2023-10-31-未来能源研究所-解开增长不确定性_贴现和气候贝塔对碳社会成本的作用_29页_485kb

Social Cost of Carbon Estimation

Key Variables

• Discount Rates: Certainty-Equivalent (CE) and Risk-Adjusted
• Growth Uncertainty: Volatility in future consumption growth
• Climate Beta: Covariance between climate damages and economic growth

Discount Rate Structures

1. Certainty-Equivalent Rate

   • Declines linearly over time with time horizon
   • Slope determined by elasticity of marginal utility (𝜂𝜂)

2. Risk-Adjusted Rate

   • Rises with time horizon under certain conditions
   • Condition for increase: 𝛽𝛽 > 𝜂𝜂
   • In GIVE model, reaches 2.7% premium by 2300

Uncertainty Effects

• Growth uncertainty typically INCREASES SCC (except in specific case)
• Effect mechanism:
  • Elevates discount rates
  • Increases expected marginal damages through right-skew effect
  • Accelerating effect due to compounding

Policy Implications

• Ignoring uncertainty's impact on expected values produces biased SCC estimates
• Reduction in climate beta ($\beta$) generally REDUCES SCC
• Current guidance disproportionately focuses on discount rate adjustments

Recommendations

1. Apply both risk adjustment to discount rates AND expected value adjustment for impacts
2. Incorporate growth projections using stochastic growth scenarios
3. Ensure independence between discount rate and damage growth parameter calculations