Shouldn't these be called median temperatures, not average temperatures? And isn't the reason they do it this way is because otherwise they can't take advantage of all the Co-op weather stations worldwide that don't gather data on an hourly basis from which one could calculate an average temperature, but rather on a twice-daily basis? (Science news in the popular press is often badly corrupted).
Last year was the fourth warmest year on average for our planet since the late 1800s, according to NASA scientists.
To determine if the Earth is warming or cooling, scientists look at average temperatures. To get an "average" temperature, scientists take the warmest and the coolest temperatures in a day, and calculate the temperature that is exactly in the middle of those high and low values. This provides an average temperature for a day. These average temperatures are then calculated for spots all over the Earth, over an entire year.