Cheung, W. W. L., Pauly, D., and Sarmiento, J. L. 2013. How to make progress in projecting climate change impacts. – ICES Journal of Marine Science, 70: 1069–1074. Scientific modelling has become a crucial tool for assessing climate change impacts on marine resources. Brander et al. criticize the treatment of reliability and uncertainty of such models, with specific reference to Cheung et al. (2013, Nature Climate Change, 3: 254–258) and their projections of a decrease in maximum body size of marine fish under climate change. Here, we use the specific criticisms of Brander et al. (2013, ICES Journal of Marine Science) on Cheung et al. (2013) as examples to discuss ways to make progress in scientific modelling in marine science. We address the technical criticisms by Brander et al., then their more general comments on uncertainty. The growth of fish is controlled and limited by oxygen, as documented in a vast body of peer-reviewed literature that elaborates on a robust theory based on abundant data. The results from Cheung et al. were obtained using published, reproducible and peer-reviewed methods, and the results agree with the empirical data; the key assumptions and uncertainties of the analysis were stated. These findings can serve as a step towards improving our understanding of climate change impacts on marine ecosystems. We suggest that, as in other fields of science, it is important to develop incrementally (or radically) new approaches and analyses that extend, and ultimately improve, our understanding and projections of climate change effects on marine ecosystems.