(Bloomberg) — Storebrand Asset Management AS, a $90 billion Norwegian fund that specializes in sustainable investing, says demand for green bonds is now so far ahead of supply that potential buyers might soon start to walk away.


According to Helena Lindahl, who oversees a portfolio of about $760 million in green bonds at Storebrand’s office in Stockholm, “The shift to green, on a broad level, is too slow, way too slow,” she said in an interview. “The green bond market is far too little.”


She warns that “the interest from investors will diminish over time” if green issuers don’t step up.


For now, the so-called greenium — the extra price investors pay to hold green debt — is “acceptable,” Lindahl said. But further price gains risk triggering an investor backlash, she said.


“The reason it is important to talk about this is that I want the green bond market to grow, and it is my responsibility as an investor to not kill the market,” she said.


Standards Storebrand is one of the largest money managers buying up sustainable debt in the Nordics, and its funds have frequently topped sustainability rankings. So far this year Lindahl’s fund, which holds only investment-grade debt, has returned about 1.5%. That’s broadly in line with the relevant benchmark indexes.


Like others, Lindahl wants more consistency in ESG reporting standards. She suggests that all corporate issuers be “obliged to report to Task Force on Climate-related Financial Disclosures and to tell the market how their way forward will be aligned with the Paris agreement.”


“It’s a lot about the accounting standards and being able to compare apples to apples, rather than every company reporting a fruit basket of different numbers,” she said.


To address the lack of supply, Lindahl says it would help if more companies became a little more sustainable, instead of waiting for a small group of solidly green issuers to add a few drops of supply.


“If green bonds account for about 5%-7% of the European bond universe, it doesn’t give us much if you make those bonds ultra green,” she said. “We’d get much more bang for the buck if we make the 95% which aren’t yet green a little greener.”


Lindahl says “the investor base is going mainstream with sustainability,” and that means all corporate issuers “need to have a good and credible ESG story — full stop!”