Food security, climate change and their complex and uncertain interactions are a major challenge for societies and ecologies (1). Global assessments of projected changes in crop yields under the effect of climate change, combined with the dynamics of international trade, suggest that disparities between countries in food production and availability will intensify (2). But climate change has already affected productivity. For example, weather factors led to a decline in world corn and wheat production of 3.8% and 5.5%, respectively, between 1980 and 2008 (3). On page 979 of this issue, Free et al. (4) report a comprehensive analysis showing a 4.1% decline in overall marine fisheries productivity between 1930 and 2010, with some of the larger ecoregions producing fish recording losses of up to 35%. Their spatial mapping can help inform future planning and adaptation strategies.