The authors confirm from five different global datasets that the global-mean surface temperature trend in the period 1998–2012 is strongly influenced by a pronounced Eurasian winter cooling trend (Fig. 1). This cooling trend was not reproduced in an influential model study attributing most of the hiatus to cooling in the tropical Pacific and hence might have different causes.
Arctic sea ice loss over interannual time scales has previously been shown to influence Eurasian winter temperatures, but whether such an influence exists for the concrete hiatus period has remained unclear. To understand the drivers of this winter-cooling trend, in their paper the authors perform three twenty-member ensembles of simulations with different prescribed sea surface temperature and sea ice in the atmospheric model ECHAM6.
Their experimental results suggest that the Arctic sea-ice loss does not drive systematic changes in the northern-hemisphere large-scale circulation in the past decades. The observed Eurasian winter cooling trend over 1998–2012 arises essentially from atmospheric internal variability and constitutes an extreme climate event. However, the observed reduction in Arctic sea ice enhances the variability of Eurasian winter climate and thus increases the probability of an extreme Eurasian winter cooling trend.
The work was supported by the Cluster of Excellence ‘CliSAP’, Universität Hamburg, funded through the German Science Foundation (DFG), and by the Max Planck Society for the Advancement of Science. All model simulations were carried out on the supercomputing system of the German Climate Computing Center (DKRZ).
Li, C., B. Stevens, and J. Marotzke (2015): Eurasian winter cooling in the warming hiatus of 1998-2012. Geophysical Research Letters, doi: 10.1002/2015GL065327.
Dr. Chao Li
Max Planck Institute for Meteorology
Phone: +49 (0) 40 41173 458
With kind permission from the MPI-M