Investors who prioritise sustainability often argue that they can support environmentally friendly initiatives without giving up financial returns. However, recent research from the Texas McCombs School of Business challenges that assumption. The findings suggest that investors may, in fact, be willing to accept slightly lower returns in exchange for environmentally responsible investments. At the same time, this behaviour presents a potential opportunity for governments to raise additional funding for sustainable projects by tapping into this preference.

Evidence from Germany’s sovereign bond market reveals that investors are quietly paying a premium for green bonds. Rather than offering higher returns, these bonds tend to yield slightly less than their conventional counterparts, indicating that investors are effectively accepting a financial trade-off. This difference, referred to as the “greenium,” reflects the added value investors place on environmentally labelled securities. The term captures the idea that sustainability itself can influence pricing in financial markets.

The study, led by Aaron Pancost alongside Stefania D’Amico of the Federal Reserve Bank of New York and Johannes Klausmann from the University of Houston, examined German government bonds issued between 2009 and 2023. Germany provided an ideal case study because each green bond is paired with a nearly identical conventional bond, sharing the same issuer, maturity, and coupon rate. This pairing allows researchers to isolate the effect of the “green” label itself, ensuring that any price difference can be attributed to investor preferences for sustainability rather than other variables.

Even so, measuring the greenium proved more complex than simply comparing yields between paired bonds. Market dynamics can influence spreads for reasons unrelated to environmental considerations. For instance, traditional German bonds are often used as safe-haven assets during periods of uncertainty or as collateral in financial transactions, which can distort pricing. To address this, the researchers developed a broader analytical approach, modelling pricing trends separately for green and conventional bonds. By comparing these patterns, they derived a more precise estimate of the greenium.

Their findings show that the greenium averaged around four basis points over time, equivalent to roughly four per cent of the yield on a ten-year bond. However, this premium was not constant. It tended to increase following major climate-related events, such as severe flooding in Germany, and during periods of heightened energy stress. After Russia invaded Ukraine, for example, the greenium rose to approximately seven basis points. By 2023, the premium was more pronounced in short-term bonds than in long-term ones, suggesting that investors expect the gap to narrow over time.

Although the difference between green and conventional bonds is relatively modest, its implications are significant. By accepting slightly lower yields, investors are effectively subsidising environmentally beneficial projects. This behaviour could allow governments to issue more short-term green bonds at reduced interest rates, lowering borrowing costs for taxpayers. While countries such as Germany, France, and the UK have already embraced green bond issuance, the United States has yet to do so at the federal level. The research highlights this as a missed opportunity, as growing investor demand indicates a clear willingness to prioritise sustainability—even at the expense of marginal financial returns.

More information: Stefania D’Amico et al, The benchmark greenium, Journal of Financial Economics. DOI: 10.1016/j.jfineco.2025.104217

Journal information: Journal of Financial Economics Provided by University of Texas at Austin