基于改进委托-代理模型的船舶碳减排政府激励效用建模与分析

Modeling and Analysis of the Effects of Government Incentives onto Reduction of Ship Carbon Emission Based on an Improved Principal-agent Model

目前碳减排激励措施主要考虑碳定价、碳税、船舶航速降低激励等,尚未针对实施碳减排的船公司给予合理补贴激励。由于船公司运行模式、减排思路、资产组成等方面与普通企业的差异,传统委托-代理模型假设无法满足航运业背景下对政府激励效用的需求,需对现有委托-代理模型进行针对性改进。为实现政府以有限基金达到社会效用最大,同时满足船公司付出最优努力获得最大收益,考虑持风险规避态度的船公司碳减排效果外生不确定性,提出船舶碳减排政府激励效用模型,根据政府能否完全观察到船公司的减排努力程度,分别在信息完全与信息不完全条件下,以政府和船公司自身收益效用最大为优化目标,求解政府最优奖惩系数和船公司碳减排最优努力程度,分析政府对船公司进行规制的最优激励合约问题,以及决定船公司碳减排内外部因素的参数对政府给与船公司的最优激励及相关参数的影响。结果表明:最优激励系数伴随外生随机变量方差和绝对风险规避系数的增加而加速下降至缓慢降低,当外生随机变量方差为8和绝对风险规避系数为4时,下降速率趋至平稳,此时,船公司对选择碳减排的风险厌恶程度极高,对实施碳减排的抵制心理十分强烈;成本系数和减排努力水平影响系数同时影响船公司实施碳减排的力度,当减排努力水平较大时,政府的激励随船公司的成本增加呈现先迅速增长后平缓的变化趋势,意味着政府在有限基金内尽可能满足船公司碳减排需求以减少实施难度,但当激励达到一定程度,增加激励不会直接影响船公司碳减排积极性;由于成本系数和减排努力水平影响系数对政府激励效用的共同影响,不同航运市场条件下都将存在1个最优激励,结合长江航运发展背景,当成本系数为0.5且减排努力水平影响系数为3,使得政府激励效用最优。

Currently,the incentives for carbon emission reduction mainly focus on carbon pricing,carbon taxes,and reduction of ship speed,while there is no subsidy incentives for shipping companies implementing carbon reduction measures.Due to the differences in operational modes,emission reduction strategies,and asset compositions between shipping companies and ordinary enterprises,the assumptions of traditional principal-agent model fail to meet the need to analyze the effect of government incentive onto the shipping industry.Therefore,specific improvements to the existing principal-agent models are required.The purpose is to achieve the maximum social benefit with limited government funds,while the shipping companies that make best efforts will receive maximum profits.Considering the exogenous uncertainty of the effect of policies onto carbon reduction for risk-averse shipping companies,a government incentive model for the reduction of ship carbon emission is proposed.Since the government cannot always fully observe the efforts of a shipping company for reducing emissions,the scenarios with complete and incomplete information are independently analyzed.Setting the optimization objectives separately for the government and the shipping companies to maximize their own benefit,the optimal reward-penalty coefficient for the government and the optimal level of efforts for reducing carbon emission from the shipping companies are found.The optimal incentive contract is also studied for the government to regulate the shipping companies.The parameters for internal and external factors determining the efforts for reducing carbon emission by the shipping companies are discussed,as well as their impacts on the optimal incentives provided by the government and the relevant parameters.Study results show that the optimal incentive coefficient decreases at a decreasing rate when the variance of exogenous random variable and the absolute risk aversion coefficient increase.When the variance is 8 and the risk aversion coefficient is 4,the rate of decrease stabilizes.At this point,the shipping companies exhibit a strong aversion to the risks of reducing carbon emission and a strong resistance to implementing the measures.The cost coefficient and the coefficient influencing the level of efforts for reducing emissions jointly affect the intensity of the companies to implement measures.When the level of efforts is high,the government incentives initially increase quickly and then level off as the cost for the shipping companies increase.This implies that the government aims to meet the needs of reducing carbon emission of the shipping companies within its limited funds to reduce difficulties within the implementation.However,once the incentives reach a certain level,further increase in incentive will not directly affect the motivation of shipping companies to reduce emissions.Due to the joint impact of the cost coefficient and the coefficient of the level of effort for emission reduction on the government incentives,there will be one optimal incentive under different shipping market conditions.Considering the development of shipping industry along the Yangtze River,when the cost coefficient is 0.5 and the coefficient of the level of effort for emission reduction is 3,the optimal impact of government incentive is achieved.