A new data set of global marine air temperature data for the years 1807--1827 is used to show the impact of volcanic eruptions in ~1809 (unlocated) and 1815 (Tambora, Indonesia). Both eruptions produced cooling exceeding that after Krakatoa, Indonesia (1883) and Pinatubo, Philippines (1991). The ~1809 eruption is dated to March--June 1808 based on a sudden cooling in Malaysian temperature data and maximum cooling of marine air temperature in 1809. Two large-scale calibrated proxy temperature records, one from tree-ring-density data, the other using multi-proxy sources are compared to the marine air temperature data. Correlation is highest with maximum latewood density data and lowest with the multi-proxy data. ¿ 2001 American Geophysical Union