Carbon.json represents a voluntary disclosure specification that brings a common structure to how digital advertising platforms report their carbon emissions data, so the environmental impact of ad-supported media can finally be measured and compared in a consistent way.
What Is Carbon.json?
Carbon.json was developed by IAB Europe’s Methodology & Framework Working Group, in close collaboration with Ad Net Zero, to address a long-standing gap in digital advertising sustainability: the lack of a common, machine-readable format for reporting emissions data. The initiative brings together ad tech companies and sustainability vendors around a single, standardised approach to disclosing infrastructure emissions intensity across the supply chain.
At its core, the specification gives advertising systems a structured way to publish their emissions intensity data. So DSPs, SSPs, exchanges, ad servers, publisher monetisation platforms, and other intermediaries can all make that data available in a format that other stakeholders can actually consume, validate, and feed into campaign- and path-level emissions calculations. Importantly, Carbon.json was built to work across a wide range of infrastructure environments, from public and private cloud to owned data centres, hybrid setups, and managed infrastructure. That scope makes it broadly applicable across the ecosystem rather than useful only for a handful of large players.
Why It Matters
For the digital advertising industry, Carbon.json offers something that has been missing for a long time: a shared language for emissions disclosure that makes data from different platforms actually comparable.
When it comes to the supply chain, programmatic buyers and media agencies can now evaluate which inventory paths they activate based on actual emissions data, not vendor claims. Publishers and SSPs, meanwhile, have a real opportunity to show where they stand on sustainability and build trust with partners who prioritise it. And for the broader ecosystem, consistent machine-readable data makes campaign-level and path-level carbon accounting more reliable and easier to integrate into sustainability reporting frameworks.
Perspectives on Adoption
That said, full adoption has its challenges. Smaller players often lack the technical resources to prioritise integration. There is no mandatory requirement to adopt the specification, and without strong demand-side pressure, sustainability disclosure can easily get deprioritised.
The public comment period for the carbon.json Voluntary Disclosure Specification runs until 19 August 2026, after which IAB Europe is expected to finalise the proposal, making the coming months a good window for industry players to contribute while the process is still open.