Until recently, virtually all studies of changes and projected changes of near-surface temperature focused on the mean temperature. This value is often derived from the average of temperatures selected at various times of the day or from the daily maximum and minimum. Information on mean temperatures has been exchanged throughout the world and, in many areas, it extends back for well over a century. Unfortunately, even elementary observations such as the daily maximum and minimum temperatures have not been routinely available, despite their fundamental importance to understanding the impact of climate change in such spheres as agriculture, water resources, and the atmosphere.