if trees could talk - west virginia university · amy e. hessl professor of geography west virginia...
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If Trees Could Talk:The Climate History Stored in the Rings of Trees
Amy E. HesslProfessor of Geography
West Virginia University
Climate
TreesHistory
Tree rings are not just a bit of dead wood…
• Annually dated - can be tied to historical events• Integrate climate over large areas• ‘Naturalistic’ recorders - sensitive
to the same variables as people, crops, and animals • Center of human action - trees
grow where people act
Genghis Khan and the Mongol Empire
Genghis Khan’s Mongol Empire: 1206-1227Energetics of Empire
Second Invasion of Poland (1259)
Crossdating: precision dating
14C Content in Tree Rings Confirm Annual Precision Globally
Büntgen, Hessl, et al. 2018. Nature Communications.
Moisture History of the Mongols
MongolPluvial
1180sDrought
Pederson, Hessl et al. 2014 PNAS
Mongol Military Strength and Tactics
Grassland Productivity >> Horsepower• 5 mounts for every warrior• 100,000 warriors per
campaign• Food supply to support
troops
Year725 750 775 800 825 850
Year
−20
2scPD
SI
Silk
Uyghur Cities
Uyg
hur C
olla
pse
Khar BalgasBaibalyk Por Bazhyn
Di Cosmo, Hessl et al. 2018
Uyghur Empire
In the game of rapid climate change…
• Energy & Mobility• Exploited elevated grassland productivity• Concentrate energy (horsepower)• Mobilize military forces• Build infrastructure
• Innovation & Migration• Uyghur innovated for 60 years of drought • Ultimate collapse and mass migration to China
How can climate history inform us about today’s changing climate?
Ancient Trees and Antarctic Ice:Time Machines for Southern Hemisphere Climate
Bloo Campbell
Scott Nichols
MRD03A1204-1536 CE
0.4
0.8
1.2
1.6
050
150Ooze Lake
0.0
0.5
1.0
1.5
050
150Moonlight Ridge
0.4
0.8
1.2
1.6
050
150
Inde
x
Sam
ple
Dept
h
Abrotonella
0.8
1.2
050
150King Billy Saddle
0.7
0.9
1.1
1.3
050
150Mesa
0.7
0.9
1.1
1.3
100
200
300
400
500
600
700
800
900
1000
1100
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1300
1400
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1600
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050
150
Year
Reservoir Lakes
Southern Annular Mode(Antarctic Oscillation)
Trees
Ice
Hessl et al 2018
SAM is the SH ‘Arctic Oscillation’
SAM is trending positive…
• Poleward shift of the SH jet
• Reduced rainfall and higher
temperatures in midlatitudes
• Causes: Ozone depletion &/or
greenhouse gas warming???
After Marshall 2003 J. Climate
1960 1970 1980 1990 2000 2010 2020
−1.5
−0.5
0.5
1.5
Year
Mar
shal
l SAM
2000 Years of SAM
• What factors affected SAM movements in the past?
• Why does the SAM behave differently from Arctic Oscillation?
• How will warming temperatures affect the SAM?
Climate Scientists to Follow on Twitter
@Khayhoe – Dir. Climate Science Center at Texas Tech (101k)@DrKateMarvel – Columbia/NASA (18.4k)@JacquelynGill – Paleoclimate (43.1k)@HeidiCullen – Communications Director MBARI (20.5k)@coralsncaves (Kim Cobb) Georgia Tech (13.1k)@GretaThunberg – 16yo climate activist (372k)