The temporal variability and spatial pattern of the Arctic Oscillation (AO) simulated in the historical experiment of 26 coupled climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) were evaluated. Spectral analysis of the monthly AO time series indicates that 23 out of 26 of the CMIP5 models exhibit no statistically significant spectral peak in the historical experiment, as seen in the observed time series. Also, these models are able to reproduce the AO pattern in the sea level pressure anomaly field during boreal winter. But the strength of AO pattern tends to be overestimated in all the models. The zonal-mean zonal wind anomalies associated with the winter AO exhibit a dipole in latitude, which is only well reproduced by a few models. Most models show significant biases in both strength and location of the meridional dipole in the zonal-mean zonal wind anomaly filed associated with the winter AO. In considering the temporal variability as well as spatial structures in both horizontal and vertical directions, the model MPI-ESM-P reproduces an AO pattern that more resembles the observation.

This study evaluates the simulation ability of winter and spring Arctic Oscillation (AO) variability carried out with coupled climate models participating in the experiment “historical” organized by CMIP5. The features of AO during 1950-2000 in twenty eight models were analyzed and compared with those in the NCEP reanalysis data and twenty two CMIP3 models. The results show that, the significant increasing trend and oscillation cycle of winter and spring AO index can be reproduced by most models although the significant feature that winter/spring AO is in significant negative phase in the first 30 years whereas positive phase in the last 20 years is not shown up in the simulation, The multi-model ensemble has improved the effect of the simulations by CMIP5 models. As CMIP5, the CMIP3 models can not catch the feature that winter/spring AO is in significant negative phase in the first 30 years and positive phase in the last 20 years, what’s more, the significant increasing trend of winter and spring AO index is not shown up in the simulation by CMIP3 models, and there is not any improvement in the result of multi-model ensemble. There is a poor simulation for the variation cycles of AO index in the CMIP3 models. The oscillations with a cycle of 2-3 years in the winter AO index is reproduced by CMIP3 models, but the spring AO index simulated by CMIP3 models does not show the oscillation cycle of 4-5 years. Although the simulations are not good enough to catch all the significant features of winter and spring AO indices by CMIP5 models, there are some improvements not only for the increase trend but also for the change cycle in the simulations by CMIP5 models relative to CMIP3 models.

Based on the dataset observed by the meteorological satellites from NOAA, the simulated Northern Hemisphere March-April snow cover fraction (SNC) in historical experiments from 23 coupled climate models attending the fifth phase of the Coupled Models for Inter-comparison Project (CMIP5) was evaluated. The 23 models were aggregated by arithmetic mean to project the changes of Northern Hemisphere March-April SNC in 2006-2099. The results show that, overall, the CMIP5 coupled models reproduce the observed snow cover extent well and catch the main characteristics in the distribution of snow cover. But the simulation of snow cover in complex terrain area such as Qinghai-Tibet Plateau is poor and the significant trend towards a reduced spring snow cover extent over 1979-2005 is underestimated. The defect of satellite data and differences of parameterization schemes used in different models may be the causes. The projection by multi-model ensemble show that, the snow cover will continue to reduce in the next few decades mainly in the central and western regions of Eurasia. Greenhouse gas emissions will have a significant impact on the change of Northern Hemisphere snow cover in the future. The northern Hemisphere snow cover will reduce the most significantly under RCP8.5 scenario. Under RCP4.5 and RCP6.0 scenarios, the reduction of snow cover is equivalent to that under RCP8.5 scenario in the first half of the 21st century, but the decreasing trend is significantly less than that under RCP8.5 scenario in the last half of the 21st century. Under RCP2.6 scenario, the reduction of snow cover will not be significant. Therefore, it is crucial to control the discharge of greenhouse gas emissions for mitigating the disappearance of snow cover over Northern Hemisphere.

The simulation for China annual average surface temperature by CMIP5 models was assessed, referring to the observation data from CRUT3v and CN05. The results show that CMIP5 models are able to simulate the warming occurring in China over 1906-2005 with a trend of 0.77℃/100a from the multi-model ensemble mean, close to the observed value of 0.84℃/100a. The simulations of warming for the late 20th century are much better than that for the early 20th century, and only 2 out of the 25 CMIP5 models can capture the anomalous warming period around the 1940s. The simulations for the China-wide distribution of 20-year (1986-2005) averaged surface temperature are broadly well. However, notable underestimations for surface temperature climatology appear almost all over China, and the largest bias and uncertainty occur over western China. On the regional scale, northern China experienced stronger warming than southern China over the period of 1961-1999, for which the CMIP5 multi-model ensemble mean provides roughly realistic simulations, but underestimates the difference in warming trends between the North and the South. To sum up, the simulations from CMIP5 models are obviously improved in the three aspects mentioned above, compared with the CMIP3 simulations.

Based on the applicability analysis of the NCEP/NCAR reanalysis I data by the radiosonde data in the Three Rivers’ Headstream region and the adjacent regions, trends of water vapor transports in the Three Rivers’ Headstream region were analyzed by applying the daily wind and specific humidity of the reanalysis data during 1971-2010. The results show that the meridional water vapor input in the Three Rivers’ Headstream region decreased significantly, causing the net water vapor budget decreasing. The decadal variations of water vapor fluxes in the 1970s and 1980s were relatively weaker than those in the 1990s and 2000s. During 1971-2010, the water vapor budget showed an obvious decreasing trend in spring, summer and autumn, while no significant trend in winter. Overall, the water vapor transport into the region decreased significantly, especially in June and September during 1971-2010, which had adverse impacts on precipitation formation.

