An acquisition announcement asks investors to process a remarkable amount of information at once.
Is the buyer paying too much? Will the expected synergies materialise? How will the transaction be financed? Does management understand the business it is acquiring? And can the two companies actually be integrated?
The question that interested me was whether investors were also asking something else: what kind of company is making the acquisition?
Our project examined whether an acquirer’s environmental performance influenced its share-price reaction around the announcement. The intuition seemed reasonable. A stronger environmental profile might signal better risk management, greater preparedness for regulation or a more credible long-term strategy. Investors could reward that—or regard it as largely irrelevant beside the price and economics of the transaction.
When the idea was tested using US M&A announcements between 2019 and early 2025, the answer was less straightforward than I had expected. Environmental rankings and carbon intensity had limited explanatory power in the main models. The market did not appear to apply a simple “green premium” to acquirers.
That result initially felt underwhelming. It eventually became the most useful part of the project.
Why the hypothesis made sense
Environmental performance can affect a company through several channels. Regulation may raise compliance costs. Carbon-intensive assets can require additional capital expenditure or become less competitive. Environmental liabilities can complicate due diligence, while a credible transition plan may improve access to capital or reduce long-term risk.
An acquisition can amplify those effects. A buyer is not simply purchasing earnings; it may also be taking on the target’s facilities, supply chain, regulatory exposure and future investment needs. If markets believe some companies are better equipped to manage those issues, their existing environmental profile could shape how investors interpret a deal.
There was also a broader question behind the project. ESG measures are widely used in screening, reporting and risk analysis, yet it is often unclear how strongly they influence prices at a specific decision point. An acquisition announcement provided a useful setting because it creates a clearly defined event and an immediate market response.
The temptation was to expect a neat relationship: environmentally stronger acquirers should be received more favourably, while carbon-intensive acquirers should face a discount. Markets rarely cooperate with hypotheses that tidy.
How the question was tested
The analysis used a sample of 328 acquisitions by US large-cap companies announced between January 2019 and February 2025. For each acquirer, it measured the share-price response around the announcement over two windows: five trading days around the event and a broader 21-day period.
Environmental performance was represented in two ways. The first was an environmental ranking from S&P, intended to capture a company’s position relative to peers. The second was carbon intensity relative to sales, a more direct measure of emissions exposure scaled by the size of the business.
The models tested whether those measures helped explain cumulative abnormal returns after accounting for deal value and sector differences. Additional specifications examined whether the relationship varied across industries and whether the SEC’s March 2022 climate-disclosure proposal appeared to change the way markets responded.
This was not an attempt to settle whether environmental performance affects firm value in general. The question was deliberately narrower: did these broad environmental measures help explain the acquirer’s short-term market reaction when a deal was announced?
The result was quieter than the hypothesis
In the main models, neither environmental ranking nor carbon intensity was statistically significant in either event window. The models explained only a modest share of the variation in announcement returns, and deal size was not significant either.
Put simply, knowing that an acquirer ranked better environmentally—or emitted less carbon relative to sales—did not provide a dependable guide to how its shares would react to an acquisition announcement in this sample.
That does not mean environmental performance is irrelevant to company value. It means something more specific: a broad environmental score, observed before an acquisition, did not appear to dominate the many pieces of new information arriving with the deal.
An environmental rating is usually known before the announcement. The offer price, financing structure, strategic logic and expected synergies are not. When the deal becomes public, investors are primarily revising their view of those newly revealed facts. A pre-existing score may provide context, but the announcement itself changes the information set in much more immediate ways.
A deal announcement is not an ESG referendum
The exercise changed how I think about event studies. An event window may be clean on a calendar, but the event itself is not conceptually clean. A single announcement can reveal management’s capital-allocation discipline, its appetite for leverage, its expectations for an industry and its confidence in delivering synergies. The market response combines all of that.
This makes it difficult for a broad characteristic to explain much on its own. Two acquirers with similar environmental rankings can announce very different transactions. One may buy a complementary business at a sensible price; another may overpay for a difficult integration. Expecting the market to reward both simply because the buyers have similar environmental profiles asks too much of the score.
Measurement matters too. Environmental rankings aggregate many dimensions into a single relative assessment. Carbon intensity is more concrete, but it still says little about the target, the combined company or whether the acquisition improves or worsens the buyer’s transition path. The variable may be relevant to long-term risk without being closely matched to the short-term question being tested.
Sector context offered a clue
The sector tests were more suggestive. The relationship between environmental ranking and announcement returns was positive for technology acquirers and weakly negative for financial companies, while the energy interaction was not significant.
Those results should be read cautiously. Splitting a sample across sectors reduces the number of observations, and isolated findings can be unstable. Still, they point towards a better way of framing the question. Environmental information may matter differently depending on the industry, the assets being acquired and the channels through which environmental exposure affects cash flows.
For a technology company, the score may be interpreted partly as a signal of governance, operational quality or preparedness for customer and investor scrutiny. For a bank, the relevant exposure may sit less in its own emissions than in its loan book. For an energy company, a single group-level ranking may conceal large differences between individual assets and transaction strategies.
The lesson is not that one sector “cares” about ESG and another does not. It is that materiality is contextual. The same metric can mean different things across business models.
Regulation did not create a clear break
The project also asked whether the SEC’s 2022 climate-disclosure proposal changed the market response to greener acquirers. If investors expected environmental information to become more comparable or financially consequential, the relationship might have strengthened after the proposal.
The analysis did not find a statistically significant change.
Again, the absence of a sharp break does not imply that disclosure regulation has no value. Policy changes are anticipated, revised and implemented over time. Companies and investors adapt gradually. A single proposal date may be too precise a boundary for a process that unfolds through consultation, litigation, compliance planning and changes in market practice.
That was another useful reminder: regulatory importance does not always arrive in markets as one clean, measurable event.
What this means in practice
For corporate-development teams, an environmental claim is more persuasive when it is connected to the economics of the transaction. How will the deal change capital expenditure, energy costs, regulatory exposure, supply-chain resilience or the value of specific assets? A general ESG score cannot answer those questions.
For investors, the more useful question may be not “Is this a green company?” but “What environmental exposure changes because of this deal?” That shifts attention from a static label to the transaction itself: what the buyer is acquiring, what it is paying and how the combined business will operate.
For research, the project suggests that more specific measures may be more informative than broader ones. Target-level emissions, environmental liabilities, transition capital expenditure, sector materiality and the change in the combined firm’s exposure could all be closer to what investors are actually evaluating.
None of this makes the original question a poor one. It makes the boundary of the answer clearer.
The value of an inconclusive result
Student research often begins with an interesting relationship and an understandable hope that the data will reveal it cleanly. Real research is usually messier. Measures are imperfect, markets process several signals at once and a sensible hypothesis may explain less than expected.
The analysis did not find a broad environmental premium in short-term M&A announcement returns. For me, its value was that it sharpened the question. Environmental performance may matter through transaction-specific exposures, sector context and long-term cash flows rather than as a simple score applied uniformly across deals.
That distinction is useful beyond ESG. Whenever a popular metric is brought into an investment decision, it is worth asking whether it is genuinely matched to the horizon and mechanism being studied. A variable can matter in principle and still add very little to a particular model.
Sometimes the most practical outcome of a project is not confirmation. It is learning what the original question was missing.