It’s Heat Records Silly Season

Photo illustration by Slate. Photos by Thinkstock.

A glance at the news aggregator shows the silly season is in full swing.  A partial listing of headlines proclaiming the hottest whatever.

  • Record-crushing heat, fire tornadoes and freak thunderstorms: The weather is wild in the West The Washington Post15:50
  • Tesla asks owners to help ‘relieve stress on grid’ during heat wave in California, charge… Electrek15:47
  • Death Valley’s 130-degree Heat Wave May Have Set a 107-year Record Travel & Leisure
  • Newsom Signs Emergency Proclamation to Free Up Energy Amid Heat Wave NBC Bay Area, California14:10
  • Dozens of heat records set to be broken this week as Western heat wave continues CNN14:10
  • Okanagan weather: Mid-30 degree heat to continue for early part of week Global News13:58
  • Heat Wave To Continue Through Thursday In San Diego County Patch13:40
  • Death Valley hits an insane 130 degrees, threatens heat records CNET13:18
  • Sunday brings more record highs as heat lingers Ventura County Star, California EU13:08
  • As West Coast Faces Historic Heat Wave & Energy Shortages, Governor Newsom Signs Heat Emergency Proclamation to Free Up … California State Portal (Press Release)13:00
  • California in grip of extreme weather: Broiling heat, fire tornadoes, lightning, blackouts Los Angeles Times11:29
  • Heat Wave Harvey? Push To Name Extreme Heat Events Warming Up KUER-FM11:20
  • Heat warnings posted for parts of B.C. as temperature records tumble The Globe and Mail10:49
  • Heat warnings issued for most of Alberta CBC.ca10:46
  • US heat wave leads to ‘hottest temperature ever’ and firenados CBBC Newsround07:34
  • 2019 State of the Climate Report: Peak greenhouse gases and record heat EarthSky06:56
  • Should We Name Heat Waves Like We Name Hurricanes? Planet Friendly News06:41
  • Meteorologists are extending the heat warning Prague Monitor04:35
  • Worst Heat Wave in Years Sets Three Temperature Records in LA County NBC Los Angeles02:35
  • Worst Heat in 70 Years Threatens to Take Down California’s Grid BNN Bloomberg02:15
  • Heat Wave Grips S. Korea KBS World Radio00:54
  • Records Tumble As San Francisco Bay Area Swelters Under Stifling Heat Wave CBS San Francisco23:31 Sun, 16 Aug
  • Sofia Richie Beats Southern California Heat Wave At The Beach In Pink Thong Bikini The Inquisitr23:25 Sun, 16 Aug
  • After Record Breaking Heat, A Gradual Cooldown In Washington Patch23:21 Sun, 16 Aug
  • Heat waves, tropical nights to continue this week The Korea Herald22:47 Sun, 16 Aug
  • Thunderstorms and excessive heat fuel wildfires in California CBS News22:21 Sun, 16 Aug
  • Heat wave grips South Korea as monsoon season ends Bernama22:14 Sun, 16 Aug
  • Las Vegas reaches 113 again, ties 1939 record as heat wave continues Las Vegas Review-Journal22:04 Sun, 16 Aug
  • This past decade was the hottest decade in Earth’s history CNN03:50 Fri, 14 Aug
  • Last Decade Was Earth’s Hottest On Record UNILAD13:27 Thu, 13 Aug
    111-Degree High Forecasted Next Week, Would Be One Of
  • Sacramento’s Hottest Days Ever CBS Sacramento13:27 Thu, 13 Aug
  • NWS warns this will be the ‘hottest weekend of the year’ in… San Antonio Express, Texas11:46 Thu, 13 Aug
  • July 2020 was record hot for N. Hemisphere, 2nd hottest for planet National Oceanic and Atmospheric Administration10:59 Thu, 13 Aug
  • London is experiencing its hottest weather since the ’60s Time Out London10:49 Thu, 13 Aug
  • Record shattered for hottest week in Dutch history NL Times10:29 Thu, 13 Aug
  • Belgium records hottest week in history Anadolu Agency10:00 Thu, 13 Aug
  • The 2010s were Earth’s hottest decade on record TheJournal.ie07:25 Thu, 13 Aug
  • Last year was one of the hottest since records began, ending the hottest decade SBS22:21 Wed, 12 Aug
  • 2019 the hottest year on earth since records began, ending the hottest decade SBS21:51 Wed, 12 Aug
  • Last decade was hottest on record as climate crisis accelerates The Independent21:25 Wed, 12 Aug
  • Hottest night in 25 YEARS recorded in Reading Reading Chronicle14:03 Wed, 12 Aug
  • London sees hottest stretch since 1960s BBC12:09 Wed, 12 Aug
  • Last decade was Earth’s hottest on record as climate crisis accelerates The Guardian11:56 Wed, 12 Aug

Time for some Clear Thinking about Heat Records (Previous Post)

Here is an analysis using critical intelligence to interpret media reports about temperature records this summer. Daniel Engber writes in Slate Crazy From the Heat

The subtitle is Climate change is real. Record-high temperatures everywhere are fake.  As we shall see from the excerpts below, The first sentence is a statement of faith, since as Engber demonstrates, the notion does not follow from the temperature evidence. Excerpts in italics with my bolds.

