The Earth : climate and anthropogenic interactions in a long time perspective

Abstract: The Earth is a highly complex and dynamic system. Life has shaped the entire planet and evolved in response to living conditions. Ecosystems are heavily affected by climate. Rapidly changing conditions imply considerable stress on several species and ecosystems, as well as to the most dominant species on the planet. The main focus of this thesis is to investigate climate and anthropogenic interactions with a longer time perspective, with an overall objective to learn from the past. Climate change, terrestrial carbon dynamics and biodiversity impacts are investigated, focusing on the Holocene time period. Climatic impacts on European biodiversity are apparent, with earlier spring events at rates of three to five days per decade and northward range shifts by tens of kilometres per decade for several species. However, responses vary greatly between species, resulting in temporal and spatial mismatches which are major concerns for the future. Pre-industrial human effect on terrestrial carbon cycling was investigated with a dynamic vegetation model (LPJ-GUESS). The effects of climate and atmospheric CO2 on increasing total terrestrial carbon storage were stronger than the opposite effect from land use, resulting in terrestrial carbon accumulation throughout most of the Holocene. An early substantial impact of human activities on terrestrial carbon cycling and climate is unlikely, but considerable uncertainties remain. Key uncertainties are identified: the climate effect on vegetation, the extent of human land use at temporal and spatial scale, and the land use effect on soil carbon dynamics. A new methodology for pollen-based land use reconstructions was developed, estimating temporal and spatial extents of early anthropogenic land use in north-western Europe. The impact of past land use on terrestrial carbon storage was estimated by vegetation modelling, and for the pollen based land use scheme found to result in a carbon release of about 25% of the potential total terrestrial carbon storage. A novel combination of ecosystem models was developed, and applied to reconstruct the Holocene range of European bison, a methodology which can be further used to improve range reconstructions and conservation planning for endangered species.