What Is the Social Cost of Carbon?

Understanding the Social Cost of Carbon

Among the diverse tools used to assess and address climate change, few are as debated or as influential as the social cost of carbon (SCC). Placing a price on carbon dioxide emissions enables policymakers and businesses to evaluate the economic damages associated with greenhouse gas emissions, guiding investments and regulations to mitigate climate change’s long-term effects. This article explores what SCC is, how it is calculated, why it matters, and how it shapes our future.

What Is the Social Cost of Carbon?

The social cost of carbon is an estimate, typically expressed in dollars, of the economic damages resulting from emitting a single additional ton of carbon dioxide (CO₂) into the atmosphere in a given year. These damages encompass a wide array of impacts, such as:

• Reduced agricultural productivity
• Human health decline and increased mortality
• Property damage from flooding and sea level rise
• Decreased worker productivity due to extreme heat
• Costs associated with modulating energy consumption

By consolidating these diverse expenses into a monetary value, SCC allows for direct comparisons in cost-benefit analyses of climate policies and regulations, helping to determine whether the expense of mitigation is justified by the avoided damages.

Why Is the Social Cost of Carbon Important?

Assigning a dollar value to CO₂ emissions provides a powerful tool for climate action. Policymakers use SCC for:

• Assessing Climate Policies: Comparing the benefits of reducing emissions with the costs of action or regulation.
• Setting Environmental Regulations: Establishing emission reduction targets and carbon pricing schemes.
• Justifying Public Investments: Allocating budgets to climate adaptation and mitigation projects based on cost-effectiveness.

Elevating the SCC figure in policy analysis generally justifies more aggressive climate action, as it assigns greater economic weight to the harms prevented by curbing emissions.

Historical Development of the SCC

The concept of the social cost of carbon emerged from decades of interdisciplinary research at the intersection of economics, physical science, and policy. Notable milestones include:

• Development of integrated assessment models (IAMs) in the late 20th century to connect emissions, climate effects, and economic consequences.
• Establishment of the Interagency Working Group (IWG) on the Social Cost of Carbon in the United States in 2009, providing standardized federal estimates for policy use.
• Regular updates (e.g., 2010, 2013, 2016) of SCC values and underlying methodologies to reflect advancing knowledge and more sophisticated modeling techniques.

Today, SCC is a pillar of regulatory analysis in the U.S., Europe, and beyond, shaping energy, transportation, and infrastructure policies globally.

How Is the Social Cost of Carbon Calculated?

Calculating the SCC is a complex process involving multiple stages and requires blending climate science, economics, and statistics. The main steps include:

1. Socioeconomic Projections: Forecasting future population, economic growth, and emission patterns to model a range of futures.
2. Climate Modeling: Estimating the climate response to additional CO₂ (e.g., changes in temperature, sea level, weather extremes).
3. Damage Assessment: Quantifying the impact of climate changes on human and natural systems, including agriculture, health, property, and energy needs.
4. Discounting Future Damages: Applying a discount rate to express future damages in today’s dollars, reflecting society’s preference for present versus future value.

These steps are combined using Integrated Assessment Models (IAMs), such as DICE, FUND, and PAGE. IAMs calculate SCC by simulating various scenarios, comparing a baseline case to one with an extra ton of CO₂, and measuring the incremental harm.

Main Integrated Assessment Models (IAMs)

Key Factors Influencing the SCC

Several key assumptions strongly shape SCC estimates. Understanding these factors is crucial:

1. Discount Rate

The discount rate reflects how much less society values future damages compared to present costs. Lower discount rates emphasize the welfare of future generations, increasing the SCC, while higher rates lower the SCC. Typical U.S. government analyses historically have used a range from 2.5% to 5%, with 3% as a common central value.

• Low discount rate (e.g., 1-2%): Higher SCC, more aggressive climate policy justified
• High discount rate (e.g., 5-7%): Lower SCC, less justification for costly action

2. Climate Sensitivity

This describes the earth’s temperature response to doubling CO₂ concentrations. High climate sensitivity means greater damages per emission, resulting in a higher SCC. Since this is uncertain, different models use a range of values.

3. Damage Functions

Damage functions mathematically relate changes in temperature or other climate variables to economic damages, such as lost crop yields or increased disease rates. Small differences in these functions can cause large swings in SCC values. Many impacts are difficult to quantify, leading to uncertainty or omissions in model results.

