Will the real hottest month on record please stand up?

As anyone who follows the climate news is aware, July 2021 was the hottest month on record for our torrid little orb, according to the National Oceanic and Atmospheric Administration (NOAA), with a combined temperature 1.67 degrees F higher than the 20th century average of 60.4 F.

NOAA noted in a Friday press release that the previous record was set in July 2016, and tied in 2019 and 2020. But as Bill Frezza, a sharp-eyed reader of Retraction Watch noticed, the agency’s website tells a different story. This press release, dated Aug. 15, 2019, and still live on noaa.gov, proclaims July 2019 to be the hottest month on record for the planet:

The average global temperature in July was 1.71 degrees F above the 20th-century average of 60.4 degrees, making it the hottest July in the 140-year record, according to scientists at NOAA’s National Centers for Environmental Information. The previous hottest month on record was July 2016. 

Of course, in a period of global warming, over time we’d expect the average temperature of the world to, well, warm. But 1.67 is decidedly not greater than 1.71, so either this July was the warmest month on record or it wasn’t.  

We put that question to NOAA’s press office, and got this response, attributed to the agency’s climate experts:

NOAA National Centers for Environmental Information calculates the global temperature anomaly every month based on preliminary data generated from authoritative datasets of temperature observations from around the globe. The major dataset, NOAAGlobalTemp version 5, updated in mid-2019, uses comprehensive data collections of increased global area coverage over both land and ocean surfaces. NOAAGlobalTempv5 is a reconstructed dataset, meaning that the entire period of record is recalculated each month with new data. Based on those new calculations, the new historical data can bring about updates to previously reported values. These factors, together, mean that calculations from the past may be superseded by the most recent data and can affect the numbers reported in the monthly climate reports. The most current reconstruction analysis is always considered the most representative and precise of the climate system, and it is publicly available through Climate at a Glance.

Our follow-up question: Any plans to add a note to the July 2019 release, or update it? We’re standing by.

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