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i

NASA/TP—2010–216375

Solar Cycle and Anthropogenic Forcing 

of Surface-Air Temperature at Armagh 

Observatory, Northern Ireland

Robert M. Wilson

Marshall Space Flight Center, Marshall Space Flight Center, Alabama

March 2010

National Aeronautics and

Space Administration

Marshall Space Flight Center • MSFC, Alabama 35812
ii

Available from:

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076 –1320

443–757–5802

This report is also available in electronic form at

<https://www2.sti.nasa.gov>
iii

Table of contents

1. INTRODUCTION ............................................................................................................ 1

2. RESULTS AND DISCUSSION ........................................................................................ 2

3. SUMMARY ...................................................................................................................... 14

REFERENCES ...................................................................................................................... 15
iv

LIST OF FIGURES

1. Temporal variation of 10-yma values of (a) ASAT, (b) SSN, (c) Aa, 

(d) HadSST1 N3.4 region sea-surface temperature, and (e) MLCO2 

for selected intervals of time between 1849 and 2003 ................................................. 3

2. The bivariate fit of 10-yma values of ASAT using Aa and MLCO2 

for the interval 1963–2003 .......................................................................................... 10

3. Estimated 10-yma values of MLCO2 for the interval 1873–2003, using 

(a) bivariate and (b) trivariate fits, and significant volcanic eruptions 

and occurrences of strong EN and LN events ............................................................ 12
v

LIST OF TABLES

1. Annual and 10-yma values of ASAT, SSN, Aa, N3.4, and MLCO2, 

and selected percentages ............................................................................................ 5

2. Significant volcanic eruptions (VEI ≥4) ...................................................................... 11

3. Strong EN and LN events .......................................................................................... 13
vi
vii

LIST OF SYMBOLS AND ABBREVIATIONS

10-yma 10-year moving average

Aa Aa geomagnetic index

AGGI Annual Greenhouse Gas Index

ASAT Armagh surface-air temperature

B1 bivariate fit 1

CH4 methane

CO2 carbon dioxide

EN El Niño 

ENSO El Niño Southern Oscillation

HadSST1 Hadley sea surface temperature dataset from the Hadley Center

LN La Niña

MLCO2 Mauna Loa carbon dioxide

N3.4 Niño 3.4 region

NO2 nitrous oxide

P1 contribution of the Annual Greenhouse Gas Index of carbon dioxide 

P2 contribution of the Annual Greenhouse Gas Index of carbon dioxide 

plus methane

P3 contribution of the Annual Greenhouse Gas Index of carbon dioxide 

plus methane plus nitrous oxide

SSN sunspot number

T trivariate

VEI volcanic explosivity index

y1 regression equation 1

y2 regression equation 2
viii
ix

Nomenclature

r coefficient of correlation

sd standard deviation

se standard error of estimate

t year
x
1

TECHNICAL PUBLICATION

SOLAR CYCLE AND ANTHROPOGENIC FORCING OF SURFACE-AIR TEMPERATURE

AT ARMAGH OBSERVATORY, NORTHERN IRELAND

1. INTRODUCTION

The Armagh Observatory temperature record is one of the longest, continuous, thermometerbased temperature records available for study.1–8 Mean monthly and annual temperatures, based on 

daily temperature readings using minimum and maximum thermometers, extend continuously from 

1844 to the present, now spanning 165 yr.

The Armagh Observatory lies about 1 km northeast of the center of the ancient city of 

Armagh, Northern Ireland,6 being located at latitude 54°21′12′′ N. and longitude 6°38′54′′ W. and 

situated about 64 m above mean sea level at the top of a small hill in an estate of natural woodland 

and parkland that measures about 7 ha. Previous studies5 have shown that its rural environment has 

ensured that the Armagh Observatory suffers little or no urban microclimatic effects and that its temperatures can be used as a good proxy for monitoring long-term trends in both northern hemispheric 

and global annual mean temperature.4

This study reexamines the extended record of Armagh Observatory annual mean temperature, in particular, as related to the solar cycle (i.e., sunspot number (SSN) and the Aa geomagnetic 

index (Aa)), the annual mean temperature of the Niño 3.4 region (N3.4) (5° N.–5° S., 120–170° W.), 

and the annual mean Mauna Loa carbon dioxide (CO2) (MLCO2) measurements. While 10-yr moving averages (10-yma) of Armagh Observatory annual mean temperatures correlate quite strongly 

with solar cycle indices, especially over the first 130 yr or so, this correlated behavior has become 

much less apparent since about 1980. Instead, the correlation over the past 30 yr or so appears better 

related to rising levels of atmospheric CO2. In fact, for the common interval 1963–2003, a bivariate fit using Aa and MLCO2 values is found to describe the 10-yma of the Armagh Observatory 

surface-air temperature very closely, having a coefficient of correlation (r)=0.948 and standard error 

of estimate (se)=0.11 °C, and a trivariate fit employing Aa, MLCO2, and SSN is slightly stronger, 

having r=0.952 and se=0.1 °C.
2

2. RESULTS AND DISCUSSION

Figure 1 displays 10-yma values of (a) the annual mean surface-air temperature at Armagh 

