When will China achieve its carbon emission peak?

2015年11月30日，第21届联合国气候变化大会在巴黎举行。中国作为目前年碳排放量最大的国家与全球应对气候变化事业的积极参与者备受瞩目。巴黎大会前，中国在“十二五”期间的大力减排、在哥本哈根气候大会上做出的郑重承诺、在会前与美国等主要经济体分别发表了应对气候变化的多个联合声明以及向联合国提交的“国家自主贡献文件”（INDC）均表明中国在以最大的决心、最大的执行力走绿色发展之路。而会上，中国态度、中国方案与中国行动，特别是“中国的碳排放是否能在2030年达到峰值”更是各方密切关注的问题。北京大学城市与环境学院方精云院士领导的研究团队对此给出了一个肯定的回答:“中国有很大的可能在2030年前达到碳排放峰值。” 这项研究结果以“When will China achieve its carbon emission peak?”为题，发表在《国家科学评论》（National Science Review, NSR）上，并在巴黎峰会上进行了展示，引起了强烈反响。法国国际新闻频道FRANCE 24 对此进行了专题采访。
 



在研究中，作者基于Kaya恒等式, 将碳排放分解为GDP与碳强度（单位GDP的碳排放量）的乘积, 并设置了六种情景进行分析。六种情景分别代表：中国延续以往（1980~2010年）的减排力度；中国未来的碳强度按照与发达国家相似的衰减过程变化；中国继续维持十二五规划的减排力度；中国实现哥本哈根承诺，使得碳强度在2020年时相比2005年下降40%，并以此速度继续减排；中国实现《国家自主贡献》的目标，碳强度在2030年时相比2005年下降60%并延续此减排速度；中国以最低减排速度恰巧在2030年时达到碳排放峰值。

 


通过对六种情景的比较与分析，结果显示：中国的碳排放量到达峰值的时间为2023~2030年, 对应的峰值为2.89~3.29 Pg C。若中国的碳强度能在未来维持每年下降3.3%，或者中国能达成哥本哈根承诺与INDC目标，并维持十二五规划的减排力度，那么中国就可以实现碳排放在2030年到达峰值的目标。
 

文中还指出，中国制定的减排目标，远比“八国集团”历史上的排放目标要严苛的多，这说明中国为推动全球携手共进，凝聚各方共识，做出了自己的努力，承担着更多的减排责任。同时，随着一系列减排目标、政策的出台与碳交易市场的开放, 中国有望通过市场机制来优化碳排放配置, 同时督促企业自觉节能减排、改进工艺, 激发企业、公众参与环境管理; 碳捕集与封存(CarbonCapture and Storage, CCS)等新技术的开发与推广使得碳强度的加速下降成为可能; 中国有机会通过巴黎谈判等会议获得来自发达国家的技术与资金支持。以上因素都可能加速中国的减排过程，使得中国的碳排放到达峰值的时间早于2030年。但值得注意的是，碳排放越早到达峰值，意味着商业、企业和消费者用于调整的时间就越少, 更多的基础设施将被过早更换, 对产业结构、能源结构及技术改进等因素的要求越高,相应的减排压力越大。因此，最理想的情况是达成各减排目标的同时, 年碳排放量峰值年份尽量趋近2030年。这需要政府在实际操作中结合经济的宏观调控, 鼓励清洁能源的发展, 发展新技术, 促进碳交易, 从而实现经济可持续发展与环境保护的平衡。

The 2015 Paris Agreement will clarify emission reduction targets for each country [13]. Comprehensive analyses of possible pathways to reach carbon reduction goals and examine the evidence as to whether China can achieve the INDC Target are urgently needed. Previous studies used model simulations (e.g. environmental Kuznets curve and carbon emission model) to create a carbon emissions peak scenario [14,15]. Based on the Kaya identity [16], the present study used six emission scenarios to analyze the pathways of the potential emissions for China between 2011 and 2050, and to evaluate the feasibility and the social implications of the INDC Target.

Data sources and definitions
The CEI data from China and major developed countries were obtained from fossil fuel emissions and GDP data from 1980 to 2010. Data from major developed countries were taken from the Group of Eight (G8): the USA, Japan, Germany, France, UK, Italy, Canada and Russia.
The data of fossil fuel emissions was sourced from the Carbon Dioxide Information Analysis Center (Oak Ridge National Laboratory, USA), which documents annual emissions from solid, liquid and gas fuel combustion, cement production and gas flaring as a global total and for all countries [17], although recently the data have been disputed [18]. GDP data are from the World Bank [19], which summarizes annual GDP for 222 countries. All GDP data were treated as constant 2005 US dollars.
The projection data of the annual growth rate for China's GDP from 2011 to 2050 (Table 1) are from the Organization for Economic Cooperation and Development (OECD), which provides predictive growth rates of GDP each year through to 2060 for OECD countries [20]. China's annual GDP from 2011 to 2050 was calculated according to China's historical GDP and future growth rates.
We estimated CEI and cumulative carbon emissions of the G8 countries using carbon emission and GDP data. Specifically, the CEI is equal to the ratio of carbon emissions to GDP for the same country in a given year. Cumulative carbon emissions are the sum of annual carbon emissions over a given period.

