New Extreme Weather Record? Not So Fast.

California’s Death Valley recorded temperatures of 130 degrees Fahrenheit this month, a measurement that could be the highest ever reliably made on Earth.

Or not. For decades the global heat record was a 136.4-degree reading from Libya in 1922, but that was thrown out about a decade ago after scientists uncovered methodological errors. The record that officially replaced it, a 134-degree reading from Death Valley in 1913, is itself disputed.

Journalists like to cover record-setting weather in real time, and for good reason: Extreme heat can have significant consequences for our health and the fate of the planet. The seven warmest years in the history of accurate worldwide record-keeping have been the past seven years, and 19 of the 20 warmest years have occurred since 2000; worldwide, June 2019 was the hottest ever recorded for the month, and June 2020 essentially tied it.

But the process of formally certifying such records can require months, or years, of nuanced vetting. Plus some expensive laboratory gear.

“If you just want to know if it is freezing outside, your small home weather station is fine,” said Andrea Merlone, a metrologist in Italy who recently helped to certify two 129.2-degree readings from Kuwait and Pakistan.

“But if you need to assess a record, then you have to go down to the millikelvin level,” he added.

Bear with us a moment. Metrology is the science of measurement, and a millikelvin is equivalent to a thousandth of a kelvin, the unit of measurement on a temperature scale that begins at absolute zero — or minus 273.15 degrees Celsius or minus 459.67 degrees Fahrenheit. One way metrologists establish the validity of purported temperature records is by checking meteorological sensors with instruments that are themselves accurate to within a thousandth of a degree Celsius, or one millikelvin.

‘This reading is a real reading’

Weather records specific to a country or region are often handled by national agencies, like the National Oceanic and Atmospheric Administration in the United States and the Met Office in Britain.

In 2016, for example, scientists from NOAA and Florida International University reanalyzed Hurricane Camille, whose estimated wind speeds of 190 miles per hour at landfall in 1969 were the highest of any Atlantic hurricane. By combining a study of the original observations from ships, weather stations, coastal radar and other data with the current understanding of hurricanes, the researchers found that Hurricane Camille’s winds — about 175 m.p.h. — were weaker than previously assumed, when it slammed into Mississippi. As a result, a pair of storms with winds of 185 m.p.h. — a 1935 hurricane that hit the Florida Keys and Hurricane Dorian in 2019 — were elevated to the top of the list of Atlantic storms with the highest wind speed at landfall.

At the international level, the job of certifying weather records falls to the World Meteorological Organization, a United Nations agency that opened a Weather and Climate Extremes Archive in 2007.

“From a W.M.O. point of view, it’s important to scientifically evaluate them with a kind of security to say, ‘This reading is a real reading, it was measured in that place and we are confident it’s the highest or lowest observation of this variable,’” said Manola Brunet, the president of the agency’s Commission for Climatology.

Dr. Brunet, a geographer at the University Rovira i Virgili in Spain, said that committees organized by the W.M.O. typically include eight to 12 experts and that at least 20 records had been evaluated since 2007. Of those, only the 1922 Libya reading was a re-evaluation of an official record; the others were newer and had not been officially confirmed.

In the Libya case, the W.M.O. research resulted in a peer-reviewed scientific article that identified a number of issues with the 1922 reading, including “problematical instrumentation” and an inexperienced observer.

In a more recent W.M.O. investigation, one of the agency’s committees accepted a reading of 18.3 degrees Celsius (64.9 Fahrenheit) from February 2020 as the Antarctic region’s highest observed temperature. It also rejected a slightly higher one, from an Antarctic permafrost monitoring station, as biased, although it noted that the station was “not badly designed for its purpose.”

Dr. Brunet said the W.M.O. might soon decide to open an investigation of another weather record: a 253 m.p.h. wind gust in Barrow Island, Australia, in 1996 that is considered the strongest on record. She said the agency was consulting mechanical engineers for their opinions about the way the anemometer, which measures wind speed, was set up on the island at the time.

Death Valley dispute

Jeff Masters, a meteorologist and a co-founder of Weather Underground, an online news service, says the reason more temperature records are not overturned is because the process is too time-consuming. A case in point, he said, is that an effort to reanalyze every named Atlantic storm since 1851, which began two decades ago, has so far reached only the year 1965.

“There are hundreds of temperature records in the U.S. alone that would not survive a re-analysis,” Dr. Masters said. “The most famous of these is the world-record hottest temperature in history of 134 degrees Fahrenheit in 1913 in Death Valley.”

Two extreme weather experts, William T. Reid and Christopher C. Burt, have argued on the Weather Underground site that the 1913 reading was “not possible from a meteorological perspective,” in part because it was not consistent with other observations made in that part of Death Valley over the same week. They say the man who recorded the temperature, at Greenland Ranch in California, appears in retrospect to have “knowingly or inadvertently” exaggerated the reading, and that he may not have even been present at the time.

But Randall Cerveny, who leads the World Meteorological Organization’s efforts to research and verify global weather records, said in an email that the 1913 reading was still recognized as the “hottest temperature recorded for the United States and for the world.”

Dr. Cerveny, who teaches geographical sciences at Arizona State University and worked with Mr. Burt to debunk the 1922 Libya record, described the research on the 1913 Death Valley record by Mr. Burt and Mr. Reid as “conjectural, not new evidence.” He added that the U.S. Climate Extremes Index, a NOAA project, has also opted not to investigate it.

“We do not dismiss records without substantial evidence proving their inaccuracy,” he said.

As for newer Death Valley records, Dr. Cerveny said the W.M.O. was still trying to verify a 129.9-degree reading from that area on Aug. 6, 2020.

If confirmed, it would be the third-highest temperature ever recorded on Earth and the second-highest in the United States. But Dr. Cerveny said the investigation is “taking a while” because his team has been testing the temperature sensor that made the reading.

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