Reconstructions of past climate on the basis of tree rings may miss the short-lived cooling events caused by volcanic eruptions, reports a paper published online this week in Nature Geoscience. The work suggests that, in particular, the tree-ring-based reconstructions may be missing cooling linked to the ad 1258-1259 eruption of an unidentified volcano.Tree-ring chronologies are often collected from regions that are at or near the minimum temperature for tree growth. Michael Mann and colleagues used numerical simulations of climate and tree growth to show that when temperatures fall abruptly for one or two growing seasons, trees in these regions undergo little or no growth. The resultant lack of a tree ring corresponding to the period of cooling thus masks the climate event in subsequent reconstructions.These results show that a 2 °C cooling associated with the ad 1258-1259 eruption (as indicated by climate models) cannot be excluded by existing tree-ring data.