 |
| Titel |
Preindustrial agriculture and the carbon cycle - a GCM study on the beginning of the Anthropocene |
| VerfasserIn |
J. Pongratz, C. H. Reick, T. Raddatz, M. Claussen |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024060
|
|
|
|
|
|
| Zusammenfassung |
| From the current state of knowledge, it is still undecided whether humankind had a
significant impact on the carbon cycle and the climate already in preindustrial times. We
address this question with state-of-the-art GCM simulations of the last millennium, coupling
the atmosphere, ocean, and the land surface including a closed carbon cycle. This setup also
applies a spatially explicit, population-based reconstruction of anthropogenic land cover
change (ALCC) and quantifies the carbon source and sink terms associated with
ALCC.
Primary emissions until the industrialization (ADÂ 1850) sum up to 53Â Gt C. Nearly
half of these emissions are, however, stored back in the terrestrial biosphere due to
land-atmosphere coupling. After ocean uptake, this leaves an airborne fraction of only 21%.
Despite the low airborne fraction, atmospheric CO2 rises above natural variability by late
medieval times. This suggests that human influence on CO2 began prior to industrialization.
Global mean temperatures, however, are not significantly altered until the strong population
growth in the 19th century.
We further investigate the effects of historic events such as epidemics and warfare on the
carbon budgets. Only long-lasting events such as the Mongol invasion are found to lead to
carbon sequestration. The reasons for this are indirect emissions from past ALCC that
compensate carbon uptake in regrowing vegetation for several decades. Concurrent
emissions from other parts of the world further contribute to atmospheric CO2.
Drops in CO2 that have been reconstructed from ice core records are thus unlikely
to be attributable to human action. Our results indicate that climate-carbon cycle
studies for present and future centuries, which usually start from an equilibrium
state around 1850, start from a significantly disturbed state of the carbon cycle. |
|
|
|
|
|
|