IFAC's recurring benchmark of large listed companies tracks who provides assurance over sustainability disclosures and against which standards. The trend it documents: reporting is converging on common standards, and audit firms now provide the majority of assurance engagements, at around three in five globally by IFAC's count.
The direction matters for private companies too. When sustainability data moves into assured territory, the informal spreadsheet culture around it has to grow up: sources documented, calculations reproducible, changes explained. That is ordinary accounting discipline applied to new numbers, and it is easier to build in early than to retrofit.