My (limited) understanding is that sensitivity due to CO2 changes is a well-understood and non-disputed fact while the sensitivity due to feedbacks in the clima

My (limited) understanding is that sensitivity due to CO2 changes is a well-understood and non-disputed fact while the sensitivity due to feedbacks in the climate system is unknown and effectively an "input" into climate models. It is the feedback sensitivity parameter that is the source of dispute between supporters of 'catastrophic global warming' theory and 'skeptics' who believe the feedback is much smaller than the values used in the models. It isn't clear from the article if the new claim is challenging the understanding of CO2 sensitivity, or the choice of feedback sensitivity.