By Bjorn Fehrm

July 25, 2025, ©. Leeham News: In October last year, we began a series on how air transport is performing against the emission goals for the year 2050.

The ambition to reduce and eventually eliminate greenhouse gas emissions began in earnest 11 years ago, when Airbus flew the Airbus E-Fan at the 2014 Farnborough Air Show (Figure 1).

Figure 1. The Airbus E-fan flying at the 2014 Farnborough Air Show. Source: Wikipedia.

The result of this inspiring flight, which utilized technology that emitted no CO2 or other greenhouse gases (if the batteries were charged with green electricity), was an avalanche of projects from established players as well as upstarts. The optimistic view was that there was a solution to the emissions from airliners.

A much harder nut to crack than thought

As we 11 years later reviewed the key projects stemming from this optimism, whether they were battery electric, hybrid, or hydrogen-based, we found that the progress is minimal. At the Paris Air Show this year, only  one prototype battery-electric six-seater flew, the Beta Technologies CX300.

In the optimism surrounding the electrification of air transport, we often overlook the size of the task. A total of 27,000 airliners carried 5 billion passengers last year. The replacement of any measurable fraction of these 27,000 aircraft with alternative propulsion types was a monumental task, and there was no clear way to go.

Battery-electric or hybrid, which works for cars, doesn’t work for our typical airliners (our site has at least 20 articles on why; use the search box on the top right).

Furthermore, new aircraft types begin production with just a few units produced in their first year, and gradually increase the production rate. Until hundreds are produced per year, it will take most of a decade (Airbus is producing fewer than 100 of the clean sheet A220s per year, nine years after introduction).

We found in the series that, if all the present projects are 100% successful, their combined influence on emissions by 2050 is around 1% to 2%. And that is only for global warming from CO2 emissions.

New studies add to the knowledge

Recent studies include the effects of CO2, but also NOx emissions and non-CO2 warming contributions, such as contrails. The knowledge base around non-CO2 effects on global warming is advancing year by year.

A recent study by U.S. researchers, published in Nature, was referenced by our sister publication AIN under the headline “New tool helps aviation cut climate impact.”

The study named “Trade-offs in aviation impacts on climate favour non-CO2 mitigation” proposes a term, Global Warming per Activity (GWA), based on the impact of activities on the Earth’s radiation balance during one year.

By comparing GWAs from CO2, NOx, and warming contrails, tradeoffs between mitigating actions can be made, such as at what extra fuel consumption is contrail avoidance still producing a positive effect?

The study also concludes that the effects of CO2, NOx, and warming contrails probably contribute about one-third each to air transport’s global warming.

The effects of mitigation efforts

If we take the results of the above study, the alternative propulsion projects address two-thirds of the problem (CO2 and NOx), as does the replacement of old aircraft with new.

SAF addresses one-third (CO2 only; NOx is primarily a function of the combustion design, equally applicable to Jet A1 and SAF).

Finally, warming contrail avoidance addresses one-third of the problem.

SAF has been described as a major contributor to the global warming goals by 2050. We can conclude that replacing old aircraft with new has a larger impact, as SAF is production expansion-limited, and the fleet is expected to grow from 27,000 to 57,000 airliners over the next 25 years.

We don’t conclude this to knock on SAF; we only contrast these actions to understand their respective impact. For mitigating the warming caused by our daily flights, both are needed.

It’s a Wrap

With the Epilogue, we finish our examination of air transport’s actions to meet the 2050 goals for global warming. We can conclude that we will most likely not reach the 2050 goal (IATA has stated an ambitious goal of zero CO2 emissions), but there is a low-hanging fruit.

At least one-third of the global warming attributed to air transport is due to warming contrails, and this is not addressed by current efforts to reduce CO2 emissions. That must change, and the good thing is that it seems easier than reducing CO2 and has a faster effect.