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Surface temperature trend for the Northern Hemisphere-updated
QUATERNARYRESEARCH
6,355-358(1976)
Surface Temperature Trend for the Northern Hemisphere-Updated WALTRAUD
A. R. BRINKMANN
Department of Geography and Institute for Environmental University of Wisconsin, Madison, Wisconsin 53706
Studies,
Received January 29, 1976 The surface temperature curve for the Northern Hemisphere was extended to include the years 1969 through 1973 following the same procedure used by H. C. Willets J. M. Mitchell, Jr., and C. H. Reitan. The analysis showed a slight warming of 0.02 C between the periods 1965-1969 and 1970-1973, and a significant decrease in the number of negative temperature changes at individual stations (indicating a decrease in the total area experiencing temperature decrease).
INTRODUCTION The most recent study of surface temperature trends for the Northern Hemisphere (Reitan, 1974) covered the period 1955-1968. Several more years of data are now available. In view of the increasing interest in this trend, it appeared useful to extend the Northern Hemisphere temperature curve established by Willett (1950) and updated by Mitchell (1961) and Reitan (1974). METHODS AND DATA Following the method of analysis adopted by Willett (1950) and continued by Mitchell (1961) and Reitan (1974), the change of temperature between the pentad 1965-1969 (the last period used by Reitan was 1965-1968) and the period 1970-1973 was computed for about 200 stations and selected points in the Pacific and Atlantic Oceans. Within each lo”latitude belt the temperature changes were averaged over all stations and ocean data points. The hemispheric trend was determined by weighting the averages of the loo-latitude belts according to the area within the belts. The basic data used to calculate the temperature changes were monthly mean temperatures for the years 1969-1973 taken from the two National Oceanic and
Atmospheric Administration publications: “Monthly Climatic Data for the World” (Environmental Data Service) and “Fishing Information” (National Marine Fisheries Service). Although continuous and homogeneous records from the individual stations are desirable, they are not absolutely necessary. The emphasis is on changes from one pentad to the next, and stations can therefore be dropped or added as necesSarY. The stations used in the present analysis were essentially the same stations used by Reitan. About 10 of the 200 stations he had used disappeared from the published climatic records during the period 1969-1973. They were replaced by nearby stations. In these cases it was of course necessary to first establish a &year mean for the period 1965-1969 in order to calculate a change between that pentad and the new period, 1970-1973. RESULTS The results of the analysis are shown in Table 1 and Figs. 1 and 2.together with the changes calculated by Reitan. It must be noted that Reitan’s original last period, 1965-68, consisted of only 4 years. The addition of the year 1969 to that pentad did not change the trend in the mean annual temperature for the
355 Copyright 0 1976 by the University of Washington All rights of reproduction in any form reserved.
356
WALTRAUD
Temperature
Total Winter Spring Summer Fall
A. R. BRINKMANN
(Table l), the greatest changes have occurred during the fall and winter. The cooling of the fall seasons has increased, while the winters have become somewhat warmer. Figure 2 shows the latitudinal distribution of surface temperature changes (not the periods area-weighted) between 1965-1969 and 1970-1973 together with Reitan’s results. Clearly, the small change between the two periods for the whole Northern Hemisphere was due to changes (slight warming trend) in the higher latitudes. How significant is this temperature change? Is an increase or decrease of less than one-tenth of a degree centigrade meaningful? As Reitan (1974) pointed out, the differences from one pentad to the next are usually not more than 2 SD from the mean and are therefore statistically not significantly different. However, several indications of an amelioration since about 1970, such as changes in Arctic sea ice and the marine climate off North Iceland (Dickson et al, 1975; Sanderson, 1975), are supporting this finding. Furthermore, the temperature for the
TABLE 1 Change between the Means of the Basic Periods
1955-1959 to 1960-1964 CC) +0.03 +0.03 +0.01 +0.01 +0.07
1960-1964 to 1965-1969 CC) -0.09 -0.31 +0.04 -0.06 -0.05
1965-1969 to 1970-1973 (“(3 +0.02 +0.13 +0.02 +o.oo -0.08
hemisphere and only slightly modified the latitudinal distribution of the temperature changes (discussed below). A redefinition of the seasons (Winter, DJF; Spring, MAM; Summer, JJA; Fall, SON; from Reitan’s definition of Winter, JFM; Spring, AMJ; Summer, JAS; Fall, OND) has also resulted in only minor changes (discussed below). The long-term trend of temperature for the Northern Hemisphere, as determined by Willett (1950) and updated by Mitchell (1961), Reitan (1974), and this study is shown in Fig. 1. The change between the periods 1965-1969 and 1970-1973 was relatively small, a rise of 0.02”C. Regarding seasonal temperature changes .8 -
‘\. ./ \
.6 0v ni z k
. .:t\\&/:-:J , , , ,y( :0*I--
. A-
1870
80
90
1900
10
20
30
\ A’\
40
XI
60
70
80
YEAR FIG. 1. Temperature change for the Northern Hemisphere as determined by Willett and updated by Mitchell, Reitan, and in this study. Values shown are deviations from the 1880-1884 pentad.
