Every carbon framework in advertising today assumes a human reviewed the buy. Sustainability reporting, carbon-weighted supply path selection, post-buy carbon audits: each of these depends, at some point, on a person making a judgement call that encodes a carbon preference into a decision. When agents do the buying continuously, without a human review step, that judgement call disappears unless it has been explicitly encoded into what the agent is told to do. An agent that has not been given a carbon objective will not pursue one. It will optimise toward whatever objective it has been given, efficiently and without hesitation, and the carbon consequences will accumulate in the post-buy report rather than being prevented in the buy.
TL;DR. Agents optimise toward their objective function and nothing else. Carbon considerations currently enter the media buying process through human judgement at the point of decision: a trader chooses a lower-carbon supply path, applies a carbon cost to a CPM calculation, or flags a placement for review. When agents make those decisions autonomously, the human judgement step is removed, and carbon constraints have to be encoded explicitly before the agent acts or they will not be enforced. The information problem compounds this: carbon data on supply paths is inconsistent and often unavailable at bidding time, so even an agent given a carbon objective may not have the data to act on it. The practical answer is to treat carbon as a named constraint, declared to the agent before it acts, enforced as a hard limit rather than a preference, and included in the deal record so both sides of the transaction share the same account of what was agreed.
Why do agents not naturally account for carbon?
An agent acts on the objective function it is given, the signals it can measure, and the constraints it has been told to respect. Nothing about an agent's architecture causes it to spontaneously include carbon weight in its decisions. If carbon is not a named constraint, it is invisible to the agent: it exists in the post-buy report and in the sustainability team's spreadsheet, but it does not exist in the decision the agent made.
This is the same mechanism that creates brand safety risk when agents are given unconstrained optimisation targets. An agent optimising toward a fill rate or a performance metric will find the cheapest or highest-performing inventory, which may be MFA sites, low-quality placements, or, for carbon purposes, supply paths with poor carbon efficiency. The agent is not making a bad choice. It is making the optimal choice against the objective it was given, which did not include carbon.
The difference between brand safety and carbon is that the advertising industry has spent years building brand safety into agent architectures as a declared, enforced constraint. Carbon has not yet reached that point.
Where does carbon currently sit in the media buying workflow?
It sits in steps that require human action: post-buy carbon reporting, sustainability team review, supply-path selection guided by carbon data that a human applies. The Ad Net Zero initiative and the Campaign Carbon Code have established frameworks for measuring and reducing advertising's carbon footprint, and a growing number of agencies and advertisers have made public commitments to net-zero advertising operations. Those commitments are real. The mechanism for enforcing them in a workflow where an agent makes the buying decisions is not yet standard.
Post-buy carbon reporting tells you what the carbon cost of a campaign was after it has run. That information is valuable for future planning, but it does not change the decisions the agent already made. If an agent ran a campaign at carbon cost X when a lower-carbon supply path was available, the post-buy report records the cost but does not undo the buy.
Supply-path carbon data is improving but inconsistent. Some platforms now expose carbon metrics at the supply-path level, allowing a human buyer to factor carbon weight into SPO decisions. For an agent to use those metrics in real-time decisions, the data needs to be available as a machine-readable signal at bidding or deal-negotiation time, not just as a dashboard figure a human reads after the campaign.
What needs to change for agents to act on carbon?
Three things need to be in place, and they are the same three things that make any constraint effective in an agentic system.
The first is declaration. Carbon requirements must be stated to the agent before it acts, as a named constraint with a defined value. Not "consider carbon where possible" but "do not accept supply paths above X grams of CO2 per thousand impressions." Preference language is not instruction language, and an agent given a preference rather than a constraint will treat carbon as friction.
The second is deterministic enforcement. The carbon constraint must sit outside the agent's optimisation in the same way brand-safety constraints do: as a hard limit the agent cannot trade against a performance metric. An agent that can override a carbon limit when fill rate is low will eventually do so, because that is what optimisation toward a performance target does. The limit has to be the kind of limit that holds regardless of what the agent's reasoning suggests.
The third is inclusion in the deal record. When a buyer's agent agrees a deal with a seller's agent, the carbon terms of that deal should be part of the shared record both sides reference. If the buyer's agent agreed a supply path on the basis that it met a carbon threshold, and the seller's agent has a different account of what was agreed, the carbon commitment is as vulnerable to divergence as any other deal term. Including carbon requirements in the structured transaction object means both sides are accountable to the same agreed standard.
What does the information problem look like in practice?
Even buyers who want to give their agents a carbon objective face a data problem. Carbon data on supply paths is not universally available at transaction time, varies significantly in methodology across the providers that do publish it, and is often at a level of aggregation too coarse for per-impression or per-deal decision-making.
This is not a reason to delay building carbon into agent instructions; it is a reason to also push supply-path providers and platforms to expose carbon signals in the machine-readable form agents can consume. The demand for that data needs to come from buyers configuring agents with carbon constraints, because agents that do not have a carbon objective create no demand signal for the data.
The practical starting point for a buyer committed to carbon targets is to require, as a minimum, that any agentic platform they pilot exposes carbon data at the supply-path level, allows carbon constraints to be declared as hard limits in the agent's configuration, and records carbon terms in the deal record alongside pricing and brand-safety conditions. An agent operating without those three capabilities cannot act on a carbon commitment even if the buyer has one.
________________
This article references the Ad Net Zero initiative and Campaign Carbon Code frameworks for advertising carbon measurement, industry analysis of brand safety enforcement in agentic advertising as a model for carbon constraint design, and the IAB Tech Lab's published agentic specifications on declared constraints and deal record structure.