Extensive astrophysical measurements, most notably from the COBE satellite, confirm that the cosmic microwave background exhibits a blackbody spectrum corresponding to a temperature of approximately 2.725 Kelvin.
The claim is a specific, empirical scientific statement about the temperature and spectral nature of the cosmic microwave background. Papers such as [5] and [10] directly report the measured blackbody temperature of the CMB near 2.73 K, and modern measurements refine this to 2.725 K as supported by subsequent literature like [2]. There are no papers refuting this well-established cosmological consensus.