Has the Northern Hemisphere been warming or cooling during the boreal winter of the last few decades?

The Intergovernmental Panel on Climate Change (IPCC) reported a significant rise of the global mean surface temperature over the last 100 years, with a rate of warming over the last few decades almost double that over the last 100 years. The rate of warming is higher at land surfaces over the Northern Hemisphere (NH), and particularly extreme warming is occurring over the Arctic. In spite of the global warming trend, some asymmetries have been observed. In a recent study, a widespread cooling over the NH during the boreal winter season was reported, although other previous studies observed a warming during this season. In this paper we report trends in winter air temperatures over the mid- to high-latitudes of the NH in the last three decades (1980–2012) using different climatic datasets at different spatial resolution (ERA-Interim, NCEP/NCAR, CRUTEM4, GHCN). Results extracted from the different datasets are consistent and show a neutral to moderate warming trend in the winter season during the last three decades. Greenland is an exception, where widespread and significant warming is observed in this time period.