Abstract: The warming trend in Beijing was analyzed based on the homogenized land surface air temperature data at Nanjiao weather observatory during 1951-2008. The analysis shows that the mean maximum and minimum temperatures increased asymmetrically at a rate of 0.26℃/10a and 0.46℃/10a, respectively. It is found that among four seasons winter is the longest season and autumn is the shortest season; summer is getting longer at a rate of 4.4 d/10a, and winter is becoming shorter at a rate of 4.7 d/10a; since 1951 the starting dates of spring and summer have become earlier at a linear rate of 3.0 d/10a and 2.5 d/10a, and on the contrary, the starting dates of autumn and winter have gradually become later at a rate of 2.0 d/10a and 1.7 d/10a respectively. The correlation analysis suggests that the starting dates of spring and summer are significantly negatively correlated with the annual mean temperature; while those of autumn and winter are remarkably positively correlated with the annual mean temperature.

Key words: warming trend, seasonal variation, annual mean temperature, Beijing