Influence of the actual weather situation on non-CO<sub>2</sub> aviation climate effects: The REACT4C Climate Change Functions

Abstract

Abstract. Emissions of aviation include CO2, H2O, NOx, sulfur oxides and soot. Many studies have investigated the annual mean climate impact of aviation emissions. While CO2 has a long atmospheric residence time and is almost uniformly distributed in the atmosphere, non-CO2 gases, particles and their products have short atmospheric residence times and are heterogeneously distributed. The climate impact of non-CO2 aviation emissions is known to vary with different meteorological background situations. The aim of this study is to systematically investigate the influence of different weather situations on aviation climate effects over the North Atlantic region, to identify the most sensitive areas and potentially detect systematic weather related similarities. If aircraft were re-routed to avoid climate-sensitive regions, the overall aviation climate Impact might be reduced. Hence, the sensitivity of the atmosphere to local emissions provides a basis for the assessment of weather related, climate optimized flight trajectory planning. To determine the climate change contribution of an individual Emission as function of location, time and weather situation, the radiative impact of local emissions of NOx and H2O to changes in O3, CH4, H2O and contrail-cirrus was computed by means of the ECHAM5/MESSy Atmospheric Chemistry model. 4-dimensional climate change functions (CCFs) were derived thereof. Typical weather situations in the North Atlantic region were considered for winter and summer. Weather related differences in O3-, CH4-, H2O-, and contrail-cirrus-CCFs were investigated. The following characteristics were identified: Enhanced climate impact of contrail-cirrus was detected for emissions in areas with large scale lifting, whereas low climate impact of contrail-cirrus was found in the area of the jet stream. Northwards of 60° N contrails usually cause climate warming in winter, independent of the weather situation. NOx emissions cause a high positive climate impact if released in the area of the jet stream or in high pressure ridges, which induces a south- and downward transport of the emitted species. Whereas NOx emissions at, or transported towards high latitudes, cause low or even negative climate impact. Independent of the weather situation, total NOx effects show a minimum at ∼250 hPa, increasing towards higher and lower altitudes, with generally higher positive impact in summer than in winter. H2O emissions induce a high climate Impact when released in regions with lower tropopause height, whereas low climate impact occurs for emissions in areas with higher tropopause height. H2O-CCFs generally increase with height, and are larger in winter than in summer. The CCFs of all individual species can be combined, facilitating the assessment of total climate impact of aircraft trajectories considering CO2 and spatially and temporally varying non-CO2 effetcs. Furthermore they allow the optimization of aircraft trajectories with reduced overall climate impact. In most regions NOx and contrail-cirrus dominate the sensitivity to local aviation emissions. The findings of this study recommend, to consider weather related differences for flight trajectory optimization in favour of reducing total climate impact.

Climate Impact Mitigation Potential of European Air Traffic in a Weather Situation with Strong Contrail Formation

“…Climate change functions (CCFs) allow for quantifying the global climate impact of local aircraft emissions as a function of emission location and time [7,13]. The aCCFs consider both CO2 and non-CO2 effects and measure global climate impact using the average temperature response integrated over a time period of 20 years (ATR20).…”

The impact of weather patterns and related transport processes on aviation's contribution to ozone and methane concentrations from NO<sub><i>x</i></sub> emissions

“…Köhler et al (2008) identified that the emission altitude strongly influences the resulting climate impact, which is generally larger for emissions at high altitudes. Frömming et al (2012) demonstrated that the overall climate impact can be reduced by adapting flight altitudes, suggesting a possible mitigation strategy. The season in which the emission occurs also influences the resulting climate impact.…”

Predicting the climate impact of aviation for en-route emissions: The algorithmic climate change function submodel ACCF 1.0 of EMAC 2.53

“…The non-CO2 effects include ozone (O3) formation and methane (CH4) depletion (causing the primary mode ozone (PMO) and stratospheric water vapour (SWV) decrease) due to aviation NOx emissions (Stevenson et al, 2004;Köhler et al, 2013;Myhre et al, 2007), contrail-cirrus (Heymsfield et al, 2010;Burkhardt and Kärcher, 2011;Schumann and Graf, 2013;Kärcher, 2018) and their alterations by aerosols direct and indirect effects (Kärcher et al, 2007;Penner et al, 2009;Myhre et al, 2013;Chen and Gettelman, 2016), and water vapour (H2O) effect (Wilcox et al, 2012). The non-CO2 effects depend not only on the emission quantity but also on the altitude, geographical location, time, and local weather conditions (e.g., Frömming et al, 2021). Therefore, it is possible to mitigate aviation's climate impact via operational measures to avoid climate-sensitive regions associated with non-CO2 effects (Grewe et al, 2017b;Sridhar et al, 2011;Yin et al, 2018;Matthes et al, 2020).…”

“…The CCFs are 5D datasets (including longitude, latitude, altitude, time, and emission type) that describe the specific climate impacts, i.e., the average temperature change in K per flown kilometre or per emitted mass of the relevant species (NOx and H2O) locally. The high fidelity CCFs were computed for eight representative weather situations (five winter patterns and three summer patterns classified by Irvine et al (2013)) for the North Atlantic region (Frömming et al, 2021;Grewe et al, 2014a). Grewe et al (2014a) discussed the development and verification procedure of CCFs thoroughly.…”