Acknowledging that Ireland’s monastic tradition nurtured scholars who wrote in Old Irish and in Latin, and who were responsible for a vibrant literary culture that included a number of forms, such as hagiography, poetry, epic, or voyage tales (immrama), this chapter analyzes the Irish annalistic tradition for evidence of climatological data. While almost a millennium passed between a scribal entry on vellum and that entry being written on paper, available for us to examine today, it is understandable that a great deal of skepticism exists around the accuracy of the texts. The analysis relies on comparatively checking the accuracy of such narratives by paying attention to alternative historical sources, calculating dates of past eclipses, referring to ice-core records, and matching them to the dates of these events as given by the early medieval texts.