The current best-estimate of the global annual mean radiative forcing (RF) attributable to contrail
cirrus is thought to be 3 times larger than the RF from aviation’s cumulative CO2 emissions. Here, we simulate
the global contrail RF 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
, 95 % confidence interval). Regionally, the contrail net RF is largest over Europe (876 mW m−2
)
and the USA (414 mW m−2
), while the RF values over East Asia (64 mW m−2
) and China (62 mW m−2
) are
close to the global average, because fewer flights in these regions form persistent contrails resulting from 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,
relative to 2019) and 2021 (−31 % and −49 %, respectively) with significant regional variations. Around 14 % of
all flights in 2019 formed a contrail with a net warming effect, yet only 2 % of all flights caused 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, engine particle number emissions, tropopause height, and background
radiation fields. Our contrail RF estimates are most sensitive to corrections applied to the global humidity fields,
followed by assumptions on the engine particle number emissions, and are least sensitive to radiative heating
effects on the contrail plume and contrail–contrail overlapping. Using this sensitivity analysis, we estimate that
the 2019 global contrail net RF could range between 34.8 and 74.8 mW m−2.