It’s been really, really hot this summer. How hot? Last Friday, the Washington Post put out a series of maps and charts to illustrate the “record-crushing heat.” All-time temperature highs have been measured in “scores of locations on every continent north of the equator,” the article said, while the lower 48 states endured the hottest-ever stretch of temperatures from May until July.

These were not the only records to be set in 2018. Historic heat waves have been crashing all around the world, with records getting shattered in Japan, broken on the eastern coast of Canada, smashed in California, and rewritten in the Upper Midwest. A city in Algeria suffered through the highest high temperature ever recorded in Africa. A village in Oman set a new world record for the highest-ever low temperature. At the end of July, the New York Times ran a feature on how this year’s “record heat wreaked havoc on four continents.” USA Today reported that more than 1,900 heat records had been tied or beaten in just the last few days of May.

While the odds that any given record will be broken may be very, very small, the total number of potential records is mind-blowingly enormous.

There were lots of other records, too, lots and lots and lots—but I think it’s best for me to stop right here. In fact, I think it’s best for all of us to stop reporting on these misleading, imbecilic stats. “Record-setting heat,” as it’s presented in news reports, isn’t really scientific, and it’s almost always insignificant. And yet, every summer seems to bring a flood of new superlatives that pump us full of dread about the changing climate. We’d all be better off without this phony grandiosity, which makes it seem like every hot and humid August is unparalleled in human history. It’s not. Reports that tell us otherwise should be banished from the news.

It’s true the Earth is warming overall, and the record-breaking heat that matters most—the kind we’d be crazy to ignore—is measured on a global scale. The average temperature across the surface of the planet in 2017 was 58.51 degrees, one-and-a-half degrees above the mean for the 20th century. These records matter: 17 of the 18 hottest years on planet Earth have occurred since 2001, and the four hottest-ever years were 2014, 2015, 2016, and 2017. It also matters that this changing climate will result in huge numbers of heat-related deaths. Please pay attention to these terrifying and important facts. Please ignore every other story about record-breaking heat.

You’ll often hear that these two phenomena are related, that local heat records reflect—and therefore illustrate—the global trend. Writing in Slate this past July, Irineo Cabreros explained that climate change does indeed increase the odds of extreme events, making record-breaking heat more likely. News reports often make this point, linking probabilities of rare events to the broader warming pattern. “Scientists say there’s little doubt that the ratcheting up of global greenhouse gases makes heat waves more frequent and more intense,” noted the Times in its piece on record temperatures in Algeria, Hong Kong, Pakistan, and Norway.

Yet this lesson is subtler than it seems. The rash of “record-crushing heat” reports suggest we’re living through a spreading plague of new extremes—that the rate at which we’re reaching highest highs and highest lows is speeding up. When the Post reports that heat records have been set “at scores of locations on every continent,” it makes us think this is unexpected. It suggests that as the Earth gets ever warmer, and the weather less predictable, such records will be broken far more often than they ever have before.

But that’s just not the case. In 2009, climatologist Gerald Meehl and several colleagues published an analysis of records drawn from roughly 2,000 weather stations in the U.S. between 1950 and 2006. There were tens of millions of data points in all—temperature highs and lows from every station, taken every day for more than a half-century. Meehl searched these numbers for the record-setting values—i.e., the days on which a given weather station saw its highest-ever high or lowest-ever low up until that point. When he plotted these by year, they fell along a downward-curving line. Around 50,000 new heat records were being set every year during the 1960s; then that number dropped to roughly 20,000 in the 1980s, and to 15,000 by the turn of the millennium.

From Meehl et al 2009.

This shouldn’t be surprising. As a rule, weather records will be set less frequently as time goes by. The first measurement of temperature that’s ever taken at a given weather station will be its highest (and lowest) of all time, by definition. There’s a good chance that the same station’s reading on Day 2 will be a record, too, since it only needs to beat the temperature recorded on Day 1. But as the weeks and months go by, this record-setting contest gets increasingly competitive: Each new daily temperature must now outdo every single one that came before. If the weather were completely random, we might peg the chances of a record being set at any time as 1/n, where n is the number of days recorded to that point. In other words, one week into your record-keeping, you’d have a 1 in 7 chance of landing on an all-time high. On the 100th day, your odds would have dropped to 1 percent. After 56 years, your chances would be very, very slim.

