Asymmetric seasonal temperature trends

Abstract

[1] Current consensus on global climate change predicts warming trends driven by anthropogenic forcing, with maximum temperature changes projected in the Northern Hemisphere (NH) high latitudes during winter. Yet, global temperature trends show little warming over the most recent decade or so. For longer time periods appropriate to the assessment of trends, however, global temperatures have experienced significant warming trends for all seasons except winter, when cooling trends exist instead across large stretches of eastern North America and northern Eurasia. Hence, the most recent lapse in global warming is a seasonal phenomenon, prevalent only in boreal winter. Additionally, we show that the largest regional contributor to global temperature trends over the past two decades is land surface temperatures in the NH extratropics. Therefore, proposed mechanisms explaining the fluctuations in global annual temperatures should address this apparent seasonal asymmetry. Citation: Cohen, J. L., J. C. Furtado, M. Barlow, V. A. Alexeev, and J. E. Cherry (2012), Asymmetric seasonal temperature trends, Geophys. Res. Lett., 39, L04705,

Attribution of divergent northern vegetation growth responses to lengthening non-frozen seasons using satellite optical-NIR and microwave remote sensing

“…In fall, the decreasing NF days' trend coincides with a positive trend in the number of TR days, implying that the fall TR season is beginning earlier and extending over a longer period. The seasonal decrease in NF days and the corresponding increase in TR days imply regional cooling in the fall; the mechanisms for this apparent HNL cooling are uncertain but are consistent with reported increases in HNL moisture and snow cover in fall attributed to summer warming and sea ice decline (Cohen et al 2012a(Cohen et al , 2012bPark et al 2013). The recent increase in fall snow cover may promote regional cooling due to an enhanced snow-albedo feedback (Déry and Brown 2007).…”

Zonally asymmetric trends of winter total column ozone in the northern middle latitudes

“…The increased SST over the Atlantic Ocean corresponds the weakening of the Azores High. In addition, the land surface temperature derived from CRU data (Harris et al 2014) shows that Central Siberia has cooled for the period 1979-2015 (Cohen et al 2012), corresponding to the deepening of the Siberian High. It is apparent that, the surface temperature trends are in accordance with the weakening of the Aleutian Low, Icelandic Low and Azores High, and their associated height changes.…”

The dynamics of the warming hiatus over the Northern Hemisphere

“…The recent cooling over NH land (Cohen et al 2012) was reversed from the previous enhanced warming, which was probably related to the circulation change over extratropical NH (Huang et al 2012;Wallace et al 2012;He et al 2014;Huang et al 2016a;Guan et al 2015;Huang et al 2016b). As suggested by Wallace et al (1995) and He et al (2014), the land-sea thermal contrast can excite feedbacks related with circulation and induces the transition between the pattern of "cold ocean and warm land" (COWL) and "warm ocean and cold land" (WOCL).…”