Monthly Surface Air Temperature Time Series Area-Averaged Over the 30-Degree Latitudinal Belts of the Globe

DOI: 10.3334/CDIAC/cli.003

Data  Graphics

Investigators

K.M. Lugina,^* P.Ya. Groisman,^** K.Ya. Vinnikov,^*** V.V. Koknaeva,^**** and N.A. Speranskaya^****

^*Department of Geography, St. Petersburg State University, St. Petersburg, Russia (deceased)
^**UCAR Project Scientist, National Climatic Data Center, Asheville, North Carolina
^***Department of Atmospheric Sciences, University of Maryland, College Park, Maryland
^****State Hydrological Institute, St. Petersburg, Russia

Period of Record

1881-2005 (relative to a reference period of 1951-1975)
1957-2005 (for the zone 60S-90S; relative to the 1957-1975 reference period)

Methods

The mean monthly and annual values of surface air temperature compiled by Lugina et al. have been taken mainly from the World Weather Records, Monthly Climatic Data for the World, and Meteorological Data for Individual Years over the Northern Hemisphere Excluding the USSR. These published records were supplemented with information from different national publications. In the original archive, after removal of station records believed to be nonhomogeneous or biased, 301 and 265 stations were used to determine the mean temperature for the Northern and Southern hemispheres, respectively. The new version of the station temperature archive (used for evaluation of the zonally-averaged temperatures) was created in 1995. The change to the archive was required because data from some stations became unavailable for analyses in the 1990s. During this process, special care was taken to secure homogeneity of zonally averaged time series. When a station (or a group of stations) stopped reporting, a "new" station (or group of stations) was selected in the same region, and its data for the past 50 years were collected and added to the archive. The processing (area-averaging) was organized in such a way that each time series from a new station spans the reference period (1951-1975) and the years thereafter. It was determined that the addition of the new stations had essentially no effect on the zonally-averaged values for the pre-1990 period.

Most changes in the station data set were made in the Northern Hemisphere. As a result, the total number of stations here increased from 301 to 384. In the Southern Hemisphere the number of stations increased from 265 to 301. The following is a list, by zone, of the number of stations added and those removed due to their operation being discontinued:

• 0°-30°N, 22 stations removed and 42 added.
• 30°N-60°N, 15 stations removed and 66 added.
• 60°N-90°N, 10 stations removed and 22 added.
• 0°-30°S, 16 stations added.
• 30°S-60°S, 15 stations added.
• 60°S-90°S, 5 stations added.

The departures of the individual station mean monthly temperatures from an average for the period 1951 to 1975 were spatially averaged. Details on the spatial averaging method may be found in Lugina (1977), Kagan (1979;1997), Vinnikov and Lugina (1982), Groisman and Lugina (1985), and Vinnikov et al. (1987, 1990).

Trends

Based on these mean monthly and annual surface air temperature anomaly data, Vinnikov et al. (1990) reported that both hemispheres were warming at a rate of 0.5°C/100 yrs. The present update of the series through 2005 shows that the northern hemisphere has warmed at a rate of 0.71°C/100 yrs, and the southern hemisphere (0°-60°S) at a rate of about 0.56°C/100 yrs. The warming rate for the globe (in this case, 90°N-60°S) is 0.64°C/100 yrs. This trend is close to the 0.70°C/100 yrs global trend calculated by Jones and Moberg (2003) for land areas over the period 1901-2000. However, it is interesting to note that the large positive anomilies found in the late 1930s and 1940s in the Jones et al. (2006) global time series are not as evident in the Lugina et al. global series, possibly due to the different reference periods used in calculating the anomalies. Relatively large positive anomalies for this period are present mainly in the Lugina et al. series for the latitude band 60°N-90°N.

In the 60°S-90°S latitude band, an increase in the annual surface temperatures is shown (0.17°C/10 yrs; most of the warming having occured by 1970), with the largest trend apparent in the winter (June-August) months (0.47°C/10 yrs). The annual trend can be compared with the Jacka and Budd (1998) finding of an Antarctic warming of 0.12°C/10 yrs and Reid and Jones (2001) with a warming of 0.15°C/10 yrs. These three data bases, while not representing the same network of stations, essentially reflect temperature changes at Antartic stations, most of which are near the coast of the continent. While these warming trends for the high latitudes of the southern hemisphere are quite large, it must be remembered that:

1. There is extreme interannual temperature variability at these latitudes;
2. The atmospheric/surface thermal inertia for this region is low;
3. This area is a rather small fraction of the globe's surface; and
4. The period of record for the region is quite short.

Therefore, one should not place nearly as much emphasis on trends for this polar region as any significant changes nearer the equator, where the atmospheric/surface thermal inertia is the largest and the percentage of the globe's surface is much larger.

In the Lugina et al. global record, as in other researchers' records, the time series show that the 1980s, 1990s, and the first several years of the twenty-first century were much warmer than the rest of the record. The most recent year of the data record, 2005, saw the warmest global mean annual temperature departure (0.84°C), the warmest northern hemisphere annual temperature departure (1.08°C), and a tie with 1998 for the warmest southern hemisphere annual temperature departure (0.57°C). It is interesting to note that while the record warmth for 2005 in the Lugina et al. analysis agrees with the analysis of Hansen et al. (2006), the analysis of Jones et al. (2006) shows 2005 as being the second warmest year behind 1998.

For the globe, the 12 warmest years of the record have all occurred since 1990. In descending order they are 2005, 1998, 2003, 2002, 2004, 2001, 1999, 1995, 1990, 1997, and 1991/2000 (tie). The record warm annual temperature anomalies for the globe and both hemispheres were, not surprisingly, driven by plenty of record warmth for individual seasons, the most pronounced case being for the months of June, July, and August (NH summer/SH winter), where the anomalies easily ranked number one over the entire period of record for the globe and both hemispheres. Several other seasonal records were also set, mainly for the globe and northern hemisphere.

References

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