Black carbon (BC) aerosol can strongly absorb the solar radiation in a very broad spectral range from the visible to infrared waveband, therefore it is thought to be a potential factor that causes the global warming. BC aerosol not only alters the radiation equilibrium of the earth-atmosphere system through its direct effect, but also indirectly affects the global or regional climate through changing cloud microphysical properties by acting as cloud condensation nuclei or ice nuclei. In this paper, we reviewed the recent progresses in the studies on the radiative forcing due to BC and its climatic effects, reported the uncertainties existing in current researches, and gave some suggestions for the relevant studies in the future.

Black carbon (BC) aerosol, a minor fraction constituent of atmospheric aerosols, is attracting increasing concern due to its impacts on air quality, human health, and particularly climate. Focusing on BC emission reduction, the paper gives a brief introduction of BC's sources and global distribution, evaluates the resulting decrease of BC emissions from such actions as global greenhouse gases (GHGs) reduction and local air quality regulation, and highlights other BC reduction approaches like control and improvement of combustion conditions, elimination of open biomass burning, and sequestration of BC by biomass pyrolysis. Some policy suggestions for China are also presented in response to the appeal for world-wide BC reduction.

Snow and ice core samples were collected from the glaciers located in the Tibetan Plateau (TP) and Xinjiang of west China. Black carbon (BC) was measured and its radiative forcing after deposition in snow was simulated. The average BC concentration in the snow of west China was about 63 ng/g, higher than the other measurements in the Northern Hemisphere; and its spatial distribution was primarily affected by surrounding emissions. Simulated mean radiative forcing caused by BC deposits in snow was about (+4.0±2.0) W/m². An ice core (aged 1951-2001) drilled in the middle Himalayas and transport analysis shows that black carbon was primarily transported from South Asia by Indian summer monsoon, causing a forcing over 4.5 W/m² in the summer of 2001. BC emitted from South Asia could penetrate into the inland of TP and might have significant effects on the surface energy balance of the glaciers in the TP.

Based on the daily precipitation observation dataset of stations from 1951-2004 in China, gamma function was used to define the extreme precipitation event and calculate the probability distribution of daily precipitation; then, relationship between ENSO and seasonal frequency of extreme precipitation events in China was studied. Results reveal that ENSO events are able to impact China'sextreme precipitation events in different regions, at different seasons. Generally, during winter and spring, extreme precipitation events may come forth in more regions during El Nino events than during La Nina events; while during summer and autumn, the opposite is true. Meanwhile, as for the time-lag relationship between ENSO and extreme precipitation frequency, the extreme precipitation events more easily occur in several regions if the central-eastern tropical Pacific is in ENSO warm phase two seasons ago. Therefore, the impact of El Nino and La Nina on the frequency of China's extreme precipitation events is asymmetrical.

By using the data of total cloud amount at 22 stations over Tibet in 1971-2008, the change trends of total cloud amount were analyzed. The results show that the annual average total cloud amount decreased remarkably in most parts of Tibet, especially in the mid-west of Naqu where the trend was -2.32%/10a; but over the southern edge of the Tibetan Plateau, the reducing trend was not significant. Correlation analysis demonstrates that total cloud amount was correlated positively with precipitation and relative humidity, and negatively with sunshine duration, average temperature and diurnal range of temperature. The Hurst index of total cloud amount shows that the total cloud amount had a decreasing trend in most parts of Tibet; this trend will continue, and will not change in a short period of time.

Based on a case study of facilitating reforestation for Guangxi section of Pearl River watershed, dynamic cost changes in carbon sequestration under the clean development mechanism (CDM) project and the five afforestation models in tCER (temporary certified emission reduction) and lCER (long-term certified emission reduction) were explored. The results show that tCER costs of the project and five models will decrease gradually, and project cost will reduce from 40.33 ￥/t CO₂ to 13.34 ￥/t CO₂. The lCER costs will be down to the minimum in the terminal of the first commitment period, and project cost will increase from 40.33 ￥/t CO₂ to 105.27 ￥/t CO₂. The costs of L. formosana plus C. lanceolata and L. formosana plus P. massoniana will be higher than P. massoniana plus S. superba and P. massoniana plus Quercus sp., and Eucalyptus sp. will be the lowest cost. The choice of discount rate will impact on cost of the project, Eucalyptus sp. in tCER and L. formosana plus C. lanceolata in lCER, and it is not obvious to P. massoniana plus Quercus sp. in tCER and lCER. The sensitivity of tCER cost to Eucalyptus sp. were also analyzed. It is found that changes in carbon storage per unit area can affect the tCER cost. The net present value of project tCER will be 13.11 ￥/t CO₂ with timber benefits in the end, thus suggesting that the implement the CDM project is feasible.

