In the last 100 years, the global climate and environment have greatly changed, which is characterized mainly by global warming. These changes have exerted prominent impacts on the climate and environment changes in China. More than 100 Chinese scientists in areas of climate change, environment, ecology, oceanography, economic and social sciences have assessed the climate and environment changes in China and their impacts on natural ecosystem and socio-economic sectors. On the basis of scientific assessment, response strategies to the adaptation and mitigation of climate change have been suggested. The present paper is extracted from the first part of this scientific assessment report, mainly dealing with the science of the climate and environment changes and the future projections of climate change.

Climate and environment changes in China have impacted not only on the nature, but also on aspects of the society, economy and politics. On the basis of the scientific assessment, the advantages and disadvantages impacts of the climate and environment changes on China are discussed in various aspects, such as ecosystem, agriculture, soil degradation, industry, traffic, service, city, and living conditions. In addition, the impacts of climate change on the regional sustainable development have been assessed, and national strategies for adaptation and mitigation of climate and environment changes in China are put forward.

The IPCC has developed an approach to the treatment of uncertainties for the Fourth Assessment Report which is an evolution of the approach established for the Third Assessment Report. Several features of this evolution are discussed briefly here and this paper serves as an introduction to the "IPCC Uncertainty Guidance Note" for lead authors which is included as an appendix. Particular attention is given to use of the terms "likelihood" and "confidence" as alternative ways of expressing uncertainty. This distinction emerged in the Third Assessment Report and was the subject of some debate before finalising the Guidance Note, however, it is now recognized that each term provides a complementary aspect of describing uncertainties.

The negotiation of the international climate regimes is a highly complicated process. Nevertheless, the determinants for post-2012 commitments still rely on the political will, economic interest and scientific knowledge of the global powers. The vehicles for post-Kyoto negotiations will be not only confined to the UNFCCC course, but bilateral, multilateral agreements and even unilateral commitments outside the UNFCCC are also likely to take place. Furthermore, the contents of agreements will cover mitigation, adaptation, technologies, and low carbon development. In the end, it is likely to become a basket of agreements to adapt and mitigate the climate change under the overall framework of sustainable development.

The paper investigates the historical agricultural exploitation in Northwest China, and its social benefits in the context of historical documents and their relationship with temperature and humidity backgrounds. Results show that during the Western Han Dynasty (206 BC-25 AD) and the early stage of Tang Dynasty (ca.7th century) climate was suitable for agriculture, leading to the success of large-scale wasteland reclamation in Gansu Province (called Hexi area in history), however during the late stage of the Tang Dynasty (ca. 8th-9th century) and the middle of the Ming Dynasty (ca.16th century), the climate there went into a cold stage, leading to the decline of stationing troops who opened up wasteland in the region; the prosperity of the Tarim Basin at the beginning of the Christian Era and its subsequent decline were linked to changes in water resources; and historically, the reclamation and later desertion were responsible for accelerating land desertification, and its typical examples are the formation of the Wulanbuhe Desert and the frequent occurrence of severe sand storm events in the warmer 13th century as the bad aftermath of the desertification.

Based on observed data from 115 meteorological stations in the Yangtze River basin from 1961 to 2000, pan (20cm diameter) evaporation (EP), reference evapotranspiration (Er) and actual evapotranspiration (Ea) as well as their trends are calculated and analyzed. Results indicate that significant negative trends of EP, Er and Ea are detected in the upper, middle, and lower as well as the whole Yangtze River basin, especially in summer. No significant trends in spring for EP, Er and Ea are observed. EP and Er in winter show significant negative trends, while Ea in winter shows a significant positive trend. The spatial distribution of this kind of negative trends is more significant over the middle and lower Yangtze River reaches than that in the upper Yangtze River reaches. However, in the same periods the observed air temperature in the Yangtze River basin shows a significantly increasing trend, which would increase evapotranspiration. A recent investigation shows that the significant decrease in net radiation and wind speed over the basin may in turn cause the decrease in evapotranspiration after compensating the increase in air temperature.

