Session: Last Millennium & Past2K
Author: Kamolphat Atsawawaranunt / K.Atsawawaranunt@reading.ac.uk / University of Reading
Co-author: Sandy P. Harrison, University of Reading;
I. Colin Prentice, Imperial College London;
Climate changes during the Last Millennium were insufficient to cause major changes in vegetation distribution, but did cause changes in vegetation productivity that are documented e.g. in peatland accumulation rates. We use a light-use efficiency model, the P model, to simulate changes in gross primary productivity driven by outputs from an ensemble of CMIP5/PMIP3 Last Millennium simulations. Temporal changes in GPP reflect changes in light (PAR) modulated by changes in cloud cover, atmospheric drought as reflected by vapour pressure deficit (VPD), growing season temperature and CO2. The relative importance of these factors varies spatially. For example, while the effect of increasing CO2 is always positive, the impact of such changes is larger in more arid regions because it enhances water-use efficiency. Although the differences in simulated climate between the Medieval Warm Anomaly (MWA: 1000-1200 CE) and the Little Ice Age (LIA: 1600-1800 CE) only resulted in moderate changes in GPP globally, regional differences can be large and thus should be discernable in palaeorecords. Despite broadscale similarities in GPP changes between members of the ensemble, there are differences between the individual simulations. Thus, comparison of the simulated temporal and spatial patterns in GPP with palaeoenvironmental records should allow discrimination between different models and different forcings. Furthermore, the impact of large volcanic events is seen in the simulated GPP, again offering the potential to evaluate the realism of alternative forcings and individual model responses.