The Warmest December and Winter
Figure 1 graphs December temperature history in New Hampshire going back to 1895, the earliest year for which we have good records.2 Although nine of the ten warmest Decembers occurred since 1980, the most recent year stands out: December 2015 was 13.7 degrees Fahrenheit above the twentieth-century average; it topped the second-warmest December (2006) by 3.7 °F and the third-warmest (2001) by 4.6 °F. Temperatures here are expressed as anomalies, or degrees above or below the twentieth-century average for this month, which is indicated by a gray line in the figure.
Erratic swings from year to year simply reflect weather, or short-term variability. For example, the cold Decembers of 1917 and 1989 were both followed by relatively warm Decembers the next year. The smoother curve in Figure 1, however, reflects climate change, or shifts in the longer-term average.3 Average temperatures warmed gradually in the early twentieth century, paused from the 1940s to early 1970s, then took off more steeply in the mid-1970s. This rise–pause–rise pattern is a signature of twentieth-century global change seen in many parts of the world.4
Figure 2 shows average temperature anomalies for New Hampshire cold seasons (December through March) from 1895–1896 to 2015–2016.5 Although the 2015–2016 anomaly was less extreme than December 2016 by itself, this was still the warmest winter in 121 years, and more than 8 °F above
the twentieth-century average.
The Granite State Poll, conducted by the Survey Center at the University of New Hampshire, carries out landline and mobile telephone interviews with random samples of New Hampshire residents about four times each year. Survey questions mostly focus on current issues and politics, but they also include questions on the environment and science.6 In February 2016, soon after the record December weather, the poll tested what people recalled:
Thinking back a couple of months, would you say that LAST DECEMBER, New Hampshire weather was generally colder, warmer, or about average?
- Colder than average for a New Hampshire December
- Warmer than average for a New Hampshire December
- About average for a New Hampshire December
The top half of Figure 3 charts the results from 687 interviews. Although unusually warm temperatures and lack of snow had many impacts on everyday life and were widely discussed in weather reports and the news media, two months later only 63 percent of respondents recalled that December 2015 had been warmer than average. Fifteen percent thought it had been about average, and 6 percent said they did not know. Sixteen percent thought the month had been colder than average for a New Hampshire December. A similarly worded question on the April 2016 survey asked about the winter as a whole.
Thinking back over the past few months, would you say that LAST WINTER, New Hampshire weather was generally colder, warmer, or about average?
- Colder than average for a New Hampshire winter
- Warmer than average for a New Hampshire winter
- About average for a New Hampshire winter
As charted in the bottom half of Figure 3, the 502 April survey respondents did somewhat better with this question. Seventy-three percent accurately recalled that the winter just ending had been warmer than average. Only 10 percent thought it was average, and 14 percent said colder.
Who Recalls a Warm Season?
It seems reasonable to wonder whether temperature on the day of interviews influenced what people recall about past weather. Some previous studies have reported daily-temperature effects on beliefs about climate change, but no temperature effects on winter-weather recollections appear in these data.7 Figure 4 illustrates by graphing daily temperatures over the February survey dates, together with percentages responding that December had been warm.8 Average temperatures were well above freezing on three of the ten survey dates, but the percentage of “warm December” responses was not systematically higher on those days.
Figure 5 looks at other variations in the rates of accurate responses.9 Bars depict percentages of people who thought that either December or the winter had been warmer than average. To show general patterns, February and April surveys are combined in this graphic.
Eighteen- to 29-year-olds were less likely to recall the warm month or season, although age-group differences fall short of statistical significance.10 Men and women appear virtually tied. Recollections of recent warmth appear stronger among married people, and respondents who have children living at home. Perhaps parents noticed more often because the weather affected outdoors activities and there were fewer school cancellations.
The two lower panels in Figure 5 show impacts from political orientation and climate-change beliefs. These differences are modest in size (13 or 14 percentage points) but statistically significant, and go in directions consistent with other research on perceptions about climate and local weather. Political independents and Tea Party supporters less often thought that December 2015 or winter 2015–2016 had been warmer than average. Respondents who agree with the scientific consensus that climate is changing due to human activities were more likely to recall the warm season.11
Weather and Climate
As average temperatures rise, the frequency of unusually warm conditions rises and the frequency of unusually cold conditions declines.12 During the era of steeper warming since 1975, only eleven New Hampshire winters (December through March) were below the twentieth-century average, whereas thirty-one were above it. The rising proportion of warm winters is another sign that New Hampshire climate is changing along with global climate.13
Figure 6 compares the smoothed trend of global temperatures with that of New Hampshire winters.14 Both curves exhibit the pattern of early twentieth-century warming, mid-century pause, and post-1975 takeoff, which is a signature of global change. But New Hampshire winters have warmed since 1975 at more than twice the global rate, with broad consequences for everything from winter recreation to forest ecosystems and insects.
