CORSIA Explained: What Airlines Must Do About Carbon Offsetting

In 2023, commercial aviation produced roughly 915 million tonnes of CO₂, accounting for 2.5 % of global emissions (IATA data). Understanding CORSIA aviation emissions is now a core compliance requirement for every airline seeking to meet ICAO standards while protecting their bottom line.

What Is CORSIA?

The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) is an ICAO‑driven market‑based measure that obliges airlines to monitor, report, and offset the growth in CO₂ emissions from international flights. The scheme operates in three phases—pilot, first, and second—spanning from 2021 to 2035. During the pilot phase participation is voluntary, but from 2024 onward the majority of airlines fall under mandatory compliance, covering about 80 % of international routes (industry data).

CORSIA does not replace existing national regulations; instead, it adds a global layer of accountability. Airlines calculate their baseline emissions for 2019 and 2020, then offset any increase above that baseline each year. Offsets must be sourced from ICAO‑approved programs that meet rigorous additionality, permanence, and verification criteria.

How CORSIA Aviation Emissions Are Calculated

Accurate calculation of CORSIA aviation emissions starts with the fuel burn data reported for each flight segment. The standard conversion factor of 3.15 kg CO₂ per kilogram of jet fuel burned is applied, as defined by ICAO. This figure is then adjusted for any fuel uplift discrepancies, fuel tankering, and the use of Sustainable Aviation Fuel (SAF), which can carry a lower carbon factor.

Airlines must align their reporting with the same units used in revenue metrics such as RPK (Revenue Passenger Kilometers) and ASK (Available Seat Kilometers). This alignment enables the calculation of carbon intensity ratios like CO₂ per RPK, which can be compared against industry benchmarks such as the IATA average of 115 g CO₂ per RPK (IATA data).

• Collect fuel uplift data from flight‑level fuel logs.
• Apply the ICAO conversion factor (3.15 kg CO₂/kg fuel).
• Adjust for SAF credits and any fuel‑efficiency measures.
• Aggregate by reporting period and compare to the 2019‑2020 baseline.

Reporting CORSIA Aviation Emissions: Key Requirements

Compliance teams must submit an annual CORSIA emissions report to the designated national authority, typically the civil aviation regulator. The report includes total fuel consumption, calculated CO₂ emissions, and the amount of offsets purchased. Reports are due by April 30 for the preceding calendar year, with a 30‑day grace period for extensions.

Data integrity is verified through an independent audit, and airlines must retain supporting documentation for at least five years. The use of the How2TakeOff Flight Estimator can streamline the data collection process by automatically converting flight schedules into fuel burn estimates, reducing manual entry errors.

Mitigating CORSIA Aviation Emissions Through Offsets

Once the excess emissions are identified, airlines must purchase ICAO‑approved carbon offsets. These offsets are sourced from projects such as reforestation, renewable energy, or methane capture. The price of offsets fluctuates, but recent market data shows an average price of $12‑$15 per tonne of CO₂ (industry data).

Strategic offset procurement can also support broader sustainability goals. For example, aligning offset purchases with the airline’s corporate social responsibility (CSR) strategy can improve brand perception and meet investor ESG criteria. Some carriers combine offset purchases with internal carbon‑reduction initiatives, such as fleet renewal to newer, more fuel‑efficient aircraft, which lowers the overall CORSIA aviation emissions baseline.

Steps to Comply with CORSIA Aviation Emissions

1. Establish a Baseline: Consolidate 2019‑2020 fuel data and calculate the baseline CO₂ emissions using ICAO’s conversion factor.
2. Integrate Data Capture: Deploy flight‑level fuel tracking tools and ensure they feed directly into the airline’s emissions management system.
3. Calculate Annual Growth: Compare current year emissions to the baseline to determine the offset requirement.
4. Source Approved Offsets: Select ICAO‑validated projects, negotiate contracts, and lock in pricing before the April 30 reporting deadline.
5. Submit the Report: Compile the annual CORSIA report, attach supporting documentation, and file with the national authority.
6. Audit and Review: Conduct an internal audit, address any findings, and refine data collection processes for the next cycle.

By following these steps, compliance teams can turn a regulatory obligation into an operational advantage, leveraging accurate emissions data to drive fuel‑efficiency initiatives, optimize CASK (Cost per Available Seat Kilometer), and improve overall RASK (Revenue per Available Seat Kilometer).

Use How2TakeOff's Free Aviation Analytics Tools

Managing CORSIA aviation emissions does not have to be a manual, error‑prone exercise. How2TakeOff offers a suite of free tools—including the Flight Estimator, emissions calculator, and benchmark dashboards—that integrate seamlessly with existing airline data warehouses. These resources help you monitor LF (Load Factor), OTP (On‑Time Performance), and other key performance indicators while staying compliant with ICAO’s CORSIA framework.

Start today by accessing the How2TakeOff Flight Estimator and turn complex compliance requirements into clear, data‑driven actions.