To:

Department for Transport (DfT),
Department for Energy Security and Net Zero (DESNZ),
and the UK Government

 

i) This petition calls on the UK Government to:

 

1.      Update all relevant legislation, policy and reporting frameworks at the earliest possible opportunity, to include the non-CO₂ warming effects of aviation, especially from contrails, including:

·       The UK Carbon Budget and Growth Delivery Plans,

·       The UK’s Net Zero Strategy,

·       Aviation decarbonisation policy frameworks, such as the Jet Zero Strategy,

·       UK Emissions Trading Scheme (UK ETS) scope and accounting rules,

·       And DfT aviation policy framework and appraisal guidance, and

2.      establish a permanent governance body to coordinate further trials of contrail mitigation strategies, and

3.      cooperate with other states to jointly implement large-scale, international contrail avoidance trials, and

4.      Follow in the footsteps of the EU by launching a mandatory non-CO2 Monitoring, Reporting and Verification scheme.

 

ii) Executive Summary

 

There is overwhelming scientific agreement that:

 

1.      Contrails are a major contributor to global warming.

2.      Even the lowest credible estimates for contrail warming indicates that policy-level action at national and international levels should be taken immediately.

3.      Contrail impact mitigation strategies are feasible and effective and should be trialled and implemented as soon as possible.

 

However, contrail mitigation requires robust regulatory and legislative frameworks to be in place.

 

iii)                Introduction

 

Condensation trails (‘Contrails’) form when soot particles and volatile particulate matter from aircraft exhaust fumes mix with cold and humid ambient air to produce ice crystal clouds.

 

The Contrail Impact Mitigation Task and Finish Group (CIMTFG), which is part of the UK’s Jet Zero Taskforce, stated in March 2026: “Aviation's contrail climate impact is significant” and “there is consensus that the annual global average radiative forcing from contrails is net positive (warming).” While there is some uncertainty on the exact magnitude of contrails’ warming effects, they are currently estimated to be responsible for 50% of aviation’s total climate impact (Global Mean Temperature Rise) over a 20-year period, and this could even be as high as 66%. Over a 100-year period, the estimated impact is still significant at 35%. In addition, the former president of the Royal Aeronautical Society, Professor Ian Poll, echoed the wider scientific community when publicly stating that the warming impact of contrails was significant enough to demand action. Moreover, according to the Climate Change Committee, the warming effects of Aviation’s non-CO₂ emissions has tripled since 1990, showing the urgency of the problem.

 

Despite this, UK aviation’s climate impact continues to be significantly underestimated as the effects of contrails are excluded from all current UK climate policy and legislation. This was recognised by the UK Parliament’s Environmental Audit Committee in a report published on 24 October 2025: “Despite the warming impact of these emissions, they are excluded from current climate calculations.” This is further highlighted in written submissions to the airport expansion inquiry by the organisations Stay Grounded and Richmond Heathrow Campaign.

 

We welcome the news on 17 April 2026 that the Government intends to include CO₂ emissions from UK-attributable international aviation in carbon budgets from 2033 onwards, but note that non-CO₂ effects are not included in the widening of this scope. This is particularly significant as long-haul flights are linked with higher levels of contrail warming.

 

iv) An indefensible policy and legislation gap

 

The Government argued in its response to the Environmental Audit Committee that non-CO₂ effects must remain excluded from policy and legislation because there is no internationally agreed-upon metric with which to measure them.

 

This position is fundamentally flawed as that logic could be used to justify inaction on any environmentally degrading human activity if it were simply too technically demanding to measure precisely. Furthermore, recent research from the University of Cambridge and Imperial College, London comprehensively demonstrates that action on contrails is preferable to inaction regardless of which metric is selected to quantify their warming effects (Borella et al., 2024​, Smith et al., 2026).

