According to NOAA’s National Climatic Data Center, July 2012 was the third warmest on record in Ohio with a mean temperature of 77.6F. So, although very hot, the temperatures in July were not completely without precedence. The only months with a higher mean temperature are July 1901 and July 1934. The mean temperature was 77.7F in July 1901 and 78.1F in July 1934. Below are two images displaying the mean temperatures for July 1901 and July 2012. The map for July 1901 is taken from the monthly Ohio Climate & Crop Report for that month; the map for July 2012 is adapted from the dynamically-created High Plains Regional Climate Center maps. I added the color to the July 1901 map. The maps are not meant to provide an identical comparison between the months, as there may be differences in data quality and accuracy of the depictions shown.
Figure 1. Map of Ohio monthly mean temperature for July 1901, adapted from the July 1901 Ohio Climate & Crop Report.
The maps show that July 1901 & July 2012 demonstrated similar temperature patterns. In both years, the coolest temperatures occurred across the far northeast and the hottest across the southwest corner of the state. In most of the state, temperatures in both months were similar. However, parts of northwest and west central Ohio were a little hotter in 2012. On the other hand, southern and northeast Ohio were somewhat hotter in 1901.
The take-home message is that extreme summertime heat is no stranger to Ohio. Indeed, the temperatures of July 2012 did not exceed the bounds of historic variation. As such, it would be hard to definitively show that climate change was the actual cause of the heat wave. Still, temperatures as warm or warmer than those of July 2012 occurred in only two other years in the past 118+ years. Moreover, a warming climate makes such events more likely. Should global warming trends persist, these summertime temperatures will likely become much more common.
Indeed, a 2011 Stanford University study projected that, by mid-century, every summer would be hotter than the hottest summers of the past 50 years. While that finding might seem surprising, especially coming fairly close on the heels of the relatively mild summer of 2009, it is not implausible. Summertime temperatures have increased sharply in recent years. The summer of 2010 was the fourth warmest on record at the time, behind only 1936, 2006, and 1934. The summer of 2011 was warmer yet, finishing as the second warmest on record behind only the scorching Dust Bowl summer of 1936. Although the summer of 2012 is not yet over, it appears likely to be among the top 5 or 10 warmest summers on record.