Climate Variability in Comprehensive Climate Simulations at the Beginning of the Common Era over Europe

Abstract:

The climate of the Common Era has yet been studied, albeit with an overall focus on the last millennium. Here we present an analysis for the period 100 BC until 300 AD. The results are based on three simulations with comprehensive climate models, the coupled atmosphere-ocean model ECHO-G (T30) and a recent simulation with the Earth System Model MPI-ESM-P (T63). The ECHO-G simulations are forced (i) only with changes in earth orbital parameters and (ii) additional solar and greenhouse gas forcings, respectively. The MPI-ESM-P simulation additionally includes the effect of volcanic activity.

In all simulations summer temperatures show a quite stable temperature level, albeit with a slight negative trend caused by a decline in shortwave insolation due to changes in earth orbit. During the 2^nd half of the 3^rdcentury AD the MPI-ESM-P simulation shows a decline in temperatures. Since this negative temperature excursion is not evident in the ECHO-G simulations, which does not include volcanic forcing, it seems plausible that a large-size tropical volcanic eruption is responsible for this cooling event. Interestingly, the historical prominent eruption of the Vesuvius in 79 AD is not clear-cut reflected within the European temperature time series, most likely because of the small amount of injections of sulfate aerosols into the stratosphere.

In comparison to the only orbitally forced ECHO-G simulation, the additionally solar and GHG forced ECHO-G simulation indicates some externally forced decadal variability connected to solar anomalous periods. Overall, the MPI-ESM-P simulation shows largest decadal variability compared to the ECHO-G simulations, most probably due to the increased horizontal resolution.

Further analysis will include a comparison with proxy data with an overall emphasis on hydrological variations. For this task, a number of Regional Climate Model simulations will be used to downscale these global simulations and obtain better insight in the interactions between large and local scales. All these simulations present a great potential for pseudo-proxy and forward modelling experiments, allowing assessments of real-world applications and their limitations towards spatially resolved gridded temperature and hydrological reconstructions.