Observatory (ASAT) for the interval 1849–2003 in °C, (b) the annual mean SSN for the interval 1849–

2003, (c) the annual mean Aa for the interval 1873–2003 in nT, (d) the annual mean sea-surface temperature in the N3.4 for the interval 1876–2003 in °C, and (e) the annual mean value of the MLCO2 

atmospheric concentration for the interval of 1963–2003 in ppmv. The thin horizontal lines represent 

the parametric means over the individual lengths of observation. The standard deviation (sd) for 

each parameter is also given. Hence, the average 10-yma value (±1 sd) of ASAT=9.20±0.33 °C, 

SSN=56.4±18.2, Aa=21.4±3.5 nT, N3.4=26.97±0.15 °C, and MLCO2=344.18±17.17 ppmv. 

Coefficients of correlation and the inferred regression equations (y1 and y2) are likewise given in 

each subpanel, comparing ASAT against the other parameters. Thus, of the two solar cycle parameters, SSN and Aa, the correlation between ASAT and Aa appears to be the stronger, having r=0.686 

over the interval 1873–2003. Limiting the fit to only those values prior to about 1980, however, one 

finds the correlation to be even stronger, having r=0.762 (inferring that nearly 60% of the variance 

in ASAT can be simply explained by the variation in Aa alone), with ASAT=7.807+0.063Aa. Obviously, the overall correlation between ASAT and Aa (i.e., the solar cycle) has greatly weakened since 

about 1980, with Aa values declining yet ASAT values rising, in contrast to the inferred correlative 

behavior prior to 1980. The correlation between ASAT and N3.4 is very weak, having r=0.268 

(inferring that <10% of the variance in ASAT can be attributed to the variation in N3.4 alone). 

The correlation of ASAT against MLCO2 is by far the strongest single-variate fit, having r=0.877 

(inferring that more than 75% of the variance in ASAT can be explained by the variation in MLCO2 

alone), although the fit only spans about 41 yr.

The lowest 10-yma value of ASAT occurred in 1883, measuring 8.44 °C, and the highest value 

occurred in 2002 and 2003, measuring 10.13 °C. Continued warming is troubling, especially if it 

continues unabated, since it would certainly mean the extinction of many life forms on planet Earth 

and radical changes to human lifestyle.9,10 A mere change of 2 °C could spell disaster for many communities, with changes of more than 2 °C resulting in even more ecological damage.11

While the record of temperature variation at Armagh Observatory can be described as episodic in nature, an undeniable rise of 1.69 °C has occurred there over the past 120 yr. The current 

10-yma value (10.13 °C) is now 0.93 °C above its long-term mean. A linear fit (y1) of ASAT with 

time for the interval 1883–2003 yields the regression ASAT=–5.251+0.00746t, where t is the year, 

r=0.792, and se=0.08 °C. Presuming a continued unabated rise, one would expect the 10-yma of 

ASAT to be about 2 °C above its long-term mean within about 200 yr. However, because the rise has 

been much steeper since 1982, it could attain 11.2 °C much sooner, in as short as about 21 yr (calculated from the 2003 last available entry) or in the year 2024, based on the inferred regression (y2) 

ASAT=–91.185+0.05059t, where r=0.989 and se=0.26 °C.
3

1850 1900 1950 2000 300

320

340

360

380

400

Year

10-yma Annual 

MLCO2

 m = 344.18 ppmv

sd = 17.17 ppmv

26.5

27.0

27.5

28.0 N3.4

1876–2003

ASAT = –7.165 + 0.607N3.4

r = 0.268

10-yma Annual 

HadSST N3.4

 m = 26.97 °C

sd = 0.15 °C

10

15

20

25

30 Aa

1873–2003

ASAT=7.735 + 0.068Aa

r =0.686

 10-yma Annual 

Aa-Geomagnetic Index

 m = 21.4 nT

sd = 3.5 nT

For 1963–2003, ASAT = 8.994 + 0.018Aa

r = 0.107

50

100 SSN

1849–2003

ASAT=8.591 + 0.011SSN

r =0.607

10-yma Annual 

Sunspot Number

 m = 56.4

sd= 18.2

 m = 9.20 °C

sd = 0.33 °C

8.0

8.5

9.0

9.5

10.0

10.5 ASAT

1849–2003

 10-yma Annual Surface-Air 

Temperature (°C)

y2 =ASAT= –91.185 + 0.05059t

 r =0.989

y1 =ASAT = –5.251+ 0.00746t

 r =0.792

MLCO2

1963–2003

ASAT = 3.664 + 0.017MLCO2

r = 0.877

(a)