SURFACE
--.6 0
TEMPERATURE
I
I
,
I
I
I
I
I
10
20
30
40
50
60
70
80
LATITUDE,
FIG. 2. The latitudinal 1959 to 1960-1964 (---);
distribution 1960-1964
The Number
‘N
of temperature change between the four periods: 1955to 1965-1969 (-); 1965-1969 to 1970-1973 (-*--.--*).
Northern Hemisphere may not only depend on the magnitude of the individual changes but also on the size of the area experiencing a temperature increase or decrease. Reitan (1974) used binomial probabilities to determine if the number of positive and negative changes are significantly different, assuming that both are equally probable. Table 2 shows that the between period temperature changes were characterized by significant differences in the number of negative changes at individual stations. The two periods during which the temperature of the Northern Hemisphere increased slightly were associated with fewer negative changes while the period during which the temperature decreased was associated
with more negative changes at individual stations. This implies that the total area experiencing a negative change has fluctuated over the past 15 years. SUMMARY The analysis indicates that the downward trend in the surface temperature of the Northern Hemisphere which started in the 1940’s and which was interrupted around 1960 by a small rise of 0.03”C between two pentads, has reversed again due to a small rise of 0.02”C. While this recent slight warming is statistically not other evidence of recent significant, amelioration support the result. In addition, the total number of negative changes has changed significantly, indicating a de-
TABLE 2 of Negative Changes at Individual 1955-1959 to 1960-1964
Number of changes, n Probability of a negative change, p Probability of a nonnegative change, q Mean,
357
TREND
(w)
Standard deviation, ( npq)1’2 Number of negative changes observed Difference (mean - observed) Number of standard deviations from the mean
198 0.5 0.5 99 7.0 83 +16 2.3
Stations 1960-1964 to 1965-1969 198
0.5 0.5 99 7.0 126 -27 3.9
1965-1969 to 1970-1973 198 0.5 0.5 99 7.0 91 +8 1.1
-
358
WALTRAUD
crease in the total area experiencing temperature decrease.
A. R. BRINKMANN
a
ACKNOWLEDGMENTS The assistance of C. H. Reitan was much appreciated. This research was supported under sponsorship of the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Grant No. 04-5-158-33.
REFERENCES Dickson, R. R., Lamb, H. H., Malmberg, S. A., and Colebrook, J. M. (1975). Climatic
reversal in northern North Atlantic. Nature (London) 256,479-432. Mitchell, J. M., Jr. (1961). Recent secular changes of global temperature. Annals of the New York Academy ofsciences 95,235-250. Reitan, C. H. (1974). A climatic model of solar radiation and temperature change. Quaternary Research 4, 25-33. Sanderson, R. M. (1975). Changes in the area of Arctic sea ice 1966 to 1974. Meteorological Magazine 104,313-323. Willett, H. C. (1950). Temperature trends of the past century. In “Centenary Proceedings Royal Meteorological Society,” pp. 195-206. London, England.
