Tracing Climate-Variability: The Search for Climate Dynamics on Decadal to Millennial Time Scales

Abstract

Prognoses regarding future climate scenarios hinge on the predictive skills of climate models. They must produce reliable estimates of the future mean climate state as well as future climate variability about the mean, resulting from the interference between natural climate variability and anthropogenic perturbations of the climate system. Natural climate variability originates from interactions between components of the climate systems and from perturbations external to the climate system. To validate model-generated climate variability against the whole range of natural variability, it is necessary to gather information on the temporal progression of Holocene climate variability. Distinct spatial climate regimes (climate-variability patterns) can be extracted from climate observations and facilitate the comparison between paleoclimate reconstructions and model results. Examples of instrumental observations and proxy data demonstrate the potential of such records to trace climate regimes through time. The dominant mode of today’s climate variability in Europe — the North Atlantic Oscillation — constitutes a climate regime, that can serve to provide an expectation in assessing Holocene climate variability. First attempts to reconstruct the history of the North Atlantic Oscillation during the last 300 years or so are summarized. Volcanic eruptions and solar variability constitute important external perturbations of the climate system that account for a significant portion of natural variability.