The climate rulebook chaos facing airlines flying through Europe
February 26, 2026
A single long-haul aircraft operating between the US, the UK and mainland Europe can now fall under multiple carbon trading systems, offsetting schemes and sustainable aviation fuel mandates, depending entirely on where it departs, lands and refuels.
That is the central message of a new legal briefing from London-headquartered law firm Watson Farley & Williams, which warns that aviation decarbonisation policy is becoming increasingly fragmented across jurisdictions.
In its latest analysis, the firm writes that navigating aviation climate rules is complex because the regimes “whilst being complementary, were not designed in a unified way”.
For airlines and fuel suppliers, that lack of alignment is no longer theoretical. It’s becoming operational.
CORSIA, EU ETS and UK SAF mandates: Five overlapping aviation climate regimes
Flights touching the UK and EU can trigger obligations under five separate frameworks:
- International Civil Aviation Organisation’s CORSIA
- The EU Emissions Trading Scheme
- The UK Emissions Trading Scheme
- The EU’s ReFuelEU Aviation regulation
- The UK Sustainable Aviation Fuel Mandate
Each instrument targets a slightly different lever.
CORSIA is a global offsetting scheme for international flights between ICAO member states. It requires airlines to purchase approved carbon credits if emissions exceed a baseline.
The EU ETS and UK ETS are cap-and-trade systems, requiring operators to surrender allowances for each tonne of CO₂ emitted. Importantly, eligible SAF is treated as zero-emission fuel under both schemes, reducing compliance exposure.
ReFuelEU and the UK SAF Mandate operate upstream, imposing blending obligations on fuel suppliers rather than airlines directly. Suppliers must meet minimum SAF percentages or face buy-out penalties.
As WFW explains, “CORSIA and the SAF Mandates specifically target the aviation sector; CORSIA sets greenhouse gas emission reduction targets for airline operators on a global scale; the UK SAF Mandate imposes obligations on fuel suppliers in the UK… and ReFuelEU imposes obligations on fuel suppliers, airline operators and union airport operators in the EU.”
The result is layered regulation rather than a single coherent system.
How flight routes determine climate rules and obligations
WFW illustrates how compliance changes depending on the flight path.
- A flight from Paris to Frankfurt falls under EU ETS and ReFuelEU.
- London to Edinburgh triggers UK ETS and potentially the UK SAF Mandate if fuel is uplifted.
- Frankfurt to New York engages CORSIA and ReFuelEU.
- New York to London falls under CORSIA.
The same aircraft, on a single rotation, can therefore face:
- A global offsetting scheme
- A UK carbon trading system
- An EU carbon trading system
- Two separate SAF blending mandates
That has implications not just for environmental reporting but for commercial decision-making.
As WFW notes, “the relevant industry stakeholders need to continuously monitor their compliance with the regulations, as and when they may apply depending on the flight plan the aircraft takes”.
SAF eligibility differs under ReFuelEU and the UK SAF mandate
Complicating matters further, SAF qualification thresholds differ between regimes.
The UK SAF Mandate requires at least a 40% lifecycle greenhouse gas reduction compared with fossil fuels and places caps on HEFA-based fuels over time. ReFuelEU imposes higher thresholds for certain fuel types, including synthetic fuels. CORSIA accepts a broader range of feedstocks but applies its own sustainability screening criteria.
Meanwhile, both the EU ETS and UK ETS treat eligible SAF as zero-rated fuel, meaning airlines avoid surrendering allowances for those emissions.
WFW highlights that “there are variances as regards fuel eligibility criteria, sustainability criteria and carbon emission reduction requirements for fuels across the regulations”.
This creates what is effectively a patchwork SAF market, rather than a single European one.
Aviation emissions compliance and carbon trading are becoming strategic
Airlines now face multiple reporting regimes and verification standards. WFW observes that operators are “subject to scrutiny from several enforcement authorities” and must manage separate monitoring, reporting and verification requirements.
The firm warns that the absence of a harmonised landscape risks “fragmenting the SAF market and complicating certification processes”, raising questions about cross-border recognition and potential trade friction.
There are moves toward alignment. The UK and EU have announced plans to explore linking their emissions trading schemes, and the European Commission has adopted a Delegated Regulation to standardise how CORSIA emissions are monitored within the EEA.
But full regulatory convergence remains distant.
Decarbonisation rules are reshaping airline network economics
For airline executives, this is no longer simply an environmental policy debate.
It affects:
- Where fuel is uplifted
- What type of SAF is procured
- Whether offset credits or allowances are purchased
- How network planning interacts with carbon exposure
Compliance strategy is increasingly route-specific.
The industry may ultimately narrow SAF sourcing to fuels that satisfy the strictest common denominator across jurisdictions. But that could increase cost and reduce flexibility in the short term.
WFW’s conclusion is clear: while the various regimes share the same decarbonisation objective, they were not built as a single architecture.
Until they are better aligned, airlines flying through Europe will need to treat climate compliance not as a background reporting exercise, but as a core element of operational and financial planning.
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