Emission scenarios and predictions
We used Equation (1) to predict carbon emissions (C), based on the relationship between GDP (G) and CEI (I): I is estimated by an exponential Equation (2) [21]: where I t is the CEI of year t, I 0 is the CEI of the base year, and b is the attenuation coefficient of CEI. In all six scenarios, the base year is 2010, therefore I 0 equals 0.59 t C per thousand of constant 2005 US dollars, and b changes with different scenarios (See Table S1, Supporting Information). Based on Equations (1) Fig. 1a). Assuming that China's CEI during 2011-50 will continue to decrease following Equation (3), then b would be 0.0426 (Table S2, Supporting Information): (2) Past G8 scenario: assuming the same average attenuation coefficient of CEI for China as that for the G8 countries from 1980 to 2010. We assume that China's CEI decreases between 2011 and 2050 in accordance with Equation (2) (Fig. 1b) Substituting the CEI under the six scenarios and the corresponding projected data of Chinese GDP into Equation (1), we therefore predict the pathway of carbon emissions, and calculate their peak values and the peak year, respectively.

RESULTS AND DISCUSSION
During 2011-2050, the annual rates of CEI decline under the Past China, Past G8, Five-Year, Copenhagen, and INDC scenarios would be 4.2%, 2.5%, 3.7%, 3.4% and 3.6%, respectively. The decline rate of the Past G8 scenario is the lowest, followed by the Copenhagen scenario, and then the other three scenarios. Based on these predictions, the year of peak carbon emissions (from soonest to latest) would be 2023 (Past China, with an emission at the peak of 2.89 Pg C yr −1 ), 2026 (Five-Year, 3.11 Pg C yr −1 ), 2026 (INDC, 3.14 Pg C yr −1 ), 2030 (Copenhagen, 3.29 Pg C yr −1 ) and 2043 (Past G8, 4.25 Pg C yr −1 ) (Fig. 2). Cumulative emissions during 2011-50 corresponding to these peak years would be 104.33, 116.10, 117.54, 124.05 and 149.82 Pg C, respectively. In other words, lowering the rate of CEI decline will delay the carbon emissions peak, with greater cumulative emissions.
All five scenarios reached a peak before or in 2030, except the Past G8 scenario, which would achieve a peak in 2043. Compared with a later peak, an earlier peak would require less time for commercial, corporate and consumer interests to adjust to lower energy consumption rules. Infrastructure would need to be replaced more quickly, stricter requirements for energy-related and technological improvements would need to be established and greater pressure for emissions reduction applied [22]. The  Carbon emissions of the Peak Scenario would peak (3.31 Pg C) in 2030, with CEI decreasing by 3.3% yr −1 from 2011 to 2050 (Fig. 2). Emissions would increase by an average rate of 1.9% yr −1 through the peak year and decrease by an average rate of 0.6% yr −1 thereafter. Cumulative emissions during 2011-50 would be 124.57 Pg C.
In summary, all scenarios would achieve peak carbon emissions before 2030 and reach the Copenhagen Commitments goal except the Past G8 scenario. However, the Chinese government would be under pressure if required to reach the peak at an earlier year [22]. Comparison between the Past G8 and INDC scenarios indicates that the INDC Target is much harsher than the 1980-2010 emission standards of the G8 countries (CEI decreased by 60% over 25 years vs. 40% over 30 years). This would necessitate China's utmost efforts in addressing climate change and taking on greater responsibility for emission reductions.

UNCERTAINTIES
We constructed six scenarios to simulate China's carbon emissions over 2011-50, and evaluated the feasibility of achieving the 2030 Goal and other targets. However, there are two uncertainties related to the outcomes in our scenarios.
(1) Uncertainty of projection data. The predicted GDP growth rates from the OECD may be lower than actual rates. Most of China's GDP projection data before 2010 estimated by the OECD were less than actual GDP [23,24]. Indeed, the OECD predicted that GDP growth rates for China are lower than those of similar studies [25][26][27]. Underestimated GDP growth rates would cause predicted future carbon emissions to be artificially low and result in underestimating the time required to reach peak carbon emissions. (2) Uncertainty of policy implementation, technological innovation, and financial support. China is expected to optimize its carbon emission configuration by implementing a series of climate-related actions and building carbon emission trading pilots. These actions will work through market mechanisms, urging enterprises to conserve energy and reduce emissions, and stimulate public participation in environmental management [28,29]. The development and promotion of carbon capture and storage and other innovative technologies may enable an accelerated decline in CEI [30]. Developed countries may agree to provide financial support and transfer technologies to developing countries during the 2015 Paris Agreement [13], which would accelerate the decline of CEI in China. Any of the aforementioned actions could cause carbon emission decline rates to accelerate, which could result in an overestimation of future carbon emissions and the time required to reach peak carbon emissions. Wang et al. [6] holds that industrialization and urbanization are inevitably accompanied by an increase of carbon emissions. Thus, reducing carbon emissions could narrow the amount of energy that can be consumed for development. Moreover, reaching peak carbon emissions too early would place increased pressure on social and economic factors for China. The ideal situation is one in which China achieves all emission reduction goals and arrives at peak carbon emissions around the year 2030. It will be difficult to achieve this goal because regulations only apply to CEI without regard for changes in GDP. Therefore, economic macrocontrol and carbon emissions reduction must be promoted in a coordinated manner in the future. Future studies should further explore how to coordinate the emission reduction and economic developments, thus reducing the adverse impact on economic developments. Furthermore, the Chinese government should optimize the combination of energies used, promote technological innovation, and establish carbon emission trading mechanisms. This could lead to multiple gains in sustainable development and emission reduction [31].