Hot Heat

A recent screed by a denier claims that none of the expected unhappy consequences of global warming has happened, not even any increase in heat waves. That claim is not only false, it’s ridiculous. One of the consequences of global warming is an increase in heat waves, and in extreme hot days — which isn’t a future consequence, it has happened already.

Let’s take another look at daily high temperature from ECA&D, the European Climate Assessment and Dataset Project. It has recently updated its daily data holdings through August of 2015, so we’ll have very current data, including this year. We’ll study the summer months of June, July, and August, and count how many “hot days” occur each year. In order for a year to be included, it had to have data for at least 85 of the 92 summer-month days. In order for a station to be included, it had to have data for at least 100 years since 1900, including at least one year in the 2010’s.

“Hot” is defined relative to what was normal for that location prior to 1980. The cutoff limit was chosen as the 99th percentile (of summer days), so we’re looking at extremely hot days — ordinarily we would expect an average of slightly less than one per year. Then we can compare how many occured at each location from 1900 through 1979, to how many each year since 1980.

Here’s a “map” of the change in the total number of hot days from the 1900-1979 time span, to years since 1980. Red circles show places with more hot days, blue circles those with fewer, the size of the cirlce indicating how much the number changed:


There are a few scattered places where the average number of very hot days has decreased — but few indeed, and not by much. There are, however, many places where very hots days are more frequent, and by a lot. Only about 11% of locations have suffered less extreme heat while 89% have suffered more.

In some places the number of very hot days has exploded, and this year (2015) was a helluva scorcher in Europe. Kremsmuenster, Austria, for instance, sweltered through 32 very hot days this year — the kind of heat you would have expected to happen, before 1980, slightly less than once per year. But this year it happened 32 times. That’s a whopper of a heat problem — and yes, it’s a problem.


But let’s not judge the whole set by one extreme location. Here’s the number of very hot days per year for each location, with different places plotted in different colors:


From this it’s evident that the severe heat problem in Europe really kicked off with the killer heat wave in 2003 — and that it has kept coming since then. In fact it’s gotten worse; if we plot the average for all stations, we see that this year has been the worst yet:


Bear in mind that by definition — since “very hot days” is defined by the 99th percentile at each location — what used to be a “slightly less than once a year on average” event has already gotten about four times more common. And that’s the average over all ECA&D stations — some places have been hit even harder.

And it’s going to get worse. Maybe not next year, maybe not the next, but soon, and for the rest of our lives.

Not only will such very hot days get more frequent than they already have, they’ll get hotter too. The impact of all that extra heat isn’t just the number of days it happens, it’s how hot the days get. And that too is on the increase.

Anybody who says that heat waves aren’t already worse than they were, is either a fool or a liar or both. Anybody who denies that they’re going to get worse, is selling something.

20 responses to “Hot Heat

  1. I’ve seen a story every day this week that caused me to comment, “Climate change isn’t climate change when it happens to other people.” That seems to be the basic foundation of the deniers’ worldview.

  2. A recent screed by a denier claims…

    I’ll look at the meat of this post later, but I have to say I like this approach. Why waste time on the unimportant details of these lightweights?

  3. If you will permit a question: how far outside of the norm does one have to stand before being called batshit crazy?

  4. michael sweet

    James Hansen has documented increases in extremely hot summers with this paper: He analyizes the combined months of JJA. Since it was published in 2012 it is getting out of date, this year was undooubtedly worse than the ones he analyzed. Does anyone have a link to updated data?

    Hansen found that 3 sigma summers occured over more than 10% of the land surface. Winter heats up more but since the standard deviation of temperature in the winter is higher there is not the increase in 3 sigma winters as observed in the summer.

    • Since Hansen, Sato & Ruedy were using decadal statistics, this isn’t the type of analysis that would necessarily benefit from annual updates. Although 2022 seems a long way away, the next consistent update would be to enter data for the period 2011-2021. (Or maybe rush ahead with 2011-2016 if you’re really impatient).

  5. thanks for taking the time and effort

  6. It just occured to me that you could overlay a map on that graph!
    Lovely work, as usual.

  7. One reason that the Europeans are united in action against climate change is that they are seeing temperatures far above the historical norm. As an example, when I worked at a Max Planck Institute in northern Germany in 1986, the temperature did not exceed 68 oF during the summer until early September. The Germans complained about the cool summer. This summer Hamburg saw temperatures in the mid 90s (oF). There is a reason why just about no homes in Germany have air conditioning. My daughter’s German school closed when the temperature was higher than 80 oF.

