Leeham News and Analysis
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Bjorn’s Corner: Air Transport’s route to 2050. Part 30.
By Bjorn Fehrm
July 11, 2025, ©. Leeham News: We feature a Corner series on the state of actions to mitigate the global warming impact from Air Transport. We try to understand why different developments have been slow.
In the last Corner, we correlated the growth of airliners between 2024 and 2050 and the growth in Greenhouse gas emissions of CO2 and NOx that would result. We also calculated the increase in warming from contrails based on the traffic increase by 2050. The results are in Figure 1.
We also discussed that the warming effects of CO2 are undisputed, whereas the impact of NOx and contrails is less mature in its complicated effects research. The performed research has a lowest and a highest warming probability. We will now do an “acid test” and see what their impact is when we apply their lowest probable effect on global warming.
Figure 1. The effects of Actions 1 to 4 on CO2 and NOx, represented as CO2e emissions by 2050. Source: Leeham Co. Click to enlarge.
What happens when we apply the research’s lowest probable effects of NOx and Contrails?
The 2021 report by Lee et al., which involved more than 20 researchers collaborating to condense the current understanding of air transport’s effects on global warming, lists an uncertainty range regarding the warming effects of the different greenhouse gases and warming contrails in its tables and graphs.
Figure 2 illustrates this probable effect span as dark lines, indicating a probable effect span from 5% to 95% probale effect from the item.
Figure 2. A summary of the main global warming effects of air transport. Source: Lee et al, 2021.
We now apply the lowest probable effect for NOx and warming contrails and observe the results. The result is in Figure 3.
Figure 3. The warming effects of Air Transport by 2050 with NOx and contrail effects at their lowest probable impact. Source: Leeham Co. Click to enlarge.
The effect of NOx is almost gone, with only 5% of the CO2e remaining. It’s the state of the research into the somewhat complicated effect of NOx on global warming that makes the lowest probable effect point so low. The NOx emitted from the engines undergoes a photochemical process that involves both Ozone (O3), Methane, CO, and reactive hydrogen (HOx), which have both warming and cooling effects. It’s the short-term and long-term balance between these processes that’s complicated, which results in the lowest probable effect value being low.
The warming effect from warming contrails remains significant even when applying the lowest probable effect value from the research. It accounts for 42% of total global warming from air transport, while CO2 is at 53%.
The acid test shows that even at the lowest probable effect, contrails will be a significant factor in global warming by 2050. What this all means is discussed in the next Corner, where we start to wrap things up.
“the warming effects of CO2 are undisputed”
Nonsense. There is a host of serious scientific work that shows that temperatures LEAD CO2 changes, not the other way around.