Green bonds are a $3+ trillion market as of 2026 (cumulative issuance, climbing fast). They are the most successful sustainable-finance product to date, partly because the structure is simple: a regular bond, where the issuer commits to using the proceeds for environmentally beneficial projects. The mechanism is transparent and easy to audit. Investors can hold them in the same fixed-income portfolios they always have, with a sustainability label attached.
The ICMA Green Bond Principles
The International Capital Market Association (ICMA) published the Green Bond Principles (GBP) in 2014. They are voluntary, market-led, and the de facto global standard. Four components:
- Use of proceeds: clearly defined eligible categories — renewable energy, energy efficiency, clean transport, sustainable water, green buildings, climate adaptation, biodiversity.
- Process for project evaluation and selection: how the issuer decides which projects qualify.
- Management of proceeds: ring-fencing, sub-accounts, tracking until full allocation.
- Reporting: annual disclosure of allocated proceeds and, where feasible, environmental impact metrics.
The label vs the standard
Most green bonds today are issued under ICMA principles. The EU Green Bond Standard (EU GBS), which entered application in 2024, layers additional requirements: alignment with the EU Taxonomy, mandatory external review, and stricter use-of-proceeds rules. EU GBS bonds command a small additional premium because the verification bar is higher.
Beyond use of proceeds: SLBs
Sustainability-linked bonds (SLBs) flip the green-bond logic. The proceeds are not ring-fenced — they can fund anything. Instead, the issuer commits to one or more sustainability performance targets (SPTs), and the coupon steps up (typically by 25-75 bps) if the targets are missed by the measurement date.
- Pros: more flexible for issuers; allows financing of general corporate purposes; aligns coupon to actual performance.
- Cons: SPTs can be set too easily; coupon step-up may be too small to deter; greenwashing risk is real and documented.
- Status: market growing fast through 2021, has flattened since 2023 amid concerns about SPT quality and step-up sufficiency.
The greenwashing question
Sustainability-linked instruments have attracted scrutiny because some SPTs are barely above business-as-usual. The Climate Bonds Initiative's 2023 review found that ~30% of issued SLBs had targets unlikely to require additional action beyond existing trajectories. The bond market reaction has been to demand better KPI design and external review; standards are tightening.
The greenium
Do green bonds price tighter than equivalent vanilla bonds? Mixed evidence, but most studies (CBI 2023, Federal Reserve 2022) find a small greenium of 2-8 basis points on average — bigger for sovereign issuers (where investor demand is highest), smaller for corporates. Some markets show no greenium; some show 10-15 bps. The premium reflects scarcity of supply and dedicated buyer mandates more than fundamental credit improvement.
Whether the greenium will persist is open. As supply scales and ESG fund AUM stabilises, the demand-supply imbalance compresses. The 2024 issuance surge from European sovereigns has narrowed the greenium on EUR sovereign green bonds to near zero. For the analyst: don't assume a meaningful pricing advantage will hold; it varies by issuer, jurisdiction, and cycle.
Exercise
Find a recent green bond issuance from a sovereign or corporate issuer. Look up the comparable vanilla bond curve from the same issuer. Calculate the apparent greenium. Then look at the use-of-proceeds disclosure — is the allocation credible? Is there an external review? Has the issuer reported on impact metrics from prior issuances?