An overview of tree-ring width records across the Northern Hemisphere

This review describes the structure and characteristics of the Northern Hemisphere tree-ring width network, and examines the associations between these data and key aspects of local climate and the global climate system. Even though all ring-width records describe the same aspect of tree growth, there are major regional differences in the nature and clarity of climate information preserved within these data across the hemisphere. In North America, many chronologies record climate variability during the growing season but winter precipitation also exerts a considerable and sometimes dominant control on tree-ring formation. Almost all ring-width records from Europe and Asia reflect the influence of climate during summer, with the effects of temperature being more prominent than precipitation. Mapping teleconnection patterns associated with major climate modes show that ENSO and the AMO have stronger and more consistent effects on tree growth than do the PDO, PNA, and NAO. The ENSO teleconnection, which seems to be communicated principally through its effect on winter precipitation, is evident within the highest number of ring-width records overall and is particularly strong in western North America. The AMO's expression in ring width is consistent across drought sensitive-records from the American Southwest and central Rocky Mountains, which may reflect its influence on moisture flux into the western interior of North America during summer. In comparison, the ring-width responses to the PDO, PNA, and NAO are less spatially coherent across the network and appear be connected through a more complex chain of causes linking climate modes, local climate and seasonal tree growth. Because the Northern Hemisphere ring-width network is now so large, it is more crucial than ever to ensure our understanding of tree-environment relations is not influenced by decisions to include or exclude certain records. As an initial step, it would be helpful if paleoclimate reconstructions derived from tree rings described more explicitly the criteria used to select ring-width records as potential predictors and specified those records excluded by that screening.