Seasonality changes in China under elevated atmospheric CO2 concentrations were simulated using nine global climate models, assuming a 1% per year increase in atmospheric CO2. Simulations of 20th century experiments of season changes in China from the periods 1961-80 to 1981-2000 were also assessed using the same models. The results show that the ensemble mean simula- tion of the nine models performs better than that of an individual model simulation. Compared the mean climatology of the last 20 years in the CO2-quadrupling experiments with that in the CO2-doubling ones, the ensemble mean results show that the hottest/coldest continuous-90-day （local summer/winter） mean temperature in- creased by 3.4/4.5℃, 2.7/2.9℃, and 2.9/4.1℃ in Northeast （NE）, Southwest （SW）, and Southeast （SE） China, respectively, indicating a weakening seasonal amplitude （SA）, but by 4.4/4.0℃ in Northwest （NW） China, indicating an enlarging SA. The local summer lengthened by 37/30/66/54 days in NW, NE, SW, and SE China, respec- tively. In some models, the winter disappeared during the CO2-quadrupling period, judging by the threshold based on the CO2-doubling period. The average of the other model simulations show that the local winter shortened by 42/36/61/44 days respectively, in the previously mentioned regions.
The temperature thresholds and timings of the 24 climatic Solar Terms in China are determined from a homogenized dataset of the surface air temperature recorded at 549 meteorological stations for the period 1960-2008 employing the ensemble empirical mode decomposition method.Changes in the mean temperature and timing of the climatic solar terms are illustrated.The results show that in terms of the mean situation over China,the number of cold days such as those of Slight Cold and Great Cold has decreased,especially by 56.8% for Great Cold in the last 10 years(1998-2007) compared with in the 1960s.The number of hot days like those of Great Heat has increased by 81.4% in the last 10 years compared with in the 1960s.The timings of the climatic Solar Terms during the warming period(around spring) in the seasonal cycle have advanced significantly by more than 6 d,especially by 15 d for Rain Water,while those during the cooling period(around autumn) have delayed significantly by 5-6 d.These characteristics are mainly due to a warming shift of the whole seasonal cycle under global warming.However,the warming shift affects the different Solar Terms to various extents,more prominently in the spring than in the autumn.The warming tendencies for Rain Water,the Beginning of Spring,and the Waking of Insects are the largest,2.43?C,2.37?C,and 2.21?C,respectively,for the period 1961-2007 in China as a whole.Four particular phenology-related climatic Solar Terms,namely the Waking of Insects,Pure Brightness,Grain Full,and Grain in Ear,are found to have advanced almost everywhere.In semi-arid zones in northern China,advances of the timings of these four climatic Solar Terms are significant,12-16,4-8,4-8,and 8-12 d,respectively,for the period 1961-2007.These quantitative results provide a scientific base for climate change adaptation,especially in terms of agricultural planning and energy-saving management throughout a year.
Recent trends in seasonal cycles in China are analyzed, based on a homogenized dataset of daily temperatures at 541 stations during the period 1960–2008. Several indices are defined for describing the key features of a seasonal cycle, including local winter/summer （LW/LS） periods and local spring/autumn phase （LSP/LAP）. The Ensemble Empirical Mode Decomposition method is applied to determine the indices for each year. The LW period was found to have shortened by 2–6 d （10 yr）-1, mainly due to an earlier end to winter conditions, with the LW mean temperature having increased by 0.2°C–0.4°C （10 yr）？1, over almost all of China. Records of the most severe climate extremes changed less than more typical winter conditions did. The LS period was found to have lengthened by 2–4 d （10 yr）？1, due to progressively earlier onsets and delayed end dates of the locally defined hot period. The LS mean temperature increased by 0.1°C–0.2°C （10 yr）-1 in most of China, except for a region in southern China centered on the mid-lower reaches of the Yangtze River. In contrast to the winter cases, the warming trend in summer was more prominent in the most extreme records than in those of more typical summer conditions. The LSP was found to have advanced significantly by about 2 d （10 yr）-1 in most of China. Changes in the autumn phase were less prominent. Relatively rapid changes happened in the 1980s for most of the regional mean indices dealing with winter and in the 1990s for those dealing with summer.
Climatic changes in the onset of spring in northern China associated with changes in the annual cycle and with a recent warming trend were quantified using a recently developed adaptive data analysis tool, the Ensemble Empirical Mode Decomposition. The study was based on a homogenized daily surface air temperature （SAT） dataset for the period 1955–2003. The annual cycle here is referred to as a refined modulated annual cycle （MAC）. The results show that spring at Beijing has arrived significantly earlier by about 2.98 d （10 yr）-1, of which about 1.85 d （10 yr）-1 is due to changes in the annual cycle and 1.13 d （10 yr）-1 due to the long-term warming trend. Variations in the MAC component explain about 92.5% of the total variance in the Beijing daily SAT series and could cause as much as a 20-day shift in the onset of spring from one year to another. The onset of spring has been advancing all over northern China, but more significant in the east than in the west part of the region. These differences are somehow unexplainable by the zonal pattern of the warming trend over the whole region, but can be explained by opposite changes in the spring phase of the MAC, i.e. advancing in the east while delaying in the west. In the east of northern China, the change in the spring phase of MAC explains 40%–60% of the spring onset trend and is attributable to a weakening Asian winter monsoon. The average sea level pressure in Siberia （55°–80°N, 50°–110°E）, an index of the strength of the winter monsoon, could serve as a potential short-term predictor for the onset of spring in the east of northern China.
