Reconstructions of past glaciations tell us about how ice sheets grow and retreat. In this study, we use speleothems (cave deposits, e.g. stalagmites) in the British Isles to help constrain the extent of past glaciations in both time and space. Speleothems require liquid water to grow, and therefore their presence indicates the absence of ice above the cave. By dating these speleothems, we can improve existing reconstructions of past ice sheets.

During at least two phases in its past, Earth was more or less covered in ice. These “snowball Earth” events probably started suddenly upon undercutting a certain threshold in the carbon-dioxide concentration. This threshold can vary considerably under different conditions. In our study, we find the thresholds for different distributions of continents, geometries of Earth’s orbit, and volcanic eruptions. The results show that the threshold might have varied by up to 46 %.