At room temp., CO2 is transparent in the UV at wavelengths longer than 205 nm; however, at temps. above 1000 K the CO2 absorption cross-section becomes significant in the region between 200 and 320 nm. Because CO2 is a major product of hydrocarbon combustion and because both the magnitude of the absorption cross-section and the shape of the UV absorption spectrum vary strongly with temp., measurements of UV optical absorption spectra offer the potential to infer gas temp. in combustion systems. In this paper, we demonstrate the first use of UV absorption measurements to det. temp. using five different exptl. examples to illustrate the utility in hydrocarbon combustion applications of this new temp. diagnostic strategy. (1) Transmission measurements of cw laser light at 266 nm are used to det. time-resolved temp. in shock-heated CO2. (2) Similar transmission measurements are used to infer time-resolved temp. behind a detonation wave in a pulse-detonation engine using absorption from equil. concns. of the CO2 combustion product. (3) The absorption of pulsed laser light near 226 nm is used to infer temp. in the burned gases of a premixed high-pressure methane flame. (4) Wavelength-resolved absorption of light from a broadband UV deuterium lamp is time-resolved with a kinetic spectrograph to acquire time-resolved absorption spectra illustrating the measurement of temp. in a system with changing temp. and CO2 mole fraction. (5) Time-gated, spectrally resolved transmission of a deuterium lamp is used to derive temp. at specific crank angles in a piston engine. These examples demonstrate that temp. measurements based on UV optical absorption of CO2 have good potential for use in a wide variety of hydrocarbon combustion applications.