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Extremely hot

Filed under: — stefan @ 26 March 2012

By Stefan Rahmstorf and Dim Coumou

One claim frequently heard regarding extreme heat waves goes something like this: ”Since this heat wave broke the previous record by 5 °C, global warming can’t have much to do with it since that has been only 1 °C over the 20th century”. Here we explain why we find this logic doubly flawed.

One can ask two different questions about the influence of global warming on heat waves (Otto et al. 2012), and we take them in turn.

1. How much hotter did global warming make this heat wave?

We have some trouble with framing the question like this, because it tacitly assumes that the same weather situation would have also arisen without global warming, only at a (say) 1 °C lower temperature level. That need not be the case, of course, since weather is highly stochastic and global warming can also affect the circulation patterns of the atmosphere.

But even if we accept the basic premise (and it could be meant in a purely statistical sense, although that is not usually how it is expressed), would an average anthropogenic warming by 1 °C in the relevant location mean that 1 °C is also the amount added to an extreme event? Only in a linear climate system. Imagine a heat wave that pushes temperatures up to 30 °C in a world without global warming. In the same weather situation with global warming, you might expect that this weather then results in a 31 °C heat wave. But that could well be wrong. Possibly in the situation with warming, the soil has dried out over the previous months because of that extra 1 °C. So now you lost evaporative cooling, the incoming sunlight turns into sensible heat rather than a large fraction going into latent heat. That is a non-linear feedback, and not an imagined one. Detailed studies have shown that this may have played an important role during the European heat wave of 2003 (Schär et al. 2004).

The basic phenomenon is familiar to oceanographers: if the mean sea level in one location rises by 30 cm, this does not mean that the high-tide level also rises by 30 cm. In some cases it will be more, due to nonlinear feedback. I.e., a higher water level increases the flow cross-section (think of a tidal inlet) and reduces bottom friction so the tide rolls in faster, reaching a higher peak. The tidal range increases as well as the mean sea level.

Numerous other non-linear mechanisms are possible, which we are only beginning to understand – think of the recent studies that show how changes in snow cover or sea ice cover as a result of global warming affect weather systems. Or think of factors that could affect the stability of particularly strong blocking events. Thus, we’d be very cautious about making an essentially linear, deterministic argument about heat extremes to the public.

In the scientific literature, the influence of global warming on extreme events is therefore usually discussed in terms of probabilities, which is more fitted to stochastic events. The typical question asked is:

2. How much more likely did global warming make this heat wave?

For this question, it is easily shown that the logic “the greater the extreme, the less global warming has to do with it” is seriously flawed. The change in probability of certain temperature values being reached can be visualised with a probability density function (see Figure). The probability distribution could be shifted unchanged towards warmer values, or it could be widened, or a combination of both (or some other deformation).

IPCC (2001) graph illustrating how a shift and/or widening of a probability distribution of temperatures affects the probability of extremes.

For illustration, let’s take the most simple case of a normal distribution that is shifted towards the warm end by a given amount – say one standard deviation. Then, a moderately extreme temperature that is 2 standard deviations above the mean becomes 4.5 times more likely (see graph below). But a seriously extreme temperature, that is 5 standard deviations above the mean, becomes 90 times more likely! Thus: the same amount of global warming boosts the probability of really extreme events, like the recent US heat wave, far more than it boosts more moderate events. This is exactly the opposite of the claim that “the greater the extreme, the less global warming has to do with it.” The same is also true if the probability distribution is not shifted but widened by a constant factor. This is easy to show analytically for our math-minded readers.

Graph illustrating how the ratio of the probability of extremes (warmed climate divided by unchanged climate – this increased likelihood factor is shown as a dashed line, scale on right) depends on the value of the extreme.

So in summary: even in the most simple, linear case of a shift in the normal distribution, the probability for “outlandish” heat records increases greatly due to global warming. But the more outlandish a record is, the more would we suspect that non-linear feedbacks are at play – which could increase their likelihood even more.

Update 29 March: New Scientist magazine cites this RC post in an article about the “summer in March”.


Our Perspective article on the unprecedented extremes of the last decade was just published by Nature Climate Change: Coumou & Rahmstorf (2012) A decade of weather extremes


Otto et al., Reconciling two approaches to attribution of the 2010 Russian heat wave, Geophysical Research Letters 2012, VOL. 39, L04702, doi:10.1029/2011GL050422

Schär, C. et al. The role of increasing temperature variability in European summer heat waves. Nature 427, 332–336 (2004).

