Temperature Covariance in Tree Ring Reconstructions and Model Simulations Over the Past Millennium

Abstract

Spatial covariance in the simulated temperature evolution over the past millennium has been reported to exceed that of multiproxy‐based reconstructions. Here we use tree ring‐based temperature reconstructions and state‐of‐the‐art climate model simulations to assess temporal changes in Northern Hemisphere intercontinental temperature covariance during the last 1000 years. Tree ring‐only approaches reveal stronger agreement with model simulations compared to multiproxy networks. Although simulated temperatures exhibit a substantial spread among individual models, intercontinental temperature coherency is mainly driven by the cooling of large volcanic eruptions in 1257, 1452, 1600, and 1815 Common Era. The coherence of these synchronizing events appears to be elevated in several climate simulations relative to their own unforced covariance baselines and in comparison to the proxy reconstructions. This suggests that some models likely overestimate the amplitude of abrupt summer cooling in response to volcanic eruptions, particularly at larger spatial scales.

Large-scale, millennial-length temperature reconstructions from tree-rings

“…4). Periods of increased variance have been shown to coincide with severe post-volcanic cooling events that synchronize temporal variance changes between continental scale temperature reconstructions and model simulations (Hartl-Meier et al, 2017).…”

Differing pre-industrial cooling trends between tree rings and lower-resolution temperature proxies

“…These reconstructions offer defensible characterizations of pre-instrumental, naturally forced climate variability at annual resolution and millennial timescales (Christiansen and Wanner et al, 2008Wanner et al, , 2015, which is essential for placing anthropogenic warming in a long-term context. Proxy data themselves provide valuable climate information needed to test and verify paleoclimate model simulations (Braconnot et al, 2012;Fernández-Donado et al, 2013;Hartl-Meier et al, 2017;Ljungqvist et al, 2019, PAGES Hydro 2k Consortium, 2017PAGES 2k-PMIP3 group, 2015). The PAGES2k database is a product of a community effort organized by PAGES (http://pastglobalchanges.org, last access: 1 April 2020), to amass the world's largest collection of proxy records covering the Common Era (CE) (PAGES2k Consortium, 2017).…”

Reconciling the Discrepancy of Post-Volcanic Cooling Estimated from Tree-Ring Reconstructions and Model Simulations over the Tibetan Plateau

“…The anomalous decrease in summer temperatures resulting from large volcanic eruptions do not only affect crop productivity [3], but could also be a main cause for dynasty collapses [4,5]. Therefore, quantitative estimations of the cooling magnitude driven by large volcanic eruptions have drawn great attention from climatologists in recent decades [1,2,[6][7][8][9]. The magnitudes of post-volcanic cooling that occurred in the pre-instrumental period are usually estimated using either proxy-based temperature reconstructions or climate model simulations.…”

“…The magnitudes of post-volcanic cooling that occurred in the pre-instrumental period are usually estimated using either proxy-based temperature reconstructions or climate model simulations. However, the two approaches often produce inconsistent magnitudes of post-volcanic cooling, especially for large tropical eruptions (e.g., the cooling magnitude after the 1815 Tambora eruption) [6][7][8][9]. Mann et al (2012) [6] suggested that the divergence is a result of underestimation by tree-ring-based reconstructions [6], but other studies argued that the divergence could originate from the overestimation of model simulations [7,9].…”