Climate variability of the mid- and high-latitudes of the Southern Hemisphere in ensemble simulations from 1500 to 2000 AD

Abstract

Abstract.To increase the sparse knowledge of long-term Southern Hemisphere (SH) climate variability, we assess an ensemble of 4 transient simulations over the last 500 yr performed with a state-of-the-art atmosphere ocean general circulation model. The model is forced with reconstructions of solar irradiance, greenhouse gas (GHG) and volcanic aerosol concentrations. A 1990 control simulation shows that the model is able to represent the Southern Annular Mode (SAM), and to some extent the South Pacific Dipole (SPD) and the Zonal Wave 3 (ZW3). During the past 500 yr we find that SPD and ZW3 variability remain stable, whereas SAM shows a significant shift towards its positive state during the 20th century. Regional temperatures over South America are strongly influenced by changing both GHG concentrations and volcanic eruptions, whereas precipitation shows no significant response to the varying external forcing. For temperature this stands in contrast to proxy records, suggesting that SH climate is dominated by internal variability rather than external forcing. The underlying dynamics of the temperature changes generally point to a combination of several modes, thus, hampering the possibilities of regional reconstructing the modes from proxy records. The linear imprint of the external forcing is as expected, i.e. a warming for increase in the combined solar and GHG forcing and a cooling after volcanic eruptions. Dynamically, only the increase in SAM with increased combined forcing is simulated.

Sixty Years of Widespread Warming in the Southern Middle and High Latitudes (1957–2016)

“…Before the influence of human-induced climate change became noticeable, the climate of the Southern Hemisphere mid-and high-latitudes was controlled by natural variability as well as volcanic and solar forcing. Over the past 500 years, the most noticeable change in the climate of the extratropical Southern Hemisphere has been a shift towards the positive phase of the Southern Annular Mode (Wilmes et al 2012). A study that has a similar goal to ours, Richard et al (2013), examined temperature trends from 1973-2002 and found a robust warming in sub-Antarctic and mid-latitude stations (Orcadas, Kerguelen, Marion, etc).…”

A 308 year record of climate variability in West Antarctica

“…F10 δD has been correlated with 2 m wind fields from ERA-Interim ( Figure 3b) to confirm that warm (less negative δD) years are associated with strengthening of the meridional winds (onshore northerlies) between~50-70°S,~100-140°W (contours in Figure 3b). This pattern is maintained in the longer reanalysis data sets, including GISS [Hansen et al, 2010 [Wilmes et al, 2012].…”

The influence of volcanic eruptions on the climate of tropical South America during the last millennium in an isotope-enabled general circulation model

“…Comparatively little attention has been given to the Southern Hemisphere, or to South America specifically (although see Joseph andZeng, 2011, andWilmes et al, 2012). Some previous work has focused on the Southern Annular Mode in the ERA-40 and NCEP/NCAR reanalysis, in addition to a previous version of NASA Goddard Institute for Space Studies (GISS) Model-E (Robock et al, 2007) and in a subset of CMIP3 models (Karpechko et al, 2010) or in CMIP5 (Gillett and Fyfe, 2013).…”