A thermometer can tell us the temperature outside one home, but Earth is much larger. Scientists need readings from many places. NASA’s global analysis uses data from more than 25,000 weather stations, together with measurements from ships, ocean buoys and research stations in Antarctica.
The stations are not evenly spread across the planet, so researchers use careful methods to combine the information. They also consider changes in where stations are located. One unusually hot town cannot represent the whole world. A reliable global result comes from many observations collected over time. Different research groups can then compare their results more confidently.