DOI: 10.25921/gpwe-4v32
title: NOAA/WDS Paleoclimatology - Hessl - Khorgo Lava Pine - PISI - ITRDB MONG039

description: Although many studies have associated the demise of complex societies with deteriorating climate, few have investigated the connection between an ameliorating environment, surplus resources, energy, and the rise of empires. The 13th-century Mongol Empire was the largest contiguous land empire in world history. Although drought has been proposed as one factor that spurred these conquests, no high-resolution moisture data are available during the rapid development of the Mongol Empire. Here we present a 1,112-y tree-ring reconstruction of warm-season water balance derived from Siberian pine (Pinus sibirica) trees in central Mongolia. Our reconstruction accounts for 56% of the variability in the regional water balance and is significantly correlated with steppe productivity across central Mongolia. In combination with a gridded temperature reconstruction, our results indicate that the regional climate during the conquests of Chinggis Khan's (Genghis Khan's) 13th-century Mongol Empire was warm and persistently wet. This period, characterized by 15 consecutive years of above-average moisture in central Mongolia and coinciding with the rise of Chinggis Khan, is unprecedented over the last 1,112 y. We propose that these climate conditions promoted high grassland productivity and favored the formation of Mongol political and military power. Tree-ring and meteorological data also suggest that the early 21st-century drought in central Mongolia was the hottest drought in the last 1,112 y, consistent with projections of warming over Inner Asia. Future warming may overwhelm increases in precipitation leading to similar heat droughts, with potentially severe consequences for modern Mongolia. 
description: Purpose of Collection: 
# Climatology - precipitation
# 
# Additional Reference:
# van der Schrier, G., J. Barichivich, K.R. Briffa, and P.D. Jones. 2013. 
# A scPDSI-based global data set of dry and wet spells for 1901-2009.
# J. Geophys. Res. Atmos., 118, 4025-4048, doi:10.1002/jgrd.50355.
# 
# Notes:
# Cores and cross-sections from living and dead Siberian pine were collected in 2010 and 2012 
# across the Khorgo lava field near Tariat, Mongolia. The trees were collected from soils that 
# were either thin or absent soils surrounded by dark basalt. 
# 
# Forty-four percent or more of these trees had some form of strip-bark. This morphology can 
# enhance short and long-term trends in tree ring widths as growth is focused to the living 
# portion of strip-bark trees. In fact, we find that strip-bark Siberian pine on the Khorgo 
# lava field had positive ring widths over the first 150-300 years of ring-width formation 
# while non strip-bark Siberian pine showed the common decline over the first 150-300 years 
# of ring-width formation (Pederson, Hessl, et al., 2014; PNAS). Not removing these trends 
# can cause long-term trends in the final tree-ring chronology from these trees that might 
# not reflect climatic trends. Please see Pederson, Hessl, et al. (2014) for further discussion 
# of the issue with this collection. 
# 
# As of February 2014, we are only sure of the dating of this record back to about 750 CE. 
# These data are likely correctly dated further back in time, but in this setting Siberian pine 
# experiences occasional missing rings and produces some false rings that look very real. 
# Our experience indicates that we need 10-20 Siberian trees in these settings to ensure 
# we have captured all false or missing rings. For this reason, users of this data set should not 
# use the data prior to 750 CE. Also, we cut off this record at 900 CE because tree replication 
# might limit recovery of 'true' climatic variation. We used all these series in this data set 
# to recover as much long-term variation during standardization from 900 CE to the present.
#  NOAA Template Raw Measurements file added 2019-04-08.