Eurasian winter cooling in the warming hiatus of 1998-2012

In this study, we investigated the relative magnitudes of the contributions of surface temperature trends from different latitude bands to the recent warming hiatus. We 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. This cooling trend was not reproduced in an influential model study attributing most of the hiatus to cooling in the tropical Pacific (Kosaka and Xie, 2013) and hence might have different causes. Arctic sea ice loss over interannual time scales has previously been shown to influence Eurasian winter temperatures (Kim et al., 2014; Mori et al., 2014), but whether such an influence exists for the concrete hiatus period has remained unclear. To understand the drivers of this winter–cooling trend, we perform three twenty-member ensembles of simulations with different prescribed sea surface temperature and sea ice in the atmospheric model ECHAM6. Our 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.

Reference:

Kosaka, Y., and S.-P. Xie, 2013: Recent global-warming hiatus tied to equatorial Pacific surface cooling. Nature, 501, 403—407.

Kim, B. M., S. W. Son, S. K. Min, J. H. Jeong, S. J. Kim, X. D. Zhang, T. Shim and J. H. Yoon, 2014: Weakening of the stratospheric polar vortex by Arctic sea-ice loss, Nature Communications, doi:10.1038/ncomms5646.

Mori M., M. Watanabe, H. Shiogama, J. Inoue, and M. Kimoto, 2014: Robust Arctic sea-ice inuence on the frequent Eurasian cold winters in past decades, Nature Geoscience, 7, 869—873, doi:10.1038/ngeo2277.