News & sources

This page is our working space for everything that moves the debate on contrail avoidance forward: new research, policy developments, real-world trials, media coverage, and the sources our work is based on.

We work on a scientific basis. Contrail avoidance is a serious field of research — which is precisely why fake news, conspiracy narratives, and unsubstantiated claims have no place here. Anyone who wants to convince airlines, policymakers, and the public needs clear facts, reliable sources, and language that stays understandable without becoming imprecise.

Credibility is essential. Not because it makes communication drier, but because this topic will only translate into practice if research, regulation, industry, and the public share a common factual basis.

We will shortly make transparent which sources our work draws on — from studies and organisations to applied projects.

News

This section is in preparation.

Here we will collect current developments in contrail mitigation — research, trials, and policy steps aimed at avoiding the contrails that are particularly harmful to the climate. Entries will be updated regularly and briefly contextualised: What is new? Why does it matter? And what does it mean for implementation in practice?

History

This section is in preparation.

This is where our source archive will take shape: an organised and filterable collection of the studies, reports, organisations, projects, and media coverage our work is based on. The aim is not to gather as many links as possible, but to make clear what we rely on: Which scientific works are central? Which organisations are driving the topic forward? Where are real-world trials taking place? Which political processes are relevant? And where are myths or false claims properly addressed?

Video

Our video series explains why contrails are more than just a visible side effect of flying — and why avoiding the most harmful ones is one of the most concrete climate opportunities in aviation.

The four parts guide viewers through the issue step by step: from the problem, to the solution, to the question of why voluntary action alone will not be enough.

Part 1: The problem

The first part explains why persistent contrails affect the climate, why they have long been underestimated in public debate, and why aviation’s non-CO₂ effects need to be taken seriously alongside CO₂.

Part 2: The solution

The second part shows that mitigation is possible: when flight planning, weather data and models work together, the most climate-damaging contrails can often be avoided through comparatively small adjustments.

Part 3: Why voluntary action is not enough

The third part explains why technical feasibility alone is not enough. For contrail mitigation to become part of everyday aviation, we need clear rules, reliable data, political responsibility and public pressure.

Part 4: One powerful click: Why airlines are ignoring the easiest solution in the sky

Did you know? One minor tweak in flight planning could slash aviation’s climate impact by almost half. So why is a new real-world study still raising questions—and what else did we learn? Find out after the click!

Our source directory: Facts by keyword

Where does the data on climate impact, prediction models, or field tests come from? In this overview, we have sorted our sources by the most important keywords. This way, you can find exactly the references you are looking for with just a single click.

Contrails

Contrails form when hot engine exhaust meets moisture in the cold upper atmosphere. They are not just an optical phenomenon but contribute significantly to global warming. Here you will find the core scientific principles.

• T&E report: Managing complexity: How to scale up contrail avoidance in Europe?
  Summary of the latest scientific findings from Transport & Environment.
• ARD Climate Update: "Small detour, big climate impact"
  The problem is regions in the sky that atmospheric physicists call "ice-supersaturated regions"—very cold areas with high humidity. Ice clouds can form there, but they need a crystallization nucleus. That’s where soot and fine particles from aircraft exhaust come in, together with lots of water vapor—the perfect ice-cloud mix.
• Tagesschau: More climate-friendly by changing flight routes?
  It sounds almost too good to be true: with small changes to flight routes, flights could be significantly less harmful to the climate, according to atmospheric research and climate organizations.
• Blue Lines
  Organization working on the climate impacts of contrails.
• Contrails.org: Comparing contrails and CO₂
  Explains the different climate effectiveness of CO₂ emissions and contrails.

Avoidance

The targeted avoidance of contrails is considered one of the fastest and most cost-effective levers in aviation climate protection. These sources highlight the specific approaches and political debates to prevent their formation from the outset.

• Contrails.org: Cost of avoidance
  Average cost of $1 to avoid warming equivalent to one tonne of CO₂.
• Hannah Ritchie: Eliminating contrails from flying could be incredibly cheap
  Comprehensive overview of contrails, their climate impact, avoidance strategies, and costs.

Climate impact

The climate impact of flying consists of more than just CO₂. According to current studies, the actual climate impact of non-CO₂ effects accounts for the larger share of global warming caused by aviation. These documents summarize the current state of research.

