Looking back on the cold, snowy winter of 2013-14 in eastern North America may tempt some to conclude that global warming has ended, never occurred, or has reversed its course. But lets remember that when considering global-scale climatic phenomena, the temperature of the Earth’s surface (including the oceans) as a whole is the relevant metric, not that of a region such as the eastern and midwestern U.S. which comprises under 10% of the Earth’s area. Global temperature patterns in January 2014 were already discussed (see “Frigid but not globally significant” under “Climate” at this site) and the pattern resembles that of March.
March 2014 was the fourth coldest March on record (starting in 1880). Departures of the March temperatures from the average values for the Earth are presented in the map from NOAA’s National Climatic Data Center. Note how eastern North America stands out, especially the northern portions. There is no other region anywhere on Earth that was as cold relative to long-term averages. In contrast, the vast land area of Siberia and adjacent Asia, Australia, and the much smaller but densely populated Europe, experienced above-average temperatures.
Although not depicted on the map, note that additional small land areas and sizable blocks of the North and South Atlantic Ocean saw record-setting warmth. Also the Indian Ocean and large areas of the tropical Pacific Ocean were much warmer than average. Overall, the areas with above-average temperatures were an order-of-magnitude higher than areas with below average temperatures. In reviewing this map keep in mind that the baseline for comparison is the mean temperature since 1981, a recent year when global warming is likely to have already been underway.
From a longer-term perspective it’s interesting to see how March has varied over the period of record (see second figure).
There’s not much doubt that within this period, the Earth north and south of the equator has been in a warm phase and has been for nearly the past half-century. Of course, even at the global scale, there is year-to-year temperature variation related to influences such as the strength and periodicity of el Nino events (particularly as this affects ocean heat storage), atmospheric pressure dynamics in the Arctic, volcanism, and sunspot cycles.
Will coming years counter-balance the recent cold years in eastern North America? This is not known for certain, of course, but computer model-based simulations suggest that over the coming decades the answer most likely is yes. Despite this, increased understanding of the dynamics of the Polar Vortex and the Arctic Oscillation suggests that over the next several years, continued colder-than-average temperatures may be in the offing in eastern North America. But again, if this is what happens, it will not indicate that global warming has ceased.