2023-09-24-IMF-物理气候风险对全球经济的影响（英）_125页_8mb

Summary of "Global Economic Impacts of Physical Climate Risks"

Core Content

This IMF Working Paper examines the economic impacts of physical climate risks—both chronic (gradual changes in temperature and precipitation) and extreme (heatwaves, coldwaves, droughts, floods)—on global productivity and macroeconomic variables. The study uses firm-level data from 20,215 firms across 48 countries and integrates these findings into a global, multisectoral, intertemporal general equilibrium model called G-Cubed to project economic consequences under two climate scenarios: SSP 1-2.6 (low greenhouse gas emissions) and SSP 2-4.5 (intermediate greenhouse gas emissions).

The analysis includes both historical and forward-looking productivity assessments, and it accounts for the persistent effects of flood damage on firms' physical capital. The paper also highlights the sectoral and regional heterogeneity in the impacts of climate risks, emphasizing the importance of general equilibrium effects in understanding these impacts.

Main Points

1. Sectoral Productivity Impacts

• Agriculture is the most vulnerable sector, with productivity losses estimated at 10–20% in most regions under the two scenarios.
• Mining also experiences significant losses, with reductions exceeding 5% in certain regions.
• Manufacturing and services are less affected, possibly due to their greater flexibility in location and lower exposure to climate risks.

2. Climate Scenarios and Projections

• The study uses Shared Socioeconomic Pathways (SSPs) to define climate scenarios:
  • SSP 1-2.6: Low emissions, with global warming of 1.7°C (2041–2060) and 1.8°C (2081–2100).
  • SSP 2-4.5: Intermediate emissions, with global warming of 2.0°C (2041–2060) and 2.7°C (2081–2100).
• The projections cover the period 2021–2100, and the results show that economic losses increase with global warming.

3. Macroeconomic Consequences

• Under SSP 1-2.6, the global economy could lose 1.2% of GDP annually on average, rising to 2.4% in 2100.
• Under SSP 2-4.5, the average annual GDP loss could be as high as 3.2%, increasing to 6.4% in 2100.
• The study illustrates changes in consumption, investment, trade balance, real exchange rate, inflation, and current account balance due to climate shocks.

4. Methodology

• Two types of damage functions are used:
  • Empirically derived for firm-level productivity impacts.
  • Existing global study (Huizinga et al. 2017) for flood impacts on physical capital.
• The firm data comes from the Orbis Database, with 59,554 firms in Sample 1 and 20,215 firms in Sample 2.
• TFP (Total Factor Productivity) is estimated for firms, and the G-Cubed model is used to project macroeconomic outcomes.

5. Key Findings

• No additional adaptation beyond 2020 is assumed, which means the results reflect current vulnerability levels.
• The study does not observe positive effects from climate change on sectors like agriculture or services, which contrasts with some existing literature.
• General equilibrium effects are crucial for understanding how different sectors and regions respond to the same climate shock.

Key Information

• Data Sources:

  • Firm-level data from the Orbis Database.
  • Historical climate data from the Climate Research Unit (CRU).
  • Projected climate data from ISIMIP and Jupiter Intelligence for flood severity.

• Climate Indicators:

  • Chronic indicators: Annual changes in temperature and precipitation from the 1961–1990 baseline.
  • Extreme indicators:
    • For temperature: MaxTemp90P, MaxTemp10P, MinTemp90P, MinTemp10P.
    • For precipitation: SPIDry and SPIWet, based on the Standardized Precipitation Index (SPI).

• Model Used: G-Cubed, a hybrid DSGE-CGE model that captures the interconnectedness of the global economy and allows for the analysis of general equilibrium effects.

• Policy Relevance:

  • The results can be used for climate risk analysis by policymakers and practitioners.
  • The study supports stress testing for banks and financial institutions to assess risks to capital and credit.

Conclusion

This paper contributes to two key areas of research: the sectoral impact of physical climate risks and the macroeconomic modeling of climate change. By using firm-level data and integrating it into a general equilibrium model, the study provides a comprehensive assessment of the global economic consequences of climate risks under two different emission scenarios. It highlights the importance of adaptation and the heterogeneous impacts across sectors and regions, offering valuable insights for climate policy and financial risk management.