Global Temperature Trend Upate: December 2010 - Warmest Year Or Not?
Every month University of Alabama in Huntsville climatologists John Christy and Roy Spencer report the latest global temperature trends from satellite data. Below are the newest data updated through December, 2010. Last year finishes in a statistical tie with 1998 as the warmest year in the past 32 years. As Spencer notes: 1998 (+0.424 deg. C) barely edged out 2010 (+0.411 deg. C), but the difference (0.013 deg. C) is nowhere near statistically significant.
Global climate trend since Nov. 16, 1978: +0.14 C per decade
December temperatures (preliminary)
Global composite temp.: +0.18 C (about 0.32 degrees Fahrenheit) above 30-year average for December.
Northern Hemisphere: +0.21 C (about 0.38 degrees Fahrenheit) above 30-year average for December.
Southern Hemisphere: +0.15 C (about 0.26 degrees Fahrenheit) above 30-year average for December.
Tropics: -0.22 C (about 0.40 degrees Fahrenheit) below 30-year average for December.
November temperatures (revised):
Global Composite: +0.27 C above 30-year average
Northern Hemisphere: +0.37 C above 30-year average
Southern Hemisphere: +0.17 C above 30-year average
Tropics: -0.12 C below 30-year average
(All temperature anomalies are based on a 30-year average (1981-2010) for the month reported.)
Notes on data released Jan. 6, 2011:
2010 finished in a photo finish with 1998 for the warmest year in the 32-year satellite temperature record, according to Dr. John Christy, professor of atmospheric science and director of the Earth System Science Center at The University of Alabama in Huntsville. 2010 was only 0.013 C cooler than 1998, an amount that is not statistically significant.
Both 1998 and 2010 were years in which an El Nino Pacific Ocean warming event raised temperatures around the globe. In recent months a La Nina Pacific Ocean cooling event has been building; temperatures in the tropics were cooler than seasonal norms for both November and December.
Annual Global Average Anomaly
(Warmest to Coolest)*
1. 1998 +0.424 C
#2. 2010 +0.411 C
3. 2005 +0.251 C
4. 2002 +0.220 C
5. 2009 +0.187 C
6. 2003 +0.185 C
7. 2006 +0.175 C
8. 2007 +0.168 C
9. 2001 +0.112 C
10. 2004 +0.104 C
11. 1991 +0.025 C
12. 1987 +0.018 C
12. 1995 +0.018 C
14. 1988 +0.017 C
15. 1980 -0.003 C
16. 1990 -0.017 C
17. 1981 -0.040 C
18. 2008 -0.041 C
19. 1997 -0.044 C
20. 1999 -0.051 C
21. 1983 -0.056 C
21. 2000 -0.056 C
23. 1996 -0.071 C
24. 1994 -0.104 C
25. 1979 -0.165 C
26. 1989 -0.202 C
27. 1986 -0.239 C
28. 1993 -0.240 C
29. 1982 -0.245 C
30. 1992 -0.284 C
31. 1985 -0.304 C
32. 1984 -0.348 C
*Compared to 30-year seasonal norms
The globe continues to warm unevenly, with warming increasing as you go north: The Arctic Ocean has warmed an average of 1.66 C (about 2.99 degrees Fahrenheit) in the past 32 years. By comparison, the Antarctic continent has cooled about 0.29 C (more than half a degree Fahrenheit) during the same time.
The continental, contiguous U.S. has warmed by about 0.67 C (about 1.21 degrees Fahrenheit) since 1979.
Climate trends since November 1979
(Degrees C per decade)
Globe Land Ocean
+0.14 +0.18 +0.12
NH Land Ocean
+0.21 +0.24 +0.17
SH Land Ocean
+0.08 +0.07 +0.08
Trpcs Land Ocean
+0.08 +0.10 +0.07
(The tropics extend from 20N to 20S latitude)
NoExt Land Ocean
+0.27 +0.28 +0.25
(NoExt goes from 20N to 85N latitude)
SoExt Land Ocean
+0.07 +0.04 +0.08
(SoExt goes from 20S to 85S latitude)
NoPol Land Ocean
+0.47 +0.44 +0.52
(The North Polar region is from 60N to 85N latitude)
SoPol Land Ocean
-0.07 -0.09 -0.06
(The South Polar region is from 60S to 85S latitude)
USA48
+0.21
Technical Note:
Beginning with this Global Temperature Report, the baseline period used to determine seasonal norms changes. It has been the 20-year (1979 to 1998) period at the beginning of the satellite record. Starting this month the report will use a new 30-year (1981 to 2010) reference average to match the climatological period normally used with climate data by the U.N.'s World Meteorological Organization.
"This will not affect the long term trend, which is the most important of the numbers we produce, but will 'reshuffle' anomalies to reflect the new base period," said Christy.
As Christy's colleague Roy Spencer further explains:
This change from a 20 to a 30 year base period has 2 main impacts:
1) because the most recent decade averaged somewhat warmer than the previous two decades, the anomaly values will be about 0.1 deg. C lower than they used to be. This does NOT affect the long-term trend of the data…it only reflects a change in the zero-level, which is somewhat arbitrary.
2) the 30-year average annual cycle shape will be somewhat different, and more representative of "normal" of the satellite record than with 20 years; as a result, the month-to-month changes in the anomalies might be slightly less "erratic" in appearance. (Some enterprising person should check into that with the old versus new anomaly datasets).
