A two-dimensional (2-D) model in which dynamics, radiation and chemistry are treated interactively is used to investigate the seasonal changes in tropospheric ozone due to current nitrogen oxide emissions from aircraft and to assess the associated radiative forcing on the climate system. Our results confirm the high efficiency of nitrogen oxide in-situ emissions in producing ozone in comparison to surface emissions. The ozone increase is characterized by a strong seasonal variation; it reaches more than 7% during summer in the upper troposphere at northern mid-latitudes. On a global average basis, the radiative forcing associated with this ozone increase appears to be small in comparison to that of other greenhouse gases. However, it may play a significant role in the anthropogenic forcing on northern hemisphere climate. ¿ American Geophysical Union 1994