After working with my heat index for a while, I’ve concluded that values >= 20 represent severe extreme heat in a given year at a given location. It makes for very informative maps when one highlights the locations that exceed the limit, i.e. that have not just a hot year, but a severely hot year. That in turn reveals that certain regions of the Northern Hemisphere extratropics are susceptible to severely hot summer temperatures, the deadly “heat wave.”

One of those regions is near the center of North America, well illustrated by the 1934 heat wave (part of the “dust bowl” years in the American midwest); I delineate it as longitudes 80°W to 105°W, latitudes 29°N to 50°N.

The area has experienced a severely hot summer many times in the past, including its most severe in 1936. I also identified four other regions of heightened heat wave activity, all in lands near the Mediterranean sea. One of them is west Europe, which brought the issue to prominence during the 2003 European heat wave:

The next deadly heat wave to attract worldwide attention hit Russia in 2010, in the upper part of the region I call “east Europe,” and also hit a large area south of it that I refer to as the “middle east.”

The fifth region, which I identify as “NorthWest Africa,” shows itself in 2016, also a year of severe summer heat in the middle east:

So far, years in the 2020s tend to show severe summer heat in more than just one region. A striking example is 2022, when heat waves hit four of my five susceptible regions and other northern-hemisphere areas as well:

When heat waves are linked to climate change, it’s the custom of climate deniers to put their blinders on. They focus on the USA, because the first region I identified as a heat-wave hotspot is in the middle of the United States, and the history of that region is dominated by the severe years of the 1930s, the dust bowl decade. It also shows just how variable it can be in this part of the world:

Values 20 or higher are severe heat for an individual location; for a large region (like this one) that applies to values of 10 or higher. For the central north American region, that has happened ten times since the year 1880. For over a century, middle America was the area of the northern hemisphere most susceptible to severe summer heat.

But if we take the blinders off and look at the history of hot heat in the hemisphere, we see a very different picture:

Hemispheric heat waves of the 20th century were so dominated by America that until 1998, the hottest year was 1936 (hottest of the dust bowl years). But during the 21st century, other regions (including those I have identified as heat wave hotspots) have felt ferocious temperatures and upward trends. The first year the Western European regional average exceeded 10 was 2003, and the consequences were genuinely deadly. It has happened again — six times (!).

East Europe (as a region) didn’t exceed a heat index of 10 for over 100 years, but since 2000 has done so five times:

The area that I’ve christened the middle east not only shows a dramatic upward trend recently, it also has very extreme regional heat index values. Summer heat there has become truly lethal, and if the trend continues it will only get hotter.

Americans, take heed! When we look beyond our own borders, the severe increase in severe heat can only be denied by fools and liars.

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