The main information transmission limitation in optical communications employing SiO2 optical fibres is imposed by the optical pulses temporal broadening, resulting from the dispersive properties of the transmission medium (chromatic dispersion). Usually, this dispersion is modelled assuming a -0.4 meV/degrees C dependence of the 11 eV gap energy. We have monitored the 4.3 eV absorption band, with temperature and obtained a thermal dependence of -0.026 meV/degrees C. With this value we can predict the first and second order chromatic dispersion for a wavelength of 1550 nm.