Conclusions

The current paradigm for Holocene climate history is that a wide array of different paleoclimatic records indicate that there have been significant changes in summer and winter temperature, seasonality, and precipitation in the past 11 500 years. Some of these changes have been gradual over millennia, others have been very rapid and have occurred at centennial or even decadal scales. Paleoclimatic records from high latitudes suggest that in these areas the major changes have been in temperature and in seasonality. Records from low latitudes suggest that there have been major changes in precipitation and in the overall hydrologic regime. There appears to have been climate variability at a wide range of temporal scales. In addition there appears to have been considerable spatial variability in climate change, particularly in moisture. The relative importance of external forcing factors such as orbital forcing, solar variability, and volcanic activity, and the complex interactions between these factors and their impacts on the Earth's climate system and its circulation and climate modes are not fully understood (Bradley 2003; Bradley et al. 2003; Labeyrie et al. 2003; Oldfield 2005). The role of human activities in determining vegetation cover and land-use and in influencing Holocene climate remains unresolved.

Global summaries of Holocene climate change now appear to be of limited relevance (Oldfield 2005). In contrast, assessments of the magnitude of changes at different latitudes are more relevant and appear to have considerable significance environmentally, ecologically, and possibly socially. This shift from global summaries attempted in the 1940s-1960s to the increasing realization of the spatial complexity of Holocene climate change has perhaps been one of the most important paradigm shifts in Holocene climate research. Holocene climate has been highly dynamic, has varied in both time and space, and has shown considerable natural variability. These temporal and spatial patterns provide the background against which recent climate changes can be compared and assessed.

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