(b)

(c)

(d)

(e)

Figure 1. Temporal variation of 10-yma values of (a) ASAT, (b) SSN, (c) Aa, (d) HadSST1 

N3.4 region sea-surface temperature, and (e) MLCO2 for selected intervals 

of time between 1849 and 2003.
4

Further examination of figure 1 suggests close behavior between ASAT and the solar cycle, 

in particular, Aa. The Aa correlates with SSN, but is slightly out of phase with respect to SSN (i.e., 

the minimum and maximum values tend to lag that of SSN). Previous studies indicate that Aa is 

directly related to the solar wind speed,12–14 so that higher values of Aa indicate faster solar wind 

speeds and lower values of Aa indicate slower solar wind speeds. Visually, the trend in the 10-yma 

values of ASAT and Aa are remarkably similar, especially, prior to about 1980 (as previously indicated above). Presuming that Aa alone can account for the observed behavior of ASAT, to obtain a 

10-yma of ASAT of 11.2 °C means that the 10-yma of Aa would have to measure about 51 nT, or 

nearly double the highest Aa previously seen (27.4 nT in 1955, associated with the largest sunspot 

cycle in the modern record, cycle 19). However, the recent behavior of Aa with respect to ASAT suggests that something has changed in the relationship between ASAT and Aa, for their behaviors are 

now in opposition (at least, for the interval 1980–2003). (For the sake of completeness, a 10-yma of 

ASAT of 11.2 °C means a 10-yma of SSN of about 237, more than twice as large as has ever been 

seen.)

Obviously, the solar cycle alone cannot account for the observed behavior of ASAT, especially its recent behavior over the past 30 yr or so. Some other effect must be driving the rise in 

ASAT values. That effect appears to be anthropogenic forcing with CO2 being the major contributor, 

accounting for more than 60% of the greenhouse gas concentration.15,16

Concerning MLCO2, its 10-yma has increased from 318.99 ppmv in 1963 to 375.60 ppmv in 

2003, an increase of 56.61 ppmv (i.e., about 18% increase) over about 40 yr. To attain a 10-yma of 

ASAT=11.2 °C, MLCO2 would have to measure about 443 ppmv, some 68 units higher than that 

measured in 2003. The values for the interval spanning 1963–2003 are consistent with an exponential 

fit, with values given approximately as log(MLCO2)=–0.971+0.00177t, where t is the year, based 

specifically on the 1963 and 2003 MLCO2 values. Extrapolating the fit forward, one finds that the 

value of MLCO2=443 ppmv would be reached about the year 2044, or in about 40 yr (from 2003). 

However, extrapolating the fit backwards to preindustrial times17 (e.g., about 1880) yields values of 

MLCO2 that are too low when compared to the generally recognized level of atmospheric CO2 concentration during the preindustrial era (about 230 ppmv, as compared to an accepted level of about 

280 ppmv), so atmospheric CO2 levels must have increased significantly in the recent past to account 

for the discrepancy. A value of about 280 ppmv would have been seen about 1930, based on an extrapolation of the exponential fit. The reader is reminded that the Mauna Loa atmospheric CO2 measurements are the longest continuous record of atmospheric CO2 concentrations available. The site is in 

a barren lava field of an active volcano located at latitude 19°32′ N. and longitude 155°35′ W. and 

3,397 m above mean sea level and does not suffer local influences of vegetation or human activity. 

Consequently, it is considered a very favorable site for a reliable indication of trends in atmospheric 

CO2 concentrations.18,19

Table 1 provides the annual means and 10-yma values for parameters as plotted in figure 1. 

The relative percentages of anthropogenic gases for the interval 1979–2008 are also included, where 

contributions to the Annual Greenhouse Gas Index (AGGI) are P1 (represents the contribution of 

CO2), P2 (the combined contributions of CO2 and methane (CH4)), and P3 (the combined contributions of CO2, CH4, and nitrous oxide (N2O)).
5

Table 1. Annual and 10-yma values of ASAT, SSN, Aa, N3.4, and MLCO2,

and selected percentages.