 

Indeed, the ‘Literature review of aviation’s non-CO2 climate impacts and evaluation of existing metrics’ commissioned by the Department of Transport and published in May 2024, made the following comments and recommendation:

 

"There is currently no integrated policy framework that accounts for both CO₂ and non-CO₂ impacts. Current policies tend to prioritise CO₂ emissions, thereby neglecting the substantial contribution of non-CO₂ impacts to global climate change. Incorporate non-CO₂ impacts into aviation climate policies, ensuring that these impacts are accounted for in regulatory frameworks and mitigation strategies. This could include conducting comprehensive assessments of existing aviation climate policies and regulations to identify gaps and opportunities for incorporating non-CO₂ impacts. It will also be key to collaborate with international organisations and governments to harmonise aviation climate policies and ensure a consistent approach to addressing non-CO₂ impacts. (emphasis added)"

 

The CIMTFG annual report reinforces this recommendation, highlighting that:

 

"No regulation currently exists in relation to contrails in the UK, and climate targets for the sector (in UK policy and ICAO Resolutions) focus on the mitigation of CO₂  emissions only (although the temperature goals of the Paris Agreement could be interpreted to include all climate impacts, including contrails, providing a supportive rationale for contrail mitigation). (emphasis added)"

 

The NGO Opportunity Green, in collaboration with the world-renowned Cornerstone Barristers, carried out legal analysis in 2025 on this possible interpretation, concluding that countries must include non-CO₂  emissions in their national climate plans to comply with their commitment to the Paris Agreement. This analysis also points out that the UK is committed under international environmental law to not only the Paris Agreement but also the precautionary principle, as set out in Principle 15 of the Rio Declaration on Environment and Development:

 

"Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation."

 

Delaying action on contrail warming because of metric uncertainty is therefore illogical, not informed by the latest science, and a clear violation of international law with regards to the Paris Agreement and the precautionary principle.

 

v) Evidence shows that action can and should be taken now

 

Further delays are even more inexcusable in the light that contrail mitigation strategies, through contrail avoidance, have been shown to be incredibly feasible and effective.

 

A number of trials over the last five years, both in Europe and North America, have now shown that contrail avoidance (which consists of minor changes in flight routes) could immediately and significantly reduce the impact of contrails.

 

It is important to reiterate that the papers previously cited (and others, like this International Council on Clean Transport 2025 report) have also shown that the biggest risk associated with contrails is not the negligible extra fuel burn (and therefore the small amount of extra CO₂  emitted) caused by contrail avoidance, but continued inaction on this issue.

 

The International Council on Clean Transportation report also stated:

 

“Contrail avoidance in particular is modelled to be the most impactful and cost-effective lever, accounting for 40% of total avoidable warming (for the aviation industry) by 2050... even with a maximum level of GHG (greenhouse gases like CO₂ ) mitigation between now and 2050, aviation would more than double its share of the remaining climate budget, from 4% of historical temperature change in 2019 to 9%. This highlights the need to identify additional mitigation levers, such as SLCP (short-lived climate pollutants like contrails) control.”  (emphasis added)

 

This shows that, regardless of how much action is taken on aviation’s CO₂ climate impacts, action on its non-CO₂ effects will still be necessary as well.

 

Thus, there is overwhelming scientific agreement that:

 

1.      Contrails are a major contributor to global warming.

2.      Even the lowest credible estimates regarding the exact magnitude of contrail-induced warming, and most conservative metric for quantifying non-CO₂ climate impacts, indicate that policy-level action at national and international levels should be taken immediately.

3.      Contrail impact mitigation strategies, such as contrail avoidance, are feasible and effective and should be trialled and implemented as soon as possible.

 

However, without recognition of the climate impact of contrails in all the relevant climate policy frameworks and legislation, the urgent need for regulation and industry-wide action will be further delayed.

 

vi) The dangers of not acting now

 

The Government has announced plans to legislate for the 7th Carbon Budget this summer. It must ensure that the effects of contrails, from both domestic and international aviation, are included in this legislation.

 

However, given the severity of the effects of contrails and the urgent need for mitigation, we urge the Government to also update and amend all of the aforementioned policy frameworks and legislation as soon as possible to reflect this.

