A paper in this week's Nature Geoscience by John Armitage et al. from Imperial College, investigates the different effects of climate and tectonic forcing on the transient grain size distribution of geomorphic systems, and the effect this has on stratigraphy. They explore the complexities in understanding the sedimentary record as an archive of climate change and tectonic events through a numerical model, including downstream changes in grain size distribution as a key control. Their results show, for example, that a doubling of precipitation rate in the catchment of an alluvial fan causes a sharp increase in sediment flux over a 0.5 Myr period, that doubles the length of the fan. The model produces beautiful cross-sections showing where particular grain sizes occur in an alluvial fan following different types of forcing, to understand the duration of stratigraphic responses and compare this to field examples. The authors even helpfully include the equations used in their model to try at home!