排放强度目标下中国最优研发及经济增长路径

Optimal R&D investment path for China to fulfill its emission intensity target and the corresponding economic growth path

以研发投资为减排手段,在最优经济增长模型框架下构建碳排放强度目标约束下的最优控制模型,并针对中国2009年提出的排放强度目标"2020年排放强度降低到2005年的40%~45%",研究了同时满足减排目标和社会福利最大化目标下的最优研发投资路径以及经济平稳增长路线。模拟发现:前轻后重的研发投资路径有利于最大化社会成员的效用,而为了完成减排目标,中国需从2014年开始大幅提高研发投资到2.85%,随后每年都要保持在3%的水平;受此影响,经济平稳增长速度在2014年出现明显回落;排放强度路径呈现从缓慢下降到迅速下降而后降速趋缓的走势;能源消费量和碳排放量总体呈增长趋势,但在2014年继一个小高峰后出现短暂的下调。

This paper selected the R&D investment as primary abatement instrument, and constructed an optimal economic growth model with the constraint of carbon intensity reduction target. The mechanism behind the carbon intensity reduction here is that R&D activity will increase the knowledge stock and further improve the efficiency of energy use. Besides, the efficiency gap with developed countries will enhance the improvement rate through spillover effect. Given the linear relationship between energy intensity and carbon intensity of GDP, the improvement of energy efficiency means the decrease of energy intensity, which can easily conduct its relationship with carbon intensity. Furthermore, based on this model, it studied the optimal R&D investment and balanced economic growth path that satisfies both targets of social welfare maximization and carbon intensity reduction proposed by China in 2009, which is to reduce the carbon intensity in 2020 by 40%-45% compared with 2005. The simulation results indicated that the social welfare can benefit from increasing the consumption-output ratio from the 2007 level-49% to the optimal level-55%, and decelerating the R&D investment enlargement. However, in order to achieve the abatement target of 40% carbon intensity reduction it is required to raise the R&D intensity of GDP to 2.85% rapidly after 2014 and keep it at 3% thereafter. Perceivably, the optimal choice for the social planner is to postpone the start point to take concrete measures to reduce the carbon intensity before it is too late. Accordingly, the economic growth will attenuate due to the energy input decline and the resource invested on R&D, the balanced economic growth rate would drop sharply after 2014 with the annual average growth rate of 6% and 9.4% respectively in the optimal and baseline scenarios, whilst the path of carbon intensity indicates it would decline smoothly before 2013, and then after 2014 it would drop significantly but with the decline rate gradually slowing down, which is in accordance with the path of R&D intensity. Meanwhile, due to the combined effects of carbon intensity and economic growth trajectories, the energy consumption and carbon emission would keep increasing by and large, with a temporary decrease after an unobvious peak showing up in 2014. By the end of 2020, the energy and carbon emissions will reach 4176 Mtoe and 3478 MtC under the baseline scenario.