210 Responses to “Extremely hot”

  1. 151
    Matt says:

    The attribution of extreme weather events to AGW seems an important topic to me. If it was possible to say that a particularly severe heatwave or other extreme weather events was probably caused by AGW, this might help might make AGW a more “real” and personal problem to those who experienced the weather event.

    So I’m interested in the possibility of frameworks for calculating the probability that AGW “caused” a particular weather event. I.e. the probability that global warming due to anthropogenic activities was a *necessary* (if not sufficient) condition for a particular weather event to occur.

    Say that climate models indicate a particular weather event W(say a heatwave of a particular extremity) has a probability P(W|AGW’) of occurring in a certain time period in the absence of anthropogenic forcings. The models also indicate that the event has a probability P(W|AGW) of occurring in the chosen time period *with* anthropogenic forcings included.

    Then it seems to me that the probability that the event was “caused” by AGW is:

    [P(W|AGW) – P(W|AGW’)] / P(W|AGW)

    i.e. This is the probability that the event would NOT have taken place in the absence of AGW, or in other words the probability that AGW was a *necessary* condition for this particular event to occur. Does this make sense, or am I missing some important issues?

  2. 152
    Jim Larsen says:

    148 Norman said, “My point is that you have 3 possibilites with AGW. More blocking patterns”

    Great question. Let’s ask Mother Nature.

    I pointed you to a list showing 47 countries with record highs and 8 with record lows in this century. This entire period was one of flattish temperatures. Had temperatures risen as they were “supposed” to, surely the ratio would have been even more lopsided. Additionally, the largest countries are in the arctic, and so are underrepresented in the data. Since they’ve been warming the most, the results could be biased low.

    Infinitely more rigourous, but still incredibly readable is Hansen’s paper. Figures 7 and 9 are very informative.

  3. 153
    Norman says:

    grypo @149

    Interesting links. Thanks. My observation of the Francis paper. Meteorologist should be able to determine if storm systems are moving slower today than they had been 30 years ago. I did find this The predictablilty of atmospheric blocking. This article gives many theories on how blocks form. By reading through some of them I am trying to determine if the paper you linked is correct reasoning based upon what is already known about blocks.

    I do have some question about your link about Arctic Amplification being a cause for the heavy snows in the US and Europe a few years back.

    Moving through the snow cover anomaly graphs, I can’t see any clear evidence that would suggest Arctic Amplification is responsible for more snow in early winter. In December on the graphs, the only thing that stands out as unusual is a few years of really low snow cover. The rest looks fairly normal. I do not know if there is enough evidence to support the conclusion (certainly does not seem overwhelming).

  4. 154
    Norman says:

    John P. Reisman (OSS Foundation) @142

    “Re. your #128 You are ignoring a tremendous amount of relevant factors in your narrowly scoped assessment of what to consider. Ever heard of thermal limits on crop growth”

    Thanks for leading me in this direction. I have been reading this article on the topic. It seems heat can be very bad for some crops. I live in corn country and it seems to do well as long as there is some rain. I also garden in the summer and have not noticed a loss of vegetables from having a hot summer. As long as I water regularly during a dry spell I have had good production for years.

  5. 155
    Jim Larsen says:

    151 Matt asks, “.e. This is the probability that the event would NOT have taken place in the absence of AGW, or in other words the probability that AGW was a *necessary* condition for this particular event to occur. ”

    Go to the leftmost graph in Fig 9. It shows distribution curves for each decade’s temperatures. Compare the 1950s and 2000s curves to the OP’s hypothetical pair in the unlabeled(!) graph depicting a one SD warming. There’s a similar increase, but the real curves show a huge increase in variability, with record lows remaining pretty constant at -3 SD, but record highs stretch from 3 to 5 SD! This has resulted in a massive increase in extreme highs worldwide. The OP’s black dotted line ends at 80 to 1, but it’s safe to say we’re getting over 100 times as many 5 SD heat events than we did in the 1950s.

    Or, in Fig 2, 3 SD events are graphed as “extremely hot”. They were a few tenths of a percent by area up until 1980. Now they’re 10% of the globe.

    Hansen says, “The increased frequency 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. “

  6. 156
    Hank Roberts says:
    “Reproductive development of many crop species is damaged by heat such that they produce no flowers or if they produce flowers they may set no fruit or seeds. The reviews of Hall (1992, 1993) discuss the detrimental effects of heat stress on reproductive development that has been reported for cowpea, common bean, tomato, cotton, rice, wheat, maize and sorghum. …”

  7. 157
    Dan H. says:

    One needs to be careful when comparing the s.d. between 1950 and now. Hansen admits that “the small variability must be an artifact of limited measurements during 1951-1980.” The curves in Fig. 9 change depending on the base period used.

