Using high resolution measurements of the impulsive nitrate events in polar ice as identifiers of solar proton events in the past, we have identified 19 events over the period 1561–1950 that equal or exceed the \textgreater30 MeV fluence measured during the August 1972 episode of solar proton events. The largest nitrate impulsive deposition event (and largest solar proton fluence above 30 MeV) occurred in late 1859 in time association with the Carrington flare of September 1859. The Carrington flare occurred near the central meridian of the sun; the interplanetary disturbance associated with the solar activity rapidly traveled toward the earth resulting in an extremely large geomagnetic storm commencing within 17.1 h of the visual observation of the solar flare. While this event was remarkable by itself, historical records indicate that the Carrington event was part of a sequence of solar activity as an active region traversed the solar disk. We compare the derived omni-directional solar proton fluence for the Carrington event of 1.9 × 1010 cm−2 above 30 MeV with the solar proton fluence from the past and from more recent episodes of solar activity. The Carrington event is the largest solar proton event identified in our ∼450 year period, having almost twice the \textgreater30 MeV solar proton fluence than the second largest event in 1895, and approximately four times the solar proton fluence of the August 1972 events.
