In order to face the challenges in machining difficult-to-cut materials as nickel and titanium alloys, many cooling methods have been developed through the years, among which is the usage of supercritical carbon dioxide (scCO2). By combining the cooling provided by the expansion of the CO2 jet, and the scCO2 solvent properties (for dissolving lubricants), it is possible to reach higher tool life and productivity, with respect to the other classical cooling methods. The purpose of this study is to compare the Background Oriented Schlieren (BOS) method with thermocouple measurements in the context of CO2 jets, whether in liquid or supercritical state. A typical BOS setup using an enlightened background pattern and a high-speed camera was used to determine the temperature of CO2 jets. While the trend of BOS centerline temperature aligns with that of the thermocouple measurements, there exist noticeable disparities between them. These discrepancies average around 20°C in favourable instances and can reach up to 60°C in the most extreme cases. These findings underscore the need to continue the investigation to identify areas for improvement. This pursuit is essential to achieve accurate results for using this method in the development of future temperature models for CO2 jets.