Sustainability bonds are debt instruments where the proceeds are used to finance a combined mix of environmental and social projects. Unlike green bonds, which fund only environmental projects, or social bonds, which fund only social projects, sustainability bonds blend both. The category was formalised by the International Capital Market Association in 2018, and the format has gained ground in India as issuers seek to fund renewable energy, affordable housing, education, and healthcare initiatives from the same instrument. Sustainability bonds sit within the broader family of labelled debt that the global market collectively calls GSS+ for green, social, sustainability, and sustainability-linked bonds.
The GSS+ Taxonomy in Brief
Labelled debt is a financial instrument that carries a label certifying the use of proceeds or the achievement of sustainability targets. The four main labels are green, social, sustainability, and sustainability-linked.
A green bond funds environmental projects such as renewable energy, clean transport, energy efficiency, and pollution prevention. A social bond funds projects with positive social outcomes including affordable housing, food security, healthcare, and access to essential services. A sustainability bond funds both categories in combination. A sustainability-linked bond is different in structure: proceeds can be used for general corporate purposes, but the coupon rate adjusts based on whether the issuer meets specific sustainability performance targets.
| Label | Use of proceeds | What it funds |
|---|---|---|
| Green bond | Restricted | Environmental projects only (renewables, clean transport, efficiency) |
| Social bond | Restricted | Social projects only (affordable housing, healthcare, essential services) |
| Sustainability bond | Restricted | Both environmental and social projects under one instrument |
| Sustainability-linked bond | Unrestricted (general purposes) | Coupon steps up or down against sustainability performance targets (KPIs) |
The ICMA Principles
The International Capital Market Association publishes the Green Bond Principles, the Social Bond Principles, the Sustainability Bond Guidelines, and the Sustainability-Linked Bond Principles. These are voluntary frameworks but most large issuers follow them because investors expect compliance.
The four core components are use of proceeds, process for project evaluation and selection, management of proceeds, and reporting. Use of proceeds must be clearly described and limited to eligible categories. Project selection should follow a transparent process disclosed to investors. Proceeds must be tracked separately from general corporate funds, often through a designated account. Reporting must occur at least annually until full allocation and should describe both the projects funded and their impact.
For sustainability bonds, the issuer applies green principles to the environmental portion and social principles to the social portion. An external review by a second-party opinion provider, certifier, or assurance auditor is recommended.
India’s Sovereign Green Bond Issuance
India launched its Sovereign Green Bond programme in FY23. The Sovereign Green Bond or SGrB is a specific instrument issued by the central government to fund eligible green expenditures within the Union Budget. The first tranche worth eight thousand crore rupees was issued in January 2023, followed by additional tranches across subsequent years.
The proceeds finance projects in renewable energy, clean transportation, energy efficiency, climate change adaptation, and sustainable water and waste management. A green finance working committee chaired by the chief economic adviser screens projects against the Indian sovereign green bond framework, which is aligned with ICMA Green Bond Principles. An annual allocation and impact report is published.
The SGrB sits within the broader fiscal architecture that includes the FRBM Act 2003 and is settled through the Consolidated Fund of India. The instrument is rupee-denominated, available in tradable form, and counts towards the central government’s market borrowing programme.
Sustainability Bonds in the Indian Market
Indian corporates have issued sustainability bonds and sustainability-linked bonds since the late 2010s. State Bank of India, Power Finance Corporation, Indian Renewable Energy Development Agency, and Adani Renewable Energy are among the issuers. Most issuance is in the international markets denominated in US dollars, although domestic rupee issuance has grown.
SEBI published a framework for green bonds in 2017 and updated guidance on sustainability disclosures in 2023 covering green, social, sustainability, and sustainability-linked debt securities. SEBI requires issuers to publish a clear use-of-proceeds statement, obtain a third-party review, and report annually on allocation and impact.
How Sustainability Bonds Differ from Green and Social Bonds
The critical distinction is the mix of eligible expenditures. A green bond is tied exclusively to environmental categories. A social bond is tied exclusively to social categories. A sustainability bond combines both, which gives the issuer flexibility to fund a broader portfolio under a single label.
This flexibility matters when an issuer’s investment plan includes both a solar plant and a hospital expansion. Issuing two separate bonds, one green and one social, is administratively heavier. A sustainability bond covers both with one instrument while still meeting investor expectations on labelling and reporting.
Sustainability-Linked Bonds: Structurally Different
Sustainability-linked bonds deserve a separate mention because they are structurally different from the other three. The use of proceeds is not restricted. Instead, the bond carries one or more key performance indicators tied to sustainability outcomes, such as a target reduction in greenhouse gas emissions or a target share of renewable energy in the issuer’s generation mix. If the targets are missed by a specified date, the coupon steps up, increasing the issuer’s cost of borrowing. If they are met, the coupon stays at the original level.
This format suits issuers that want capital for general purposes but want to demonstrate commitment to sustainability outcomes at the entity level rather than at the project level.
FAQs
What are sustainability bonds?
Bonds whose proceeds finance a combined mix of green and social projects, following the ICMA Sustainability Bond Guidelines.
How are sustainability bonds different from green bonds?
Green bonds fund only environmental projects. Sustainability bonds fund both environmental and social projects under one instrument.
What are sustainability-linked bonds?
Bonds where proceeds can be used for general purposes but the coupon adjusts based on whether the issuer meets specific sustainability targets.
Who publishes the global standards for these bonds?
The International Capital Market Association publishes the Green Bond Principles, Social Bond Principles, Sustainability Bond Guidelines, and Sustainability-Linked Bond Principles.
What is the Sovereign Green Bond in India?
A government-issued green bond launched in FY23 to fund eligible green expenditures within the Union Budget, with proceeds tracked through a dedicated framework.
Are external reviews mandatory for green and sustainability bonds?
External review is strongly recommended under ICMA principles and is required under SEBI regulations for Indian-listed green debt securities.
Where does India’s green finance regulation sit?
SEBI handles issuance, listing, and disclosure rules. RBI plays a role in green finance through priority sector lending norms and climate risk supervision.
What is greenwashing in bond markets?
Greenwashing is the practice of labelling a bond as green or sustainable without ensuring that proceeds actually fund eligible projects with credible impact.
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