ACA Level 5 — Net Zero: Deep Reductions and Carbon Removals for Airport Decarbonisation
The most stringent level of Airport Carbon Accreditation. What airports must achieve, why only carbon removals qualify for residual emissions, and which removal technologies and nature-based approaches meet Level 5 requirements.
By Koorosh Behrang & Abhishek Das • • 10 min read
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≥90%
Absolute Reduction — of Scope 1+2 vs baseline (e.g. 2010)
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≤10%
Residual Emissions — only removals permitted, no avoidance
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Removals
Biological + technological pathways required
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What Level 5 (Net Zero) Requires |
Level 5 is the pinnacle of ACA accreditation. To reach this level, an airport must have progressed through all previous levels (1 through 4+). This sequential requirement means Level 5 is a strategic destination, not a shortcut. It requires genuine, foundational transformation rather than incremental improvement.
The core requirement at Level 5: achieve ≥90% absolute reduction in Scope 1+2 emissions versus baseline year (e.g. 2010). The remaining ≤10% of residual emissions must be neutralised using carbon removals only — and this applies to both Scope 1+2 residuals and Scope 3 staff business travel (carried forward from Level 3+). Traditional avoidance or reduction credits are not permitted for any residual category at Level 5. For broader Scope 3, airports must extensively map all relevant categories and commit to Scope 3 net zero by 2050 or sooner. This combination — deep Scope 1+2 reduction, removals-only for all residuals, plus a credible Scope 3 trajectory — is what sets Level 5 apart.
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Critical Rule: Removals Only, No Avoidance Credits Avoidance/reduction credits (e.g., REDD+, cookstove projects, renewable energy credits from elsewhere) do NOT qualify at Level 5. Only credits representing actual CO2 removal from the atmosphere are accepted. This aligns with SBTi Net-Zero Standard and the GHG Protocol Land Sector & Removals Standard. Very few airports have achieved this level, reflecting the stringency of genuine net zero. |
This alignment with international standards is deliberate. The aviation industry, under pressure to demonstrate authentic climate commitment, has moved Level 5 to match where the global carbon standards are heading. Level 5 is not merely a higher tier — it represents a fundamentally different approach to carbon neutrality.
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Why Removals Only? |
The science is clear. The IPCC defines net zero as near-total elimination of emissions plus removal of residual CO2 from the atmosphere. An avoidance credit reduces future emissions but does not remove CO2 already in the atmosphere. Only removals achieve genuine net zero.
Example: A coal plant closure credit prevents future emissions from that facility. This is valuable for climate action and important for mitigation. But an airport cannot offset 20 years of historical aviation emissions with a coal closure credit — the historical CO2 is already in the atmosphere. Only by removing CO2 directly can the airport be considered net zero.
Credibility and Market Direction
Level 5 is where the global standard is heading. SBTi V2, ISO Net Zero Guidelines (IWA 42), and corporate commitments from major emitters are all moving toward removal-only requirements for residual emissions. By anchoring Level 5 to removals-only, the ACI is future-proofing airport climate commitments. An airport that reaches Level 5 today is compliant with tomorrow's standards.
This is also why Level 5 is separate from Level 4+, not merely an extension of it. Levels 1–4+ represent a spectrum of carbon management maturity using traditional offset mechanisms. Level 5 represents a threshold into genuine net zero — a fundamentally different destination.
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Eligible Carbon Removal Pathways |
Removal pathways fall into two broad categories: biological (nature-based) and technological (engineered). Both are eligible for Level 5, and most airports will use a portfolio approach combining both.
Biological Removals
Afforestation / Reforestation (A/R)
Establishing new forests on previously non-forested land or restoring forests. CO2 is sequestered in above-ground and below-ground biomass over decades.
Soil Carbon Sequestration
Enhanced agricultural practices (reduced tillage, cover crops, rotational grazing) that increase soil organic carbon stocks.
Biochar
Pyrolyzed biomass locked in soil, providing long-term carbon storage (100+ years) with agronomic co-benefits.
Blue Carbon
Mangrove, seagrass, and salt marsh restoration. These coastal ecosystems sequester carbon at rates 10-40x higher than forests.
UK Woodland Carbon Code
UK-specific forestry credits with rigorous additionality and permanence criteria. Widely recognised and readily available.
Technological Removals
Direct Air Carbon Capture and Storage (DACCS)
Machines that extract CO2 directly from ambient air and store it in geological formations. Highest permanence, currently most expensive.
Bioenergy with Carbon Capture and Storage (BECCS)
Biomass burned for energy with the resulting CO2 captured and stored geologically. Combines renewable energy with removal.
Enhanced Weathering
Accelerating natural mineral carbonation processes at industrial scale. Emerging but scalable pathway.
Ocean-Based CDR
Marine alkalinity enhancement and other ocean-based carbon removal methods. Early-stage but high potential.
Biological vs Technological: Quick Comparison
| Attribute | Biological (e.g., A/R) | Technological (e.g., DACCS) |
| Cost per tCO2e | $10–40 | $400–1000+ |
| Permanence | 30–100 years | 10,000+ years |
| Scalability | Moderate (land constraints) | High (location agnostic) |
| Availability Now | Widely available | Limited / emerging |
Most Level 5 airports will use a blended portfolio: biological removals for cost-effectiveness and immediate availability, technological removals for permanence and scalability. The mix depends on the airport's risk tolerance, budget, and timeline.