The characteristics of different timescale drought variations from 1961 to 2012 in Southwest China were studied, by using a new drought index (standardized precipitation evapotranspiration index, SPEI) as the division standard of droughts. The level was calculated based on the monthly precipitation and average air temperature data from 86 meteorological stations. The results show that the drought frequency at 12-month timescale presents a significant declining trend in the Yunnan-Guizhou border zone, but an inconsistent and unclear trend in other regions. The drought frequency at 6-month timescale shows a significant increasing trend in the dry period (November -April in the following year) in the whole research area, but a slowly decreasing trend in the rainy period (May-October) in most regions, particularly in southern Sichuan. The drought frequency at 3-month timescale does not indicate a significant trend in spring, but shows a significant increasing trend in autumn and winter, especially in 2000-2012.

Using the observational data of Shijiazhuang meteorological station and township stations (Shenzhou and Jinzhou) at the same latitude from 1957 to 2010, the inter-decadal variations of sultry days and sultriness indices and their differences between Shijiazhuang and township station were analyzed. In addition, the inter-decadal variations of temperature, relative humidity and absolute humidity at 14:00 BT in summer and sultry weather were also analyzed. The results show that during 1957-2010, sultry days in Shijiazhuang increased gradually, while the township station showed bimodal distribution. The variation of sultry days at Shijiazhuang was consistent with the variation of temperature at 14:00, which indicates that temperature plays a leading role in enhancing sultry level. The sultry days at Shenzhou were related to the temperature and humidity at 14:00, with major role in humidity. Under urbanization, urban heat island effect at Shijiazhuang was getting stronger than that at Shenzhou from the late 1980s, and the dry island effect was enhanced after the middle 1990s. The sultry days in Shijiazhuang were mainly affected by the urban heat island effect and global warming, while the drop of relative humidity due to the urban dry island effect had an adverse impact on the formation of sultry weather, which reduced part of the possibility of sultry weather.

In the last 30 years, China has achieved a great success in the increase of both forest area and stocking volume. However, a large scale of low-value forests, in terms of timber yield and ecological services, have appeared all over China, mainly resulted from illegal logging, inappropriate choice of tree species for specific site conditions, insufficient unit investment for forestation, poor quality of seedlings and lack of effective tending and forest management, as well as frequent natural disasters. In recent years, Chinese government has initiated and enhanced the improvement of low-value forests including establishing financial incentive mechanism, and formulated a quantitative target in the Guidelines on the National Forest Plan (2010-2020). However, few studies on the carbon sequestration potential of the improving low-value forests have been conducted. Through scenario analysis on the case of improving low-value Chinese fir and masson pine forests implemented in Southeast Guizhou Province, we found that the carbon sequestration potential of improving low-value forests depends highly on existing state of low-value forests, measures for improvement to be taken and the management goals. For the purpose of long-term timber forests (without final harvest within 30 years), apparent net carbon credits are expected relative to the baseline scenario. However, for the purpose of short-term industrial material or fast-growth timber forest, the net carbon credits are very limited, with a long-term carbon stock in the tree biomass in some cases even lower than the baseline scenario. Selective harvest would largely increase the long-term carbon stock and result in apparent net carbon credits relative to the baseline scenario. We concluded that for the purpose of carbon sequestration, especially for the carbon offsetting, short-rotation should be avoided. Long-term rotation and selective harvest or no harvest are desired measures in order to increase the long-term carbon stock.

The Kaya identity has been widely used to disaggregate and identify the drivers for the variations in carbon emissions, providing an important role in understanding historical emissions change at macro-level. Kaya identity, with a simple mathematical form, can decompose drivers without residuals. However there are also some limitations with respect to its policy implications. First, Kaya identity can only explain the changes in carbon emissions flow, with limited or no attention to the existing stock of carbon emissions. Second, drivers in Kaya identity are proximate and it誷 difficult to assess their actual impacts on the total emissions. Third, policy implications derived from the conclusions using Kaya identity decomposition can be fuzzy and in conflict with common understanding and practice in reality. This indicates that Kaya identity as an analytical tool requires further examination and investigation with respect to its policy implications.

This paper explores residents’ perception and knowledge of local climate change and its impacts, and examines their attitudes to adapt to climate change impacts by means of a detailed questionnaires survey of 202 farm households in the Mt. Yulong region, southeastern Tibetan Plateau. The results indicate that, overall, residents’ perception intensity of temperature, snow cover, glacier and phenophase changes is highly consistent with scientific research in the region. Residents’ perception intensity of climate change impacts on the agriculture system is not very strong, and the residents think that climate change does not affect crops’ growing and their yields, however, they hold a favorable opinion to crop pests’ increasing slightly and crop growth period’s extending. Residents’ perception intensity of climate change and its adaptation shows a significant correlation with elevation on the whole, yet their perception intensity of climate change and its impacts is significantly correlated with their ages. Climate change has already forced residents to adjust industrial structure, develop water-saving agriculture economy, participate actively in the mountain tourism, and work in cities in order to adapt to climate change and make up for meager farm income. At the same time, they also expect that the government can provide them some compensation and relief for the disasters (e.g. drought and late spring coldness).