Based on the1960-1999 daily radiosounding data from twelve stations in Xinjiang, which is divided into four sub-areas, the Altai Mountains, the northern and southern slopes of Tianshan Mountains and the Kunlun Mountains by climate features and latitude distribution, trends of the annual mean heights and spatial differences of the first tropopause in the past 40 years were analyzed, and tests of the abrupt change of mean heights conducted by Mann-Kendall and successive running t-test. The results showed that there was an overall increasing trend of mean height for the first tropopause over Xinjiang during 1960-1999, in particular during 1987-1999. From the view of the interdecadal change, the mean height obviously decreased from the 1960s to the early 1970s, and afterwards gradually increased with an accumulated height increment more than 100 m. The successive running t-test showed that a remarkable abrupt change of mean height occurred in the Altai Mountains in 1972, the southern slopes of the Tianshan Mountains in 1976, and the northern slopes in 1979, but no remarkable change happened in the Kunlun Mountains. The mean height obviously increased all over Xinjiang except the Kunlun Mountains. Although there were various differences in four sub-areas of Xinjiang, the increasing trend of mean height was rather consistent from the end of 1980s to 1999 over Xinjiang.

The key vulnerability and dangerous level of climate change are hot issues in current international climate change research. This paper briefly outlines the basic concept of dangerous climate change and its uncertainties to determine quantitatively the dangerous anthropogenic interference with the climate system. Simulation results suggest that a 2.2-3.9℃warming in next 50-80 years with adaptation will not threaten wheat and maize production severely. To mitigate or avoid dangerous climate change, the strategy of adaptation is suggested for regional sustainable development in China.

The changes of surface air temperature and precipitation in the three time-slices of the 21st century under SRES A2, B2 scenarios is firstly analyzed using the regional climate model system-PRECIS, then followed by analysis on the possible change trend of surface air temperature and precipitation under B2 scenario over China. It is shown that the future extreme maximum temperature and precipitation events would increase, while the future extreme minimum temperature events would decrease during 2071-2100 under B2 scenario over China relative to baseline (1961-1990) average. It can be seen that the temperature in Northeast China, North China, and Northwest China would increase, while the precipitation would decrease under B2 scenario in 2071-2100, the climate would obviously become warmer and drier over these three regions in the northern part of China; and the precipitation over Central China, East China, and South China would increase largely in summer, while not so much in winter, especially the precipitation in South China in winter would obviously decrease. It means that both the flooding in summer and drought in winter would be enhanced over these three regions in the southern part of China.

Global warming and rising sea level have been observed to exert great impacts on China's coast in the past century, including increased coastal erosion, degraded coastal ecosystems, exacerbated saltwater intrusion, and enhanced storm surges. The impacts of climate change and the adjustments of coastal systems are significantly site specific, resulting from local differences in climate change, coastal physiographic and ecological conditions, and resilience of coastal systems. Anthropogenic activities also exert increasing influences on coastal systems. Societal vulnerabilities to climate change are greatly influenced by their adaptive capacities and selective adjustment, which are greatly determined by local socioeconomic conditions, so they are also highly localized. Coastal systems do not behave linearly to climate change. The projected increasing global warming and accelerating sea level rise will undoubtedly impose more threats to coastal systems. However, it is still difficult to determine the coastal socio-ecological thresholds to climate change without full understandings of coastal physical and biological processes, and adaptation responses of coastal ecosystems and human societies.

Observed global warming has impacted on ecosystems directly and indirectly. Governments, enterprises and common people in the world pay attention to the climate change of mainly global warming. General recognition for coping with the negative impact of climate change is to adopt adaptation and mitigation strategies, which are two aspects of sustainable development supporting each other. According to the definition of "dangerous anthropogenic interference with the climate system" addressed by the Article 2 of UNFCCC, "dangerous climate" to which man can not adapt is taken as the "threshold" of the impact of climate change on different systems. Such a threshold is the integrated result of climate impact level and the adaptive capacity of a system. Lagged studies and uncertainties of climate change make the threshold still unquantified. Therefore, when, where and how would mitigation be implemented has not been clear. This paper focuses on the impact of climate change on ecosystem, and analyzes key issues for determining the threshold, such as the definition, processes, criteria and assessment of ecosystem adaptive capacity. Simulation and assessment of China's ecosystems are performed with the CEVSA model and an artificial neural network (ANN) model. Preliminary results show that ecosystems of China are mainly in ecological baseline, slightly and moderately unadapted states, and the completely unadapted state does not occur. The B2 climate scenario (about 3.2℃ rising) has a certain positive impact on ecosystem in Northeast China, while the A2 climate scenario (about 3.89℃ rising) has a negative impact on ecosystem in East China.

