Problems with the Iowa Climate Statement

The 2014 Iowa Climate Statement was recently released, and this provides us with the opportunity to further fact-check many of the claims being made about climate change in the Hawkeye State.

According to an article in The Des Moines Register about the release of the state's latest climate statement, Iowa is seeing “more-frequent and more-severe rain and heat events leading to injury, disease and mental health problems.”  The claims of “more-severe” rain events in the state was included in the “Climate Change Impacts on Iowa: 2010” report to the governor and Iowa General Assembly – and was also used in the latest National Climate Assessment – but when I looked at the source data back in May, I did not find significant trends in the number of heavy precipitation events throughout the state.  Nor are there any trends in maximum daily rainfall amounts across Iowa over the past century.

More severe heat events leading to injury, disease, and mental health problems?  In the Dubuque climate sub-region, there is a highly (p<0.001) statistically significant decline in the number of very hot days (>95º F) each year since records began in 1875.  Back in 1936, this region had 23 days above 95º F.  That is more very hot days in 1936 alone than the Dubuque area has had in total since 1989.  Actually, it is almost twice as many very hot days in 1936 than since 1989 (a total of only 12 very hot days during the last 25 years).  How many days above 95º F did the Dubuque climate sub-region have during 2014?  Zero.

There is a similarly highly statistically significant decline in the number of very hot days each year for the Waterloo climate sub-region – a region that had 206 very hot days during the 1920s and 1930s alone, but only 181 very hot days in the entire period since 1940.  In the Des Moines and Sioux City climate regions, no significant trend in very hot days exists since records began in 1879 and 1890, respectively.  Record hot days in each of the state's climate sub-regions were also set well in the past, not recently: 111º F in the Sioux City region during 1939; 110º F in the Des Moines region during 1936; 112º F in the Waterloo area during 1936; and 110º F in the Dubuque region during 1936.  High temperatures in recent years haven't come close to breaking these records.  Indeed, the hottest it has gotten in the Dubuque area since 1936 is 102º F, and this took place in 1940.

As I also showed in my previous article:

There has been no significant trend [in Iowa's annual temperature] since 1900... I get no significant trend in Iowa's average winter temperatures since the NOAA database begins in 1895. Nor is there one in summer.

According to a report in the Iowa State Daily, “'one issue concerning scientists is the increase in precipitation, resulting in more frequent floods,' the statement said.”  Increase in precipitation?  There have been no significant trends in annual precipitation in the state since 1970, nor over the past three decades.

Apparently, “Iowans are experiencing the very real impacts of climate change, including ... a longer growing season.”  As the USEPA defines the length of the growing season with regard to climate change discussions, “the length of the growing season is defined as the period of time between the last frost of spring and the first frost of fall, when the air temperature drops below the freezing point of 32 F.”  On the contrary, I find absolutely no significant trends towards a longer growing season within the state's climate sub-regions since records began in the 19th century.  In fact, in the Sioux City and Dubuque regions, there are statistically significant trends toward shorter growing seasons, not longer.  In the Waterloo area, there is almost a perfect non-correlation since the start of records in 1895, and in the Des Moines area, the trend is almost statistically significant towards a shorter growing season since the 1800s.  These findings appear to directly contradict the Iowa Climate Statement.

The path forward is clear: get the climate science right.

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