Ship-borne ozone (O3) measurements over the Atlantic Ocean during the period from 1977 to 2002 show that O3 trends in the northern mid-latitudes are small. In contrast, remarkably large O3 trends occur at low latitudes and in the Southern Hemisphere, where near-surface O3 has increased by up to a factor of 2. The likely cause is the substantial increase of anthropogenic emissions of nitrogen oxides (NOx) associated with energy use in Africa, which has added to NOx from biomass burning and natural sources.