Upward trends tell one part of the story, but New Hampshire’s gradual warming is not the only thing that made December 2015 so extreme. Other factors contributed too, in ways that should become clearer as we gain perspective over the next few years. Unusually warm conditions occurred in many parts of the world in late 2015 and were partly attributed to El Niño, the warm phase of an ocean-atmosphere oscillation.15 In 2015–2016, the El Niño effects were added to those of global warming, and the combination helped set new global records. Correlations between El Niño and New Hampshire temperatures are not clear-cut, however. There are no significant differences in average New Hampshire temperatures during El Niño, La Niña, and neutral winters (climatologically defined as December through February). For example, globally stronger El Niño conditions occurred around 1982–1983 and 1997–1998 without extreme Granite State weather.
Although research has convinced most active scientists that humans are changing Earth’s climate,16 many politicians, political commentators, and a large fraction of the U.S. public reject this conclusion. Climate-change questions prove to be some of the most politically divisive items on surveys.17 Over the seven years that we have been asking such questions in New Hampshire, public agreement that human-caused climate change is real has risen gradually, from the low 50s in 2010 to about 65 percent in April 2016.18 Ideological divisions have narrowed somewhat, although they still remain wide. Directly experienced shifts in the weather, such as the growing frequency of warm rather than cold winters, may play a role in persuading nonscientists that climate is indeed warming.
Many studies have noted correlations between political orientation and climate-change beliefs.19 Political orientation and climate beliefs also affect perceptions about climate-related physical realities, whether these are scientific measurements such as CO2 levels20 or personally experienced events like weather.21 These studies often take a long-term perspective, appropriate for the study of climate. Our study, in contrast, simply asked about the warmth or coldness of a past month or season, just after both set records. Most respondents accurately recalled the recent warmth, but statistically significant differences in accuracy occurred with respect to marital status, parenthood, political orientation, and climate-change beliefs. The marital and parenthood effects might be practical, reflecting such things as heightened awareness from participating in outdoors activities.
The political and climate-belief effects on winter recollections seen in Figure 5 are significant but not large. Much larger gaps, but in similar directions, have been observed by other studies that asked about longer-term trends. Questions about multidecade trends more clearly evoke people’s thoughts about climate change, whether the topic is global, such as Arctic sea ice,22 or local, such as fire-season warming in eastern Oregon23 or flood damage in New Hampshire.24 Responses to our very short-term December/winter weather questions suggest that even on such an immediate, local, and directly experienced scale, beliefs exert some influence on perceptions.
1. The first blooms began the second week of March in southern New Hampshire.
2. Statewide New Hampshire temperature anomalies here are defined from the unweighted average of National Oceanic and Atmospheric Administration (NOAA) climate divisions 1 and 2, which together cover the whole state. Such calculations can easily be replicated, or performed for other regions, using data from the NOAA website: http://www.ncdc.noaa.gov/monitoring-references/maps/us-climate-divisions.... A more nuanced calculation could use area-weighted averages, which yield slightly different numbers but support the same general conclusions.
3. The smoothed curve is calculated by lowess regression, a statistical technique often used to reveal patterns in rapidly varying data. For an explanation see L.C. Hamilton, Statistics with Stata, Version 12 (Belmont, CA: Cengage, 2013).
4. Intergovernmental Panel on Climate Change, Climate Change 2013—The Physical Science Basis: Summary for Policy Makers (Geneva, Switzerland: IPCC, 2013).
5. Climatologists ordinarily define northern winter as the months of December, January, and February. In New Hampshire the cold season, often with snow on the ground, generally lasts through March as well. Because this longer cold season is what most New Hampshire residents understand and experience as winter, we employ the term “winter” in this brief to mean the months of December through March.
6. L.C. Hamilton, “Do You Trust Scientists About the Environment? News Media Sources and Politics Affect New Hampshire Resident Views” (Durham, NH: Carsey School of Public Policy, 2014), http://scholars.unh.edu/carsey/213/; L.C. Hamilton, “Conservative and Liberal Views of Science: Does Trust Depend on Topic?” (Durham, NH: Carsey School of Public Policy, 2015), http://scholars.unh.edu/carsey/252/.