The weather isn’t random, though; we know it’s warming overall, from one decade to the next. That’s what Meehl et al. were looking at: They figured that a changing climate would tweak those probabilities, goosing the rate of record-breaking highs and tamping down the rate of record-breaking lows. This wouldn’t change the fundamental fact that records get broken much less often as the years go by. (Even though the world is warming, you’d still expect fewer heat records to be set in 2000 than in 1965.) Still, one might guess that climate change would affect the rate, so that more heat records would be set than we’d otherwise expect.

That’s not what Meehl found. Between 1950 and 2006, the rate of record-breaking heat seemed unaffected by large-scale changes to the climate: The number of new records set every year went down from one decade to the next, at a rate that matched up pretty well with what you’d see if the odds were always 1/n. The study did find something more important, though: Record-breaking lows were showing up much less often than expected. From one decade to the next, fewer records of any kind were being set, but the ratio of record lows to record highs was getting smaller over time. By the 2000s, it had fallen to about 0.5, meaning that the U.S. was seeing half as many record-breaking lows as record-breaking highs. (Meehl has since extended this analysis using data going back to 1930 and up through 2015. The results came out the same.)

What does all this mean? On one hand, it’s very good evidence that climate change has tweaked the odds for record-breaking weather, at least when it comes to record lows. (Other studies have come to the same conclusion.) On the other hand, it tells us that in the U.S., at least, we’re not hitting record highs more often than we were before, and that the rate isn’t higher than what you’d expect if there weren’t any global warming. In fact, just the opposite is true: As one might expect, heat records are getting broken less often over time, and it’s likely there will be fewer during the 2010s than at any point since people started keeping track.

This may be hard to fathom, given how much coverage has been devoted to the latest bouts of record-setting heat. These extreme events are more unusual, in absolute terms, than they’ve ever been before, yet they’re always in the news. How could that be happening?

While the odds that any given record will be broken may be very, very small, the total number of potential records that could be broken—and then reported in the newspaper—is mind-blowingly enormous. To get a sense of how big this number really is, consider that the National Oceanic and Atmospheric Administration keeps a database of daily records from every U.S. weather station with at least 30 years of data, and that its website lets you search for how many all-time records have been set in any given stretch of time. For instance, the database indicates that during the seven-day period ending on Aug. 17—the date when the Washington Post published its series of “record-crushing heat” infographics—154 heat records were broken.


That may sound like a lot—154 record-high temperatures in the span of just one week. But the NOAA website also indicates how many potential records could have been achieved during that time: 18,953. In actuality, less than one percent of these were broken. You can also pull data on daily maximum temperatures for an entire month: I tried that with August 2017, and then again for months of August at 10-year intervals going back to the 1950s. Each time the query returned at least about 130,000 potential records, of which one or two thousand seemed to be getting broken every year. (There was no apparent trend toward more records being broken over time.)

Now let’s say there are 130,000 high-temperature records to be broken every month in the U.S. That’s only half the pool of heat-related records, since the database also lets you search for all-time highest low temperatures. You can also check whether any given highest high or highest low happens to be a record for the entire month in that location, or whether it’s a record when compared across all the weather stations everywhere on that particular day.

Add all of these together and the pool of potential heat records tracked by NOAA appears to number in the millions annually, of which tens of thousands may be broken. Even this vastly underestimates the number of potential records available for media concern. As they’re reported in the news, all-time weather records aren’t limited to just the highest highs or highest lows for a given day in one location. Take, for example, the first heat record mentioned in this column, reported in the Post: The U.S. has just endured the hottest May, June, and July of all time. The existence of that record presupposes many others: What about the hottest April, May and June, or the hottest March, April, and May? What about all the other ways that one might subdivide the calendar?

Geography provides another endless well of flexibility. Remember that the all-time record for the hottest May, June, and July applied only to the lower 48 states. Might a different set of records have been broken if we’d considered Hawaii and Alaska? And what about the records spanning smaller portions of the country, like the Midwest, or the Upper Midwest, or just the state of Minnesota, or just the Twin Cities? And what about the all-time records overseas, describing unprecedented heat in other countries or on other continents?

Even if we did limit ourselves to weather records from a single place measured over a common timescale, it would still be possible to parse out record-breaking heat in a thousand different ways. News reports give separate records, as we’ve seen, for the highest daily high and the highest daily low, but they also tell us when we’ve hit the highest average temperature over several days or several weeks or several months. The Post describes a recent record-breaking streak of days in San Diego with highs of at least 83 degrees. (You’ll find stories touting streaks of daily highs above almost any arbitrary threshold: 90 degrees, 77 degrees, 60 degrees, et cetera.) Records also needn’t focus on the temperature at all: There’s been lots of news in recent weeks about the fact that the U.K. has just endured its driest-ever early summer.

