A once niche corner of finance is attracting unprecedented attention from investors, governments and institutions as demand grows for assets linked to long-term resilience and future-focused development.
Sustainable debt is rapidly becoming one of the most influential segments of global finance as governments, companies and public institutions seek funding for climate-related investments and long-term economic resilience.
According to the latest figures from the Climate Bonds Initiative (CBI), annual issuance of GSS+ bonds, covering green, social and sustainability-linked debt instruments, has surpassed the $1 trillion mark for the third consecutive year. The growth reflects rising investor demand for projects tied to climate action and infrastructure designed to withstand future environmental and economic risks.
Recent debt offerings demonstrate the strength of market appetite. Spain’s latest 20-year green bond attracted demand worth more than 20 times its €4 billion issuance target, while Italy’s newly issued 12-year green bond was more than 13 times oversubscribed.
For Sean Kidney, co-founder and chief executive of the Climate Bonds Initiative, the growth represents a dramatic transformation. When the organisation began promoting green bonds in 2009, only about $2 billion worth of such debt existed globally. Today, the amount outstanding exceeds $7 trillion.
Kidney argues that investors increasingly view sustainable debt as a way to protect long-term returns in an era marked by climate threats, economic instability and rising uncertainty. Institutional investors are no longer debating whether climate risks exist. Instead, the focus has shifted toward finding enough high-quality sustainable assets to invest in.
Demand is being driven by both investors and issuers. Non-financial companies and financial institutions each account for 23 per cent of issuance, followed by development banks at 20 per cent, government-backed entities at 19 per cent and sovereign issuers at 12 per cent.
The appeal extends beyond environmental objectives. For many issuers, green bonds provide a mechanism to finance infrastructure that strengthens economic resilience while addressing climate-related challenges.
Stronger Standards Help Build Trust In Sustainable Debt Markets
One example cited by Kidney is the Tokyo Metropolitan Government, which recently issued a €300 million green bond. The proceeds are helping finance infrastructure intended to protect the city’s 14 million residents from storm surges and other climate-related threats while supporting broader economic stability.
Market expansion has also been supported by regulatory developments designed to improve transparency and credibility. Recent examples include the European Union’s Green Bond Standard introduced in 2024 and China’s updated green taxonomy that came into effect in late 2025.
The International Capital Market Association has also played a key role through its Green Bond Principles, which provide widely used guidelines on how bond proceeds are allocated and managed.
Meanwhile, the Climate Bonds Initiative has developed its own Climate Bonds Standard. Under the voluntary framework, 95 per cent of bond proceeds must align with strict climate objectives, while the remaining portion can be directed toward other sustainability goals.
To support consistency, financial markets have increasingly embraced taxonomies, effectively rulebooks outlining which activities qualify as green investments. The European Union’s framework remains among the most comprehensive, but more than 50 jurisdictions, including China, India, South Africa, Brazil, Chile, Colombia, Mexico and ASEAN, have implemented similar systems.
Differences remain between regions. The EU taxonomy allows certain new gas projects subject to strict emissions limits, while China’s framework excludes fossil fuel-related projects entirely. Kidney maintains that these variations reflect different economic conditions rather than a rejection of climate science.
The sector has also faced scrutiny. Earlier projects marketed as environmentally beneficial did not always deliver intended outcomes, reinforcing the need for stronger oversight and verification. The Climate Bonds Initiative has publicly challenged transactions it believes conflict with internationally recognised climate pathways.
Despite occasional controversy, Kidney believes sustainable finance principles are gradually becoming embedded within broader capital markets. In his view, investors ultimately focus on resilience because resilience improves the likelihood that debt will be repaid.
He points to Jamaica’s experience following a major hurricane in 2025. A $150 million catastrophe bond arranged by the World Bank helped support recovery efforts, and the country’s long-term credit rating was later upgraded by Moody’s. For investors, Kidney argues, that outcome demonstrates why resilience-focused financing is increasingly becoming a financial necessity rather than a niche sustainability product.