Using inelastic neutron scattering techniques, the temperature dependence of spin waves propagating in the two-dimensional easy-plane ionic ferromagnet Rb2CrCl4 have been measured between 5.3 and 62.7K at three wavevectors in the ( zeta zeta 0) direction: with zeta =0.1, 0.25 and 0.4, and at one wavevector in the ( zeta 00) direction: zeta =0.15. At all wavevectors discrete spin waves are observed to persist above the Curie temperature, Tc approximately 53K. As the temperature increases from 5.3K it is found that the low-energy, long-wavelength, spin waves renormalise more rapidly than those at higher energy. The system should provide a good test of recent theories of spin wave renormalisation.