What Is ESG Investing? How ESG Scores Are Built, and Why Raters Disagree

Same Company, Opposite Grades: AAA From One Rater, "High Risk" From Another

Picture a single listed company. MSCI rates it AAA — top of its industry. Sustainalytics classifies the same company as carrying "high unmanaged ESG risk." Two rating agencies, looking at the same disclosures, reaching opposite conclusions — this isn't a rare glitch. Academic studies have repeatedly found that correlation between major ESG raters' scores sits below 50%. Compare that to something like a P/E ratio or a debt-to-equity ratio, both computed from the same financial statement line items — you'd never see that kind of divergence there. Understanding why ESG scores split so widely between providers is the key to knowing what "this company has a high ESG rating" actually means — and, just as importantly, what it doesn't.

What ESG Investing Actually Is: Pricing In What the Balance Sheet Misses

ESG stands for Environmental, Social, and Governance — a framework for folding non-financial risks and opportunities, the kind that don't show up cleanly in a financial statement, into investment decisions. Environmental (E) covers things like carbon emissions, energy and water use, and waste management. Social (S) covers labor practices, workplace safety, supply-chain oversight, and data protection. Governance (G) covers board independence, executive pay structures, shareholder rights, and accounting transparency. The important point is that ESG investing isn't a moral slogan about "backing good companies" — it starts from the premise that these non-financial factors eventually show up in financial performance and share prices. Tighter carbon regulation reshapes the future cost structure of refiners and steelmakers; a board that fails to keep management in check opens the door to governance blowups like related-party tunneling or accounting fraud, either of which can crater a stock overnight. ESG analysis, at its core, is an attempt to catch these risks before they've worked their way into the financial statements.

How Investors Actually Apply It: Exclude, Tilt, Integrate, or Engage

There isn't one single way to "do" ESG investing. The simplest is negative screening — excluding entire industries outright, such as tobacco, weapons, or coal power. Best-in-class investing takes the opposite approach: it doesn't exclude a sector, but picks the top ESG performers within it. An oil major that manages its ESG risk better than its industry peers can still make the cut here — which lines up exactly with how MSCI's relative, industry-benchmarked methodology works, covered below. A third approach, ESG integration, skips screening altogether and instead folds ESG factors directly into valuation and risk models alongside standard financial variables — for example, building tighter carbon regulation into a DCF model as a future cost increase, or adding a governance-risk premium to the discount rate. A fourth, stewardship (engagement and proxy voting), works by staying invested and pushing for change through shareholder votes and dialogue with management, rather than selling out. This overlaps in spirit with shareholder activism, but typical stewardship aims for incremental change through dialogue and voting rather than a direct fight for control. Finally, impact investing treats measurable social or environmental outcomes as an investment objective in their own right, alongside financial return — renewable energy projects and social enterprises are common examples. Two funds both labeled "ESG" can hold wildly different portfolios and risk-return profiles depending on which of these approaches they actually use, which is why reading a fund's prospectus for its actual methodology tells you far more than its ESG rating number ever will.

How an ESG Score Gets Built: Picking the Issues That Matter, by Industry

Every ESG rating provider does it differently in the details, but the underlying skeleton is similar. First, using an industry classification system like GICS, the rater picks out which issues are financially material to that specific industry. MSCI, for instance, works from a master list of 35 ESG "key issues" but applies only 2 to 7 of them to any given company, based on its specific sub-industry. An oil refiner gets evaluated heavily on carbon emissions and safety incidents; a bank gets evaluated on data security and fair lending practices instead. The rater then gathers quantitative disclosures (greenhouse gas emissions, board gender composition, injury rates) and controversy data (lawsuits, regulatory violations, incident history) for each selected issue, normalizes them against the best and worst performers in that industry, and converts the result into a score. Those individual issue-level scores are then weighted and combined into a final rating. It looks like an objective calculation on the surface, but deciding which issues count as "material," how to estimate what a company hasn't disclosed, and how heavily to penalize a controversy — all of that is exactly where a rater's own judgment enters the process.

Why Raters Disagree: Relative Risk Management vs. Absolute Risk Exposure

The single biggest reason MSCI and Sustainalytics scores diverge so often is that the two firms are measuring genuinely different things. MSCI asks, in relative terms, "how well does this company manage ESG risk compared with its industry peers?" — so an oil company that outmanages its industry rivals can still land AAA. Sustainalytics instead asks, in absolute terms, "of the total ESG risk this company is exposed to, how much remains unmanaged?" — a lower number is better. Under that framework, an oil company can manage its risk about as well as it's possible to, and still score poorly, simply because its industry carries high risk exposure to begin with. Weighting choices compound the gap further: MSCI tends to lean more heavily on governance (G), while different providers emphasize different environmental sub-issues — some weight climate action most heavily, others weight biodiversity or water management more. The upshot: "this company has a high ESG rating" isn't a self-contained fact the way a P/E ratio is. It only means something once you know which provider produced it, under what methodology, and against what benchmark.

