This investigation completes the line of work on the thermal evolution of the Mediterranean region (Murcia and Valencia regions) in the National Plan on Climate Change. The study was undertaken to analyse the active regional thermal series over the 1950–1999 period, rigorously treated by the SNHT (Standard Normal Homogeneity Test) method. In this context, ﬁfteen years later, it was considered judicious to verify the validity of the trends and conclusions that the regional climate offered at the end of the 20th century. The objectives of this study are twofold: the veriﬁcation of the Signiﬁcant Climate Warming in the Spanish Mediterranean concluded in the National Plan on Climate Change (1950-1999) and the evaluation of the importance that the Urban Heat Island (UHI) has on the warming process. Within the context of the thermal evolution of the region over the 1950–2013 period, this veriﬁcation has been supported by an experimental research plan aimed at analysing the thermal processes inherent to the urbanisation effect. Although the effect is undeniable, its importance is a matter of controversy. The results obtained have shown both the nature of the phenomenon and its signiﬁcant magnitude. This magnitude could account for between 70 and 80% of the recorded warming trend in Western Mediterranean cities. Therefore, failure to take this process into account might seriously bias any analysis of regional thermal evolution, the main aim of this study and an aim that equally affects the hypothesis of global climate change.