    Hansen chose his base period for most figures as 1951-1980. Is it any wonder that a greater number of higher sigma events occurred during the recent warmer years, than the previous, cooler ones. Since Hansen states that temperatures during this interval increased by one s.d., the occurrance of 2-sigma warming events today, would equal those of 1-sigma events 50 years ago, and the reverse for cold events.

    If it can be shown that global warming is responsible for the recent blocking events, then he would have a much stronger case for his asertions. This also applies to the recent blokcing this winter in the U.S. and Europe. Both the U.S. and Russia experienced a similar blocking events in the 1930s. Most of the U.S. record summer highs were set then, while in Russia, they were set last year. I am also curious how someone can “imply” something with a high degree of confidence.

  8. 158
  9. 159
    Hank Roberts says:

    > Is it any wonder that a greater number of higher sigma events
    > occurred during the recent warmer years, than the previous, cooler ones.

    Conflating the average with the variability?

  10. 160
    Jim Larsen says:

    157 Dan H said, “temperatures during this interval increased by one s.d., the occurrance of 2-sigma warming events today, would equal those of 1-sigma events 50 years ago, and the reverse for cold events.

    If it can be shown that global warming is responsible for the recent blocking events, then he would have a much stronger case for his asertions. ”

    Temps went up one SD, but the distribution widened from 6 SD to 8 SD. Hansen used half of the data for the base period and gave excellent reasons for his choice, primarily centered on that this technique reveals the moving trend the best. You, (surprise!) feel it is the worst technique because it reveals the moving trend the best. If you’re actually concerned about the length of the base period, perhaps you could widen it by adding in years prior to 1951.

    While you’ve been away, we’ve been linking and discussing papers and articles about the causes for the recent increase in blocking patterns. Essentially, lower equator to pole temperature differential –> slower jet stream –> blockages and sluggishness in jet stream variations.

    i.e. the jet stream whips around more the faster it goes.

    Arctic amplification will only increase, so I think this one goes on the “It’s worse than we thought” shelf. Do you agree, Dan?

  11. 161
    Hank Roberts says:

    “… researchers led by Sirpa Häkkinen, an oceanographer at NASA’s Goddard Space Flight Center in Greenbelt, Md., analyzed atmospheric data from the 20th century and found a correlation between periods of warmer-than-usual waters in the North Atlantic, and a higher frequency of blocking events….
    … Clusters of blocking events can divert the normal track of hurricanes … In some cases, this change can speed up or slow down large, circulating currents in the ocean known as gyres ….

    Slower, weaker gyres allow warm waters to escape farther north.

    ‘These warmer and more saline waters then invade the sub-polar ocean and cause a series of impacts,’ Peter Rhines, an oceanographer at the University of Washington, Seattle, and co-author of the new study, said ….”


    for 2009
    Richter-Menge, J., and J.E. Overland, Eds., 2009: Arctic Report Card 2009,

    “It is apparent that the heating of the ocean in areas of extreme summer sea ice loss is directly
    impacting surface air temperatures over the Arctic Ocean, where surface air temperature
    anomalies reached an unprecedented +4°C during October through December 2008…..

    … There is evidence that, by creating a new major surface heat source, the recent extreme loss of
    summer sea ice extent is having a direct feedback effect on the general atmospheric circulation
    into the winter season (Francis et al., 2009)…. the effect of higher air temperatures in the lower Arctic atmosphere is contributing to changes in the atmospheric circulation in both the Arctic and northern mid-latitudes. For example, Honda et al. (2009) suggest a remote connection between loss of Arctic sea ice and colder temperatures over eastern Asia….”

    Current page:

    “What’s new in 2011?

    Persistent warming has caused dramatic changes in the Arctic Ocean and the ecosystem it supports.

    Ocean changes include reduced sea ice and freshening of the upper ocean, and impacts such as increased biological productivity at the base of the food chain and loss of habit for walrus and polar bears.

    Atmosphere Significant change
    Higher temperatures in the Arctic and unusually lower temperatures in some low latitude regions are linked to global shifts in atmospheric wind patterns….”

  12. 162
    Dan says:

    Link to the Francis/Vavrus abstract:
    Evidence linking Arctic amplification to extreme weather in mid-latitudes

    “Arctic amplification (AA) – the observed enhanced warming in high northern latitudes relative to the northern hemisphere – is evident in lower-tropospheric temperatures and in 1000-to-500 hPa thicknesses. Daily fields of 500 hPa heights from the National Centers for Environmental Prediction Reanalysis are analyzed over N. America and the N. Atlantic to assess changes in north-south (Rossby) wave characteristics associated with AA and the relaxation of poleward thickness gradients. Two effects are identified that each contribute to a slower eastward progression of Rossby waves in the upper-level flow: 1) weakened zonal winds, and 2) increased wave amplitude. These effects are particularly evident in autumn and winter consistent with sea-ice loss, but are also apparent in summer, possibly related to earlier snow melt on high-latitude land. Slower progression of upper-level waves would cause associated weather patterns in mid-latitudes to be more persistent, which may lead to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.”