The abrupt climate change of wetness in China from 2100 BC to 1800 BC is examined according to historical documentations, archaeological evidences and palaeo-climatic proxy data. The results show that there was a period with predominance of floods before the foundation of the Xia Dynasty (2070 BC). The folklore of "Regulation of floods by Great Yu" marked the ending of the period with floods. Climate turned to dry around the establishment of the Xia Dynasty. There are evidences to show that the annual precipitation reduced by 20% within a period less than 300 years. This change may be acknowledged as an event of abrupt climate change. The evidences show that change from wet to dry condition probably caused the collapse of archaeological cultures in China except in the central part of the main land area, where development of Chinese civilization leaded to the foundation of the Xia Dynasty.

Results and progresses of studies on the impact of global warming on the water resources system in the upper reaches of Yellow River in the recent years are introduced based on relevant papers published in various Chinese natural science journals. The studies show that the hydrological and water resources system in the basin is quite particular, because the basin is geographically situated in the Qinghai-Tibetan Plateau, where the average altitude is over 3000 m and the climate is very cold, so it is very sensitive to climate changes, especially to precipitation changes. The surface runoff in the basin increases with precipitation increasing and decreases with temperature rising. The evolutional trend of water cycle in the upper reaches of Yellow River in the 21st century is that the transpiration increases, and the surface runoff decreases with persistent temperature rising. As global temperature rising, the evaporation on land and ocean and the moisture in the atmosphere will generally increase, and the global mean precipitation will also increase, which would seemingly increase the probability of precipitation in the upper reaches of Yellow River. However, the increment in evaporation resulted from temperature rising not only cancels out to a great extent the potential increment of precipitation, but also makes water resources decrease to a certain extent because the range of precipitation increase is very limited. Therefore the future situation of water resources in the upper reaches of Yellow River is still not optimistic. It is necessary to solve the problem of water resources shortage in north and northwest China through various approaches, such as the South-to-North Water Diversion Project, so as to abate and adapt to the unfavorable impact of future climate changes.

Ten high-resolution time series of climate proxy data of the Holocene were synthesized. Comparison of the chronologies of cold events in the North Atlantic with which of monsoon failures in the Asian-African monsoon region shows great identity. All together nine cold events in the Holocene are identified with the weak monsoon events, while the monsoon rainfall decreased.

The monitoring data of permafrost temperature in the Qinghai-Tibetan Plateau during 1995-2004 are analyzed, and results show that under the impact of global warming, the permafrost are changing remarkably in recent 10 years, the thickness of active layer is increasing notably, and this kind of trend is even more evident in the warm permafrost region than in the cold permafrost region. The temperatures both near permafrost table and at the depth of 6 m are rising evidently, and the rising rate of temperature in the cold permafrost region is greater than one in the warm permafrost region. There is clear responsibility between permafrost changes of the Qinghai-Tibetan Plateau and global warming.

China is a developing country, and the most important thing for China is to develop economy and to improve the living standard of its people. It is reasonable for China to say that after becoming a medium developed country, it will take on quantitative commitments. Compared with some EU countries that can increase CO2 emission, the per capita energy consumption, per capita CO2 emission, per capita GDP and some human development indicators of China are much lower than them. It is reasonable that China should increase CO2 emission in order to meet the basic demand of economic and social development. Before becoming a medium developed country, China could consider taking on non-binding commitments, such as to keep the stabilization of the emission intensity per GDP in a certain period of time.