Global sustainable bonds issuance ( including green, social, sustainability, sustainability-linked and transition bonds ) is projected to reach US$900 billion in 2026, slightly higher than the 2025 levels, but below the volumes recorded between 2021 and 2024, according to a recent report.

The increase in 2026 sustainable bond issuance will benefit from the refinancing needs of maturing sustainable bonds issued in 2021, a time at which global issuance peaked at over US$1.1 trillion, finds the report from ratings agency Moody’s Ratings.

Around US$520 billion of sustainable bonds, Moody’s estimates, had an original 2026 maturity date, up from US$425 billion in 2025, based on figures from Environmental Finance Data. However, there is uncertainty on whether issuers will switch from the labelled structure to the conventional structure when they refinance.

Green bonds remain to be the most prevalent instrument. The issuance of green bonds in 2026 is set to value US$530 billion, the Moody’s report forecasts, accounting for 60% of the sustainable bond issuance. Issuances of social, sustainability and sustainability-linked bonds in 2026 are expected to value US$115 billion, US$190 billion and US$25 billion, respectively, roughly consistent with 2025 levels.

On the other hand, the issuance of niche transition bonds is expected to surge in 2026 to value  US$40 billion, doubling its record figure of US$21 billion in 2024.

The issuance of transition bonds is likely to be more frequent because – following the publication of the Climate Transition Bond Guidelines by the International Capital Market Association ( ICMA ) in late 2025 – the guidelines permit the financing of transition projects that may not qualify as green projects, but still contribute to broad climate transition progress. This benefits companies in high carbon-emitting sectors, such as oil and gas, cement, and metals and mining.

Another nascent segment under the broad sustainable bond group that is rising quickly is that of nature-related bonds. A record 29 nature-related bonds were issued in the first 11 months of 2025, totalling US$5 billion, data from MorningStar show, compared with 12 for the whole of 2024, totalling US$1.5 billion.

Similar to transition bonds, the boom in nature-related bond issuance also benefitted from the ICMA’s launch of the optional nature bond label in 2025, which provides issuance clarity and reduces greenwashing risks.

Other drivers of nature-related financing are investors’ heightened awareness of nature-related risks and their urgency to translate commitments into tangible actions, leading to greater investment in adaptation.

Notably, 63% of respondents believe nature-related risks and opportunities, according to the TNFD 2025 Status Report, are likely to be as significant as, or even more significant than, climate-related ones.

Reflecting this shift, adaptation- and nature-related projects, Moody’s estimates, represented about 22% of green and sustainability bond project categories in 2025, up from 16% in 2020.