Evidence from ecological studies, eddy flux towers and satellites shows that many tropical forests ‘green up’ during higher sunlight annual dry seasons, suggesting they are more limited by light than water. Morton et al. reported that satellite-observed dry-season green up in Amazon forests is an artefact of seasonal variations in sun-sensor geometry. However, here we argue that even after artefact correction, data from Morton et al. show statistically significant increases in canopy greenness during the dry season.