Arellano-Nava, B., Halloran, P. R., Boulton, C. A., Scourse, J., Butler, P. G., Reynolds, D. J., & Lenton, T. M. (2022). Destabilisation of the Subpolar North Atlantic prior to the Little Ice Age. Nature Communications, 13(1), 5008. https://doi.org/10.1038/s41467-022-32653-x
The cooling transition into the Little Ice Age (a period of bitter winters and mild summers that affected Europe and North America between the 14th and 19th centuries) was the last notable shift in the climate system prior to anthropogenic global warming. It is hypothesised that sea-ice to ocean feedbacks sustained an initial cooling into the Little Ice Age by weakening the subpolar gyre circulation; a system that has been proposed to exhibit bistability (two stable states). Empirical evidence for bistability within this transition has however been lacking. Using statistical indicators of resilience in three annually-resolved clam shell proxy records from the North Icelandic shelf, the authors of this study show that the subpolar North Atlantic climate system destabilised during two episodes prior to the Little Ice Age. This loss of resilience indicates a reduced attraction to one stable state, and a system vulnerable to an abrupt transition. The two episodes preceded wider subpolar North Atlantic change, consistent with subpolar gyre destabilisation and the approach of a tipping point, potentially heralding the transition to Little Ice Age conditions.