  13. 163
    adelady says:

    Matt@ 151 “the probability that global warming due to anthropogenic activities was a *necessary* (if not sufficient) condition for a particular weather event to occur.”

    Recently I’ve begun to think that the necessary/sufficient distinction could be very useful even in non-technical statements for general public consumption. Most people have come across the necessary v. sufficient concept before. Those who fancy themselves as well versed in technical matters even more so.

    Saying that warming has given us a constant ‘necessary’ condition for extreme events sets things up for both expected (say during El Nino events) and unexpected outcomes (WACCy weather being one). When other variables come into play in certain places and conditions, we can get ‘sufficient’ factors for an unusual flood, an extended heatwave or an exceptional drought.

    (And the argument also works quite neatly in reverse – but I think the way I’ve expressed it is the correct one, as well as being more persuasive. I’ve got a biological parallel/analogy in mind that has the same characteristics, but the words won’t come together neatly. I’ll leave it for later.)

  14. 164
    John Pollack says:

    Norman @ 148 No, I do not have sources that would allow me to state the trend for blocking events under future AGW. However, I don’t see why there has to be one trend. It could well be location dependent, sensitive to changes in SSTs, etc.

    Meanwhile, the observed empirical trend is toward greater extremes of precip. and warm events, but not cold events. That’s just what we expect of AGW in general. BTW, the Omaha March mean temp. record set in 1910 was the most extreme of any monthly anomaly, except perhaps the cold Dec. 1983, and has now been exceeded by 1.8F. Furthermore, the 1910 warm March was followed by a hard freeze in April. There is a decent chance that won’t happen this year, as there isn’t even much of a cold pool in Canada. Time will tell.

  15. 165
    Norman says:

    John Pollack @164

    The long term forecast for Omaha in April is cooler temperatures (at least much closer to the normal for this time of year).

    I did find this link to global and US climate patterns (heat waves, preciptiation etc.).

    Except for overall warming and night time warming my visual accuity is not fine enough to see a trend to the extreme.

    US heat wave index does not seem to be rising. Amount of US area with above normal highs is rising but nothing special in the historical context.

    US drought index for the last 10 years is static (some years worse than others).

    Now for Global effects, the graph of global precipitation does not show this frightening increase above the historical norm.

    Abnormally high annual rainfall in the US is creeping up in area affected but not at an alarming rate with respect to the historical average, it is a very dynamic nature that varies alot on a yearly basis.

    North Atlantic cyclone intensity is a flatline since 1950.

    I will keep an open mind that my observations of this data are not correct but I will let you view it yourself to form your own conclusions.

  16. 166
    Dan H. says:

    I do not disagree with that explanation for the increase in recent blocking events, and there is sufficient evidence for an increase in the past 50 years. However, similar conditions are thought to have contributed to the increase in blocking events presumed to have occurred in the 1930s.

    My issue was not in adding years prior to his data set, but rather that the choice in base period affected his results. It is not surprising that a greater s.d. occurs, when the base period differs from the dataset. In Hansen’s Fig. 9, the s.d. is less when the current decade is plotted against the base period in which the temperatures occurred. When using the entire base period, 1951-2011, he s.d are similar for all decades, just shifted higher. This is exemplified in his Fig. 2.

  17. 167
    Steven Franzen says:


    How are you coming along with reading SREX report Chapter 3? A point you were previously capitalising on is blocking patterns:

    So far I have not seen the topic of blocking patterns discussed in the IPCC SREX report.

    My claim is that exterme weather patterns (drought, heat wave, cold snap, or flooding) are created by known phenomena and are not random fluctuations of the temperature field. The phenomena that generates these extremes is atmospheric blocking patterns. All the recent heat waves have been attributed to these blocking patterns.

    If AGW will increase the number and length of blocking patterns then I will completely agree that global warming will lead to more extreme weather.

    So, what if it can’t be found that AGW increases the number and length of blocking patterns, or if extreme weather is not solely caused by atmospheric blocking? Would that make you “incompletely agree” or completely reject the statement that global warming will lead to more extreme weather?
    Because the SREX report does mention some issues you seem to have in Chapter 3, page 130:

    Some processes –
    particularly those involving feedbacks (Section 3.1.4), and this is
    especially the case for climate extremes and associated impacts – are
    still poorly represented and/or understood (e.g., land-atmosphere
    interactions, ocean-atmosphere interactions, stratospheric processes,
    blocking dynamics) despite some improvements in the simulations of
    others (see Box 3-2 and below). Therefore, limitations in computing
    power and in the scientific understanding of some physical processes
    currently restrict further global and regional climate model improvements.

