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Hansen’s Temperature Analysis: Today’s Normal is Yesterday’s Extreme–and Nobody Cares

By Chip Knappenberger -- August 23, 2012

Yesteryear’s climate extremes are today’s climate normals. Yet we are largely oblivious and better off. A hundred years from now the same will be true. Ho hum….

But not everyone thinks this way. Take NASA’s James Hansen for example.

Hansen has recently published a prominent paper (in the Proceedings of the National Academy of Sciences, PNAS) and placed a prominent op-ed (in the Washington Post) that are aimed at raising the public’s awareness of the impacts of climate change, both now and in the future. In a rather candid admission for a scientific paper (and one which in most cases would have resulted in an immediate rejection), Hansen (and co-authors) proclaim that “…we were motivated in this research by an objective to expose effects of human-made global warming as soon as possible…” To drive the point home further, Hansen’s op-ed was headlined “Climate change is here — and worse than we thought.”

What Hansen wants us to know, is that as temperatures increase, temperatures at the high end of the scale that were once statistically very rare (i.e., extreme) will become considerably less rare.

I agree completely.

However, Hansen is of the opinion that once this knowledge becomes widely known and associated with human greenhouse gas emissions (one of the many ways that human activity can alter the climate), that the majority of people will hasten to support actions (legislative, regulative) aimed at curtailing such emissions.

I completely disagree.

For one thing, it is not clear to me that warmer (and higher atmospheric CO2 levels) isn’t in many ways better. Robert Murphy pointed to recent economic analyses that found this to be the case, at least for some additional warming. And there are plenty of other potential benefits.

For another, as Roger Pielke Jr. points out, there is a lot of evidence that folks who already accept that human activities are impacting the climate still don’t clamor for actions to mitigate that influence—at least very expensive ones.

And thirdly, a changing climate is quickly and thoroughly absorbed in everyday life such that no one really cares about how it used to be and simply adjusts to how it is.

In fact, the next generation usually rolls their eyes at the weather stories of the previous. The Christmas morning “when I was a kid the snow used to reach up to my eyeballs” stories are met more often with, “whatever, Grandpa, now can I go outside and play my new soccerball,” than “Jeez, Grandpa, I’d be willing to give up some of my gifts to higher taxes and an effort to try to get back to that kind of weather.” The new generation just accepts the weather for what it is as climate changes meld with daily routines. What was formally a big deal, no longer is even much of a bother.

Nowhere is this more evident than in the statistics of heat-related mortality. This is a point that I belabor in these pages. As temperatures rise heat-related mortality rates decline. Whatever problems were once associated with “extremes” have been overcome through adaptation (in its many forms).

And while this phenomenon has been repeatedly demonstrated (including in my own research), it goes virtually ignored. Overwhelmingly, evidence suggests that rising temperatures will lower heat-related mortality rates, but the writers of impact assessments, the proposers of legislation, the crafters of regulations, and professional and amateur worriers alike always make an appeal to the contrary. And mislead in doing so.

The decline in heat-related mortality is just one specific example of the overall human adaptive response to a warming climate. Most adaptations occur generally, without undue effort, and largely without a second thought.

“Extreme” Temperatures

In his PNAS paper, Hansen defines “extreme” high temperatures as being at least three standard deviations above the average—an event which should only occur about 0.13% of the time based on a normal (bell-shaped) distribution. Hansen points out that as the average temperature increases, the distribution of observed temperatures will shift to the right (toward higher temperatures), with the consequence that the occurrence of extremes will increase dramatically when judged by the old distribution. Figure 1 shows this.

