There is currently a drive to operate proton exchange membrane fuel cells at temperatures above 80 degrees C. To achieve this, all aspects of the fuel cell need to be investigated to ensure that performance and durability are maintained. In this work we systematically investigated carbon corrosion from 70 degrees C to 120 degrees C and 40 and 70 % relative humidity (RH). The investigation was done by cyclic voltammetry up to 1.4 V vs RHE with simultaneous mass spectrometry measurements to quantify the produced carbon dioxide. The obtained results were modelled to differentiate the effects of temperature, water partial pressure and different types of carbon corrosion. The results show that the carbon corrosion is mainly affected by the water partial pressure, which increases exponentially with temperature if RH is kept constant. This explains why an increase of temperature (at constant humidity) and an increase of humidity (at constant temperature) lead to faster corrosion kinetics. With current materials, to contrast the effect of the water partial pressure, the upper cell voltage limit in operation must be lowered. The combination of temperatures above 100 degrees C with high relative humidity at high voltage requires material improvement or additional mitigation strategies to avoid excessive carbon corrosion.