This paper summarizes the research progress of winter air temperature variations of three provinces (i.e. Liaoning, Jilin, Heilongjiang) in Northeast China. The basic characteristics of interannual and interdecadal variations of average, maximum and minimum air temperatures in the last 100 years or recent several dacades are briefly reviewed. This overview deals with various atmosphere-ocean general circulation factors closely associated with interdecadal and interannual climate variations of winter air temperature of three provinces in Northeast China. Winter air temperature has risen in Northeast China in recent 100 years, and an abrupt warming occurred in about 1987. Arctic Oscillation, Siberian high, and East Asian winter monsoon are the major factors affecting the interannual variations of winter temperature in Northeast China; the persistentce of Arctic Oscillation, East Asian winter monsoon, and circulation pattern over the mid-high latitudes of East Asia are the major factors affecting the interdecadal variations of winter temperature. The climate change possessing multiple characteristics in the late 1970s is worth further discussing. It is necessary to deeply study the short-term climatic prediction methods of winter temperature in the three provinces of Northeast China. Besides, we should pay more attention to the in-homogeneity problems of observed temperature series in Northeast China.

Long-term climate change mitigation target would highly constrain global carbon emissions in future. Carbon permit allocation under the long-term mitigation target would impact development space for all countries, involving the fundamental interests. Some developed countries advocate the principle of per capita emission convergence while China and other developing countries propose the principle of convergence of accumulative emission per capita to consider historical responsibility. If the latter is used for carbon permit allocation, CO₂ emissions of developed countries since the industrial revolution have far exceeded their allocated permits. Developed countries?high per capita emissions at present and for quite a long period in future would continue to occupy emission spaces for developing countries. Therefore, developed countries must commit deeper emission reduction rate for the next commitment period at the Copenhagen conference in order to achieve the emission pathway under the long-term emission reduction target, and to save necessary development space for developing countries. At the same time, developed countries should provide adequate financial and technical support as compensation for their overuse of the development space for developing countries, to improve developing countries?capacity to respond to climate change under the framework of sustainable development. On the one hand, we should insist on the principle of equity to obtain reasonable emission space for our country in the international climate change negotiation; while on the other hand, we should enhance development toward low-carbon economy to protect global environment and to achieve sustainable development.

Based on a review of international adapting initiatives to climate change, the tracks and trends of international adaptation policies, especially of UNFCCC, are introduced. The national adaptation strategies of Australia, India, Russia, Japan, USA, Canada, and some main countries of Europe are analyzed. It is concluded that key adaptation options include the measures to deal with extreme climate events, natural disasters, fresh water supply, infrastructure, food safety, and an efficient coordination mechanism.

As an intermediate conference between the Bali and Copenhagen conference, the Poznan conference of December 2008 not only comprehensively reviewed the implementation of Bali roadmap, but also prepared for the future Copenhagen negotiations; therefore it is an extremely important conference. Two negotiation camps, three major forces engaged in a struggle over the principle of "common but differentiated responsibilities"and relevant issues, such as emission reduction target, adaptation, transfer of technologies, and finance support, etc. In 2009, the Obama administration fundamentally changed the position of the United States on climate change, thus moving close to the European Union. At the same time, the emerging powers become more prominent in the political situation, and some other nations also adjust according to their own interests. Obviously, China has been in a very critical position in the formation and development of international climate change regime. How to defense the interest of the whole developing countries, develop the image of responsible stakeholder and realize domestic low-carbon development still need to be seriously addressed.