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We examine the effect of photodarkening-induced pump light absorption on Yb-doped fiber thermal loading. In these experiments, the fiber is cladding pumped at 915 nm, air cooled by natural convection, and monitored with a midinfrared thermal camera. The fiber temperature is found to correlate with progressive photodarkening. The maximum observed fiber temperature was 120 [degrees]C, recorded at a pump power of 10.5 W. The observed increase in fiber temperature can be explained by a model that takes into account the combined effects of the Yb-silica quantum defect, the temperature dependence of the Yb-absorption cross section, and photodarkening-induced loss at 915 nm. We hypothesize that the latter effect results in the progressive activation of temperature-dependent photochemical processes (e.g., bleaching) and is ah important consideration with regard to the accurate modeling of Yb-doped fiber photodarkening kinetics. OCIS codes: 140.3510, 160.5690, 140.6810, 140.3615.