ESG rating agencies compared: MSCI vs Sustainalytics vs ISS vs CDP scoring methodologies and coverage

Why It Matters

A landmark study by Berg, Kölbel, and Rigobon at MIT Sloan (2022) found that the correlation between ESG ratings from different providers averages just 0.54, compared with 0.92 for credit ratings from Moody's and S&P. Updated analysis by the OECD (2025) confirmed that divergence has not narrowed, with pairwise correlations between major raters still ranging from 0.38 to 0.71 depending on the pillar. For the more than $35 trillion in assets now managed under ESG-integrated strategies globally (Global Sustainable Investment Alliance, 2025), this divergence creates material consequences: a company rated a leader by MSCI may simultaneously be flagged as high-risk by Sustainalytics. Portfolio managers who rely on a single provider without understanding its methodology risk mispricing ESG risk, misallocating capital, and failing to meet fiduciary obligations. As the EU's CSRD and ISSB standards reshape corporate disclosure, the interplay between reported data and third-party ratings is becoming the central tension in sustainable finance.

Key Concepts

Materiality frameworks define which ESG issues matter for a given company or sector. MSCI uses an industry-specific materiality map that emphasizes financial materiality: the ESG factors most likely to affect enterprise value. Sustainalytics applies a similar financially material lens but frames its output as unmanaged risk exposure. ISS ESG assesses both financial materiality and impact materiality, aligning more closely with the EU's double-materiality standard. CDP focuses on environmental disclosure quality rather than aggregated ESG scores, evaluating how comprehensively companies report climate, water, and forest data.

Scoring architecture varies substantially. MSCI assigns letter grades from AAA to CCC on a relative, industry-adjusted basis. Sustainalytics produces an absolute ESG Risk Rating in which lower scores indicate lower risk, measured in units of unmanaged risk exposure. ISS ESG uses a four-point performance scale (A+ to D-) benchmarked against sector peers. CDP assigns letter grades from A to D- based on the quality and completeness of environmental disclosure.

Data sources range from public filings, sustainability reports, and regulatory databases to company questionnaires, media monitoring, and NGO reports. MSCI and Sustainalytics rely primarily on public data supplemented by company engagement. CDP collects data directly through its annual questionnaire, which over 24,000 companies completed in 2024 (CDP, 2025). ISS ESG combines public data with a proprietary company feedback process.

Controversy and incident monitoring is handled differently. MSCI integrates controversies into its overall rating, potentially capping the score regardless of policy strength. Sustainalytics separates its controversy rating from its core ESG Risk Rating, allowing investors to weight incidents independently. ISS ESG flags norm-based controversies under its Global Norms module. CDP does not provide a standalone controversy overlay.

Head-to-Head Comparison

Correlation patterns. The OECD (2025) documented that MSCI and Sustainalytics ratings for the same company diverge in direction (one rating positive, the other negative) approximately 30 percent of the time. Berg, Kölbel, and Rigobon (2022) identified three sources of divergence: scope (which categories are measured), measurement (how each category is quantified), and weight (how categories are aggregated). Scope divergence accounts for the largest share, meaning providers fundamentally disagree about which issues are material for a given industry. A 2025 analysis by the CFA Institute found that blending scores from at least two providers reduced portfolio ESG risk misclassification by 38 percent compared to single-provider reliance (CFA Institute, 2025).

Real-world divergence example: Tesla. MSCI upgraded Tesla to AA in 2024, citing its contribution to clean transportation and strong governance improvements. Sustainalytics simultaneously rated Tesla as "high risk" (score of 32.5), flagging labor practices, workplace safety incidents, and governance controversies. ISS ESG placed Tesla in the middle of its automotive peer group with a C+ rating. This single example illustrates why multi-provider analysis is essential for informed decision-making.

Real-world convergence example: Microsoft. Microsoft consistently scores in the top tier across all four providers: MSCI AAA, Sustainalytics negligible risk (score of 14.2), ISS ESG A, and CDP A-list for climate. Strong disclosure practices, ambitious science-based targets, and transparent governance create convergence even across different methodologies.

Real-world mixed example: JPMorgan Chase. JPMorgan receives divergent scores that reflect methodological priorities. MSCI rates the bank A, recognizing its sustainable finance commitments and governance strength. Sustainalytics assigns a medium-risk score of 26.4, weighting exposure to fossil-fuel financing. CDP has scored JPMorgan B, reflecting room for improvement in climate transition planning relative to its financed emissions footprint.

