The room-temperature Raman spectra of aragonite and dolomite have been recorded up to 30 GPa and 25 GPa respectively and no phase changes were observed during compression, at variance with calcite. The effect of temperature on the room-pressure Raman spectra of calcite, aragonite and dolomite is reported up to 700-900 K. The measured relative pressure and temperature-shifts of the Raman lines are greater for the lattice modes than for the internal modes of the CO3 groups. These shifts are used to calculate the mode anharmonic parameters of the observed Raman modes; they are negative and their absolute values are smaller (close to 0) for the internal CO3 modes than for the lattice modes (4-17 10(-5) K-1).