the curve is more spread out indicating larger standard deviation of temperature anomalies.

The surface temperatures have increase over the recent 3 decades. And, the number of extreme high heat events beyond 3σ has increased.

As stated by Hansen...

We have shown that these “3-sigma” (3σ) events, where σ is the standard deviation — seasons more than three standard deviations removed from “normal” climate — are a consequence of the rapid global warming of the past 30 years. Combined with the well-established fact that the global warming is a result of increasing atmospheric CO2 and other greenhouse gases, it follows that the increasingly extreme climate anomalies are human-made.
Below is an animation of the data presented by Hansen and his colleagues.

Q&A with James Hansen

Hansen supplied a number of answers and explanations which you can access at this link. The link is to a 4 page pdf titled Q&A of The New Climate Dice. He addresses several questions, in particular, how the coming years are going to be like rolling a loaded dice for extremes of high temperature anomalies. They are going to be more frequent and more severe. There will still be the occasional colder than normal year. But, hotter than normal will be more frequent and worse. Not a good prospect.

Some questions he considers are...
1. What is the most important finding of the paper?
2. Why is such an anomaly important? Isn't it just a few degrees warmer than average?
3. Didn't 3-sigma events occur in the past?
4. So you can use your old metaphor of "loaded" climate dice to describe the situation?
5. Why are you also introducing the "bell curve?" Isn't that too esoteric for the public?
6. How is the "bell curve" related to "loaded climate dice?"
7. You note that the bell curve has become "squashed". Is that important?
8. How do you know that the bell curve will continue to shift to the right?
9. What are consequences of the increasing extremes?
10. Are we necessarily going to see more and more extreme climate? Gloom and doom?
11. Could we just redefine what is normal climate, obtaining a new symmetric bell curve?
12. Did you write this paper and your 1988 paper because of the extreme droughts?
13. Are there other effects that should be noticeable, besides the climate extremes?

Originally posted to SciTech on Wed Aug 22, 2012 at 08:00 AM PDT.

Also republished by Climate Change SOS and J Town.

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Comment Preferences

  •  Impact this year on the Mississippi River level. (25+ / 0-)

    The river is flowing much lower than normal. And, it is much lower than this time last year. Low levels are attributed to record heat and drought conditions. Click on the image to view the Earth Observatory page for comparison images. Below the image from last summer is a button to View Image Comparison. That will give you a slider control.

    Difference between stupidity and genius...genius has its limits. ~ Einstein

    by jim in IA on Wed Aug 22, 2012 at 07:13:51 AM PDT

  •  2012 is a very cold year (10+ / 0-)

    By the end of the 21st century, we'll be counting 2012 as among the coldest years in the century.  Ahh, the good old days, when we only lost 1/3rd of our crops.

  •  Very clear presentation of how to read the (10+ / 0-)

    statistical evidence. Your graphics do an excellent job. Too bad more of right wing nut deniers in congress could not see this. I don't know if it would help them but if not, then we would know for sure that they were either really stupid or dementned.

    Excellent piece.

    "There is nothing - absolutely nothing - half so much worth doing as simply messing about in boats ..." - Kenneth Grahame -

    by RonK on Wed Aug 22, 2012 at 08:37:49 AM PDT

  •  At risk of getting flamed again, here is Cliff (0+ / 0-)

    Mass at UW objecting to Hansen's exaggerations:

    "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."

    "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."

    "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."

    Where are we, now that we need us most?

    by Frank Knarf on Wed Aug 22, 2012 at 11:30:20 AM PDT

    •  Frank, you agree we are causing climate (2+ / 0-)
      Recommended by:
      jim in IA, Bronx59

      change, but your every post seems skeptical. You claim to respect the science, yet your every post questions the science.

      No, I won't flame you. I just want you to know that despite your claims to the contraryy, your every post convinces me you are trying to sow doubt.

      There is only one planet suitable for human habitation in our solar system.

      by too many people on Wed Aug 22, 2012 at 01:31:30 PM PDT

      [ Parent ]

      •  There is a big difference between sowing doubt and (0+ / 0-)

        trying to describe the problem with making unwarranted claims that are likely to backfire.  I think the post by Cliff Mass summarizes my concerns with the Hansen paper.  The current heat wave and drought in the US presents a tempting opportunity to replace analysis with advocacy.  There is nothing wrong with advocacy, and I actually support many of the alternative energy initiatives that  will help to slow the build up of CO2.  But we are likely to see climate variation that will tempt the other side as well.  A better approach is to honestly evaluate the scientific evidence and present to the public a realistic assessment of the risks and costs involved with policy alternatives.

        Where are we, now that we need us most?

        by Frank Knarf on Wed Aug 22, 2012 at 05:01:30 PM PDT

        [ Parent ]

        •  There is a big difference between a weather (1+ / 0-)
          Recommended by:
          jim in IA

          blogger and a climatologist. I will go with the climatologist.

          There is only one planet suitable for human habitation in our solar system.

          by too many people on Wed Aug 22, 2012 at 09:56:29 PM PDT

          [ Parent ]

          •  Which one? (0+ / 0-)

            Where are we, now that we need us most?

            by Frank Knarf on Thu Aug 23, 2012 at 04:05:45 PM PDT

            [ Parent ]

            •  Okay, you win that point. (0+ / 0-)

              Nevertheless, I would like to hear why you are not panicked by the melting of the arctic. Also, it seems that the pace of change is much quicker than predicted. The models seem too conservative.
              Also, would you concede that if there is even a small probability that things are/will procede very badly, then it is past time to take drastic action?

              There is only one planet suitable for human habitation in our solar system.

              by too many people on Thu Aug 23, 2012 at 10:40:43 PM PDT

              [ Parent ]

              •  It is certainly past time to take action on energy (0+ / 0-)

                policy.  I have long argued that appeal to the precautionary principal is the right way to move public opinion.  My rather Quixotic conflict with some of the more enthusiastic Kossacks on this topic has to do with the danger of making claims not supported by evidence, or confusing uncertain model projections with absolute truth.

                Where are we, now that we need us most?

                by Frank Knarf on Fri Aug 24, 2012 at 07:44:10 AM PDT

                [ Parent ]

    •  I respectfully disagree, Frank Knarf. (3+ / 0-)

      After reading much of what Mass had to say in your link, and comments of the followers, I was left with very little of substance supporting their opposition. It seemed he and others were saying 'Hansen is wrong' with little to substantiate that statement. I don't find that a convincing scientific argument.

      Thanks for stopping by.

      Difference between stupidity and genius...genius has its limits. ~ Einstein

      by jim in IA on Wed Aug 22, 2012 at 02:01:13 PM PDT

      [ Parent ]

      •  Mass is wrong (1+ / 0-)
        Recommended by:
        jim in IA

        First of all, Dr. Hansen's paper was peer reviewed and PNAS is, of course, a very respected journal.

        It is important to note that Dr. Hansen's paper is not based on climate models and is not a prediction.  It is based on a statistical analysis of 60 years of actual, measured temperature data.  To avoid "urban heat island effects", the study excludes stations located near areas that are lit up in nighttime satellite images.  The 5000% increased in "Extremely Hot Summers" (anomalies 3 standard deviations above the mean) in 50 years ALREADY HAPPENED!

        If you don't believe it, you can download the data set (or another temperature data set) and do the analysis yourself!  All it takes it some Statistics 101 knowledge.

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