How to measure the carbon footprint of your Google Ads

What is the GMSF and why does it matter?

The Global Media Sustainability Framework is Ad Net Zero's standard for calculating and reporting greenhouse-gas emissions from media, covering six channels including digital. Its major June 2025 update tightened the methodology, and the IPA has since shipped a media carbon calculator with the GMSF built in. The point of a shared framework is comparability: your number and a competitor's number mean the same thing, which is what separates accounting from a marketing claim.

What drives an ad impression's emissions?

• Format: video weighs up to five times a static display impression; plain search text ads sit lightest
• Delivery chain: every ad-tech hop between advertiser and screen adds compute; direct buys run leaner than long programmatic chains
• Device and network: mobile over 4G costs more energy than desktop on broadband, and connected TV carries heavy embodied loads
• Grid intensity: the same impression served in a coal-heavy market emits multiples of one served on a cleaner grid

Those four factors explain the wide 1–5g range, and why channel mix is the lever an advertiser actually controls. You cannot change the grid; you can absolutely change how much of your budget buys video impressions through a six-hop chain.

How do you build the monthly estimate?

1. Export impressions by campaign and network from Google Ads: Search, Shopping, Display, YouTube split out.
2. For Performance Max, open the channel performance report (standard in all accounts since November 2025, with data back to June 2025) and take its per-channel impression split; PMax stopped being a black box the day that shipped.
3. Assign each network a per-impression factor from the GMSF-aligned calculator, light end for search text, heavy end for video.
4. Multiply, sum, and convert to kilograms CO2e per thousand impressions and per month.
5. Print it in the monthly report next to spend and return, so the trade-offs are visible in one row.
6. Re-check factors quarterly; the framework and grid data both move.

A worked example, using the write-up account

The shape is the lesson: a quarter of the impressions produced two-thirds of the estimated emissions. That is the refill-goods account's pre-cap month, and it is why capping PMax's heavy formats cut estimated media emissions by roughly a third while the return rose from 2.1 to 3.4, the trade documented in the refill-goods write-up. The output is an estimate, and honest reporting says so; it is directionally solid where it matters, because the ranking of channels by weight survives every methodology refinement so far.

Which decisions should the number change?

Three recur across our accounts. Placement mix, per the worked example above. Waste removal: every wasted impression is spend and grams for nothing, so the waste write-up's £23,400 cut was also the account's largest single emissions cut. Chain length: preferring direct, short-chain buys where returns allow. None of these sacrifices performance; they remove the parts of the plan that were paying for nothing twice.

Where does regulation stand?

The EU's CSRD pulls Scope 3 emissions, purchased advertising included, into mandatory reporting for large companies, with the December 2025 Omnibus changes adjusting thresholds and timing. Most DTC brands are below the line today. Their stockists, marketplaces, and investors often are not, and supplier questionnaires now ask for exactly the number this guide produces. Producing it from the GMSF today costs an afternoon a month; retrofitting it under deadline costs considerably more. Our own agency estimate is published quarterly per the carbon method, same math, applied inward.