4. Socioeconomic Scenarios

SCC calculations use different scenarios about how population, technology, and the economy might evolve. These affect both future emissions and how vulnerable societies might be to climate impacts.

Limitations and Sources of Uncertainty

Despite its value, the SCC is an inherently uncertain estimate due to:

• Unpredictable future technologies and economic/political changes
• Difficulty quantifying non-market damages (e.g., loss of biodiversity, displacement of people)
• Challenges in capturing global versus region-specific effects
• Uncertain valuation of rare, catastrophic outcomes (“tail risks”)

Researchers strive to improve models, incorporate additional climate and economic impacts, and update damage functions, but uncertainty can never be fully removed.

Global Variations: Applying the SCC Around the World

SCC estimates and applications vary by country and institution:

• The United States uses the SCC in federal cost-benefit analyses of regulations. As of 2021, the U.S. government reverted to a value of about $51 per metric ton CO₂, pending further review and update.
• European Union employs SCC in calculating the price for emission trading systems and assessing climate impacts in policy evaluations.
• Developing countries may adopt different values reflecting local circumstances, though international negotiations often reference global SCC estimates for equity and shared responsibility.

Some countries price carbon emissions below their estimated SCC, while others set a market price that more closely matches estimated social damages.

Policy Uses of the Social Cost of Carbon

The SCC is foundational for:

• Cost-Benefit Analysis: Comparing net benefits of environmental regulations, infrastructure investments, and climate adaptation initiatives.
• Setting Regulatory Standards: Justifying limits on power plant emissions, fuel economy standards, and investment in renewable energy.
• Carbon Pricing: Informing decisions about carbon taxes and cap-and-trade programs to reflect the true cost of emissions.

In all these applications, SCC helps ensure that today’s choices consider economic losses that future generations would otherwise bear.

Debates and Challenges

The SCC’s use in policy is not without controversy.

• Ethics: How should society balance present versus future interests when selecting a discount rate?
• Scope: Should SCC calculations focus on domestic damages, global damages, or both? The broader the perspective, the higher the SCC, since climate change is a worldwide issue.
• Modeling Uncertainty: Is it possible to accurately model and value all the ways that climate change affects people and ecosystems?
• Equity: How should the SCC account for disparate impacts on vulnerable populations?

These questions shape ongoing efforts to revise and improve SCC methods, balancing practical applications with ethical and scientific rigor.

The Future of the Social Cost of Carbon

The future of SCC is evolving, driven by advances in climate science, economics, and environmental policy. Key trends include:

• Improved modeling: Researchers regularly update IAMs to better reflect empirical observations and integrate newer risks.
• Inclusivity: Efforts grow to consider additional damages—like species extinctions, ocean acidification, and tipping points—that were long ignored.
• Transparency and public engagement: SCC estimation processes are becoming more participatory, integrating stakeholder input.
• Low discount rates: There is increasing preference for valuing future generations more highly, leading to higher SCC figures.

By providing a transparent accounting of the costs imposed by carbon emissions, SCC remains a critical tool for informed, responsible climate decision-making.

Frequently Asked Questions (FAQs)

Q: What does the social cost of carbon actually measure?

A: The social cost of carbon quantifies the total economic damages—such as impacts on health, agriculture, infrastructure, and ecosystem services—resulting from emitting one more ton of CO₂ into the atmosphere. These damages are expressed in today’s dollars for ease of policy comparison.

Q: How often is the SCC value updated?

A: SCC values are periodically revised to incorporate new scientific data, improved climate modeling, and evolving economic insights. In the U.S., federal SCC estimates have been updated several times since 2010.

Q: What is the current U.S. government figure for the social cost of carbon?

A: As of early 2021, the interim U.S. government estimate was about $51 per metric ton of CO₂. This value is under review and subject to change as analytical methods advance and new data emerges.

Q: Why is there debate over the discount rate used in SCC calculations?

A: The discount rate determines how much less future harms are valued compared to present-day costs. A low rate places more value on long-term impacts, raising the SCC and bolstering arguments for stronger climate action. A high rate discounts the future more steeply, lowering SCC values and making ambitious mitigation seem less economically justified.

Q: Are all damages from carbon emissions included in SCC estimates?

A: No, not all damages are captured in current models. Many non-market effects—such as losses to biodiversity, cultural heritage, or ecosystem stability—are excluded or highly uncertain, rendering SCC a conservative (lower-bound) estimate of the true social damage from CO₂ emissions.

Summary Table: Key Elements of the Social Cost of Carbon