Greenwashing: When the Rating Runs Ahead of the Reality

As ESG ratings and disclosures started influencing where asset managers put money, loan terms, and even stock valuations, a predictable side effect followed: greenwashing, where marketing outpaces actual practice. A widely cited example is the 2023 case in which both the US SEC and Germany's financial regulator (BaFin) fined DWS, a major global asset manager, over allegations that it overstated how deeply ESG factors were actually integrated into some of its funds relative to what its disclosures and marketing materials claimed. It's also common to see companies publish ambitious net-zero targets or renewable-transition roadmaps in their sustainability reports while actual capital spending and emissions reductions fall well short. In response, the EU's Sustainable Finance Disclosure Regulation (SFDR) now requires funds to be categorized by their actual level of ESG integration, and regulators have been tightening the bar for which funds are even allowed to use words like "ESG," "green," or "sustainable" in their names. The practical takeaway for investors: don't take a rating or a fund name at face value — check what data the rating is actually built on, and whether stated targets are backed by concrete, trackable numbers rather than aspirational language.

Does a Good ESG Score Mean a Better Stock? Still an Open Question

Whether companies with strong ESG scores deliver better long-term stock performance remains a genuinely unsettled debate in the investment industry — there's no consensus answer yet. Some research finds that higher-rated companies carry lower regulatory and reputational risk and, over time, a lower cost of capital. Plenty of other research finds that ESG funds have failed to beat, or have actually lagged, conventional benchmarks over the same periods. This showed up especially clearly during energy-price spikes, when fossil-fuel companies — typically underweighted or excluded in ESG portfolios — rallied hard, temporarily dragging down ESG funds' relative performance. Viewed through the lens of the efficient market hypothesis and behavioral finance, this makes sense: whatever ESG information is already public is likely already priced in, and outperformance only comes from spotting something the market hasn't fully priced yet. In other words, an ESG rating isn't a guaranteed source of alpha — it's best treated as one more risk-assessment tool among several, not a magic number.

Korea's Mandatory ESG Disclosure: Phasing In From 2028

Korea is moving from today's voluntary disclosure regime, where companies choose which ESG metrics to publish, toward legally mandated disclosure on a set timeline. As of 2026, the confirmed plan has mandatory sustainability disclosure starting in 2028 for roughly 100 KOSPI-listed companies with consolidated assets of ₩10 trillion or more, expanding to companies with ₩5 trillion or more in 2029 and ₩2 trillion or more in 2030. Scope 3 emissions disclosure — the portion covering a company's supply chain — gets a three-year grace period from the mandate's start date given the burden on smaller suppliers, and third-party assurance (typically from accounting firms) becomes mandatory two years after disclosure itself begins. This timeline followed several earlier postponements, and the exact dates or thresholds could still shift depending on legislation and further regulatory guidance. Once mandatory disclosure takes hold, the market will start accumulating far more standardized, comparable ESG data than today's self-selected sustainability reports provide — a shift that connects directly to the governance-reform conversation running through Korea's Value-Up program aimed at closing the "Korea discount".

Takeaway

• ESG investing folds environmental, social, and governance factors into investment decisions on the premise that these non-financial issues eventually affect financial performance.
• ESG ratings are built by selecting industry-material issues, then normalizing quantitative and qualitative data against industry peers — but which issues "count" is a judgment call each rating provider makes differently.
• MSCI (relative, peer-benchmarked risk management) and Sustainalytics (absolute unmanaged risk) measure genuinely different things with different weightings, so the same company can land on opposite ends of their scales.
• As ratings and disclosures started moving capital, greenwashing — marketing that outpaces actual practice — became a real problem, prompting tighter rules in the EU and US.
• There's no established evidence that a high ESG rating reliably predicts better stock returns, and Korea's own mandatory ESG disclosure regime starts phasing in from 2028 for its largest KOSPI companies.

FAQ

Does investing in a high-ESG-rated company reduce my investment risk?

It may help reduce specific tail risks — a governance blowup or an environmental-regulation shock, for instance — but it doesn't eliminate broader market volatility or industry-cycle risk. Treat an ESG rating as one input among several risk signals, not a guarantee of safety.

If I invest in an "ESG fund," do I not need to worry about greenwashing?

No — if anything, assuming a fund is genuinely sustainable just because "ESG" or "green" appears in its name, without checking its actual holdings or screening criteria, makes you more exposed to greenwashing, not less. Get in the habit of checking a fund's prospectus for its real screening methodology and top holdings.

Where can I check a Korean company's ESG rating?

The Korea Institute of Corporate Governance and Sustainability (KCGS) publishes its own ESG ratings for domestic listed companies, and some asset managers also rely on international providers like MSCI or Sustainalytics. Given how much ratings can diverge between providers, as explained above, it's worth comparing more than one source rather than relying on a single rating.

⚠️ This article is for informational and educational purposes only and is not a recommendation to buy or hold any specific stock or fund. ESG rating methodologies, regulatory rules, and Korea's disclosure mandate timeline reflect the situation as of this writing and are subject to change — check the latest guidance from Korea's Financial Services Commission, the Korea Exchange, and the relevant rating providers before making investment decisions.