6,355-358(1976)
Surface Temperature Trend for the Northern Hemisphere-Updated WALTRAUD
A. R. BRINKMANN
Department of Geography and Institute for Environmental University of Wisconsin, Madison, Wisconsin 53706
Studies,
Received January 29, 1976 The surface temperature curve for the Northern Hemisphere was extended to include the years 1969 through 1973 following the same procedure used by H. C. Willets J. M. Mitchell, Jr., and C. H. Reitan. The analysis showed a slight warming of 0.02 C between the periods 1965-1969 and 1970-1973, and a significant decrease in the number of negative temperature changes at individual stations (indicating a decrease in the total area experiencing temperature decrease).
INTRODUCTION The most recent study of surface temperature trends for the Northern Hemisphere (Reitan, 1974) covered the period 1955-1968. Several more years of data are now available. In view of the increasing interest in this trend, it appeared useful to extend the Northern Hemisphere temperature curve established by Willett (1950) and updated by Mitchell (1961) and Reitan (1974). METHODS AND DATA Following the method of analysis adopted by Willett (1950) and continued by Mitchell (1961) and Reitan (1974), the change of temperature between the pentad 1965-1969 (the last period used by Reitan was 1965-1968) and the period 1970-1973 was computed for about 200 stations and selected points in the Pacific and Atlantic Oceans. Within each lo”latitude belt the temperature changes were averaged over all stations and ocean data points. The hemispheric trend was determined by weighting the averages of the loo-latitude belts according to the area within the belts. The basic data used to calculate the temperature changes were monthly mean temperatures for the years 1969-1973 taken from the two National Oceanic and
Atmospheric Administration publications: “Monthly Climatic Data for the World” (Environmental Data Service) and “Fishing Information” (National Marine Fisheries Service). Although continuous and homogeneous records from the individual stations are desirable, they are not absolutely necessary. The emphasis is on changes from one pentad to the next, and stations can therefore be dropped or added as necesSarY. The stations used in the present analysis were essentially the same stations used by Reitan. About 10 of the 200 stations he had used disappeared from the published climatic records during the period 1969-1973. They were replaced by nearby stations. In these cases it was of course necessary to first establish a &year mean for the period 1965-1969 in order to calculate a change between that pentad and the new period, 1970-1973. RESULTS The results of the analysis are shown in Table 1 and Figs. 1 and 2.together with the changes calculated by Reitan. It must be noted that Reitan’s original last period, 1965-68, consisted of only 4 years. The addition of the year 1969 to that pentad did not change the trend in the mean annual temperature for the
355 Copyright 0 1976 by the University of Washington All rights of reproduction in any form reserved.
356
WALTRAUD
Temperature
Total Winter Spring Summer Fall
A. R. BRINKMANN
(Table l), the greatest changes have occurred during the fall and winter. The cooling of the fall seasons has increased, while the winters have become somewhat warmer. Figure 2 shows the latitudinal distribution of surface temperature changes (not the periods area-weighted) between 1965-1969 and 1970-1973 together with Reitan’s results. Clearly, the small change between the two periods for the whole Northern Hemisphere was due to changes (slight warming trend) in the higher latitudes. How significant is this temperature change? Is an increase or decrease of less than one-tenth of a degree centigrade meaningful? As Reitan (1974) pointed out, the differences from one pentad to the next are usually not more than 2 SD from the mean and are therefore statistically not significantly different. However, several indications of an amelioration since about 1970, such as changes in Arctic sea ice and the marine climate off North Iceland (Dickson et al, 1975; Sanderson, 1975), are supporting this finding. Furthermore, the temperature for the
TABLE 1 Change between the Means of the Basic Periods
1955-1959 to 1960-1964 CC) +0.03 +0.03 +0.01 +0.01 +0.07
1960-1964 to 1965-1969 CC) -0.09 -0.31 +0.04 -0.06 -0.05
1965-1969 to 1970-1973 (“(3 +0.02 +0.13 +0.02 +o.oo -0.08
hemisphere and only slightly modified the latitudinal distribution of the temperature changes (discussed below). A redefinition of the seasons (Winter, DJF; Spring, MAM; Summer, JJA; Fall, SON; from Reitan’s definition of Winter, JFM; Spring, AMJ; Summer, JAS; Fall, OND) has also resulted in only minor changes (discussed below). The long-term trend of temperature for the Northern Hemisphere, as determined by Willett (1950) and updated by Mitchell (1961), Reitan (1974), and this study is shown in Fig. 1. The change between the periods 1965-1969 and 1970-1973 was relatively small, a rise of 0.02”C. Regarding seasonal temperature changes .8 -
‘\. ./ \
.6 0v ni z k
. .:t\\&/:-:J , , , ,y( :0*I--
. A-
1870
80
90
1900
10
20
30
\ A’\
40
XI
60
70
80
YEAR FIG. 1. Temperature change for the Northern Hemisphere as determined by Willett and updated by Mitchell, Reitan, and in this study. Values shown are deviations from the 1880-1884 pentad.
