Recent observations of coronal holes with Hinode show with unprecedented detail the launching of fast and hot jets. Many of these jets are found to coincide with the emergence of new magnetic flux, and it is generally assumed that the jets are initiated by magnetic reconnection between the new emerging flux and the existing open magnetic field. Further to this a comparison of a larger sample of jets show that about 70% of these are followed by the formation of plumes within minutes to an hour. How do we understand these events from a physical point of view? To investigate this we have carried out numerical 3D MHD experiment modeling the emergence of magnetic flux from the upper convection zone into an open magnetic flux region resembling a coronal hole. The emergence process drives the formation of a strong and highly localised current sheet. Time-dependent reconnection in the current sheet gives rise to a high-velocity jet that eventually flows along the previously open coronal field lines. Initially the jet has transition region temperature, but as time progresses it eventually exceeds the coronal temperature in the model. Investigating the development of the structure of the magnetic field, it is found that it changes in a very characteristic way, leading to a horizontal drift of the jet. The experiment also shows how the reconnection speed influences the dynamical properties of both the jet parameters and the evolution of the underlying magnetic structure. Towards the end of the experiment the jet speed decreases and leaves a large funnel-like region above the emerging flux domain with an enhanced temperature and density distribution.