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The ≥90% Reduction Challenge |
This is where Level 5 becomes difficult. The 90% reduction threshold is not achieved through offset purchases. It requires fundamental operational transformation of the airport and its ecosystem.
Core Decarbonisation Measures
- Full electrification of ground fleet — All GSE, tugs, and ground support vehicles must be electric or hydrogen-powered.
- 100% renewable electricity — Direct power purchase agreements (PPAs) with renewable generators, not just green tariffs. This covers terminal operations, lighting, ground operations, charging infrastructure.
- Building energy efficiency retrofits — HVAC upgrades, insulation, LED lighting, waste heat recovery in all airport facilities.
- Sustainable Aviation Fuel (SAF) adoption — While SAF is largely a Scope 3 (airline) responsibility, airports can incentivise and facilitate SAF uptake through infrastructure and tariff alignment.
- Surface access modal shift — Rail connectivity, bus rapid transit, cycling, and pedestrian infrastructure to reduce car dependency.
- Tenant engagement for Scope 3 — Active collaboration with airlines, catering, retailers, and service providers to decarbonise their operations on airport grounds.
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Level 5 Cannot Be Bought Most airports targeting Level 5 are aiming for 2040–2050. Only a handful of small, well-positioned airports have achieved it so far. The 90% threshold means airports must transform operations before offsetting — removals are only for genuine residuals, not a shortcut to net zero. |
This is also why Level 5 carries such weight. Achieving it signals real decarbonisation, not credit purchasing.
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Procuring Carbon Removals |
Carbon removal credits are more expensive and less abundant than traditional avoidance offsets. Current market pricing ranges from $30–1000+/tCO2e (vs avoidance credits at $5–30/tCO2e). However, the volume needed is much smaller because it applies only to residual emissions.
Example: An airport that reduces from 100,000 tCO2e baseline to 10,000 tCO2e needs only 10,000 removal credits, not 100,000. This significantly reduces total procurement cost despite higher per-tonne prices.
Approved Removal Credit Programmes
Only credits from ACA-approved registries are eligible:
- Verra — Largest VCM registry; wide range of removal projects
- Gold Standard — High integrity standard; strong co-benefits focus
- American Carbon Registry (ACR) — US-focused; solid permanence requirements
- Climate Action Reserve (CAR) — Specialises in emissions reductions and removals
- UK Woodland Carbon Code — Domestic UK forestry credits
- Puro.earth — Emerging focus on engineered removals (DACCS, enhanced weathering). Check current ACA approval status.
Forward contracting is essential. Removal credit supply is currently constrained. Airports should enter long-term purchase agreements (3–5 year forward contracts) to secure availability and lock in pricing, especially for emerging removal technologies like DACCS.
Most Level 5 airports will mix biological removals (lower cost, available now) with technological removals (higher permanence, future-proofing). This portfolio approach balances cost, availability, and permanence risk.
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How Canopy Supports Level 5 Airports |
Climate Decode's Canopy platform is purpose-built for airports navigating the Level 5 transition. Here is what it provides:
Core Canopy Features for Level 5
- Residual Emissions Identification — Post-abatement analysis to isolate the final ≤10% that requires removal credits.
- Removal-Only Credit Curation — Access to verified removal credits only; no avoidance/reduction credits mixed in.
- Biological vs Technological Pathways — Separate tracking and reporting of nature-based and engineered removal solutions.
- Forward Procurement Management — Tools for locking in long-term contracts for emerging removal technologies, including DACCS pre-purchase agreements.
- Audit-Ready Reporting — Level 5–specific reports showing removal provenance, permanence profiles, registry alignment, and compliance with ACA requirements.
- Cost Optimisation — Portfolio modelling to balance biological (lower cost) and technological (higher permanence) removals based on airport budget and climate goals.
Level 5 Is Where Carbon Markets Meet Deep Tech
Canopy helps airports navigate the transition from traditional avoidance offsets to verified removals — connecting procurement strategy with emerging technologies and nature-based solutions. This is not just carbon accounting; it is strategic climate investment.
Airports pursuing Level 5 need a partner who understands both the science of net zero and the market mechanics of removal credits. Canopy provides that capability.
References
- ACI Europe, Airport Carbon Accreditation Level 5 Net Zero Requirements (2024)
- IPCC AR6 Working Group III, Chapter on Carbon Dioxide Removal and Safeguards (2023)
- SBTi Corporate Net-Zero Standard V2 (2024)
- GHG Protocol, Land Sector and Removals Standard V1.0 (January 2027 effective)
- Smith et al., "State of Carbon Dioxide Removal 2024" — Annual Report, Carbon Gap (2024)
- ISO Net Zero Guidelines (IWA 42:2022)
- Climate Decode, "Airport Carbon Accreditation 101" — VCM Series
From Deep Reductions to Verified Removals
Build your airport's path to Level 5 net zero with expert guidance on abatement strategy and removal procurement.
Written by
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Koorosh Behrang Founder, Climate Decode |
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Abhishek Das Voluntary Carbon Markets & Residual Emission Procurement Strategy, Climate Decode |