The analysis take the data published by "Instituto de Estadística" de la "Comunidad de Madrid". Data are registered by a meteorological station based in the Retiro, the main park in Madrid. http://www.madrid.org/iestadis/fijas/estructu/general/otros/clehre.htm The purpose is study the last 20 years records in order to see if the capital of Spain is affected by an increment of temperatures and see posibles tendencies.