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SUMMARY:Large CO2 emissions from pre-industrial land use change – Does t
 he carbon budget add up? - Benjamin Stocker. Department of Life Sciences\,
  Imperial College London
DTSTART:20160512T163000Z
DTEND:20160512T173000Z
UID:TALK65539@talks.cam.ac.uk
CONTACT:Della Murton
DESCRIPTION:CO2 emissions from preindustrial land use change (LUC) are sub
 ject to large uncertainties with model-based estimates ranging from 60 to 
 360 GtC (Olofsson and\nHickler\, 2008\; Pongratz et al.\, 2009\; Kaplan et
  al.\, 2011\; Stocker et al.\, 2011). Thus\, early anthropogenic impacts r
 ose to significance between 7-3 kyr BP depending on reconstruction and may
  have altered the natural carbon (C) cycle and climate states to a degree 
 that would lend support for the definition of a correspondingly\nearly ons
 et of the Anthropocene. However\, the reconstructed parallel evolution of 
 atmospheric CO2 and its 13C-signature indicate only 36+/-37 Gt loss of ter
 restrial C during the last 5 millennia (Elsig et al.\, 2009). It has been 
 argued that this is the result of compensating effects of large LUC emissi
 ons and C sequestration in northern peatlands\, which is estimated to be o
 n the same order as upper-end estimates of\npreindustrial LUC (Ruddiman an
 d Ellis\, 2009). \n\nHere\, we combine updated observation-based and model
 -based reconstructions of peat C buildup (∆Cpeat) and model-based LUC em
 ission estimates for a range of\nrecently published reconstructions (Kapla
 n et al.\, 2009\; Klein Goldewijk and Verburg\, 2013) and accounting for c
 hanging land management regimes over time and space.\nUsing the independen
 t constraint on the total terrestrial C budget from ice core measurements 
 of CO2 and d13C (∆Ctot)\, we assess the compatibility of different LUC\n
 scenarios with ∆Ctot and ∆Cpeat.\n\nThis reveals that large LUC emissi
 ons required to explain the observed CO2 rise between 7 and 5 kyr BP canno
 t be reconciled with ∆Ctot and ∆Cpeat unless a large additional terres
 trial sink is invoked. Furthermore\, this analysis points to the importanc
 e of other\, non-anthropogenic impacts for explaining the ~150 Gt terrestr
 ial C source between 5 and 2 kyr BP\, where scenarios suggest emissions of
  only 20-50 GtC. More highly resolved ice core (Bauska et al.\, 2015) and 
 peat C balance data (Charman et al.\, 2013) covering the last millennium f
 urther reveals that only extreme assumptions on the extent of post-Columbi
 an reforestation in the Americas can close the C budget between 1500 and 1
 650 CE and that upper-end scenarios of preindustrial LUC are incompatible 
 with the C budget between 1760 and 1920 CE.
LOCATION:Thirkill Room\, Clare College
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