EPA Say Heatwaves Much Worse in 1930’s
By Paul Homewood
Tucked away on the EPA website is the above graph. EPA explain how the index is derived:-
While there is no universal definition of a heat wave, this indicator defines a heat wave as a four-day period with an average temperature that would only be expected to occur once every 10 years, based on the historical record.
The index value for a given year could mean several different things. For example, an index value of 0.2 in any given year could mean that 20 percent of the recording stations experienced one heat wave; 10 percent of stations experienced two heat waves; or some other combination of stations and episodes resulted in this value.
They go on to comment:-
- Heat waves occurred with high frequency in the 1930s, and these remain the most severe heat waves in the U.S. historical record (see Figure 1). Many years of intense drought (the "Dust Bowl") contributed to these heat waves by depleting soil moisture and reducing the moderating effects of evaporation.
- There is no clear trend over the entire period tracked by the index. Although it is hard to see in Figure 1 (because of the extreme events of the 1930s), heat wave frequency decreased in the 1960s and 1970s but has risen since then.
There has never been any debate about the 1960’s and 70’s being a much colder period than before or since. What is surprising, though, is that the EPA acknowledge that the 1930’s saw much more severe heat waves and that there is no trend to heat waves becoming worse.
They also put up two other graphs, which show the percentage of the USA affected by heat waves, one for maximum temperatures and the other for minimums. In their own words,
The recent period of increasing heat is distinguished by a rise in extremely high nighttime temperatures.
And they still deny Urban Heat Islands have nothing to do with it?