Climate change is more pronounced in boreal forests than in other terrestrial ecosystems, and thus aboveground biomass and species composition of boreal forests have already been altered by increasing temperature and precipitation. There are substantial uncertainties in predicting aboveground biomass and species composition of boreal forests in response to climate change since the uncertainty in climate change predictions. This makes it challenging to design forest management strategies for promoting boreal forests to adaption climate change. In this study, we designed a factorial experiment and a model coupling framework to quantify the sensitivity of aboveground biomass and species composition of boreal forests in response to climate change. Our results showed that the uncertainties in temperature and precipitation predictions caused the divergent responses of aboveground biomass and species composition to climate change in the boreal forests of northeastern China. Aboveground biomass of boreal forests is more sensitive to precipitation than temperature. There are divergent responses of tree species to temperature and precipitation over the 21^st century. This suggests that it is necessary to quantify and reduce the uncertainty in climate change predictions through statistical analysis methods before applying the predictions from general circulation models (GCMS) to study the effects of climate change on forest ecosystems.