The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018

Abstract

Global aviation operations contribute to anthropogenic climate change via a complex set of processes that lead to a net surface warming. Of importance are aviation emissions of carbon dioxide (CO 2 ), nitrogen oxides (NO x ), water vapor, soot and sulfate aerosols, and increased cloudiness due to contrail formation. Aviation grew strongly over the past decades (1960–2018) in terms of activity, with revenue passenger kilometers increasing from 109 to 8269 billion km yr −1 , and in terms of climate change impacts, with CO 2 emissions increasing by a factor of 6.8–1034 Tg CO 2 yr −1 . Over the period 2013–2018, the growth rates in both terms show a marked increase. Here, we present a new comprehensive and quantitative approach for evaluating aviation climate forcing terms. Both radiative forcing (RF) and effective radiative forcing (ERF) terms and their sums are calculated for the years 2000–2018. Contrail cirrus, consisting of linear contrails and the cirrus cloudiness arising from them, yields the largest positive net (warming) ERF term followed by CO 2 and NO x emissions. The formation and emission of sulfate aerosol yields a negative (cooling) term. The mean contrail cirrus ERF/RF ratio of 0.42 indicates that contrail cirrus is less effective in surface warming than other terms. For 2018 the net aviation ERF is +100.9 mW (mW) m −2 (5–95% likelihood range of (55, 145)) with major contributions from contrail cirrus (57.4 mW m −2 ), CO 2 (34.3 mW m −2 ), and NO x (17.5 mW m −2 ). Non-CO 2 terms sum to yield a net positive (warming) ERF that accounts for more than half (66%) of the aviation net ERF in 2018. Using normalization to aviation fuel use, the contribution of global aviation in 2011 was calculated to be 3.5 (4.0, 3.4) % of the net anthropogenic ERF of 2290 (1130, 3330) mW m −2 . Uncertainty distributions (5%, 95%) show that non-CO 2 forcing terms contribute about 8 times more than CO 2 to the uncertainty in the aviation net ERF in 2018. The best estimates of the ERFs from aviation aerosol-cloud interactions for soot and sulfate remain undetermined. CO 2 -warming-equivalent emissions based on global warming potentials (GWP* method) indicate that aviation emissions are currently warming the climate at approximately three times the rate of that associated with aviation CO 2 emissions alone. CO 2 and NO x aviation emissions and cloud effects remain a continued focus of anthropogenic climate change research and policy discussions.

Greater fuel efficiency is potentially preferable to reducing NOx emissions for aviation’s climate impacts

“…CO 2 accumulates in the atmosphere due to its fractional millennial timescale which means that its climate effect is determined by the cumulative emissions over time. As a consequence, the RF in 2018 from aircraft CO 2 emissions is around twice greater than that from aircraft NO x emissions 32 . However, what is even more important is the difference in the nature of their responses (Supplementary Fig.…”

Tourism, Transport and Climate Change: The Carbon Footprint of International Air Traffic on Islands

“…In this regard, the wealth created by mass air transport should also be considered not only in terms of the high GHG emissions responsible for climate change on the planet, but also in terms of large-scale air pollution [10,15]. It should not be forgotten that, despite the relative proximity of the Canary Islands to the European continent, the distances, with respect to the emitting countries, are notably greater than those of the other European archipelagos or islands such as the Greek Islands, Malta, Sardinia, or the Balearic Islands.…”

“…Consequently, socioeconomic factors are the key to explaining the increase in the use of this transport, as well as investment in the tourism sector [6]. On a continental scale, Asia is the continent that has grown the most in air connections and, therefore, in polluting emissions [10].…”

Air traffic and contrail changes during COVID-19 over Europe: A model study

“…Contrails induced by water vapor and soot emissions from aircraft flying in cold and humid air masses are responsible for a large part of the climate impact of aviation (Lee et al, 2021). Contrails cause positive longwave (LW) and negative shortwave (SW) instantaneous radiative forcing (RF) components at top-of the atmosphere (TOA) (Meerkötter et al, 1999).…”

“…A positive net effect (sum of LW and SW contributions) induces a warming of the Earth-atmosphere system. Contrails and aircraft engine emissions interact with the atmosphere in a complex manner and not all aspects are well understood Kärcher, 2018;Lee et al, 2021). For example, contrails and aviation induced aerosols affect ambient cirrus clouds, potentially causing negative RF (Lee et al, 2010;Penner et al, 2018).…”