For almost a century, the world's hottest temperature was believed to be a 136-degree Fahrenheit measurement recorded in El Azizia, Libya, on September 13, 1922. This month, the World Meteorological Organization (WMO) threw that record out. They gave their reasons in a study published in the September issue of the Bulletin of the American Meterological Society. The story of how the extreme temperature was refuted involves a two-year quest by a blogger, an investigation by the head of the Libyan National Meteorological Center who disappeared for six months during the country's revolution, and the amazing recovery of handwritten temperature records from a destroyed building.
Weather Underground blogger Christopher C. Burt first called into question the validity of the 136-degree temperature on October 10, 2010, with a meticulously researched post. He didn't stop there. He engaged in a correspondence with the head of the Libyan National Meteorological Center, Khalid Ibrahim El Fadli, who was able to track down photographs and written records from the site. Fadli disappeared for six months, from February of 2011 to August of 2011, during the revolution in Libya. Like so many others, he lost contact with the outside world during the fighting. Eventually, Fadli resurfaced and found the records still intact, though the building that housed the evidence had been destroyed. Burt put the findings together and handed them to the WMO, which had never overturned a historical temperature record before. The WMO decided to strike the El Azizia record for five reasons, which I've listed below in bold. The additional explanation below each reason is derived from Burt's most recent blog and the 26-minute-long documentary, Dead Heat. (Watch the movie to see the full investigation by Burt and Fadli.)
POTENTIALLY PROBLEMATIC INSTRUMENTATION
The thermometer at El Azizia was a Bellani Six, an instrument more often used for household measurements than official temperature recordings. It had a slide that covered a roughly seven-degree area on the thermometer. If someone read the top of that slide, rather than the bottom—as they should, the temperature could be recorded seven degrees higher than it actually was.
A PROBABLE NEW AND INEXPERIENCED OBSERVER AT THE TIME OF OBSERVATION
On September 11, the handwriting recorded on the temperature log at El Azizia switched. Temperatures were often logged in the wrong columns, and they were much higher on average than they had been in the past. It's possible a new person recording the temperature used the top of the Bellani Six slide to indicate temperature, rather than the bottom of the slide, and ended up with a reading that was off by seven degrees.
UNREPRESENTATIVE MICROCLIMATE OF THE OBSERVATION SITE
The thermometer was placed over a tarred area of concrete. Official temperatures should be recorded in a shaded area, above the ground, in an area out of direct sunlight.
POOR CORRESPONDENCE OF THE EXTREME TO OTHER LOCATIONS
No other site in Libya had a recorded measurement above 117 degrees during the time that the high temperatures were recorded at El Azizia. Prior to the handwriting change on the temperature sheets, the temperatures at the other locations corresponded closely to the temperatures at El Azizia. After the handwriting change, they did not. The World Meteorological Society also modeled temperatures to see if it was possible for such a high temperature anomoly to occur at El Azizia, and their analysis said that it was not.
POOR COMPARISON TO SUBSEQUENT TEMPERATURE VALUES RECORDED AT THE SITE
When the temperature station was moved from the tarred area of concrete, only two temperatures above 122 degrees were ever recorded.
With the refutation of that 136-degree record in El Azizia as the world's hottest temperature, Death Valley, California, took the title for a temperature recorded almost a century ago. In Dead Heat, a National Park employee describes what is known about the historic day. On July 10, 1913, Greenland Ranch observer Oscar Denton wrapped a wet towel around his head and walked outside to the thermometer and recorded a temperature of 134 degrees Fahrenheit. When he went back inside, the towel was dry. If that doesn't give an idea of the heat, perhaps another one of Denton's observations might. He saw a flock of swallows fall dead to the ground.