Diagram demonstrating how to measure global average temperature

Credit: Lisa Gardiner/UCAR Center for Science Education

Each year, global average surface temperature is calculated. How do we measure the temperature of the entire planet? It takes thousands of thermometers, but the math is pretty simple. Here are the steps.

  1. Measure temperature above land and the ocean in THOUSANDS of places around the world.
  2. Subtract the temperature you measure at each location from the usual temperature on that day.  The difference is called the anomaly.
  3. Repeat steps 1 and 2 for each day of the year.
  4. Divide the planet into a grid of 2,592 squares.  Calculate the average temperature anomaly for each square.  At the end of the year you will have 946,080 temperature anomalies resulting from 2,592 locations in the grid multiplied by 365 daily temperatures.  
  5. Take the average of all temperature anomalies from all over the world.  Compare this with other years.