“Record-breaking” summer weather, then, can apply to pretty much any geographical location, over pretty much any span of time. It doesn’t even have to be a record—there’s an endless stream of stories on “near-record heat” in one place or another, or the “fifth-hottest” whatever to happen in wherever, or the fact that it’s been “one of the hottest” yadda-yaddas that yadda-yadda has ever seen. In the most perverse, insane extension of this genre, news outlets sometimes even highlight when a given record isn’t being set.

Loose reports of “record-breaking heat” only serve to puff up muggy weather and make it seem important. (The sham inflations of the wind chill factor do the same for winter months.) So don’t be fooled or flattered by this record-setting hype. Your summer misery is nothing special.


This article helps people not to confuse weather events with climate.  My disappointment is with the phrase, “Climate Change is Real,” since it is subject to misdirection.  Engber uses that phrase referring to rising average world temperatures, without explaining that such estimates are computer processed reconstructions since the earth has no “average temperature.”  More importantly the undefined “climate change” is a blank slate to which a number of meanings can be attached.

Some take it to mean: It is real that rising CO2 concentrations cause rising global warming.  Yet that is not supported by temperature records.
Others think it means: It is real that using fossil fuels causes global warming.  This too lacks persuasive evidence.
WFFC and Hadcrut 2018Over the last five decades the increase in fossil fuel consumption is dramatic and monotonic, steadily increasing by 234% from 3.5B to 11.7B oil equivalent tons. Meanwhile the GMT record from Hadcrut shows multiple ups and downs with an accumulated rise of 0.74C over 53 years, 5% of the starting value.

Others know that Global Mean Temperature is a slippery calculation subject to the selection of stations.

Graph showing the correlation between Global Mean Temperature (Average T) and the number of stations included in the global database. Source: Ross McKitrick, U of Guelph

Global warming estimates combine results from adjusted records.

The pattern of high and low records discussed above is consistent with natural variability rather than rising CO2 or fossil fuel consumption. Those of us not alarmed about the reported warming understand that “climate change” is something nature does all the time, and that the future is likely to include periods both cooler and warmer than now.

Background Reading:

The Climate Story (Illustrated)

2020 Update: Fossil Fuels ≠ Global Warming

Man Made Warming from Adjusting Data

What is Global Temperature? Is it warming or cooling?


  1. Hifast · August 17, 2020

    Reblogged this on Climate Collections and commented:
    The Furnace Creek thermometer is sited between two long strips of asphalt.


  2. rw · August 22, 2020

    Ron, what do you think of Clive Best’s analysis that showed that late in the past decade the CRU people dropped hundreds of North American temperature stations and substituted others, mostly from Russia? The result was that the hiatus disappeared. (My personal hypothesis concerning this is that with the Climate Reference Network showing no trends and thus restraining any adventurous adjustments of the USHCN records by the NCDC guys, the CRU people decided to ‘go elsewhere’ for their temperature data.) So who knows what’s happening to the global average these days.


    • Ron Clutz · August 22, 2020

      rw, Clive did a later analysis that showed the hiatus was warmed by adjustments to station data. See:
      I found the same effect from adjustments in US station records.


      • rw · August 23, 2020

        Thanks, Ron. I will add your work to an essay I’m currently writing.

        Incidentally (or not incidentally), if one goes through the published literature on temperature reconstruction and averaging, one finds rationales for most of the adjustments (although I have no idea why so many data points were deleted). For the USHCN the shift from evening to morning readings after WWII shifts the TOB from positive, i.e. greater than midnight or hourly readings, to negative. To ‘correct’ this, earlier temperatures are reduced, while later ones are elevated. Also, the shift from CRS (Stevenson screens) to MMTS lowers the temperatures – other things being equal (which they’re not). Interestingly, I saw nothing in the literature about: (i) the fact that MMTS stations are often moved closer to buildings to reduce the length of the electric cords – and this will, ceteris paribus, elevate the temperatures, (ii) Anthony Watts’ observation that changing the Stevenson screen paint from whitewash to latex (which according to Watts occurred in the late 70s) increases the temperature, (iii) the fact that some observers (like the guy in Bridgehampton) took readings twice a day; if the times are reasonable, this serves to eliminate the TOB. (Frequency histograms are given in some papers showing the frequency of different times of observation, but nothing about observers taking temperatures more than once a day.) So my conclusion is that the data are hopelessly compromised – and the process is wide open to bias and fraud.


      • Ron Clutz · August 23, 2020

        IMO most of the adjusting comes from pairwise homogenizing algorithms by which one station’s numbers are changed for another’s to “improve” accuracy.


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