  18. 168
    wili says:

    Thanks hank and Xiedaoan. I just wondered if there was some well-known major scientist who has been talking about heating in the range of 10-20 degrees that anyone knows about but I somehow missed. It sounds like there is not.

  19. 169
    wili says:

    OK, I approached it from the other direction. I thought about which prominent scientists say the most grim things about the likely future in regard to GW and James Lovelock came to mind. I did find a number of blogs that seem to be quoting him sometime in the mid aughts as saying that global temperatures could rise ten degrees in the next decade. Of course, they did not give the source, but it sounds like it might have been something in his “Revenge of Gaia.” If someone has that on hand or can give me a better source, I would appreciate it.

  20. 170
    wili says:

    Sorry for the back-to-back posts, but I tracked it down to a Washington Post article:

    “The nature of Earth’s biosphere is that, under pressure from industrialization, it resists such heating, and then it resists some more.

    Then, he says, it adjusts.

    Within the next decade or two, Lovelock forecasts, Gaia will hike her thermostat by at least 10 degrees. Earth, he predicts, will be hotter than at any time since the Eocene Age 55 million years ago, when crocodiles swam in the Arctic Ocean.”

    From “The End of Eden” by Michael Powell Sept. 2, 2006.

    So we are now only four years from when we should have a ten degree hotter temperature, according to Lovelock in this article, at least going by his closest extimate. Things will have to heat up pretty fast if this is to come true.

    I do think his point about complex systems’ propensity to go through sudden, rapid change is important to keep in mind.

  21. 171
    Hank Roberts says:

    > Norman says: …
    > view it yourself to form your own conclusions.

    See, this is the reason you’re having problems with science.

    Humans excel at finding patterns, whether there’s reality there or not.
    This served you well; you are descended from a long line of primates with sufficient skill to _always_ detect the leopard lurking in the shadows and escape up a tree. The cost of mistakenly imagining a leopard was trivial; the cost of mistakenly not detecting a leopard was a notable lack of grandchildren.

    You don’t need to believe in evolution; all you need to understand is that for whatever reason, you are typically human and excel at seeing patterns — whether or not there’s a pattern in the actual reality.

    Your eyes aren’t reliable.

    This is why statistics has been invented — to correct our lying eyes.

  22. 172
    Andy says:

    I read Wallace’s opinion piece and it makes perfect sense to me. He’s simply stating that we need to take a longer and broader look at the negative affects of global warming and to not ignore the other dire environmental degradation occurring on our planet.

    I think a good lesson is what was learned from the discussion surrounding the “Population Bomb”. Most of the dire consequences of our high population growth are now unfolding; but since the predictions weren’t evident shortly after its publication they were viewed by the public as being incorrect. Didn’t matter that the authors stated it would be decades for the effects to become evident; some environmentalists screamed that the end was nigh and when that didn’t happen the book’s warnings were tossed in the trash heap and now we’ve got 7 billion and counting and we’re still debating use of birth control.

    So it will be with global warming’s worst effects which are still many decades out. By the time they are evident to the general population, beyond our weather’s not infrequent extremes, it will be too late. Use these events as teachable moments. A portend of what’s to come. Otherwise we simply build a better tornado warning system, hurricane proof homes, more dams and the problem’s solved right? Then in 80 years time we wake up and half of this earth’s organisms are gone, it’s always too hot to work in the yard on Saturday, the kids don’t know why anyone would ever want to play outside or go camping like in the “olden” days and we’re taking underwater tours of Louisiana. Bad weather is going to be the least of our problems.

    And it does no good to be able to say “I told you so”.

    Therefore, Wallace is saying let’s use a different strategy. I agree. Otherwise it’ll be heads we lose, tails they win.

  23. 173
    Brian Dodge says:

    “US heat wave index does not seem to be rising.” Norman — 3 Apr 2012 @ 11:21 PM

    My sources disagree –

    “Like the heat wave index, the percentage of the United States affected by heat waves has also risen steadily since the 1970s (see figures 2 & 3). The recent period of increasing heat is distinguished by a rise in extremely high nighttime temperatures.” (a disproportionate rise in night vs day temperatures is a signature of AGW.)

    What’s your source that the heat index “seems” not to be rising?

