No Evidence That Weather Extremes Becoming More Frequent or Intense: (1) Heat Waves

Climate reporting of the last few years has routinely promoted the mistaken belief that weather extremes are worsening be­cause of climate change.

But the perception that weather extremes are increasing in frequency and intensity is false. The perception actually results from modern technology – the Internet and smart phones – which has revolutionized communication and made us much more aware of extreme weather than we were 50 or 100 years ago.

To demonstrate how extreme weather has not changed or even declined over time, this and subsequent posts will present observational evidence showing long-term trends over the past century or so for heat waves, droughts, floods, hurricanes, tornadoes and wildfires.

Heat Waves and Historical Temperature Records

We’ll start with heat waves. It’s commonly argued that heat waves today are hotter than ever before. That is possible, but only because global warming has raised the baseline temperature by 1.3 degrees Celsius (2.3 degrees Fahrenheit) since preindustrial times – so we would expect heat waves to be that much hotter too.

Even so, there’s no evidence that current heat waves are hotter on average than they were in the past. The figure below shows the frequency and magnitude of heat ­waves in the U.S. from 1901 to 2018. The frequency (top panel) is defined as the annual number of calendar days the average U.S. maximum temperature exceeded the 90th percentile for 1961–1990 during at least six consecutive days, in a window centered on that calendar day; it repre­sents the average duration of all heatwaves of six days or longer in that year.

Long-Term U.S. Data Show No Upward Trend

It’s clear that there were far more frequent and/or longer U.S. heat waves, and they were hotter, in the 1930s than in the present era of global warming. The average annual heat wave or warm spell duration (top panel) is seen to have dropped from 11 days during the 1930s to about 6.5 days during the 2000s. The peak heat wave index (bottom panel) in 1936 was a full three times higher than in 2012 and up to nine times higher than in many other years.

In addition, the aver­age maximum temperature during any particular U.S. heat wave has declined slightly from 38 degrees Celsius (101 degrees Fahrenheit) in the 1930s to 37 degrees Celsius (99 degrees Fahrenheit) since the 1980s. This can be seen indirectly in the next figure, which plots the average number of days per weather station with maximum temperatures above 35 degrees Celsius (95 degrees Fahrenheit) for the conterminous U.S. (bars) and regions (lines, 11-year averages).

With the exception of the Pacific southwest (dashed blue line) and the Four Corners states (Arizona, Utah, Colorado and New Mexico, dashed black line), all other regions exhibit a declining trend. The absence of any trend in the U.S. as a whole is clearly evident.

The Heat Waves of the 1930s Remain Unmatched

As I’ve documented in a GWPF report, the hottest years of the 1930s in the U.S. were 1934 and 1936. In the summer of 1934, Fort Smith, Arkansas recorded an unbelievable 53 consecutive days with maximum temperatures of 38 degrees Celsius (100 degrees Fahrenheit) or higher. Topeka, Kansas, had 47 days, Oklahoma City had 45 days and Columbia, Missouri had 34 days when the mercury reached or passed that level. Approximately 800 deaths were attributed to the widespread heat wave, at a time when the U.S. population was about 60% smaller than today.

In comparison, the U.S. heat wave during July 2023, which was falsely trumpeted by the main­stream media as the hottest month in history, did not outmatch the scorching heat of 1934. El Paso, Texas did experience 44 consecutive days with maximum temperatures above 38 degrees Celsius (100 degrees Fahrenheit), somewhat shorter than Fort Smith’s 53 days in 1934 just mentioned. And Phoenix, Arizona saw the maximum there exceed 43 degrees Celsius (109 degrees Fahrenheit) – a comparable baseline for a city with a hotter climate than El Paso – but only for 31 days in a row.

Extreme Heat Was Not Confined to the United States

Heat waves lasting a week or longer in the 1930s were not confined to North America; the Southern Hemisphere baked too. Adelaide on Australia’s south coast experienced a heat wave at least 11 days long in 1930, and Perth on the west coast saw a 10-day hot spell in 1933. Not to be outdone, 1935 saw heat waves elsewhere in the world, including India, France and Italy.

That today’s heat waves are nothing extraordinary is apparent from the following table, which depicts all-time record high tem­peratures for the seven continents. Three records date from the 1930s or before, while only Europe and Asia have set new records in the 21st century.

Recent European Heat Waves Do Not Break with the Past

The record high temperatures during the deadly recent heat wave in Europe, which ranged up to 41.7 degrees Celsius (107 degrees Fahrenheit), are still lower than the continent’s all-time record in the table, set on the Italian island of Sicily five years ago. And the recent European heat wave’s duration pales in comparison with the U.S. heat waves described above.

Next: No Evidence That Weather Extremes Becoming More Frequent or Intense: (2) Droughts