Fig. 1  The left hand (blue) bell curve represents the distribution of a set of temperature observations from some period in time. The average (or “mean”) temperature is indicated by the red blue vertical line. The standard deviation (and its multiples) are indicated on the x-axis. Only 0.13% of the data points exceed (lie to the right) of a value of three standard deviations from the mean. The right hand (red) bell curve represents the distribution of a set of temperature observations from a warmer climate. The shape of the distribution is the same, but the average temperature (red vertical line) is higher (by a value of one standard deviation) from the original climate. In the warmer climate, the number of observations that exceed three standard deviations from the original climate (region filled in dark red) has greatly increased (to a value of 2.28% of the observations).

Let’s look at the numbers in Figure 1 a bit more closely. I’ll use an example of climate change where the average temperature increases by an amount equal to the value of one standard deviation (a standard deviation is a measure of variability such that two-thirds of all observations fall within one standard deviation of the average of all observations). In this new, warmer climate (with a variability the same as the old, cooler climate) the occurrence of events exceeding three standard deviations above the old average increases by about 17.5 times. Specifically, a high temperature event that used to occur only about 0.13% of the time, now occurs about 2.28% of the time. Or, if you wanted to add a more attention-getting spin, you could say that the occurrence of extreme events has increased by over an order of magnitude.

Temperatures in the real world over the past 50 years or so have behaved somewhat like my example.

In his paper, Hansen notes that globally, since the 1950s, the average temperature has increased by about a standard deviation, and as expected, the occurrence of extreme (greater than 3 standard deviations above the old mean) temperatures has increased considerably.

Here is how Hansen et al. describe their findings:

The most important change…is the appearance of a new category of extremely hot summer anomalies, with mean temperature at least three standard deviations greater than climatology. These extreme temperatures were practically absent in the period of climatology, covering only a few tenths of one percent of the land area, but they are occurring over about 10% of global land area in recent years. The increase of these extreme anomalies, by more than an order of magnitude, implies that we can say with a high degree of confidence that events such as the extreme summer heat in the Moscow region in 2010 and Texas in 2011 were a consequence of global warming.

Several commentators around the web have taken umbrage to the final sentence above, arguing that the role of global warming in those specific weather events has been overstated, and/or improperly calculated. Others are fully supportive. But rendering an opinion about this is not the subject of my commentary.

Instead, I want to show that it really doesn’t matter. While these events may be noteworthy now, if temperatures continue to rise into the future, they will eventually become status quo and ho hum. And while that that may sound frightful now, by then, we’ll not even notice.

So, don’t worry.

Case and Point: Temperatures in Washington DC.

Over the past 142 years (from official records starting in 1871), the average summer temperature in our nation’s capital has increased by about 4.5°F from a variety of causes (Figure 2).

Fig. 2  The summer average temperature from Washington DC, 1871-2012 (the last point is an estimate).

The standard deviation (of the detrended data) is about 1.5°F.

This means that the average summer temperature in Washington DC has increased by a value equal to three standard deviations since the late 1800s. Or, to put it another way, the average Washington D.C. summer temperature of today is one which would have been considered to be “extreme” by Hansen’s definition applied 140 years ago. And probably no one living in Washington DC today even knows this, or cares.

A bit of clarification about that last line is in order.

This summer included an intense and extended heatwave in DC that, no doubt, was particularly uncomfortable. And the past three summers in DC have been the three hottest in the 142 year record. Folks living there have no doubt noticed this and probably most wish that it would have been more “normal” and not so hot. But by normal, they probably are thinking about the conditions marking the past several decades for which they have grown accustomed, rather than the conditions of the late 1800s, of which they have no idea. And of the past 30 years, 15 of them had an average summer temperature that was more than 3 standard deviations above the summer temperature at the beginning of the record—in other words, “extreme” by late 19th century standards.

My guess is that few folks living in DC consider the general conditions during the past 30 summers (with the possible exception of the past three) to have been “extreme”, instead they were just taken as the typical climate. You probably would get a different answer if you were to ask folks of the late of the 19th/early 20th century DC to rate the summer conditions of the late 20th/early 21st century DC.

Perhaps by the mid-to-late the 21st century, conditions like the past three DC summers won’t raise an eyebrow either.

