Carbon offsetting for events: the guide for organisers

The minute

• Audience travel (air and ground) is often the largest share of an event’s footprint; industry estimates commonly put it at 40% to 60%
• Catering and accommodation come next, and vary a lot with the menu and the hotel category
• Exhibitors and production (booth, materials, freight) form their own category, separate from the general audience

Why it matters: Offsetting without measuring each category separately tends to underestimate the real footprint, because travel is easy to miss when nobody asks how people got there.

The categories in the math

Travel (air and ground, for both audience and exhibitors), accommodation (nights times hotel category), catering (by meal type), venue energy and materials (badges, signage, booths). Each has its own emission factor.

How to do it, step by step

The process has five stages. Skipping one usually means the final number is wrong.

1. Define the boundary

Decide what is inside the calculation and what is not. The GHG Protocol divides emissions into three scopes: direct emissions the organiser controls (scope 1), purchased energy for the venue (scope 2), and everything else (scope 3). For events, scope 3 is almost always the largest share, because it includes attendee travel, hotel stays, catering supply chains, and freight. Leaving scope 3 out, which some organisers do to simplify the math, removes the majority of the footprint from the count.

2. Collect activity data

For travel, this means asking attendees where they are coming from and how. A registration form with origin city and transport mode is the simplest method. For catering, the data is the number of meals by type (meat, vegetarian, vegan) and whether ingredients are sourced locally or imported. For accommodation, the number of room-nights and the hotel’s energy profile matter. For production, the weight of shipped materials and the distance they travel are the key inputs.

3. Apply emission factors

Each activity (one passenger-kilometre by air, one hotel night, one beef meal) has a published emission factor, usually expressed in kilograms of CO2 equivalent. Governments and research bodies publish these factors, and they vary by country and by year. Using a factor from the wrong region or an outdated dataset introduces error that compounds across thousands of attendees.

4. Buy and retire credits

Once the total is calculated, the organiser purchases carbon credits equal to that tonnage. The critical step is retirement: the credit must be cancelled in the registry so it cannot be resold. Until a credit is retired, the offset has not happened. The two most widely used voluntary registries are Verra (which issues Verified Carbon Standard credits) and Gold Standard. Both maintain public databases where anyone can verify that a specific credit has been retired.

5. Disclose

Publish the methodology, the total tonnage, the project that generated the credits, and the retirement serial numbers. Without this disclosure, the offset claim is unverifiable and, increasingly, a regulatory risk.

The most common mistake

Treating exhibitors like regular attendees. Exhibitors usually travel further, stay longer for set-up, and carry freight, all of which change the travel and accommodation math for that group.

A second common mistake is buying credits without checking for additionality. A carbon credit is additional only if the project it funds would not have happened without the revenue from selling credits. Renewable energy projects in markets where renewables are already cheaper than fossil fuels, for example, may fail the additionality test, because they would have been built regardless.

Avoidance credits versus removal credits

Most credits on the voluntary market today are avoidance credits: they fund projects that prevent emissions from happening (protecting a forest that would otherwise be cut, capturing methane from a landfill). Removal credits fund projects that take CO2 out of the atmosphere (reforestation, direct air capture). Removal credits are generally more expensive and harder to scale, but they address the emission after it has occurred rather than preventing a different emission elsewhere. The distinction matters for disclosure, because some frameworks and corporate buyers now treat the two categories differently.

When to offset

A pre-event estimate, with a safety margin, lets organisers buy the credit and publish the badge before the event happens. A post-event adjustment, when the real figure diverges a lot from the estimate, is good practice, though still rare in the industry today. The gap between estimate and reality tends to be largest for travel, because actual attendance and travel modes only become clear after the event.

The Brazil angle

Brazil established a regulated carbon market (the Sistema Brasileiro de Comércio de Emissões, or SBCE) through legislation signed in late 2024. The system introduces a cap-and-trade mechanism for companies above a defined emissions threshold and creates a central registry (the Registro Central do SBCE) to track credits and allowances. For event organisers operating in Brazil, the practical change is that credits purchased for voluntary offsetting now coexist with a regulated market. Credits allocated to a regulated obligation cannot also be claimed for voluntary purposes, so organisers need to confirm that the credits they buy are eligible for voluntary retirement. Brazil’s voluntary market is large, with many forestry and REDD+ projects concentrated in the Amazon and Cerrado biomes, but the new regulated framework adds a layer of verification that did not exist before.

What is still unresolved

Article 6 of the Paris Agreement governs how carbon credits can be transferred between countries. Under its rules, when a credit generated in one country is used by a buyer in another, the host country must apply a “corresponding adjustment” so the same reduction is not counted twice. For events with international attendees, this raises a question the industry has not settled: if an organiser in one country buys credits from a project in another, and the host country has not implemented corresponding adjustments, the credit may carry a double-counting risk. Until the rules are fully operational across all major credit-supplying countries, this remains an open gap in the system.

Frequently asked questions

Is offsetting a whole event expensive?
It depends on size; mid-sized events (200 to 500 people) usually land in the low thousands of dollars in credits.

Who pays, the organiser or the attendee?
Both models exist: the organiser covers everything, or the organiser covers operations and each attendee offsets their own share.

Do I need an audit to publish the badge?
Not a legal requirement today, but the retired credit needs to be publicly registered for the badge to hold up.

What is the difference between a carbon credit and a carbon allowance?
A credit is generated by a project that reduces or removes emissions and can be bought voluntarily. An allowance is a permit issued by a government under a cap-and-trade system, giving the holder the right to emit a set amount. They serve different purposes and trade in different markets.

Read next: how to calculate a footprint.
Read next: what a carbon credit is.

Primary sources: Corporate Value Chain (Scope 3) Standard (GHG Protocol, 2011); Law 15,042/2024 creating the SBCE, official text in Portuguese (Presidency of Brazil, 2024); Paris Agreement, official text, Article 6 (UNFCCC, 2015); Decisions 2/CMA.3 and 3/CMA.3, rules for Article 6.2 and 6.4 (UNFCCC, 2022).