 

Otherwise:

 

1.      The UK’s Net Zero strategy will continue to systematically underestimate the country’s warming contributions, leaving the Government liable to legal action and undermining the UK’s climate leadership on the global stage. The UK Government’s Jet Zero Taskforce recently corroborated this view: “[Contrails provide] the opportunity for the UK to show global leadership on this issue.”

 

2.      The aviation industry will continue to be exempt from responding to a large share of its climate impact, jeopardising cross-sectoral collaboration on the transition to net zero. In addition, the combined non-CO₂  and CO₂  warming effects of aviation is estimated to constitute 19% of the remaining global temperature budget if the +2°C warming limit set by the Paris Agreement is to be avoided. This is exacerbated by the fact that aviation is proving to be a difficult sector to decarbonise. Immediate action on contrails is therefore urgent to recover a significant part of this budget.

 

vii) The UK’s responsibility as a first mover on contrails

 

It is becomingly increasingly clear that the UK has a responsibility to be a first mover on contrails.

 

Firstly, much of the global share of warming caused by contrails occurs due to long-haul flights in the airspace above the North Atlantic, many of which fly into and from UK airports like Heathrow. By some estimates, the North Atlantic accounted for 5% of the total flight distance flown in 2019 but a disproportionate 10-11% of the annual contrail warming effects.

 

Secondly, the UK’s flag carrier airline, British Airways (BA), was ranked fourth in the world by Estuaire.com for creating the most warming from contrails in 2025. The most damaging BA flight route was London Heathrow to John F. Kennedy International Airport in New York, which created the CO₂  equivalent of 135,000 kilograms of emissions through contrail warming, the 5th highest of any flight route in the world and highest of any European airline.

 

Lastly, while international aviation contributes 2-4% of global annual warming effects, 7-8% (not accounting for contrails) of the UK’s total emissions originate from domestic and international aviation, showing that the UK is disproportionately responsible for aviation-induced climate change. Aviation is on course to be the highest emitting sector in the UK by 2040, according to the Climate Change Committee.

 

All of this shows that the UK has a responsibility to be a leader in tackling the climate impact not only of aviation generally, but also of contrails specifically, as a disproportionate amount of contrail-induced warming occurs due to UK-attributable aviation. Given the UK's academic excellence in this area, this should be more than feasible.

 

viii) What we are asking for

 

The first step to solving a problem is recognising that there is one in the first place, and so the effects of contrails must be included in the aforementioned pieces of legislation and policy frameworks.

 

We call on the Government to:

 

1.      Incorporate non-CO₂ warming effects into all aviation and national climate policies and legislation frameworks, applying the precautionary principle in the selection of CO2e conversion metrics.

 

We also call on the Government to adopt the recommendations of the reports produced by the Contrail Impact Mitigation Task and Finish Group, by:

 

2.      Establishing a permanent governance body to coordinate further trials of contrail mitigation strategies and ensuring that all workstreams reach level 3 of the Contrail Impact Maturity Framework by the end of the year.

 

3.      Cooperating with other states to jointly implement large-scale, international trials in airspace where the UK contributes to ATC services, especially over the North Atlantic, by the end of the year.

 

4.      Following in the footsteps of the EU by launching a mandatory non-CO₂ Monitoring, Reporting and Verification scheme for airlines operating flights departing from and arriving at UK airports as a necessary first step to implementing effective regulation against the formation of warming contrails.

 

ix) Conclusion and summary

 

Science and international law clearly shows that action on contrails is necessary, urgent and possible, in spite of remaining uncertainty. The first step to ensuring effective regulation and responsible and proportionate industry-wide action in the UK is to incorporate the climate effects of contrails into all relevant UK climate legislation and policy frameworks.

 

The UK Government should adopt its own advice so that “the UK can move from a reactive to a proactive state, effectively addressing aviation's significant non-CO₂ impacts and ensuring efforts are aligned with its net-zero ambitions.”

 

The UK Government must account for the full climate impact of all UK-attributable aviation at the earliest possible opportunity. Inaction is no longer justifiable.