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New EPA Climate Change Indicator is deceptive

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Ralph Alexander

New climate change indicators on the U.S. EPA (Environmental Protection Agency) website are intended to inform science-based decision-making by presenting climate science transparently. But many of the indicators are misleading or deceptive, being based on incomplete evidence or selective data.

A typical example is the indicator for heat waves. This is illustrated in the left panel of the figure below, depicting the EPA’s representation of heat wave frequency in the U.S. from 1961 to 2019. The figure purports to show a steady increase in the occurrence of heat waves, which supposedly tripled from an average of two per year during the 1960s to six per year during the 2010s.

Unfortunately, the chart on the left is highly deceptive in several ways. First, the data is derived from minimum, not maximum, temperatures averaged across 50 American cities. The corresponding chart for maximum temperatures, shown in the right panel above, paints a rather different picture – one in which the heat wave frequency less than doubled from 2.5 per year in the 1960s to 4.5 per year in the 2010s, and actually declined from the 1980s to the 2000s.

This maximum-temperature graph revealing a much smaller increase in heat waves than the minimum-temperature graph displayed so boldly on the EPA website is dishonestly hidden away in its technical documentation.

A second deception is that the starting date of 1961 for both graphs is conveniently cherry-picked during a 30-year period of global cooling from 1940 to 1970. That in itself exaggerates the warming effect since then. Starting instead in 1980, after the current bout of global warming had begun, it can be seen that the heat wave frequency based on maximum temperatures (right panel) barely increased at all from 1981 to 2019. Similar exaggeration and sleight of hand can be seen in the EPA indicators for heat wave duration, season length and intensity.

A third deception is that the 1961 start date ignores the record U.S. heat of the 1930s, a decade characterized by persistent, searing heat waves across North America, especially in 1934 and 1936. The next figure shows the frequency and magnitude of U.S. heatwaves from 1900 to 2018.

The frequency (top panel) is the annual number of calendar days the maximum temperature exceeded the 90th percentile for 1961–1990 for at least six consecutive days. The EPA’s data is calculated for a period of at least four days, while the heat wave index (lower panel) measures the annual magnitude of all heat waves of at least three days in that year combined.

Despite the differences in definition, it’s abundantly clear that heat waves over the last few decades – the ones publicized by the EPA – pale in comparison to those of the 1930s, and even those of other decades such as the 1910s and 1950s. The peak heat wave index in 1936 is a full three times higher than it was in 2012 and up to nine times higher than in many other years.

The heat wave index shown above actually appears on the same EPA website page as the mimimum-temperature chart. But it’s presented as a tiny Figure 3 that is only 20% as large as the much more prominent Figure 1 showing minimum temperatures. As pointed out recently by another writer, a full-size version of the index chart, from 1895 to 2015, was once featured on the website, before the site was updated this year with the new climate change indicators.

The EPA points out that the 1930s heat waves in North America, which were concentrated in the Great Plains states of the U.S. and southern Canada, were exacerbated by Dust Bowl drought that depleted soil moisture and reduced the moderating effects of evaporation. While this is undoubtedly true, it has been suggested by climate scientists that future droughts in a warming world could result in further record-breaking U.S. heat waves. The EPA has no justification for omitting 1930s heat waves from their data record, or for suppressing the heat wave index chart.

Although the Dust Bowl was unique to the U.S. and Canada, there are locations in other parts of North America and in other countries where substantial heat waves occurred before 1961 as well. In the summer of 1930 two record-setting, back-to-back scorchers, each lasting eight days, afflicted Washington, D.C.; while in 1936, the province of Ontario – also well removed from the Great Plains – experienced 43 degrees Celsius (109 degrees Fahrenheit) heat during the longest, deadliest Canadian heat wave on record. In Europe, France was baked during heat waves in both 1930 and 1947, and many eastern European countries suffered prolonged heat waves in 1946.   

What all this means is that the EPA’s heat-wave indicator grossly misrepresents the actual science and defeats its stated goal for the indicators of “informing our understanding of climate change.”