Heat: how daily temperature records are measured – 7/8/2023 – Environment

The heat broke new daily world records this week, according to preliminary data from specialized agencies.

The instruments that make these measurements can provide early warning of extreme heat outbreaks, although they are not as accurate as monthly and annual reports from major agencies, experts say.

Understand below how the daily records are calculated.

Who produces the data?

The University of Maine, in the United States, created an online page called Climate Reanalyzer, which shows the average global temperature curves for each day since 1979.

On Monday, July 3, this curve peaked at 17.01°C. This record was surpassed on Tuesday (4), with 17.18°C, and again on Thursday (6), with 17.23°C.

The European observatory for climate change Copernicus, which has a similar tool, later confirmed Monday’s and Tuesday’s records, albeit with slightly different values: 16.88°C and 17.03°C, respectively.

How do they arrive at the numbers?

These estimates are produced by combining actual temperature measurements from ground stations, satellites and more with computer models.

The two tools are conceptually similar, but they differ in their exact sources and methods, which lead to slightly different results.

The University of Maine relies on public model output data produced by the US National Oceanic and Atmospheric Administration (NOAA) to make predictions.

But NOAA says that while it reports record hot surface temperatures in many places around the world, it could not “validate the methodology or conclusion of the University of Maine analysis”.

Noaa is responsible for its own monthly and annual temperature reports.

The fact that both results converge is reassuring, Zeke Hausfather, climatologist at the independent climate data organization Berkeley Earth, told AFP.

The European tool is considered “very advanced” by the community at large, he added.

What are the limitations?

“These are estimates, unofficial records,” climatologist Sean Birkel of the University of Maine, who developed the Climate Reanalyzer, told AFP.

“More emphasis should be placed on an annual and monthly timescale,” he explained, adding that these reports are subject to greater control and verification than is possible for daily records, which are based on near real-time information.

On Thursday, Copernicus separately published its analysis of last month, announcing that it was the hottest June on record. A similar monthly report from Noaa is now expected next week.

These reports are based “solely on observations” from land and sea and collect many more data points, explained Hausfather.

In general, climate experts prefer to focus on long-term trends and changes to eliminate simply climate-related variations.

Furthermore, the concept of global average temperature is somewhat abstract and not necessarily meaningful to the general public.

“No one lives at the global average,” argued Hausfather.

What is the value of daily log estimates?

Despite these limitations, the value of the daily level estimates is that “we can start to identify extreme events” that could have a big impact on the planet’s climate, Birkel said.

While temperature on the daily scale refers to time, not climate, adding 40-year data provides important climate context, he said.

“These partial records provide further evidence of changes in global weather patterns due to climate change and the evolution of the El Niño episode,” said Omar Baddour, head of climate monitoring at the WMO (World Meteorological Organization).

“I think this is a sign that we are entering a very warm era. June was the hottest June on record by a very large margin,” Hausfather said.

“At this point, it looks increasingly likely that 2023 as a whole will be the warmest year since records began in the mid-19th century,” he said.