  24. 174
    Dan H. says:

    Based on the link to the epa heat wave index, the value has risen since the relatively cool 1970s, but is still much lower than the 1930s. So I would say that both your statements about the heat index are correct; they just need to be put in the proper timeframe. Short-term – yes, long-term – no. The same can be said of daily high temperatures, higher than the 1970s, but not the 30s (although much closer than the heat index). The higher nighttime lows is dramatically higher recently.

  25. 175
    sidd says:

    Mr. Norman writes on the 3rd of April 2012, at 11:21 PM:

    “…global precipitation does not show this frightening increase above the historical norm.”

    Global precipitation is interesting. The mode is moving down, while the extremes are kicking up. The following plot is a histogram of deviation from local average vs local standard deviation on a 2.5 degree grid, lumping the events at larger than 5 sigma.


  26. 176
    sidd says:

    i should say that the data fro the graphs i posted are monthly, and here is the same data on a log scale

    which show the increase in hi sigma events


  27. 177
    Norman says:

    Hank Roberts @170

    “This is why statistics has been invented — to correct our lying eyes.”

    This would be great if statistics were always used correctly and with good intent but people are what they are. Not only are humans excellent at pattern recognition but they also seem to have an ability to decieve. Statistics can mislead, they are as valuable as the person who is using this tool. Science is the same way, an excellent tool when used correctly, but humans are still what they are. That is why one must always question all and the truth will come out. My questions do not mean my view is correct, but they are necessary for science to remain the useful tool it was designed to be.

    Remember the saying “There are three kinds of lies: lies, damned lies, and statistics.”

  28. 178
    Norman says:

    Brian Dodge @172

    I would agree that the heat index rose from 1970 to current. Just from 2000 to current it does not appear to be rising and it is no where near the level of the 1930’s. In the historical context it does not appear to be rising and it does not show a pattern of a rapid increase at this time.

    That is why I posted the link with my observations. Here is my claim “I will keep an open mind that my observations of this data are not correct”

    So I thank you for considering them and responding. It keeps the most important aspect of any science alive, thinking.

    One of the reasons I post on extreme weather threads is it seems too many just accept what is said without thinking about it or investigating the claims on their own. Doing some research.

    There is a claim global droughts are increasing. In this paper it shows that globally droughts are not showing any sign of increasing from 1950 to 2000 (page 444 of this article has a series of graphs, the first is global then many regional graphs). Some regions have increasing droughts, others have decreasing. Globally there is no apparent change.

    “Concurrent changes in drought spatial extent are
    evident, with a global decreasing trend of 0.021% to
    0.035% yr1.” From the summary of the above linked report.

  29. 179
    Norman says:

    Brian Dodge @172

    From this source I would certainly agree that extent of very warm area has increased from 1983. But it also looks like is is going down a bit.

    Each month’s extent of very warm area is given in the bar below the graph. If you are interested I can put the data in an excel sheet and determine the trend line. It is time consuming and only would do this if you think the task of value.

  30. 180
    Hank Roberts says:

    That 2006 quote says “set the thermostat” — so

    Assume he meant what he says.

    The next two decades are 2010-20 and 2020-30, if you’re counting by tens.

    Change the thermostat by ten degrees sometime in there — whatever that means for Lovelock — and it’d still take a long time to show up as a higher than expected increase in warming.

    Sure, you can imagine awful stuff. How about an outbreak of some unknown microorganism that trickles down with the rainwater and causes the Antarctic ice cap to slip loose and fall apart? Or something that lives in the top layer of the ocean and produces lots of hitherto unknown chlorinated greenhouse gases metabolized by consuming all our floating plastic scrap.

    But those are monster-under-the-bed notions, Gaia being the monster.
    The Medea hypothesis is quite sufficient for me.

  31. 181
    Norman says:

    Steven Franzen @166

    “So, what if it can’t be found that AGW increases the number and length of blocking patterns, or if extreme weather is not solely caused by atmospheric blocking? Would that make you “incompletely agree” or completely reject the statement that global warming will lead to more extreme weather?”

    No, I am not an absolutist. I like evidence based science the best when possible. You have a theory why weather would get more extreme. The current theory is warmer atmosphere has more energy and more water evaporation should lead to more intense storms and warmer temps should lead to more severe droughts. These are possibilites but they may not take place as expected. One is the Arctic Amplification may lessen storms, since the arctic is warming faster than the poles the potential energy is reduced. Even though the overall atmpospheric energy has increased, it is not total energy that drives a system but differences in energy between two regions.

    The only one that I can really conclude from global warming is that average precipitaion will increase (what goes up must come down, equilibrium) and that average temperatures will increase. That more extremes will develop is only a theory at this time and I am still looking for solid evidence to suggest it is more than such. It might be out there, I just have not found an really convincing amount of evidence.

