Either on a global or regional context, analysis of the instrumental records show significant increases of surface air temperature. On a global basis, surface air has warmed about 0.6º C over the period 1861-1999. But this warming has not taken place in a monotonic fashion, as different subperiods of warming can be seen: from early 1920s to the mid-1940s and from the mid-1970s to the present (Jones, 2001). Similarly, on a regional scale, Spain shows significant temperature increases of 0.9º C over the last 130 years mainly registered during two periods, early 1900s to later 1920s and from the mid-1970s onwards. Furthermore, seasonal contribution to annual warming presents the largest rates of warming for winter, as well as greater contribution of daily maximum temperature in comparison with daily minimum temperature to long-term trend of daily mean temperature (Brunet, et al. 2001b).

To further investigate recent warming over Spain and how unusual has been the last period of abrupt and strong increases in temperature, we have compared, characterised and estimated rates of temperature increases between the different sections of Spanish Temperature Series (STS). A new and more extensive, adjusted and gridded dataset of monthly averages of daily maximum, minimum and mean temperatures has been used. This dataset contains 48 meteorological stations obtained from Spanish Meteorological Office (INM). These data are gridded to produce a regional time series extending from 1870 to 2000. The long-term behaviour of each variable and its contribution to warming have been studied on a seasonal and annual basis. Comparative analysis of rates of warming, trends change points, interannual and interdecadal variability, seasonal contribution and large-scale mechanism of change have been produced.

Preliminary analysis of STS (Brunet et al., 2001a,b) have shown a different contribution to long-term temperature trends of the extreme daily temperatures. Daytime temperature increases at fast warming rates than nighttime temperatures, leading to a larger contribution of maximum temperature to the total trend of daily mean temperature, especially during twentieth century, where the two periods of more significant warming have been observed. On the other hand, several differences of warming rates and temporal behaviour between extreme daily temperatures have been found. On a similar way, seasonal contribution to annual values shows differences in the duration and extension of warming phases. Altogether depicts a complex temporal pattern with changing rates of warming, which seems well correlated with recent changes of the large-scale modes of variability (NAO, SOI).