Key Players

Established Leaders

• MSCI — Dominant provider for index-linked ESG strategies; ESG ratings integrated into over $16 trillion in benchmarked assets globally
• Sustainalytics (Morningstar) — Largest coverage universe at 16,000+ companies; ESG Risk Ratings embedded in Morningstar fund sustainability ratings used by retail and institutional investors
• ISS ESG (Deutsche Börse Group) — Strong in proxy advisory integration and EU regulatory alignment; used by over 1,600 institutional clients
• CDP — Non-profit operating the world's largest environmental disclosure platform; A-list recognition drives corporate competitive benchmarking
• S&P Global ESG Scores — Underpins the Dow Jones Sustainability Index; covers 9,400+ companies using Corporate Sustainability Assessment data
• Bloomberg ESG Data — Integrated into Bloomberg Terminal; broad raw data coverage used by quantitative and fundamental investors

Emerging Startups

• Clarity AI — Machine-learning platform analyzing 70,000+ companies using alternative data sources; raised $80 million in 2024 (Clarity AI, 2025)
• Arabesque S-Ray — Combines big data and AI with UN Global Compact principles to score 9,000+ companies in near-real time
• RepRisk — Specializes in controversy and reputational risk monitoring using natural language processing across 100,000+ sources daily
• Util — UK-based platform mapping company revenues to UN SDG impact, offering granular product-level sustainability analysis

Key Investors/Funders

• Norges Bank Investment Management (NBIM) — World's largest sovereign wealth fund ($1.7 trillion); actively pushes for ESG rating transparency and methodology convergence
• BlackRock — Largest asset manager ($10.5 trillion AUM); uses multiple ESG data providers and publicly advocates for improved corporate ESG disclosure
• PRI (Principles for Responsible Investment) — UN-supported network of 5,300+ signatories representing $120 trillion; funds research on ESG data quality and provider accountability

Action Checklist

1. Map your ESG data needs. Identify whether the priority is portfolio screening, risk management, index construction, regulatory compliance, or client reporting. Each use case favors different providers.

2. Subscribe to at least two providers. Given documented divergence rates of 30 percent or more (OECD, 2025), relying on a single source creates blind spots. Pair a broad-coverage provider (Sustainalytics or MSCI) with a disclosure-focused source (CDP) for complementary perspectives.

3. Understand the methodology before using the score. Read each provider's published methodology document. Pay particular attention to materiality definitions, weighting schemes, and controversy-handling rules. A rating that looks comparable across providers may be measuring fundamentally different things.

4. Separate controversy signals from overall ratings. Use Sustainalytics' standalone controversy rating or RepRisk's incident monitoring to track emerging risks that may not yet be reflected in annual ESG scores.

5. Engage with the rated company. Cross-reference third-party scores against the company's own sustainability report and CSRD or ISSB filings. Ask investor relations teams to explain discrepancies between their disclosure and external ratings.

6. Build internal ESG scoring capacity. Use raw data from Bloomberg, CDP questionnaire responses, or company filings to develop proprietary views. Internal scores calibrated against multiple providers reduce dependency on any single methodology.

7. Monitor regulatory developments. The EU's ESG Rating Regulation, expected to take effect in 2026, will require rating providers to disclose methodologies, manage conflicts of interest, and separate credit-rating from ESG-rating activities (European Council, 2025). Prepare for shifts in provider transparency and potential methodology revisions.

8. Review annually and document rationale. Record why specific providers were selected and how scores informed investment decisions. Regulatory expectations for audit trails are increasing under SFDR, CSRD, and the UK SDR.

FAQ

Why do ESG ratings from different providers diverge so much? The primary driver is scope divergence: providers disagree about which ESG issues are material for a given industry. MSCI may emphasize carbon emissions and energy management for an oil company, while Sustainalytics may weight community relations and water stress more heavily. Measurement divergence (different indicators for the same issue) and weight divergence (different aggregation formulas) compound the problem. Berg, Kölbel, and Rigobon (2022) found that scope differences alone explain over half the total rating disagreement.

Is one ESG rating provider objectively better than the others? No single provider is universally superior. MSCI excels at industry-relative peer comparison and is the most widely used for index construction. Sustainalytics offers the broadest company coverage and a useful absolute-risk framing. ISS ESG aligns most closely with European double-materiality requirements. CDP provides the most transparent, company-reported environmental data. The best approach depends on the investor's use case, geographic focus, and regulatory context.

How should portfolio managers handle contradictory ratings for the same company? Treat the divergence as information, not noise. When providers disagree, investigate the underlying drivers: different scope, different data vintage, or different weighting of a specific controversy. A structured process that documents the rationale for relying on one score over another, or for blending scores, strengthens both investment decisions and regulatory defensibility. The CFA Institute (2025) recommends building a composite ESG view that weights providers according to their demonstrated predictive power for specific risk factors.

Will regulation standardize ESG ratings? Partially. The EU ESG Rating Regulation will impose transparency, conflict-of-interest, and governance requirements on providers operating in Europe (European Council, 2025). IOSCO has also published recommendations for ESG rating and data product providers. However, these regulations focus on process transparency rather than mandating a single methodology. Divergence in materiality definitions and scoring architecture will persist, making multi-provider analysis a permanent feature of responsible investment practice.

How much do ESG data subscriptions cost? Enterprise data feeds from major providers typically range from $30,000 to $500,000+ annually, depending on coverage breadth, data granularity, and integration requirements. CDP disclosure data is free for reporting companies; third-party access to aggregated datasets is available through licensing. Smaller asset managers can access basic Sustainalytics risk ratings through the Morningstar platform at lower cost, while Bloomberg Terminal subscribers receive integrated ESG data as part of their existing subscription.