    • You probably meant 86 °F (30 °C) or 90°. The Germans have become soft and whiny, but not that much.

  8. I keep waiting for the denihilists to proclaim that we’re starving the Earth of coal smoke and so Gaia has been running a fever since 1970 — and that wildfires, agricultural burning, and then fossil fuels were all the planet’s way of producing sufficient magic pixie dust to maintain homeostasis.

    Shorter: atmospheric cleanliness leads to ghastliness.

    Yeah, it’s Hallowe’en coming on.

    • That’s a neat turnaround. I’m feasting on this which has the same flavor, which Tamino has picked up in his most recent (h/t Rabett via BoingBoing):

      Plot idea: 97% of the world’s scientists contrive an environmental crisis, but are exposed by a plucky band of billionaires & oil companies.
      — Scott Westerfeld

      • I’ve seen that before. It still cracks me up!

      • Whenever I return from the task of melting the ice caps, I have to return all the extension cords and hair dryers I borrowed. thank you all. .– hard work, but we did the job… tough to keep the real cause of melting a secret. Next Spring I will need to borrow those cords and heaters again, and we still need more volunteers.

  9. Pete Dunkelberg

    Routine. When denial gets harder, deniers deny harder.
    Good analysis as usual.

  10. What I have wondered ever since I read Gerard Meehl’s 2009 study of US temperature extremes and the Hansen paper cited above by Sweet is why these kinds of analyses are not highlighted and presented more often to the general public. For most people without a statistical education, means and standard deviations, are far removed from their experience and have little impact on their thinking and beliefs. Thus, the minor impact of yearly world temperatures trends on the general public and the ease with which deniers can argue the faux pause–and convince people. People understand frequencies because they are easier to relate to experience. Analyses of frequencies ring a bell for many people: “yeah, it does seem like we are having more hot days and nights than when I was a kid.” How about animated charts in the vein of the famous shrinking ice cube graphic showing arctic warming? I am thinking growing stacks of hot day icons or some such. Also, another great post, Tamino.

  11. One of the obvious points that seems to (deliberately) escape many of our skeptical friends is that extremes are disproportionately dangerous. A single fifteen minute hailstorm can wipe out a farmer’s entire crop, as can a single hard frost. People are killed during sudden floods or days-long heat waves and cold snaps. Long-lived mammals can die due to a few critical weeks of drought, bad foraging or bad hunting, and whole breeding seasons can be lost due to similar badly-timed events.

    The importance of such events and the relative ease of studying them in the era of digital data makes me wonder why we don’t see more studies on these fat-tail events. (To be fair, maybe they are being done and I’m just not coming across them.)

    There’s an old joke about statistics with many variations, but the basic idea being that someone with his head in the freezer and his feet in the oven is comfortable, on average. That almost everyone understands the absurdity of the joke makes it all the more puzzling that the risks outlined by Hansen and others are so casually brushed aside by the denialists and their political allies.

  12. Philippe Chantreau

    Very nice data presentation. I recently had an exchange on SkS with a poster who compared the risk posed by climate change to some absurdly remote hypothetical situation. I had remind him that events with an extremely low probability are happening on a regular basis these past few years. These events are either predicted by the standard model of Earth climate under the current conditions, or entirely consistent with the expectations from a warming climate. Both the floods in South Carolina and in Southern France are 1 in 1000 years types of events and they happened the same week-end. Then we have all the wildfires, in the Western Us and in Australia. And the heat waves. And the Arctic sea ice, loss of permafrost, forest fires. I’m thinking that when (not if) the next gigantic chunk of Antarctic ice shelf goes floating they will still continue to deny. Sometimes you have to wonder what it will take…

  13. PJ Kar: “Sometimes you have to wonder what it will take…”

    Well, the more you pay, the more it’s worth. These guys have already sunk such high costs in terms credibility, they may never be able to admit they are wrong. Max Planck said, “Physics advances one funeral at a time.” This may be similar.

  14. I’ve been going to Austria for 2-5 weeks in the summer most years since 1987, and this summer was indeed exceptionally hot and dry, and for a much longer contiguous period than I’ve ever seen before. Our campsite/gasthof spring has never run dry before. Just a bit of anecdotal data, but absolutely congruent with tamino’s analysis. Only the dramatic heatwave for over a week 2 years earlier makes it seem slightly less extreme.