Aviation needs to reduce its CO2 emissions to zero not far beyond 2050. Making people take the train instead of the plane is one of the options. I assessed the potential reduction in CO2 from intra-European aviation, by such a modal shift. Download the the study Air2Rail. Main conclusion is that 4 to 7 megaton CO2 can be avoided. This reduction corresponds with 6 to 11% of the emissions from intra-European aviation and with 2 to 4% of CO2 from flights from European airports.