Volcanic cooling signal in tree ring temperature records for the past millennium

Abstract

Tree rings are an important proxy for understanding the timing and environmental consequences of volcanic eruptions as they are precisely dated at annual resolution and, particularly in tree line regions of the world, sensitive to cold extremes that can result from climatically significant volcanic episodes. Volcanic signals have been detected in ring widths and by the presence of frost-damaged rings, yet are often most clearly and quantitatively represented within maximum latewood density series. Ring width and density reconstructions provide quantitative information for inferring the variability and sensitivity of the Earth's climate system on local to hemispheric scales. After a century of dendrochronological science, there is no evidence, as recently theorized, that volcanic or other adverse events cause such severely cold conditions near latitudinal tree line that rings might be missing in all trees at a given site in a volcanic year (“stand-wide” missing rings), resulting in misdating of the chronology. Rather, there is a clear indication of precise dating and development of rings in at least some trees at any given site, even under adverse cold conditions, based on both actual tree ring observations and modeling analyses. The muted evidence for volcanic cooling in large-scale temperature reconstructions based at least partly on ring widths reflects several factors that are completely unrelated to any misdating. These include biological persistence of such records, as well as varying spatial patterns of response of the climate system to volcanic events, such that regional cooling, particularly for ring widths rather than density, can be masked in the large-scale reconstruction average.