Research-Present and future climate change

 

Recent climatic warming and its elevation dependency in the Tibetan Plateau and the surrounding areas

 
 

    Adequate knowledge of climatic change over the Tibetan Plateau (TP) with an average elevation of more than 4000 m above sea level (a.s.l.) has been insufficient for a long time owing to the lack of sufficient observational data. In the present study, monthly surface air temperature data were collected from almost every meteorological station on the TP since their establishment. There are 97 stations located above 2000 m a.s.l. on the TP; the longest records at five stations began before the 1930s, but most records date from the mid-1950s. Analyses of the temperature series show that the main portion of the TP has experienced statistically significant warming since the mid-1950s, especially in winter, but the recent warming in the central and eastern TP did not reach the level of the 1940s warm period until the late 1990s. Compared with the Northern Hemisphere and the global average, the warming of the TP occurred early. The linear rates of temperature increase over the TP during the period 1955C1996 are about 0.16<C/decade for the annual mean and 0.32<C/decade for the winter mean, which exceed those for the Northern Hemisphere and the same latitudinal zone in the same period. Furthermore, there is also a tendency for the warming trend to increase with the elevation in the TP and its surrounding areas. This suggests that the TP is one of the most sensitive areas to respond to global climate change. (Liu and Chen, 2000, International J. Climatology).

    Elevation dependency in the Tibetan Plateau and its surroundings is also examined based on model projected climate changes in future scenarios (Liu et al., 2009, Global and Planetary Change). The modeling approach overcomes the issues of uneven distribution of weather stations at different elevation zones and provides the tool to explore the physical processes that are responsible for the elevation dependency of warming. The data used in this analysis include results from two sets of modeling experiments under future global warming conditions. One dataset is the output of the NCAR Community Climate System Model (CCSM3) for the scenario of annual 1% increase in atmospheric CO2 for future 100 years. The other one is the physically-based downscaling analysis from the NCAR CAM3/CLM3 model during three 20-year mean periods (1980C1999, 2030C2049 and 2080C2099) for the IPCC mid-range emission (A1B) scenario. The modeling results confirmed that the warming is more prominent at higher elevations than at lower elevations, especially during winter and spring seasons. The elevation dependency is not only observed in the second half of the 20th century, but may continue in the future climate change scenarios. The combined effects of cloud-radiation and snow-albedo feedbacks are most likely the main cause of the elevation dependency of warming. (Liu et al., 2009, Global and Planetary Change)

Liu X.D. and B.D. Chen, 2000: Climatic warming in the Tibetan Plateau during recent decades, International Journal of Climatology, 20(14), 1729-1742.

Liu X.D., Z.G. Cheng, L.B. Yan and Z.Y. Yin, 2009: Elevation dependency of recent and future minimum surface temperature trends in the Tibetan Plateau and its surroundings, Global and Planetary Change, 68, 164-174.

Locations of the used weather stations (Total 197 weather stations with 97 stations over 2000m). The dashed line shows the 2000m contour of the Tibetan Plateau.

Annual average surface temperature anomaly trends for 1961C1990 categorized according to the 24 elevation ranks of the 197 stations in the Tibetan Plateau and its surrounding areas

Modeling domain of the experiment.

       

Left: Linear trends of spring, summer, autumn, winter and annual mean temperature simulated in the 1% per year CO2 increasing experiment with CCSM3 for the last 100 years as a function of 11 elevation categories in the entire Tibetan Plateau and its surroundings (70o-105oE, 26o-42oN) .

Right: Linear trends of annual-mean total cloud amount (a), snow depth (b), surface-reflected solar radiation (c), and surface-absorbed solar radiation (d) in the annual 1% CO2 increasing experiment with CCSM3 for the last 100 years as a function of 11 elevation zones in the Tibetan Plateau and its surroundings.