Global surface temperature have risen during the past century, which in turn has altered Winter Climate , but it is still uncertain whether human activty is responsible for Global Warming in particular regions of the planet. The largest warming has occurred over the Northern Hemisphere were Winter Climate data has seen some warming. Historical Temperatures have risen by several degrees during the 20th century. (In comparison, the global, annual average temperature has increased by only half a degree).

These dramatic local changes are related to recent shifts in atmospheric wind patterns during the course of the winter. It is more likely that they arise from a redistribution of heat around the globe, rather than purely from an enhanced "greenhouse effect", whereby heat is trapped near Earth's surface by pollutants such as CO₂. The question, is  the Global Climate Change another aspect of the windshift or merely part of a long term cycle of whether they are linked to the increasing greenhouse effect.

Wind speeds in the Northern U.S and Southern Canada during the winter months are strongly correlated with sea-level pressure. Historical variations of sea-level pressures have been studied intensely. The dominant pattern of Northern Hemisphere change, is referred to as the Arctic Oscillation (AO) . The AO is an extension of the more familiar North Atlantic Oscillation to all longitudes, including the North Pacific. Variability of these two oscillation patterns is highly correlated. The AO is the second largest climate cycle on Earth, after the El Niño/La Niña cycle. Strengthened westerly winds at midlatitudes bringing warm, wet air over northern Europe/Asia and North America occur during the positive phase of the AO, corresponding to a decrease in high-latitude sea-level pressure and an increase in midlatitude sea-level pressure.

For more information on this topic and global climate change, go to Nasa's Goddard Institute for Space Studies web site.