While this may be cringeworthy to think of now, by then, it won’t garner a second thought—just as we don’t give a second thought to today’s climate normals being “extreme” compared to the climate of a century ago. This is true not only in DC, but, I would guess, in every major city across the country, and probably in many rural areas in between. Acclimation and adaptation happen quickly, and often with positive outcomes.

Over the course of the past century and a half, while the climate was becoming “extreme,” Washingtonians are living longer and are less effected by high temperatures (even by today’s standards) than ever before. So, too, are most other Americans.

So is climate change worse than we thought? When it comes right down to it, I doubt that most people even care.


  1. Ed Reid  


    Beginning in the early 1800s, children were fascinated by Rumplestiltskin’s ability to spin straw into gold. Today, as a result of the great advancements in science, straw (questionable temperature data) is spun into gold (“reliable global surface temperature record”) on a daily basis. Why, today, modern climate scientists can spin “nothing” (missing temperature data) into gold through the simple act of “infilling”. Modern science is truly wonderful. (sarc off)

    The greater metropolitan District of Comedy is a massive Urban Heat Island, as are most other major metropolitan areas. While the Hansen et al PNAS paper attributes recent temperature conditions in DC to increasing CO2 concentrations, it is arguable that the UHI effects have a greater impact, particularly on Tmin, as described in the linked blog posts from Dr. John Christy:

    Once the “straw” has been spun into “gold”, it can be difficult to appreciate the intrinsic qualities of the “straw”, since they have been so magically (scientifically?) changed in the spinning process.


    I plan to continue looking for the “pony” which must certainly be lurking somewhere. 🙂


  2. Eddie Devere  

    I generally agree with your analysis (and other people’s stand) that if we are wealthier then we will be able to adapt to climate change and be better off than if we were to try to stop climate change by destroying the economy. But that is a choice for individuals to make when they vote for politicians. On a side note, I want to point out that you’ve made a logical error in this post and hopefully can fix this when you write a similar articles in the future.

    You are talking about two different kinds of standard deviations in the post as if they were the same thing. First , you talk about the standard deviation of temperatures in any given summer day. Hansen’s standard deviation discussion is about the fluctuation of temperatures about some average temperature in the summer at mid-day. The value of this standard deviation is on the order of 10 deg F. Then, later in the post, you discuss the standard deviation of the average yearly summer temperature over the last hundred or so years. This is on the order of 1.5 degF. But these are two different standard deviations.

    The correct statement is that there has been an increase in temperature in Washington D.C. by roughly 4.5 degF over the last century or so. This secular trend in the climate is roughly half of the value of the standard deviation of summer mid-day temperatures due to the fact that weather is a chaotic system.

    Despite this error, I’m glad that there are people like you who trying to remove the fear and alarmism from climate change discussion. We need to have a real discussion so that we all can vote for politicians who will implement the climate change policies that we think will best help life and its economy grow.

    I think that we need to let the people across the globe have a say in whether they want to try to prevent climate change. (Which is pretty much what we are doing already by electing politicians…but there are some places where the people don’t have a voice, such as China.) The seven billion people across the globe should vote on whether they want to try to stop climate change. Some people may want warmer climates and vote for politicians who won’t enact climate change legislation. Some people might want to stop climate change because it will effect them negatively.
    We shouldn’t demonize people who want a warmer climate and we shouldn’t demonize people who don’t want a warmer climate.

    We should demonize those governments that don’t allow the people to vote for politicians that reflect their voice on whether we should try to stop the climate from getting warmer. We should also demonize those people who purposely lie about the facts of climate change. The truth is that we have no way of knowing what is the best way to grow the global economy. The best solution we developed so far appears to be to allow people to vote for politicians who pass legislation that echoes the voice of the majority of the people, but without violating anybody’s basic human rights, such as rights to free speech and freedom of religion, rights to reproduce, rights to vote, rights to a legal defense if charged, etc…
    The tough questions are: if we don’t try to stop climate change, should those people who benefit from increased temperatures compensate those people who are affected negatively? Or conversely, if we do try to stop climate change, should those people who benefit from the legislation (perhaps certain energy companies) compensate those people who are negatively affected by the legislation? It’s not a simple question to answer.


