Climatic history of the northeastern United States during the past 3000 years

Abstract

Abstract. Many ecosystem processes that influence Earth system feedbacks -vegetation growth, water and nutrient cycling, disturbance regimes -are strongly influenced by multidecadal-to millennial-scale climate variations that cannot be directly observed. Paleoclimate records provide information about these variations, forming the basis of our understanding and modeling of them. Fossil pollen records are abundant in the NE US, but cannot simultaneously provide information about paleoclimate and past vegetation in a modeling context because this leads to circular logic. If pollen data are used to constrain past vegetation changes, then the remaining paleoclimate archives in the northeastern US (NE US) are quite limited. Nonetheless, a growing number of diverse reconstructions have been developed but have not yet been examined together. Here we conduct a systematic review, assessment, and comparison of paleotemperature and paleohydrological proxies from the NE US for the last 3000 years. Regional temperature reconstructions (primarily summer) show a long-term cooling trend (1000 BCE-1700 CE) consistent with hemispheric-scale reconstructions, while hydroclimate data show gradually wetter conditions through the present day. Multiple proxies suggest that a prolonged, widespread drought occurred between 550 and 750 CE. Dry conditions are also evident during the Medieval Climate Anomaly, which was warmer and drier than the Little Ice Age and drier than today. There is some evidence for an acceleration of the longer-term wetting trend in the NE US during the past century; coupled with an abrupt shift from decreasing to increasing temperatures in the past century, these changes could have wide-ranging implications for species distributions, ecosystem dynamics, and extreme weather events. More work is needed to gather paleoclimate data in the NE US to make inter-proxy comparisons and to improve estimates of uncertainty in reconstructions.

Hydrological and temperature variations between 1900 and 2016 in the Catskill Mountains, New York, USA

“…Pederson et al (2013) show that the pluvial between around 1970 and 2012 may be unprecedented in our region during the last 500 years, even when compared to the early 1900s; that the period of 1901-1907 is among the top 10 pluvial events in the Catskill watershed in the past 500 years; but, in contrast, that the 1960s drought may be comparable to 16th and 17th century droughts of similar duration and magnitude. Marlon et al (2017) demonstrate that the recent trend toward warmer and wetter conditions is a reversal of millennial-scale trends prior to the 1800s, and also that seasonal differences have been prominent for at least 3,000 years.…”

“…For example, the precipitation gauge records indicate that the first five or so years of the 20th century were as wet as, or wetter than, the recent period, while in the stream gauge record and a previously published tree ring analysis (Pederson et al, 2013), the first few years of the 20th century appear wet, but not as wet as the recent period. Taken in the context of paleoclimate reconstructions based on proxy data over hundreds (Pederson et al, 2013) or thousands (Marlon et al, 2017) of years, it appears that some aspects of recent hydroclimatic variations are unusual or unique.…”

“…Over longer time scales, tree ring records suggest that the northeastern United States has gradually become wetter over the past 3,000 years (Marlon et al, 2017). In the Catskills, the wet period that followed the drought of the 1960s and continues into the 21st century appears to be unprecedented over the past 500 years (Pederson et al, 2013).…”

The potential role of intrinsic processes in generating abrupt and quasi‐synchronous tree declines during the Holocene

“…A key challenge to such approaches is the scarcity of colocated paleohydrological proxy data for the Holocene (Marlon et al 2017), although this is improving, particularly for the last two millennia (Rodysill et al 2018, Shuman et al 2018). An additional challenge is the simultaneous statistical fitting of multiple taxa from multiple sites, accounting for potential differences among taxa and, for the same taxon, differences in dynamics among sites.…”

“…For instance, theoretical work has explored potential mechanisms for the discrepancy between rapid northward expansion after glacier retreat and the measured dispersal ability of species (Reid's paradox; Kot et al 1996, Clark 1998, Moorcroft et al 2006). Dynamic vegetation models, widely used to study past and future forest dynamics during periods of environmental change, are a promising avenue for studying Holocene tree collapses, but they face the challenges of significant uncertainties and not-yet-reconciled disparities among observational and modeled time series of precipitation variability during the Holocene (Marlon et al 2017). Given the rich literature modeling population dynamics in other systems that exhibit abrupt population collapses (Carpenter et al 1999, Scheffer and Carpenter 2003, Mumby et al 2007, Ives et al 2008, Staver and Levin 2012, process-based community modeling approaches are promising, yet heretofore largely unexplored avenues for understanding the multiple factors contributing to mid-Holocene tree declines and community stability (Clark and McLachlan 2003).…”