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SUMMARY:Anthropogenic land cover change in the last millennium - a GCM stu
 dy on the effects on climate and the carbon cycle
DTSTART:20090323T161500
DTSTAMP:20260922T014107Z
UID:b576240fbaecd3042defa8a0375c0ad0fa2cb92d5b9d73a0200e6cdb
CATEGORIES:Conferences - Seminars
DESCRIPTION:Julia Pongratz\, Max Planck Institute for Meteorology\, German
 y\nAnthropogenic land cover change (ALCC) represents one of the most subst
 antial human impacts on the Earth system\, altering land surface propertie
 s and carbon fluxes. In this study\, the role of ALCC for climate and the 
 carbon cycle are assessed for the last millennium using a complex climate 
 model. A special focus is placed on the preindustrial period\, for which o
 nly few studies exist. First\, a population-based method is developed to r
 econstruct spatially explicit changes in global agricultural areas and the
  resulting ALCC over the last millennium. This reconstruction is applied t
 o calculate radiative forcing (RF) from ALCC-induced surface albedo change
 s. While RF is found to be small throughout the preindustrial period on th
 e global scale (negative with a magnitude less than 0.05 W/m2)\, an early 
 anthropogenic impact on the energy balance is found for the regional scale
 .  In transient coupled climate simulations the effects of ALCC are isolat
 ed by applying ALCC as the only climate forcing. Primary emissions are qua
 ntified to 53-61 Gt C and 108 Gt C over the preindustrial and the industri
 al period\, respectively. A high restorage of carbon by the biosphere due 
 to the coupling to climate and atmospheric CO2 occurs over the preindustri
 al period (48% of the primary emission). The rise of CO2 caused by ALCC th
 erefore remains lower than suggested e.g. by the “early anthropogenic hy
 pothesis”\, but still becomes significant with 5-6 ppm prior to the Indu
 strial Revolution. Historic events such as epidemics and warfare are found
  unlikely to be the cause for drops in ice-core CO2. Global mean temperatu
 re increase due to ALCC amounts to 0.13-0.15 K in the 20th century\, but r
 emains within natural variability in the preindustrial era. A simulation i
 s performed to quantify the contribution from only the biogeophysical effe
 cts of ALCC in addition to the full climate response. Biogeophysical effec
 ts are found to contribute a weak cooling (-0.03 K in the 20th century). T
 he rise in CO2 from ALCC emissions is therefore the driving force of the s
 imulated global warming.
LOCATION:GR B30
STATUS:CONFIRMED
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