REACT4C is a project that received European funding to investigate whether air traffic across the North Atlantic Ocean can be rerouted such that the resulting climate impact is reduced. The project considered 400 daily flights in each direction. Eight frequently occurring weather situations were identified, based on the strength and location of the jet stream between North America and Europe. It was found that the climate impact could be reduced to a large extent, although the impact reduction potential heavily depends on the direction of flight, the weather pattern under consideration, the climate metric used to quantify climate impact, and the relative importance of climate impact and economic cost during the optimization. The way in which climate-optimal trajectories compare to their cost-optimal counterparts, is still largely unknown. This research examines how the routes are affected by the climate optimization. Two kinds of studies are performed. The first one is a case study, in which the trajectories of one combination of direction, climate metric, weather type and level of climate optimization are compared with the cost- optimal routes. The influence of each of these four case differentiators on the flights is examined as well, using a one-factor-at-a-time approach. A tool is made that can be used to analyze the trajectories of any combination of flight direction, climate metric, weather pattern and level of climate optimization. The second study is a general analysis of the REACT4C routes, taking into account all combinations of the four case differentiators. This study is conducted to unravel general trends in the way direction, metric, weather and level of climate optimization influence the way in which flights are rerouted. The following characteristics are used to quantify how routes are altered. First, the percentage of affected flights is determined. Then, the flight duration and flight distance increments with respect to the cost-optimized flights are computed. Furthermore, the shift in latitude and altitude is also considered. Finally, frequently occurring rerouting schemes are identified, and the percentage of flights belonging to each scheme is determined. It was found in both the case study and the general analysis that the way in which climate-optimized routes compare to their cost-optimized counterparts, highly depends on the direction of flight, the weather pattern and the relative importance of economic cost and climate impact during the optimization. However, the choice of climate metric proved to have hardly any influence on the rerouting strategies. Because of the substantial cross-case differences, the preferred strategy to investigate rerouting characteristics is by making use of the case analysis tool that was created. Nonetheless, the general study unravelled some general trends. The trajectories in general are altered such that the flight duration and flight distance are increased, and the cruise altitude is lowered. Furthermore, generally there are more shifts towards the south than there are towards the north. Increasing the level of climate optimization is shown to result into more extreme route alterations. Flights towards Europe are in general more often north of the original routes than in westbound direction. The climate metric used during the optimization has little to no influence on the way the routes are changed. Finally, no trends in trajectory alterations are distinguishable between the eight weather patterns.