The world's largest sustainability rater keeps corporate scores artificially high to keep investors from getting annoyed.
April 24, 2026
Original Paper
The Traffic Light Effect in ESG Ratings
SSRN · 6630858
The Takeaway
MSCI, a dominant force in ESG ratings, systematically avoids downgrading companies to prevent triggering expensive portfolio rebalances for its clients. This traffic light effect creates a cluster of companies sitting just above the threshold for good ratings. While these scores are marketed as objective measures of environmental and social performance, they are often massaged for the convenience of the financial industry. Investors rely on these numbers to prove they are green, but the ratings frequently reflect consensus rather than actual corporate behavior. This manipulation undermines the entire goal of using capital to drive social change.
From the abstract
<span>ESG ratings increasingly govern index construction and investment mandates, creating a conflict of interest for investor-paid raters: because rating changes trigger rebalancing costs for subscribers, raters face pressure to favor stability over timeliness. We document a </span><span>traffic light effect</span><span> at MSCI, the world’s largest ESG rater: companies systematically bunch just below letter-rating thresholds, as if queued behind a red light. By reverse-engineering MSCI’s bench