The evolution of the plasma environment of comet 67P/Churyumov-Gerasimenko (CG) the target comet of the European Space Agency's (ESA) Rosetta mission is investigated as the comet approaches the Sun. The plasma environment is calculated in three dimensions with a hybrid plasma model. The model treats the dynamics of the solar wind protons and the cometary ions in the framework of the macroparticle approach while the electrons are treated as a massless, charge-neutralizing fluid. The simulation starts at 4.2AU and finishes at 1.3AU, when the comet is at its perihelion position. Two dimensional contour plots of the absolute value of the cometary ion mass flux and the magnetic field in the orthogonal plane of the interplanetary magnetic field are shown. The undisturbed solar wind flows from left to right. The convective electric field points downwards. The nucleus is in the middle of the simulation box. The coma is assumed to consist of water vapor and it increases by several orders of magnitude as the comet approaches the Sun. Therefore, the size of the simulation box is adapted as an animation above the contour plots shows.