  3. Andrew  

    I really don’t think one can claim, as Hansen is doing, that the climate is getting “more extreme” by looking at the standard deviations of summer season temperature anomalies. For one thing, extremes of temperature refers, properly, to the tails of the actual temperature distribution. Hansen will find variance of anomalies increasing if cold places have warmed more in summer than warm places. In actuality, the temperature distribution’s variance would be decreased by such a change.

    If one were to look at daily absolute temperatures for all seasons he’d probably have found that “cold warms more” and the variance decreases…


  4. cknappenberger  

    Eddie Devere (#2),

    Thanks for the insightful comment.

    As far as standard deviation go, I am referring to average summer temperature throughout my article and the variability of this average temperature from season to season, not day-to-day. So, no mistake has been made. Perhaps I was not overly clear about that and so I apologize for the confusion. In any case, the discussion of Figure 1 could be generic and apply to whatever the observations are that make up the distribution–be they average summer temperature from year to year, average daily temperature, or any other Gaussian distributed unit.



  5. Mnestheus  

    OK. Chip, it’s the middle of the 20th Century and you’re a utility exec, responsible for keeping the lights lit for the Space Program in an arc from Cape Kennedy to Mission Control in Houston.

    You sleep soundly, knowing from the weather stats that the annual odds against a heat wave hot enough to compromise one of your plants are nearly a thousand to one, so the odds are long in your favor that a decade will pass without your system experiencing a single blackout

    Two generations, and less than eight tenths of a degree of continental warming later, your successor awakes to discover that mother of all free market blogs, The Economist on his breakfast table reporting a modest shift in temperature stats since the glory days of Lyndon Johnson- the peak of the temperature distribution has migrated one sigma to the right, dragging the bell curve’s the high and low temperature tails along with it.

    Instead of a rat’s tail lost in the noise just 0.13% above zero, the 3 sigma outliers have grown into a pile of black swan eggs full 8 % high.

    But relax- 8% still means 12 to 1 odds your favorite power plant won’t fail its peak load test this summer . But what about your system’s oddds? One twelth times a couple of dozen plants means not one but two crashes each summer in the here and now, and given climate business as usual, a fair prospect of outlier driven outages from here to eternity.

    Must yesterdays extreme innumeracy be Master Resource’s new normal


  6. cknappenberger  

    Mnestheus (#6),

    I am not advocating stationarity in the face of change. But the contrary–adaptation to evolving conditions.

    If the life-cycle of your project is long enough that it could be subject to conditions beyond what the current climate yields, then it would be wise to think about how you may respond to such conditions if they were to occur. Admittedly, this is a challenging problem.



  7. Jon Boone  

    I’ve asked the novelist Jane Austin for her opinion on the issue. Here’s some of her reply:

    “If you cannot think of anything appropriate to say. you will please restrict your remarks to the weather.”

    “What dreadful hot weather we have! It keeps one in a continual state of inelegance.”

    “The weather was most favourable for her. The ground covered with snow, and the atmosphere in that unsettled state between frost and thaw, which is of all others the most unfriendly for exercise, every morning beginning in rain or snow, and every evening setting in to freeze, she was for many days a most honourable prisoner.”

    If only Austen had known of the importance of–uh–climate….


  8. Mnestheus  

    Chip:’s subjuctive :

    “it could be subject to conditions beyond what the current climate yields, ”

    morphs into an imperative when current climate is changing, which it is , and has been since the beginning of the last century, to a degree commensurate with the modest rise in radiative forcing from rising CO2.

