Anthropogenic land cover change in the last millennium - a GCM study on the effects on climate and the carbon cycle
Event details
| Date | 23.03.2009 |
| Hour | 16:15 |
| Speaker | Julia Pongratz, Max Planck Institute for Meteorology, Germany |
| Location |
GR B30
|
| Category | Conferences - Seminars |
Anthropogenic land cover change (ALCC) represents one of the most substantial human impacts on the Earth system, altering land surface properties 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 only few studies exist. First, a population-based method is developed to reconstruct spatially explicit changes in global agricultural areas and the resulting ALCC over the last millennium. This reconstruction is applied to calculate radiative forcing (RF) from ALCC-induced surface albedo changes. While RF is found to be small throughout the preindustrial period on the 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 isolated by applying ALCC as the only climate forcing. Primary emissions are quantified to 53-61 Gt C and 108 Gt C over the preindustrial and the industrial period, respectively. A high restorage of carbon by the biosphere due to the coupling to climate and atmospheric CO2 occurs over the preindustrial period (48% of the primary emission). The rise of CO2 caused by ALCC therefore remains lower than suggested e.g. by the “early anthropogenic hypothesis”, but still becomes significant with 5-6 ppm prior to the Industrial Revolution. Historic events such as epidemics and warfare are found unlikely to be the cause for drops in ice-core CO2. Global mean temperature increase due to ALCC amounts to 0.13-0.15 K in the 20th century, but remains within natural variability in the preindustrial era. A simulation is performed to quantify the contribution from only the biogeophysical effects of ALCC in addition to the full climate response. Biogeophysical effects are found to contribute a weak cooling (-0.03 K in the 20th century). The rise in CO2 from ALCC emissions is therefore the driving force of the simulated global warming.
Practical information
- General public
- Free
Contact
- A. Berne