As the curtain falls on the climatological winter (December-February) of 2010-11 in the U.S., we are left shivering.
For the second year in a row, the winter temperature when averaged across the contiguous United States came in below the average temperature for the 20th century. This marks the first time since the winters of 1992-93 and 1993-94 that two winters in a row have been below the long-term normal, and it makes for the coldest back-to-back winter combination for at least the past 25 years.
Figure 1 shows the history of winter temperatures averaged across the Lower 48 as compiled by the U.S. National Climatic Data Center (NCDC) for the winters from 1895-96 through 2009-2010. Although all the data have yet to be completely processed by NCDC for the winter of 2010-11, when the final numbers are in the average winter temperature will probably fall within the oval we added at the end of the record. If it does so, it will mean that the combined average temperature for the past two winters will be colder than any two-winter combination since 1983-84 and 1984-85, and perhaps even as far back as the all-time back-to-back coldest winters of 1977-78 and 1978-79.
Figure 1. Average winter (Dec.-Feb.) temperature for the contiguous United States (data source: NCDC). The oval of the right hand side of the data series contains our guess as to the value for the winter of 2010-2011.
[Update: March 8, 2011. NCDC’s final numbers are in for winter 2011, and the U.S. winter temperature history looks like this.]
What’s global warming got to do with any of this? It is hard to say. But what we can say for sure, is that whatever influence it may have, the end product during recent winters is nothing out of the ordinary—at least as far as can be ascertained by looking at the seasonal average temperature history of the U.S.
Over the longer term (i.e. since 1895-86) there has been a statistically significant increase in the NCDC-compiled U.S. winter temperature history. And recent decades have been dominated by warmer than average winters (including many that have been much warmer than average). But as the last two winter seasons have aptly demonstrated, cold snowy winters have not been relegated to a thing of the distant past.
Whether or not all the winter warming exhibited by the NCDC-compiled record is actual warming of the broader-scale climate (there are indications/suggestions/contentions that some of the warming may result from artificial warming from microclimate or instrument changes), what is undoubtedly true is that whatever your tastes in winter may be, we are sure that you will continue to get your fill from winters to come.