• T&E report: Managing complexity: How to scale up contrail avoidance in Europe?
  Summary of the latest scientific findings from Transport & Environment.
• Nature: Climate effects of contrail avoidance (2025)
  Peer-reviewed study on the climate effects and uncertainty ranges of contrail avoidance.
• Ian McKay on the Solving for Climate podcast
  About 2% of contrails form into cirrus clouds, contributing roughly 2% of human-caused climate warming.
• Contrails.org: Comparing contrails and CO₂
  Explains the different climate effectiveness of CO₂ emissions and contrails.
• DLR: Climate impact of aviation
  One third of aviation's climate impact comes from CO₂, two thirds from non-CO₂ effects like contrails.
• ScienceDirect: Contrails and global warming
  Contrails are responsible for approximately 2% of global warming.
• Hannah Ritchie: Eliminating contrails from flying could be incredibly cheap
  Comprehensive overview of contrails, their climate impact, avoidance strategies, and costs.

Cirrus clouds

When contrails do not dissolve in cold, humid atmospheric layers, they spread into long-lasting, artificial cirrus clouds. These veil clouds heavily intensify the greenhouse effect. Here you can find the sources on this phenomenon.

• T&E report: Managing complexity: How to scale up contrail avoidance in Europe?
  Summary of the latest scientific findings from Transport & Environment.
• ingenieur.de: 80% of contrails form where nobody expects them
  German-language article about the Nature study on unrecognized contrail cirrus clouds.
• Nature: Previously unrecognized cirrus clouds from contrails
  November 2025 study shows 80% of contrails form where nobody expected them.
• Ian McKay on the Solving for Climate podcast
  About 2% of contrails form into cirrus clouds, contributing roughly 2% of human-caused climate warming.

Warming

The atmospheric warming caused by contrails (known as radiative forcing) is a critical factor in aviation's climate footprint. The following sources provide the data behind this effect.

• ScienceDirect: Contrails and global warming
  Contrails are responsible for approximately 2% of global warming.

Water vapor

Water vapor is an inevitable byproduct of burning jet fuel. Combined with soot particles, it forms the nucleus for contrails. The sources collected here explain the physical processes.

• Wikipedia: Humidity and temperature
  The colder the air, the less water vapor it can carry – the basis for contrail formation.

Forecast Model

To purposefully avoid contrails, meteorologists must precisely predict where ice-supersaturated regions are located. Modern models use satellite and weather data for real-time calculations. Learn more about the state of the art here.

• TUI Livestream from August 22, 2025
  Pilot Tony Schweigert confirms the high accuracy of contrail prediction models in real operations.

Flight planning

Sometimes a minimal altitude adjustment of just a few hundred meters is enough to avoid a critical atmospheric layer. Climate-optimized flight routing integrates these avoidance maneuvers. The following sources show how this works.

• Flightkeys
  According to its own claims, the only flight planning software that can already plan routes for contrail avoidance.

Software

Calculating climate-friendly flight paths requires complex algorithms. Modern flight planning software helps airlines integrate weather data into route optimization automatically. Technical reports and analyses can be found here.

• Flightkeys
  According to its own claims, the only flight planning software that can already plan routes for contrail avoidance.

Feasibility

Can aviation really avoid contrails across the board in busy, dense airspace? These sources examine the operational feasibility, potential fuel penalties from detours, and logistical challenges.

• DLR Project D-KULT: Feasibility of eco-efficient flight trajectories (completed)
  Completed project demonstrating the feasibility of eco-efficient flight trajectories considering non-CO₂ emissions.
• DLR: Avoidance of persistent contrails successfully demonstrated
  2023 DLR study provides first proof that avoiding persistent contrails in real flight operations is possible.

Field test

Theory is good, practice is better. In recent years, research institutions and airlines have conducted real test flights to trial contrail avoidance in everyday operations. You can find the reports and field trials here.

• DLR: Climate strategy in practice – reducing contrails
  Practical tests reveal difficulties in route planning due to weather changes or delays (November 2025).

Aviation

The global aviation industry faces the mammoth task of becoming climate-neutral. Alongside decarbonization, managing non-CO₂ effects offers an immediate opportunity to drastically reduce its footprint. These sources view the topic within the wider industry context.

• Our World in Data: Global aviation emissions
  Aviation accounts for 2.5% of global CO₂ emissions (excluding contrails).