The inventories of global anthropogenic emissions of mercury for years from 1979/1980 to 1995 suggest a substantial reduction in the 1980s and almost constant emissions afterwards. In contrast to emission inventories, measurements of atmospheric mercury suggest a concentration increase in the 1980s and a decrease in the 1990s. Here we present a first attempt to reconstruct the worldwide trend of atmospheric mercury concentrations from direct measurements since the late 1970s. In combination, long term measurements at 6 sites in the northern, 2 sites in the southern hemispheres, during 8 ship cruises over the Atlantic Ocean (1977--2000) provide a consistent picture, suggesting that atmospheric mercury concentrations increased in the late 1970s to a peak in the 1980s, then decreased to a minimum at about 1996, and have been nearly constant since. The observed trend is not consistent with the published inventories of anthropogenic emissions and the assumed ratios of anthropogenic/natural emissions, and suggests the need to improve the mercury emission inventories and to re-evaluate the contribution of natural sources.