The historical climate record includes periods of strong surface cooling after major volcanic eruptions. The cooling effect is caused when the most explosive eruptions emit substantial sulfur dioxide to the stratosphere, causing an elevated stratospheric aerosol layer that scatters more solar radiation back out to space.

In contrast to preceding decades, the 1960s period had a series of such large magnitude explosive eruptions, but the amount of SO2 each emitted is highly uncertain, and the magnitude of the stratospheric aerosol enhancement included in climate models is mainly based on solar radiation measurements from the ground.

This presentation analyses recently recovered balloon measurements of the 1965-68 stratospheric aerosol layer, progressing from a recent analysis of the 1963-1965 post-Agung period. Both analyses are part of a data recovery activity within the APARC 'Stratospheric Sulfur and its Role in Climate' activity ( https://www.sparc-ssirc.org/data/datarescueactivity.html ), whose aims are to combine stratospheric aerosol measurements with models to improve the representation of volcanic impacts in climate models.