Indian heatwave highlights temperature ‘record’ checking challenge

The recording of 52.9 degrees Celsius (127.2 Fahrenheit) in a Delhi suburb on Wednesday — surpassing the national record — was an outlier compared to other stations, and the India Meteorological Department said it was reviewing the data and sensors.

The incident underscored the critical importance of verifying temperature readings, notably for monitoring and understanding how the climate is changing — and responding accordingly.

The United Nations‘ World Meteorological Organization is responsible for signing off on global, continental and hemispherical temperature records.

The Geneva-based WMO maintains a global weather and climate extremes archive, which logs records for temperature, pressure, rainfall, hail, aridity, wind, lightning and weather-related mortality.

Its lengthy verification process involves months and even years of careful scientific checking, and sometimes sees measuring flaws and equipment errors bring down claimed records.Lengthy evaluation
The WMO first contacts the national weather service of the country concerned, and the organisation that captured the supposed record in order to get the raw data. That includes details on the exact location of the reading, the equipment used, its calibration, and the regional weather conditions at the time.

An initial assessment is carried out by the WMO Commission for Climatology and by Randall Cerveny, the organisation’s rapporteur of weather and climate extremes, who heads up the records archive.

An international panel of atmospheric scientists then reviews the raw data and provides Cerveny, a geographical sciences professor at Arizona State University, with recommendations for his final verdict.

Database started in 2007
In 2005, while watching US news coverage of Hurricane Katrina’s trail of destruction in New Orleans, Cerveny was struck by television presenters repeatedly calling it the worst hurricane of all time.

He knew otherwise: while Katrina caused 1,800 deaths, a tropical cyclone in 1970 killed an estimated 300,000 people in what is now Bangladesh.

Cerveny co-wrote a scientific article calling for an official global records database.

And in 2007, the WMO asked him to set one up, to keep world, hemispherical and regional records for particular extreme weather events.

Measuring climate change
Knowing the existing weather and climate extremes is critical in determining exactly how much and how fast the world’s climate is changing, according to the WMO.

The information is also important for health and civil engineering planning. For example, architects need to know the maximum possible wind speed when designing a bridge.

Another reason for maintaining the records database was to advance science — and help the media to put weather events in perspective.

All-time heat record overturned
The WMO also re-examines records from before 2007, and sometimes delists them.

The best-known case is that of the long-standing world record temperature of 58 C (136 F) measured in 1922 in El Azizia, in what is now Libya.

Following a two-year investigation conducted in dangerous conditions during the Libyan revolution of 2011, the record was invalidated due to five major concerns, including potentially problematic instrumentation and “a probable new and inexperienced observer”.

Since then, the 56.7 C (134.1 F) registered on July 10, 1913 in Furnace Creek, in Death Valley in the United States, has held the world heat record.

In July 2021, the WMO recognised a new record high temperature for the Antarctic continent, confirming a reading of 18.3 C (64.9 F) made at Argentina’s Esperanza research station on the Antarctic Peninsula on February 6, 2020.

But crucially, the WMO rejected an even higher temperature reading of 20.75 C (69.35) reported on February 9, 2020 at a Brazilian automated permafrost monitoring station on nearby Seymour Island.

It found an improvised radiation shield led to a demonstrable thermal bias error for the permafrost monitor’s air temperature sensor, making its reading ineligible as a record.