Seasonal patterns of warming amplification of high-elevation stations across the globe

Elevation-dependent warming in high-elevation regions is of great interest to many researchers, but global assessment of seasonal signals of elevation-dependent warming has received little attention. Here, using monthly mean temperatures from 2,104 global stations for the period 1961-2010, we find that the temperature trends are highly significant in all seasons for the high-elevation stations (>500 m a.s.l.) as well as their low-elevation counterparts over the study period. For the high-elevation stations, the warming is the strongest in winter, followed by autumn, spring and summer, with the magnitudes of 2.165, 1.355, 1.344 and 1.256 degrees C/50 year, respectively. With the exception of spring, the trend in three other seasons is clearly higher for the high-elevation stations than their low-elevation counterparts. A significant altitudinal amplification trend is detected for all seasons for the high-elevation stations based on the elevation band method, and the amplification amplitude for autumn and winter is about two times that for spring and summer. Furthermore, stepwise regression analysis reveals that the trends of each season for the high-elevation stations are closely related to altitude and latitude, suggesting that there exist not only an altitudinal amplification trend but also a latitudinal amplification trend on the seasonal scale for the high-elevation stations in the past 50 years. It was also found that the warming in each season for the high-elevation stations is linearly related to the temperature lapse rates in altitudinal and latitudinal directions due in large part to the mathematical shape of Stefan-Boltzmann law in these two directions.