    Unless Master Resource intends to drop the fossil energy business for some other line of work – Not many Hoover Dams or uranium mines in Texas, it behoves you to stop playing catch up with climate science , or worse , trying to argue your way around it


  9. Ed Reid  

    Mnestheus 9,

    Climate has been changing (warming) since the mid-17th century, the trough of the Little Ice Age. CO2 concentrations have been increasing since the mid-18th century; and, so , are a lagging phenomenon. Climate has arguably paused this warming over the past 15 years, though the increases in atmospheric CO2 concentrations have continued apace, or accelerated.

    GW is a historical fact.
    AGW is a hypothesis.
    CAGW is a SWAG based on a hypothesis. (See Hansen’s 1988 projections.)
    Climate science is still dealing with a significant number of known unknowns and an unknown number of unknown unknowns. (Apologies to Donald Rumsfeld.)


  10. Ed Reid  

    cknappenberger 7,

    “Predictions are hard, especially about the future.”, Yogi Berra


  11. Amber  

    Has anyone checked, Hansen is an astronomer.He no climate science degree of any kind,I have been involved in climate science for 15 years,Hansen is a Joke.Saying he has knowledge of climate is like saying im a doctor,wake up he is a lier.


  12. Brian H  

    Ed Reid { 08.23.12 at 2:52 pm }

    Mnestheus 9,

    You are too kind. How about someone do a correlation study of growth rates of Global GDP and temperature, going back a few thou years.

    I betcha it’s very large and very positive. And has a range much wider than present wobbles.


  13. Chip Knappenberger: Hansen’s Temperature Analysis: Today’s Normal is Yesterday’s Extreme–and Nobody Cares | JunkScience.com  

    […] MasterResource Share this:PrintEmailMoreStumbleUponTwitterFacebookDiggRedditLike this:LikeBe the first to like this. This entry was posted in Climate Change and tagged climate fraud, climate hysteria, climate research, dioxycarbophobia, weather superstition. Bookmark the permalink. ← New paper finds unjustified assumptions on clouds in most climate models […]


  14. Denier comment of the day, August 25, 2012 | uknowispeaksense  

    […] The way conspiracy theorist deniers carry on about new taxes and how its going to affect them or tea party idiots in the USA complain about healthcare is symptomatic of the two main conditions afflicting them…selfishness and greed. They don’t want to change their way of life for the greater good and certainly not if they think its going to cost them money. And so they wrap themselves up in a wilfully ignorant blanket and refuse to see what’s going on outside their own little world. Well today’s denier is sort of like that except he doesn’t deny that the climate is changing or even that it is our doing. What he does deny is that it is going to have a serious effect on anybody. Everyone will just adapt apparently. Anyway, his name is Chip Knappenberger and here is his comment. […]


  15. Ed Reid  

    Once the term “denier” is used, all credibility is lost.

    Ah, the untold joy of the ad hominem attack combined with the argument from authority, absent the authority.

    “uknowispeaksense” (sic) has apparently adopted some definition of “the greater good” and feels bound to berate those who do not conform to his approaches to achieving that “greater good”.


  16. Jon Boone  

    Yet another version, Ed, of the Repent, the End is Nigh sackcloth and ashes routine…. Cartoonists find this a staple: http://www.cartoonstock.com/directory/e/end_of_days.asp


  17. Ray  

    Dr. Hansen is MS astronomy, Phd physics .


  18. Otter  

    I have seen comments from ùknowispeaksense`before.

    He Does not, and never will, speak sense. Opening with `denier`means he already lost the argument. Only closed minds would listen to the likes of him.


  19. Mnestheus  

    If Ed Reid were less credulous, he would be less apt to elide the unabridged reality of the climate record with polemic inventions carpentered to cater to oil patch sensibilities.

    For all the ups and downs of the industrial age , continental temperatures
    and CO2 levels have risen in lockstep with population growth .

    The problem is less closed minds on either side, than an abundance on both of minds half empty and half filled with factoids .


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