Resumen
It has been claimed that air temperature (averaged over all latitudes) has increased by about 0.5ºC during the last 100 years. Since models are not able to simulate regional variations, it is of interest to explore temperature trends, especially in tropical areas where the climate change signal is likely to be smaller than at higher latitudes and therefore, more difficult to be distinguished from natural variability. Using mean annual minimum temperatures, an attempt is made to examine climatic change in a tropical region over the past half century. The following are the main findings from this analysis. Urban warming is evident in stations located in tropical cities with rapidly growing populations like Leon and Mexico City. Temperature records from smaller cities (less than 50,000 inh.) tend to duplicate the global temperature changes (warming before the 1940's and cooling in the 1960-1970's). For rural stations, however, no appreciable warming trend is evident in the 1980's.