Forests play a leading role in regional and global carbon (C) cycles. Detailed assessment of the temporal and spatial changes in C sinks/sources of China's forests is critical to the estimation of the national C budget and can help to constitute sustainable forest management policies for climate change. In this study, we explored the spatio-temporal changes in forest biomass C stocks in China between 1977 and 2008, using six periods of the national forest inventory data. According to the definition of the forest inventory, China's forest was categorized into three groups: forest stand, economic forest, and bamboo forest. We estimated forest biomass C stocks for each inventory period by using continuous biomass expansion factor (BEF) method for forest stands, and the mean biomass density method for economic and bamboo forests. As a result, China's forests have accumulated biomass C (i.e., biomass C sink) of 1896 Tg (1 Tg=10(12) g) during the study period, with 1710, 108 and 78 Tg C in forest stands, and economic and bamboo forests, respectively. Annual forest biomass C sink was 70.2 Tg C a(-1), offsetting 7.8% of the contemporary fossil CO2 emissions in the country. The results also showed that planted forests have functioned as a persistent C sink, sequestrating 818 Tg C and accounting for 47.8% of total C sink in forest stands, and that the old-, mid- and young-aged forests have sequestrated 930, 391 and 388 Tg C from 1977 to 2008. Our results suggest that China's forests have a big potential as biomass C sink in the future because of its large area of planted forests with young-aged growth and low C density.

Forest carbon offset (FCO) projects play an increasingly important role in mitigating climate change through market mechanisms in both compliance and voluntary markets. However, there are challenges and barriers to developing an FCO project, such as carbon leakage and cost-effectiveness. There have been few attempts to summarize and synthesize all types and aspects of existing challenges and possible solutions for FCO projects. This paper systematically reviews and discusses the current challenges involved in developing FCO projects, and then draws on the experience and lessons of existing projects to show how those challenges were addressed in world-leading voluntary carbon standards, namely the Verified Carbon Standard, the American Carbon Registry, the Climate Action Reserve, and Plan Vivo. These voluntary markets have rich experience in FCO projects and are responsible for a significant share of the market. From the 53 publications used in this analysis, three broad thematic categories of challenges emerged. These were related to methodology, socio-economic implications, and implementation. Methodological challenges, particularly additionality, permanence, and leakage, were the focus of 46% of the selected research papers, while socio-economic challenges, including transaction, social, and opportunity costs, were addressed by 35%. The remaining 19% of the research articles focused on implementational challenges related to monitoring, reporting, and verification. Major voluntary standards adequately addressed most of the methodological and implementational barriers by adopting various approaches. However, the standards did not adequately address socio-economic issues, despite these being the second most frequently discussed theme in the papers analyzed. More research is clearly needed on the socio-economic challenges involved in the development of FCO projects. For the development of high-quality forestry carbon offset projects, there are many challenges and no simple, universal recipe for addressing them. However, it is crucial to build upon the current science and move forward with carbon projects which ensure effective, long-term carbon sinks and maximize benefits for biodiversity and people; this is particularly important with a growing public and private interest in this field.

Emissions trading schemes (ETSs) have been a central component of international climate change policies, as a carbon pricing tool to achieve emissions reduction targets. Forest carbon offset credits have been leveraged in many ETSs to efficiently meet emission reduction targets, yet there is little knowledge about the perceptions, experiences, and challenges associated with the forest carbon offsetting in existing and pilot ETS. Given that the future inclusion of forest carbon offset in ETS management activities and policies will require strong support and acceptability among the institutions and experts involved in ETS, this study explores the experiences and lessons learned with 16 globally engaging experts representing major existing ETSs (North America, Europe, and New Zealand) and Chinese pilot ETSs towards the inclusion of forestry offsets, major concerns and challenges with existing implementation models. Findings revealed that many respondents particularly from North America, New Zealand, and Chinese pilot systems portrayed positive attitudes toward the inclusion of forestry carbon offsets and its role in contributing to a viable ETS, while European experts were not supportive. Respondents cited leakage, permanence, additionality, and monitoring design features as the major challenges and concerns that inhibit the expansion and inclusion of forest carbon offsetting. Respondents from Chinese pilot schemes referenced a unique set of challenges related to implementation, including the increasing cost of afforestation and reforestation projects, the uncertainty in the future supply and demand for their national Certified Emissions Reduction (CER) scheme and landowner engagement. Existing and future ETSs should learn from and address the challenges experienced by global experts and carbon pricing mechanisms to design, evaluate, or enhance their forest carbon offset programs for an effective and viable system that successfully contributes to GHG mitigation practices globally. We recommend inclusion of forest carbon offsets at the early stages of ETS improves the perceptions and experience of policy makers and practitioners toward the success and potential of forestry offsets in ETS ensuring familiarity and confidence in the mechanism.

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Given that international collaborative efforts to reduce greenhouse gas (GHG) emissions are urgent and crucial, a critical understanding of challenges and opportunities of linking China’s newly established national ETS with existing domestic or regional ETSs is essential in order to achieve global emission targets, and may attract other jurisdictions to join in global carbon market development. In this backdrop, we analyzed the experiences, lessons, and insights from three key global carbon markets, namely North America, the EU and China, in terms of the barriers to linking the global carbon market, with a focus on China, using thematic analysis. The four most commonly cited linkage design elements (barriers) were the legal basis; monitoring, reporting, and verification; political feasibility; and the price-management mechanism. Like-minded jurisdictions with similar political views and design features will have a higher chance of linking. Additionally, sustaining market liquidity, widening sectoral coverage, minimizing carbon leakage, ensuring offset quality, and a transparent allowance and cap setting rules are crucial steps towards linkage. These outcomes can be used as an ETS linkage-ready design framework for CETS and ETS under development to overcome barriers to future international ETS linkages.