Open Mind

I’m prepared to predict, even two weeks before it’s over, that summer 2026 will end up as England’s hottest on record.

Central England Temperature (CET, data available here) records the average temperature over a large region of central England, starting on January 1st, 1772, and includes both daily high and overnight low temperatures since 1878. What does it have to say about summer heat? Here’s the summer average (June/July/August) for daily high temperature:

The upward trend recently is plainly evident. The final value, for 2026, is hottest of all, but will change as new data arrive. When “the smoke clears” it is overwhelmingly likely it will still exceed any previous year.

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Until recently, the hottest month on record for USA48 (a.k.a. the “lower 48 states” of the USA) was July 1936, with two of the five hottest months from the 1930s (the “dust bowl” era). Not any more. According to data from NOAA, we just set a new record; now the hottest of all is July 2026, and four of the five hottest are after the year 2000. In the following graph, this July is circled in red:

Perhaps of greater interest, at least scientifically, is the trend in USA48 temperature, which is clear from yearly average temperature anomaly (the last value is year-to-date for 2026):

The average warming rate since 1975 is 0.31 ± 0.09 °C/decade (0.56 ± 0.16 °F/decade, intervals are ± 2σ), which is more than 50% larger than the global average rate.

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The forest in Canada is burning, and the smoke is a big problem for both Canadians and Americans as it makes its way across their country and into ours. Our president has blamed Canada for mismanaging their forests and threatens to hold them responsible, but the truth is:

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The Berkeley Earth surface temperature project provides monhly averages of high temperature, and high temperature anomaly (how different it is from “nominal”), on an equal-area grid over all the land areas on Earth. I computed, for each year and for each grid, the summer high-temperature anomaly as an indicator of just how hot each summer was, for each grid. So far, I’ve only done the northern hemisphere extratropics, so this is a report on summer (June/July/August) heat for land areas north of latitude 23°, an area which is home to much of the world’s population.

I surveyed the results to identify the year, and the summertime anomaly, of the hottest summer for each grid. Here’s a map showing which grids peaked before the year 2000 in blue, and those which peaked after 2000 in red, with the size of the dots indicating how intense the hottest summer was.

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Most of the world shows a notable, and statistically significant, rise in extreme summer heat. That’s not an opinion, it’s a fact. The reason is: global warming. That’s a fact. The consequences include a lot of unnecessary deaths, a tremendous financial cost to cope with the heat, and massive financial loss from reduced productivity. Each year it costs tens of thousands of lives and billions of dollars, and that’s a fact.

When it comes to this year’s heat waves, the focus has been on western Europe. There are numerous indexes of how heat wave intensity has changed from year to year (I’ve developed a few of my own), but one of the most easy-to-use and easy-to-acquire is simply to calculate, for each year, the average daily-high-temperature anomaly during the summer months (June, July, and August). It’s not a perfect measure, but is a surprisingly good one, and in Europe, temperature records extend far enough back in time to give us good estimates of just that quantity over more than 200 years.

For France, I acquired such data from the Berkeley Earth surface temperature project, but it only extends up to the year 2018 so I supplemented it with ERA5 data, covering the time span from 1950 through 2025. Here’s what they say about summer average high-temperature anomaly in France:

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Like most of Europe, England has suffered through extreme heat this June. This is unsurprising, given what we know about global warming. But there are still those who wonder, has summer heat in England really gotten worse — not just this year, but over time? Does it show a trend (and is it statistically significant)? What does history have to say about it?

Fortunately, one of the regions richest in early temperature records is central England, with enough data for modern researchers to piece together a temperature time series centuries in the past. It is a daunting task to combine different data from different sources, some in different locations and on different scales, all the while compensating for the ways in which coverage and instrumentation have changed over the years. But it has been well worth the effort, yielding a daily record referred to as Central England Temperature (CET), the average temperature over a large region of central England, starting on January 1st, 1772. Further research has managed to estimate CET going all the way back to 1659, but based on less data and of less precision, so those are not estimated daily values of CET but monthly averages. The CET data, both its daily and monthly-average versions, is still maintained as the world’s longest continuous thermometer record.

What does CET have to say about summer heat? Since 1878 it includes both daily high and overnight low temperatures, so I’ll focus on daily high temperature. First, I’ll compute its yearly average from 1878 through 2025:

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