Climate change, as one of the major global challenges, refers to persistent alterations in weather patterns that have profound impacts on the environment, economy, and human societies. The aim of this study is to analyze and compare the mean temperature across Iran during two distinct time periods: the distant past (1965–1994) and the recent past (1995–2024), and to examine the trend of these changes on a monthly and annual basis. In this research, ERA5-Land atmospheric reanalysis data were used. The results indicate that the average temperature in Iran has increased in the recent past compared to the distant past, with monthly increases ranging from 0.5°C to 1°C. During the distant past (1965–1994), the temperature trend in some months such as February, March, May, and October was stable or decreasing; however, in the recent past, all months generally show an increasing trend. Findings also reveal that since around the year 2000, both monthly and annual temperature anomalies have shown a consistent positive trend, with the highest anomalies occurring during the warmest months—particularly July and August. In contrast, prior to 2000, anomalies were more variable, including both positive and negative values. The annual temperature trend has increased from approximately 0°C per decade in the distant past to about 0.35°C per decade in the recent period, indicating a significant and persistent warming trend in Iran. This growing trend underscores the importance of implementing effective policies to mitigate the adverse effects of global warming and highlights the need for precise planning in the country’s environmental and economic sectors.