Unexpected cooling Eurasia during February of global-warming slowdown: Roles of North Atlantic and Arctic Oceans

Abstract

The latest global mean surface temperature (GMST) indices from several datasets all show a significant warming trend during the so-called period of global-warming slowdown (i.e., 1998–2012), albeit at a more modest rise compared with the satellite era in the 20th century. Via the Mann-Kendall trend test, this study further examined the trend of GMST from a monthly perspective. It is surprising to find that a significant negative trend occurs only in February and the robust cooling is most evident in the mid–high latitudes of Eurasia. Then an empirical orthogonal function (EOF) based on multi-sources data (MS-EOF) was applied on the February surface air temperature (SAT) over Eurasia. Focus is given on the characteristics and factors of the leading MS-EOF mode (MS-EOF1), as in the trend pattern, which features a uniform cooling mode dominating the mid–high latitudes of Eurasian continent. The key circulation features a large-scale eastward-shift North Atlantic Oscillation (NAO)-like pattern, which is, in a negative phase, favourable for weakening the polar-front jet stream and transporting cold air from the Arctic regions to the mid-high latitudes of Eurasian continent. Relevant precursor signals can be traced back to the anomalous North Atlantic sea surface temperature (SST) and Barents–Kara sea ice in the preceding autumn, together contributing significantly to the cooling February over middle- to high-latitude Eurasia and is verified by a linear baroclinic model. This finding emphasizes the important contribution of cooling February to the famous global-warming slowdown.