the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Global aviation contrail climate effects from 2019 to 2021
Roger Teoh
Zebediah Engberg
Ulrich Schumann
Christiane Voigt
Marc Shapiro
Susanne Rohs
Abstract. The global annual mean radiative forcing (RF) attributable to contrail cirrus is comparable to the RF from aviation’s cumulative CO2 emissions. Here, we simulate the global contrail climate forcing for 2019–2021 using reanalysis weather data and improved engine emission estimates along actual flight trajectories derived from Automatic Dependent Surveillance–Broadcast telemetry. Our 2019 global annual mean contrail net RF (62.1 mW m-2) is 44 % lower than current best estimates for 2018 (111 [33, 189] mW m-2). Regionally, the contrail net RF is largest over Europe (876 mW m-2) and the US (414 mW m-2), while the RF over East Asia (64 mW m-2) and China (62 mW m-2) are close to the global mean value because fewer flights in these regions form contrails as a result of lower cruise altitudes and limited ice supersaturated regions in the subtropics due to the Hadley Circulation. Globally, COVID-19 reduced the flight distance flown and contrail net RF in 2020 (-43 % and -56 % respectively vs. 2019) and 2021 (-31 % and -49 % respectively) with significant regional variation. Around 14 % of all flights form a contrail with a net warming effect, yet only 2 % of all flights account for 80 % of the annual contrail energy forcing. The spatiotemporal patterns of the most strongly warming and cooling contrail segments can be attributed to flight scheduling factors, aircraft–engine particle number emissions, tropopause height, background cloud and radiation fields, and albedo. Our contrail RF estimates are most sensitive to corrections applied to the global humidity fields, followed by assumptions on the aircraft-engine particle number emissions, and is least sensitive to radiative heating effects on the contrail plume and contrail-contrail overlapping. Accounting for the sensitivity analysis, we estimate a 2019 global contrail net RF of 62.1 [34.8, 74.8] mW m-2.
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Roger Teoh et al.
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CC1: 'Comment on egusphere-2023-1859', Louis Meuric, 26 Oct 2023
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Hello
- It would be very useful to calculate and disseminate the ERF for each country of the northern hemisphere : there are still obvious differences (Spain / Norway)
- Moreover, a study carried out on the Tibetan plateau, where warming accelerated during the winter months at the end of the 20th century, shows that increased surface humidity leads to an increase in long-wave radiation (= heat) and can locally and temporarily raise temperatures at altitude. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2009GL037245
Is it possible to have induced ERF at an altitude between 1500 2500m ?
Thanks a lot
All the best
Louis
Citation: https://doi.org/10.5194/egusphere-2023-1859-CC1 -
CC2: 'Comment on egusphere-2023-1859', Louis Meuric, 28 Oct 2023
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Hi
the monthly distribution of the contrail coverage is slightly different from the one reported for year 2002 in the publication below, from Stuber & Forster :
https://acp.copernicus.org/articles/7/3153/2007/
page 4
but 2002 was a special year, just after september 11
Louis
Citation: https://doi.org/10.5194/egusphere-2023-1859-CC2 -
CC3: 'Comment on egusphere-2023-1859', Louis Meuric, 29 Oct 2023
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About the monthly distribution, please find another source :
https://commons.wikimedia.org/wiki/File:Contrails_1994_1995_Nasa_US_Air_Force.jpg?uselang=fr
Both statistics show a rebound in october and a high level, rather in February-April. This is important because one can link it with the first snows in october and the melting in march-april.
Louis
Citation: https://doi.org/10.5194/egusphere-2023-1859-CC3 -
CC4: 'Comment on egusphere-2023-1859', Adam Durant, 21 Nov 2023
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This is a much needed bottom up flight by flight assessment of the global annual radiative impact from aircraft contrails. The work that has gone into the analysis is impressive. Congratulations ot the authors.
One aspect that does require a little more explanation is the use of a global climate model water vapour dataset, adjusted through a statistical fit against IAGOS in situ data, to drive highly specific trajectory based analyses of radiative forcing from COCIP.
The data presented in supplementary tables shows "ratio compares the false positive and false negative rate and is computed by (NIAGOS/YHRES (%) − 1). A positive value indicates YIAGOS/NHRES (%) that the ERA5 HRES underpredicts contrails, a value of zero indicates a symmetrical false positive and false negative rate, while a negative value indicates that the ERA5 HRES overpredicts contrails."
On semantics, this metric predicts ISSR occurrence, not contrails. The FP and FN rates are hidden in the ratio. The ETS values appear quite low.
Contrail formation and persistence will be highly sensitive to the vertical distribution of water vapour in the atmosphere. Given the authors have access to all the IAGOS data, it would be helpful and instructive to present more data on TP/FP/TN/FN rates (e.g., in the vertical and also by region) and to relate this to the challenges of doing a trajectory based COCIP analysis with all the associated specifics of aircraft type, engine emissions, etc. How does water vapour uncertainty propagate into a calculation of radiative impact at the global scale? There are no errors presented on annual net RF values. What are these errors and how much is attributed to water vapour uncertainty?
Citation: https://doi.org/10.5194/egusphere-2023-1859-CC4
Roger Teoh et al.
Roger Teoh et al.
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