4Air study shows flight altitude has big impact on warming

Private jets can make big reductions in non-CO2 emissions through small changes in flight altitude per 4Air.

By Doug Gollan, May 28, 2024

A study of over 16,000 private jet flights shows that small adjustments in flight altitude would significantly reduce the warming impact of non-carbon emissions created through contrails.

The analysis conducted by 4Air found that flying at a different altitude on just 50 flights out of 16,888 could reduce the contrail’s impact immediately by more than 50%.

It comes ahead of a new EU monitoring scheme that begins in 2025 and includes the non-CO2 emissions in a flight operator’s monitoring and reporting obligations.

Private jets with higher service ceilings had the largest opportunity to fly higher than the contrail formation region, reducing CO2 emissions and their contrail impact instead of needing a tradeoff between the two.

However, trading higher does come with a slightly higher impact from NOx.

According to 4Air, more research is needed to better understand the lifecycle of NOx emissions and compare it to CO2.

Contrails, or condensation trails, are a product of aircraft engine emissions interacting with the right combination of temperature and humidity in the upper atmosphere.

Depending on the location and time of day, long-lasting contrails can trap and absorb heat that otherwise would radiate back into space.

The impact of contrails and non-CO2 emissions is about twice that of CO2 alone, contributing to two-thirds of aviation’s global warming impact.

4AIR President Kennedy Ricci noted, “The results of this study demonstrate both the challenges and opportunities with reducing aviation’s footprint from contrails.”

He added, “Effectively reducing our contrail warming impact requires considering contrails on every flight, but successfully avoiding contrails on just a handful of flights would have a major impact, potentially without CO2 tradeoffs.”

4Air findings

Key results of the study include:

  • Of the over 16,000 flights, if just 0.3%, or 50 flights, had been able to minimize their contrails, the overall contrail impact would have reduced to 51%; minimizing contrails from 0.73%, or 123 flights, would have reduced it to 75%.
  • Of the 23 flights with the highest contrail impact, accounting for around 35% of the total contrail impact, 65% could have avoided or minimized their impact by flying higher, resulting in CO2 and contrail impact reductions.
  • About 18% of flights created a contrail, and 69% of those contrails had warming impacts.
  • 31% of contrails were estimated to have cooling effects, but they only offset the total contrail warming impact by about 13%.
  • The average contrail was estimated to persist for around 2.5 hours, with the more impactful warming coming from contrails that persisted for around 6.5 hours.

As part of the research, 4AIR spent six months working with Flexjet in Europe on a contrail avoidance pilot program.

The program incorporated contrail forecasts into the dispatch process.

Flight paths were then optimized to minimize the time spent in contrail-forming regions.

Flight paths were adjusted to modify cruising altitudes above these regions where possible.

Notes were shared with pilots to calibrate climbs or descents to minimize time spent in the contrail regions.

Flexjet and sister company Sentient Jet already include 300% carbon offsets.

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