Does the location of aircraft nitrogen oxide emissions affect their climate impact?

We present results from 112 one-year global chemistry-transport model integrations: a base case, then variants with extra aircraft nitrogen oxide (NOx) emissions added to specific regions in the first month (July). The NOx stimulates ozone (O3) production and methane (CH4) destruction. Responses vary spatially: low background NOx regions are most sensitive. Integrated (100-year time horizon) radiative forcings (IRF) are calculated. Net (O3 + CH4) IRFs for July aviation NOx are generally negative: the global average, weighted by emissions, is −1.9 mWm−2 yr (TgNO2)−1. The positive IRF associated with the short-term O3 increase (4.1 mWm−2 yr (TgNO2)−1) is overwhelmed by the effects of the long-term CH4 decrease. Aircraft NOx net IRFs are spatially variable, with July values over the remote Pacific approximately balancing the IRF associated with aviation CO2 emissions (28 mWm−2 yr (TgNO2)−1). The overall climate impact of global aviation is often represented by a simple multiplier for CO2 emissions. These results show that this is inappropriate.