How the hottest temperatures in the world are verified

When an extreme, potentially record-breaking global weather event occurs today, the UN's World Meteorological Organization sends in a team of investigators. They verify it happened.

The National Weather Service reported a 130 degree Fahrenheit temperature in Death Valley, Calif. on Aug. 16, amid a heat wave of rare intensity. The World Meteorological Organization (WMO) has already started organizing a panel of atmospheric scientists to carefully examine the observation, said Randy Cerveny, the agency's rapporteur (or lead reporter) for extreme records.

If verified, the 130 F mark would be the highest temperature recorded on Earth since at least 1931, according to the WMO. Though, importantly, some meteorologists think the new 130 F measurement would be the highest temperature ever reliably recorded on Earth. Previous observations (like a 134 F reading in Death Valley from July 1913) have notable reliability problems. Either way, it's likely that Aug. 16 was the hottest August day, by far, ever recorded in Death Valley.

"It was definitely one of the hottest days ever in Death Valley, if not the hottest day," said Chris Burt, a weather historian currently with the weather reporting company Weather Underground. Burt has worked on three WMO extreme event investigations.

What goes into these investigations? Above all, slow, careful scrutiny.

"The key is that we do it right," said Cerveny, who is also a professor of geographical sciences at Arizona State University. "In the 13 years of [the WMO's extreme record] operation, never has one of our official WMO evaluations been overturned."

That's "a testament to the high-quality and rigorous evaluation process handled by some of the top atmospheric scientists in the world," he said.

Getting it right means at least months of work. "Our evaluations are very detailed and consequently somewhat time-consuming," explained Cerveny. "It may take upwards of six to nine months to finish."

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The WMO verification team's investigation of this new extreme observation in Death Valley will include, among other things, the following:

• They'll compare the reading, recorded at Furnace Creek, Death Valley, to other weather stations in the area. Investigators will look if the observation is radically different from other nearby weather measurements. "If it's way off the chart they'll discount it," said Burt. Importantly, the National Weather Service didn't note any outward issues with the observation, and labeled the high temperature as "preliminary pending a formal review." "There’s already a lot of corroboration in the valley for the measurement," said Burt

• The actual weather station will be closely examined, said Cerveny. The National Weather Service maintains this Death Valley site, and Burt said the agency's Las Vegas team will remove the equipment over the weekend so it can be formally assessed. The equipment will be calibrated, to confirm it accurately recorded the weather.

These 21st century observations have the benefit of such close scrutiny and modern technology. In contrast, the WMO's record for the second hottest temperature ever observed, a 131 F observation from 1931 in Kebili, Tunisia, carries some glaring problems, explained Burt. The measurement was taken at a French colonial fort, and there likely weren't meteorologists collecting reliable weather measurements. Rather, such observations were documented by the likes of a surgeon, or whoever was able, he said. Did temperatures really hit 131 F in Tunisia in 1931? Well, since WWll that region hasn't eclipsed 119 F, noted Burt. It's a problematic record. "It was unreliable," he said.

Around the globe, extreme or high-temperature records will likely be continually set this century. That's a consequence of a relentlessly warming climate. With boosted background temperatures, higher temperatures inevitably occur, and old records fall.

In 2019, for example, 364 all-time high temperatures were set, compared to just 70 all-time lows. In 2020 (as of Aug. 2019), 123 global record high temperatures have been set, versus 17 low records. Overall, high records have outpaced low records by two to one over the last decade or so.

"In fact, we are seeing an increase in daily heat records, and we are NOT seeing an increase in daily cold records," Michael Mann, a climate scientist at Penn State University, told Mashable last year.  

"The trend is in exactly the direction we would expect as a result of a warming planet," Mann said.

Globally, nineteen of the last 20 years have been the warmest on record.