  32. 182
    sidd says:

    Grr, I cannot type. Let me begin again. The data are for monthly precipitation on a 2.5 degree grid from

    I calculate the deviation for local average divided by local standard deviation for each grid point. Then i plot the histogram, lumping the counts for events greater than 5 sigma from the local mean.

    The results are at

    the latter on a semilog scale to better show the increase at large sigma.


  33. 183
    Tokodave says:

    Norman @ 179 “That more extremes will develop is only a theory at this time…” There are a number of metrics that suggest more extremes have developed; the number of FEMA declared disasters, increase in the amount of rain falling as “very heavy precipitation”, insured losses related to weather, significant weather related U.S. electric grid disturbances, relative number of high temperature records compared to cold temperature records, and of course the record number of billion dollar extreme weather events in 2011. Some of these have a cultural component, for example what FEMA declares a disaster, but collectively these suggest we are in fact seeing the very extremes you’re looking for.

  34. 184

    There is a claim global droughts are increasing.

    What ‘global droughts’ are you referring to Dr. Norman Page, petroleum geologist and frequent WUWT commentator?

  35. 185
    Hank Roberts says:

    Norman, have you taken a statistics class?

  36. 186
    Dan H. says:

    Unfortunately, people use those statistics which support their viewpoint, and ignore those that do not. The same can be said for data. I am always suspect when someone uses only part of the data, or analyzes the data in an unusual way.

  37. 187

    #177 Norman Grinvalds

    The problem is clear, you’re not using science correctly in your analysis, you’re using your own bias confirmation.

    That’s not scientific at all. Examine the confidence intervals re status of current understanding and underlying foundations that have survived peer response and maybe those cataracts will get better.

  38. 188

    #186 Dan H.

    Are you saying you have never made a claim inferring that there is no warming in the recent trends, or anything similar to that effect in relation to climate science?

  39. 189
    Dan H. says:

    Your words, not mine. I have stated repeatedly that we should be looking at the long term, not short term shifts. Looking at the warming or cooling over the short term is only important in attempting to correlate these changes with other forces.

  40. 190
    Norman says:

    Tokodave @183

    I am looking into the billion dollar disasters here.

    The Texas drought/heat wave of 2011 was listed as a $10 billion disaster.

    Scroll down on the link I provided and you see in 1988 the heatwave/drought was a $40 billion (adjusted to 2007 dollars I believe) that killed 5000 to 10000 people. Then in 1980 you have another heat wave and drought that was a $20 billion disaster that killed 10000 people. So in a historical context it is not so clear that heat waves and droughts are actually getting worse in time. You can look through other disasters as well.

    Seven of the 14 billion dollar disasters were casued by tornadoes. It was just a freak year for tornadoes and many hit cities. If an F4 or F5 hits a major city you are almsost assured it will cause a billion dollars worth of damage.

    Here is another possibility that can explain an increase in weather related disasters without an actual increase in number of extreme weather events (disasters involve people and property). This pattern is happening in the US and it is possible it is global (have not researched the global aspect yet).

    Look at the map of where the billion dollar US disasters are taking place.

    Now combine that information with this map.

    The link above shows that population growth along the coasts has increased 45% since 1970. Now look again at where most the disasters are taking place. Along the coasts.

  41. 191
    Norman says:

    Hank Roberts @185

    Unfortunately I never did take a statistics course (I wish I had). I have Calculus. I am learning statistics as I go. I certainly would not have your knowledge of the math, but I can learn it.

  42. 192
    Norman says:

    Thomas Lee Elifritz @184

    I am not using the best of grammar in my communications. It does not mean droughts that cover the globe. Just a global assessment of droughts, the conditions given in the article I linked to would be mean drought duration, number of droughts, and extent of droughts on a global scale (as opposed to a regional or national scale).

    But it is not Norman Page the petroleum geologist. I am Norman Grinvalds just a lab tech. No PhD for me. I think I posted once or twice on WUWT. I mainly was posting on Skeptical Science.

  43. 193
    John Pollack says:

    Norman @165 I looked at the climate change indicators that you referenced. Of course, the data goes up to about 2008, and misses some recent extreme events. Even within the period you refer to, there is a strong rise in warm minimum temperatures, which now greatly exceed the 1930s. There is also a substantial rise in extreme precipitation events.

    It is not clear to me whether the heat wave index covers the whole year, or merely the summer. If it is the latter, it ignores warm extremes that occur the rest of the year, when extremes are more easily generated by blocking. These extremes, such as our recent warm pattern, can be extremely disruptive to the life cycles of plants and animals, even when they are not uncomfortable to humans (at least, to those without pollen allergies.)