7. L.C. Hamilton and M.D. Stampone, “Blowin’ in the Wind: Short-Term Weather and Belief in Anthropogenic Climate Change,” Weather, Climate,
and Society 5, no. 2 (2013):112–19,
L.C. Hamilton and M. Lemcke-Stampone, “Arctic Warming and Your Weather: Public Belief in the Connection,” International Journal of Climatology 34 (2014):1723–28, doi: 10.1002/joc.3796.
8. New Hampshire average daily temperatures are approximated for Figure 4 by taking the average each day from the stations of record, which are at Durham, Keene, Hanover, and First Connecticut Lakes. In any given part of the state, temperatures could have been colder or warmer, but they probably followed a similar up and down pattern.
9. A standard question about Tea Party support was not asked in some of the February interviews, so those are not counted for the political party analysis; Significance tests for Figure 5 are based on F tests from probability-weighted logit regression of warm/not warm responses on the independent variable (age, gender, party, etc.) in each chart.
10. Respondent ages are grouped to make a readable bar chart in Figure 5, but the grouping does not affect basic conclusions. Even in continuous form, from 18 to 96 years, age does not significantly influence responses about the warm weather.
11. The climate question asks whether people think that climate change is happening now, caused mainly by human activities; happening now but caused mainly by natural forces; not happening now; or they just don’t know.
12. National Academies of Sciences, Engineering, and Medicine, Attribution of Extreme Weather Events in the Context of Climate Change (Washington, DC: National Academies Press, 2016), doi: 10.17226/21852, http://www.nap.edu/catalog/21852/attribution-of-extreme-weather-events-i....
13. C.P. Wake et al., Climate Change in Northern New Hampshire: Past, Present, and Future, Climate Solutions New England Report (Durham: Sustainability Institute at the University of New Hampshire, 2014a), http://sustainableunh.unh.edu/sites/sustainableunh.unh.edu/files/images/... C.P. Wake et al. Climate Change in Southern New Hampshire: Past, Present, and Future, Climate Solutions New England Report (Durham: Sustainability Institute at the University of New Hampshire, 2014b), http://sustainableunh.unh.edu/sites/sustainableunh.unh.edu/files/images/....
14. The smoothed trends are calculated by lowess regression; see note 3.
15. National Oceanic and Atmospheric Administration, El Niño Theme Page (2016), http://www.pmel.noaa.gov/tao/elnino/nino-home.html.
16. J. Cook et al., “Consensus on Consensus: A Synthesis of Consensus Estimates on Human-Caused Global Warming,” Environmental Research Letters 11, no. 4 (2016), doi:10.1088/1748-9326/11/4/048002.
17. Hamilton (2014).
18. Updated from L.C. Hamilton et al., “Tracking Public Beliefs About Anthropogenic Climate Change,” PLOS ONE 10, no. 9 (2015): e0138208, doi: 10.1371/journal.pone.0138208.
19. S.T. Marquart-Pyatt et al., “Politics Eclipses Climate Extremes for Climate Change Perceptions,” Global Environmental Change 29 (2014): 246–57, doi: 10.1016/j.gloenvcha.2014.10.004.
20. L.C. Hamilton, “Did the Arctic Ice Recover? Demographics of True and False Climate Facts,” Weather, Climate, and Society 4, no. 4 (2012): 236–49, doi: 10.1175/WCAS-D-12-00008.1.
21. M.J. Cutler, “Seeing and Believing: The Emergent Nature of Extreme Weather Perceptions,” Environmental Sociology 1, no. 4 (2015): 293–303, doi: 10.1080/23251042.2015.1085117; P.D. Howe and A. Leiserowitz, “Who Remembers a Hot Summer or a Cold Winter? The Asymmetric Effect of Beliefs About Global Warming on Perceptions of Local Climate Conditions in the U.S.,” Global Environmental Change 23, no. 6 (2013): 1488–1500, doi: 10.1016/j.gloenvcha.2013.09.014; W. Shao, “Are Actual Weather and Perceived Weather the Same? Understanding Perceptions of Local Weather and Their Effects on Risk Perceptions of Global Warming,” Journal of Risk Research (2015), doi: 10.1080/13669877.2014.1003956.
22. L.C. Hamilton, “Polar Facts in the Age of Polarization,” Polar Geography 38, no. 2 (2015): 89–106, doi:10.1080/1088937X.2015.1051158.
23. L.C. Hamilton et al., “Wildfire, Climate, and Perceptions in Northeast Oregon,” Regional Environmental Change (2016), doi: 10.1007/s10113-015-0914-y.
24. L.C. Hamilton et al., “Flood Realities, Perceptions, and the Depth of Divisions on Climate,” Sociology (2016), doi: 10.1177/0038038516648547.