SURFACE
--.6 0
TEMPERATURE
I
I
,
I
I
I
I
I
10
20
30
40
50
60
70
80
LATITUDE,
FIG. 2. The latitudinal 1959 to 1960-1964 (---);
distribution 1960-1964
The Number
‘N
of temperature change between the four periods: 1955to 1965-1969 (-); 1965-1969 to 1970-1973 (-*--.--*).
Northern Hemisphere may not only depend on the magnitude of the individual changes but also on the size of the area experiencing a temperature increase or decrease. Reitan (1974) used binomial probabilities to determine if the number of positive and negative changes are significantly different, assuming that both are equally probable. Table 2 shows that the between period temperature changes were characterized by significant differences in the number of negative changes at individual stations. The two periods during which the temperature of the Northern Hemisphere increased slightly were associated with fewer negative changes while the period during which the temperature decreased was associated
with more negative changes at individual stations. This implies that the total area experiencing a negative change has fluctuated over the past 15 years. SUMMARY The analysis indicates that the downward trend in the surface temperature of the Northern Hemisphere which started in the 1940’s and which was interrupted around 1960 by a small rise of 0.03”C between two pentads, has reversed again due to a small rise of 0.02”C. While this recent slight warming is statistically not other evidence of recent significant, amelioration support the result. In addition, the total number of negative changes has changed significantly, indicating a de-
TABLE 2 of Negative Changes at Individual 1955-1959 to 1960-1964
Number of changes, n Probability of a negative change, p Probability of a nonnegative change, q Mean,
357
TREND
(w)
Standard deviation, ( npq)1’2 Number of negative changes observed Difference (mean - observed) Number of standard deviations from the mean
198 0.5 0.5 99 7.0 83 +16 2.3
Stations 1960-1964 to 1965-1969 198
0.5 0.5 99 7.0 126 -27 3.9
1965-1969 to 1970-1973 198 0.5 0.5 99 7.0 91 +8 1.1
-
358
WALTRAUD
crease in the total area experiencing temperature decrease.
A. R. BRINKMANN
a
ACKNOWLEDGMENTS The assistance of C. H. Reitan was much appreciated. This research was supported under sponsorship of the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Grant No. 04-5-158-33.
REFERENCES Dickson, R. R., Lamb, H. H., Malmberg, S. A., and Colebrook, J. M. (1975). Climatic
reversal in northern North Atlantic. Nature (London) 256,479-432. Mitchell, J. M., Jr. (1961). Recent secular changes of global temperature. Annals of the New York Academy ofsciences 95,235-250. Reitan, C. H. (1974). A climatic model of solar radiation and temperature change. Quaternary Research 4, 25-33. Sanderson, R. M. (1975). Changes in the area of Arctic sea ice 1966 to 1974. Meteorological Magazine 104,313-323. Willett, H. C. (1950). Temperature trends of the past century. In “Centenary Proceedings Royal Meteorological Society,” pp. 195-206. London, England.