    There is a systematic weakness in these measures of heat which exclude dew points. For example, the Midwest heat wave of July 1995 produced are temperatures which were not extreme compared to the 1930s, but the upper air heights and temperatures were quite extreme. So were the dew points. A lot of people in Chicago died.

  44. 194
    Norman says:

    John P. Reisman (OSS Foundation)@187

    “The problem is clear, you’re not using science correctly in your analysis, you’re using your own bias confirmation.”

    Here is my position on the topic from my post at 178.

    “It keeps the most important aspect of any science alive, thinking.

    One of the reasons I post on extreme weather threads is it seems too many just accept what is said without thinking about it or investigating the claims on their own. Doing some research.”

    I am not staking a claim I am right, I am questioning what seems to be a lack of questions and more just accepting based on authority. Science lives when those in it raise questions. I am not sure many people actually look into past weather or climate to see what has already happened when it comes to extreme weather events. You may believe my path to be misguided but I am old fashioned. I like evidence based science. The motto is “prove it!” I have linked to various places which at this time do not show an obvious direction into extreme weather taking place.

    In my own research I was logging wind speeds from thunderstorms (70 knots and above) in the United States. I pasted a copy of an email exchange in Post 99. Wind speed showed these sudden jumps in reported numbers. Where things really getting much worse in very rapid fashion? I emailed one of the meteorologists in charge of the data and he was kind enough to reply and supply the answers. That indicates a lot of the increase in extreme weather now being reported may not be an actual increase in what is actually happening but just an increase in reporting of what is going on.

    I do link to data and information that does demonstrate my points (not just my opinion of things). As I stated, I like evidence based science. Let the evidence determine the reality of extreme weather.

  45. 195
    Tokodave says:

    Norman @ 190 As I mentioned there is clearly a cultural (and political…) component to some of the metrics reflecting more extremes but the NOAA map you reference actually shows billion dollar weather events are surprisingly well distributed across the country. It would only make sense that extreme events affecting the coasts are more likely to result in billion dollar costs, that’s where the people/cities/towns are. It’s only going to get worse
    The increase in the amount of rain falling as “very heavy precipitation” and relative number of high temperature records compared to cold temperature records are independent measures of the new normal. The sharp nationwide increase in insured losses related to weather and significant weather related U.S. electric grid disturbances cover the period from 1990 to 2007, so the 45% increase in coastal population since 1970 is unlikely to be a major factor particularly since the highest coastal growth is concentrated in a relatively small number of counties, many of them in Florida. Let’s watch how a higher sea level plays out down there.

  46. 196

    #189 Dan H.

    What do you mean by long-term? what is your context for your claims inferences and assertions?

    Decades? Centuries? Millennia? Hundreds of thousands of years? Millions of Years.

    Context is key.

    Therefore time scale and attribution in that time scale is key.

  47. 197

    #194 Norman Grinvalds

    Questioning the science is great when it’s done scientifically, but a guy on a blog, looking at regional data and trying to imply that means something globally does not good ‘global’ science make.

    There are no lack of questions in science. The basis of science is questions, boatloads of them.

    Science is examining myriad evidence lines for extreme events and even historical literature, paintings and music to look at correlates in extreme weather. Just because ‘people’ don’t’ does not mean science is not looking.

    Your own local research means nothing globally. Regional variances even with climate change will vary depending on what you are looking at.

    I’ve reviewed studies showing statistical significance on extremes pertaining to global warming. I don’t recall them off the top of my head (you can do some digging if you really want to get to the truth), but you should look at those. The evidence is only getting better in the attribution as more study is done.

    Your own analysis does not change those analyses. And until you get yours published and in context, your analysis does not have significance.

  48. 198
    Dan H. says:

    So far, no one has shown a clear connection between global warming an increased “blocking,” although much speculation has gone down that road. Conditions existed that created perceived blocking patterns for extended periods in the 1930s, but there is little evidence that these patterns have increased significantly. This is an area to watch in the future, as many are predicting an incrase in extreme heat and cold.

  49. 199
    Hank Roberts says:

    > Dan H. … So far, no one has shown

    Dan H. teaches the controversy.

    Paste his words into a Scholar search.

  50. 200
    Hank Roberts says:

    Multiple flow equilibria in the atmosphere and blocking
    Charney et al. 1979

    –> Cited by 605 subsequent papers.

    Charney, Jule G., John G. DeVore, 1979: Multiple Flow Equilibria in the Atmosphere and Blocking. J. Atmos. Sci., 36, 1205–1216.