Ever Wonder How Earth’s Global Average Temperature is Measured?

Climate change is a hot topic (pun intended). It is a serious issue, especially as wild fires, flooding, droughts, and hurricanes are making a large impact. The United States experienced a historic heat wave this summer with July 2023 deemed the “hottest month ever recorded on Earth” and the year of 2023 on track to be considered “the hottest year on record”. How do scientist measure the average global temperature? Is there some extraordinarily giant thermometer used for such a task? Although that would be interesting to see, scientists actually use thousands of thermometers and take thousands of temperature readings across the globe. It is somewhat of a methodical process, but it can be simply summarized in five steps.

1. Measure the temperature above land and in the ocean….THOUSANDS of times across THOUSANDS of places across the globe.
2. Then the difference between the temperature measured at each land and ocean location is subtracted from what is considered ‘normal’ for that location. The normal temperature is a long-term average measured over the course of 30 years. This calculated differences are called anomalies. Anomalies are important because they are a way for scientists to understand what kinds of temperature changes occur over time.
3. You repeat steps 1 and 2 every single day for the entire year.
4. The Earth is then divided into a grid of 2592 squares. The average temperature anomaly is calculated for each of 2592 squares for each day of the year, 365 days. This will produce a grand total of 946,080 temperature anomalies.
5. Finally, the average of 946,080 temperature anomalies is calculated, which is called the Global Average Temperature.

Scientists that study global temperatures utilize data from four major data sets:

1. HadCRUT4, produced by UK Met Office Hadley Centre and the University of Easy Anglia’s Climatic Research Unit
2. MLOST, produced by the National Oceanic and Atmospheric Administration
3. GISTEMP, produced by NASA Goddard Institute for Space Sciences
4. Japan Meterological Agency produces the fourth data set

Check them out if you are curious and want to do a deeper dive into the topic.