An investigation on the temperature dependence of spectroscopic parameters of trivalent thulium ions is important for the design of high-power, thulium-doped fiber lasers and amplifiers. In this Letter, the thulium absorption/emission cross sections are determined in the spectral range 700-2200 nm and in the temperature range from -196°C to 300°C. The spectra are obtained from the absorption and emission measurements of a thulium-doped fiber and from measured thulium concentration profiles. Attempts were made to estimate the temperature dependence of the spectra where the measurements are not accessible. Firstly, the spectra are fitted to a multi-Gaussian model with temperature dependent parameters. Secondly, a physically motivated model of the cross section spectra is proposed and analyzed.