Land use and land cover change(LUCC)is one of the important human forcing on climate.However,it is difficult to infer how LUCC will affect climate in the future from the effects of previous LUCC on regional climates in the past.Thus,based on the land cover data recommended by the Coupled Model Intercomparison Project Phase 5(CMIP5),a regional climate model(Reg CM4)was used to investigate the climate effects of future land use change over China.Two 15-year simulations(2036–2050),one with the current land use data and the other with future land cover scenario(2050)were conducted.It is noted that future LUCC in China is mainly characterized by the transition from the grassland to the forest.Results suggest that the magnitudes and ranges of the changes in temperature and precipitation caused by future LUCC show evident seasonality,which are more prominent in summer and autumn.Significant response of climate to future LUCC mainly happens in Northeast China,North China,the Hetao Area,Eastern Qinghai-Tibetan Plateau and South China.Further investigation shows that future LUCC can also produce significant impacts on the atmospheric circulation.LUCC results in abnormal southwesterly wind over extensive areas from the Indian peninsula to the coasts of the South China Sea and South China through the Bay of Bengal.Furthermore,Indian tropical southwest monsoons and South Sea southwest monsoons will both be strong,and the abnormal water vapor convergence from the South China Sea and the Indian Ocean will result in more precipitation in South China.
The Fourth Assessment Report (AR4) of the Intergovernmental Panel of Climate Change (IPCC) concluded that the climate projection using climate models that took account of both human and natural factors provided credible quantitative estimates of future climate change; however, the mismatches between the IPCC AR4 model ensembles and the observations, especially the multi-decadal variability (MDV), have cast shadows on the confidence of the model-based decadal projections of future cli mate. This paper reports an evaluation of many individual runs of AR4 models in the simulation of past global mean tempera ture. We find that most of the individual model runs fail to reproduce the MDV of past climate, which may have led to the overestimation of the projection of global warming for the next 40 years or so. Based on such an evaluation, we propose an al ternative approach, in which the MDV signal is taken into account, to project the global mean temperature for the next 40 years and obtain that the global warming during 2011–2050 could be much smaller than the AR4 projection.
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.
The NCAR Community Atmosphere Model(CAM4.0)was used to investigate the climate efects of land use/land cover change(LUCC).Two simulations,one with potential land cover without significant human intervention and the other with current land use,were conducted.Results show that the impacts of LUCC on diurnal temperature range(DTR)are more significant than on mean surface air temperature.The global average annual DTR change due to LUCC is–0.1℃,which is three times as large as the mean temperature change.LUCC influences regional DTR as simulated by the model.In the mid-latitudes,LUCC leads to a decrease in DTR,which is mainly caused by the reduction in daily maximum temperature.However,there are some diferences in the low latitudes.The reduction in DTR in East Asia is mainly the result of the decrease in daily maximum temperature,while in India,the decrease in DTR is due to the increase in daily minimum temperature.In general,the LUCC significantly controls the DTR change through the changes in canopy evaporation and transpiration.
Greenhouse gas emissions and land use/land cover change(LUCC)are two human activities notably affecting climate change.Will temperature and precipitation increase significantly during global warming resulting in more pronounced LUCC climatic effects?Considering the interannual forcing of these two factors,the NCAR Community Atmosphere Model(CAM4.0)was used in this study to investigate the importance of climatological background to LUCC impacts.Experiments based on the difference in the background climate,the greenhouse gas concentrations in 1850 and in the present age indicate contrary changes in climate sensitivity through estimations of the radiative forcing associated with LUCC,which are 0.54°C/(W/m2)and 0.26°C/(W/m2),respectively.Therefore,the background climate appears to play an important role in the regional impact of LUCC,especially at higher latitudes.In addition,global warming predominantly influences snow-albedo feedback in the mid-latitudes,thus determining the impact of LUCC,whereas the regional difference in precipitation caused by global warming is responsible for the differing climate response to LUCC in the tropics and subtropics.
Trends in the frequencies of four temperature extremes （the occurrence of warm days, cold days, warm nights and cold nights） with respect to a modulated annual cycle （MAC）, and those associated exclusively with weather-intraseasonal fluctuations （WIF） in eastern China were investigated based on an updated homogenized daily maximum and minimum temperature dataset for 1960–2008. The Ensemble Empirical Mode Decomposition （EEMD） method was used to isolate the WIF, MAC, and longer-term components from the temperature series. The annual, winter and summer occurrences of warm （cold） nights were found to have increased （decreased） significantly almost everywhere, while those of warm （cold） days have increased （decreased） in northern China （north of 40°N）. However, the four temperature extremes associated exclusively with WIF for winter have decreased almost everywhere, while those for summer have decreased in the north but increased in the south. These characteristics agree with changes in the amplitude of WIF. In particular, winter WIF of maximum temperature tended to weaken almost everywhere, especially in eastern coastal areas （by 10%–20%）; summer WIF tended to intensify in southern China by 10%–20%. It is notable that in northern China, the occurrence of warm days has increased, even where that associated with WIF has decreased significantly. This suggests that the recent increasing frequency of warm extremes is due to a considerable rise in the mean temperature level, which surpasses the effect of the weakening weather fluctuations in northern China.