Year ASAT 10-yma SSN 10-yma Aa 10-yma N3.4 10-yma MLCO2 10-yma P1 P2 P3

1844 9.20 – 15.0 – – – – – – – – – –

1845 9.02 – 40.1 – – – – – – – – – –

1846 10.40 – 61.5 – – – – – – – – – –

1847 9.63 – 98.5 – – – – – – – – – –

1848 9.19 – 124.7M – – – – – – – – – –

1849 9.42 9.46 96.3 66.3 – – – – – – – – –

1850 9.71 9.46 66.6 64.9 – – – – – – – – –

1851 9.55 9.39 64.5 60.4 – – – – – – – – –

1852 9.62 9.38 54.1 53.7 – – – – – – – – –

1853 8.74 9.43 39.0 46.5 – – – – – – – – –

1854 9.43 9.46 20.6 42.8 – – – – – – – – –

1855 8.71 9.39 6.7 44.2 – – – – – – – – –

1856 9.45 9.30 4.3m 46.3 – – – – – – – – –

1857 10.25 9.24 22.7 47.2 – – – – – – – – –

1858 9.58 9.22 54.8 47.7 – – – – – – – – –

1859 9.68 9.21 93.8 49.2 – – – – – – – – –

1860 8.07 9.22 95.8M 51.7 – – – – – – – – –

1861 9.31 9.24 77.2 53.5 – – – – – – – – –

1862 8.77 9.16 59.1 53.4 – – – – – – – – –

1863 9.22 9.10 44.0 51.7 – – – – – – – – –

1864 8.69 9.09 47.0 49.9 – – – – – – – – –

1865 9.63 9.12 30.5 51.0 – – – – – – – – –

1866 9.02 9.17 16.3 54.9 – – – – – – – – –

1867 8.94 9.18 7.3m 58.7 – – – – – – – – –

1868 9.79 9.16 37.6 62.0 21.2 – – – – – – – –

1869 9.29 9.15 74.0 63.0 23.9 – – – – – – – –

1870 9.05 9.14 139.0M 62.2 25.2 – – – – – – – –

1871 9.33 9.11 111.2 61.2 24.4 – 26.61 – – – – – –

1872 8.95 9.10 101.6 61.2 26.7M – 26.35 – – – – – –

1873 8.64 9.04 66.2 59.8 23.2 19.5 26.37 – – – – – –

1874 9.03 8.90 44.7 54.7 17.6 18.3 25.99 – – – – – –

1875 9.13 8.80 17.0 45.9 14.2 17.1 26.29 – – – – – –

1876 8.97 8.73 11.3 37.8 12.5 16.1 26.56 26.74 – – – – –

1877 8.65 8.67 12.4 32.8 11.9 15.7 28.30 26.74 – – – – –

1878 8.87 8.65 3.4m 30.6 10.2 15.5 27.62 26.80 – – – – –

1879 7.40 8.64 6.0 31.4 10.0m 15.4 26.38 26.89 – – – – –

1880 8.93 8.60 32.3 34.1 14.5 15.6 26.69 27.01 – – – – –

1881 8.11 8.52 54.3 36.6 16.6 16.3 27.02 27.05 – – – – –

1882 8.90 8.47 59.7 37.3 26.0M 17.3 26.60 26.94 – – – – –

1883 8.46 8.44 63.7M 37.5 20.6 18.1 26.80 26.87 – – – – –

1884 9.01 8.50 63.5 37.7 17.1 18.7 27.23 26.91 – – – – –

1885 8.27 8.58 52.2 36.5 18.4 19.0 27.44 26.89 – – – – –
6

Year ASAT 10-yma SSN 10-yma Aa 10-yma N3.4 10-yma MLCO2 10-yma P1 P2 P3

1886 8.19 8.61 25.4 34.3 23.6M* 19.1 26.29 26.85 – – – – –

1887 8.56 8.59 13.1 34.0 19.4 19.3 26.46 26.83 – – – – –

1888 8.33 8.59 6.8 35.7 18.4 19.4 27.88 26.76 – – – – –

1889 9.02 8.64 6.3m 37.5 15.5 19.7 26.97 26.66 – – – – –

1890 8.99 8.63 7.1 38.9 13.7m 20.1 25.78 26.59 – – – – –

1891 8.59 8.67 35.6 40.3 20.0 20.1 27.06 26.66 – – – – –

1892 7.96 8.74 73.0 41.7 27.2M 19.9 26.23 26.73 – – – – –

1893 9.55 8.83 85.1M 43.4 20.0 19.7 25.81 26.70 – – – – –

1894 8.82 8.92 78.0 44.7 23.8M* 19.7 26.14 26.64 – – – – –

1895 8.25 8.93 64.0 45.1 21.1 19.6 27.04 26.76 – – – – –

1896 9.11 8.93 41.8 43.6 20.9 18.9 27.63 26.85 – – – – –

1897 9.00 8.99 26.2 38.5 16.6 17.4 27.13 26.93 – – – – –

1898 9.64 9.00 26.7 32.1 18.1* 16.3 26.50 27.07 – – – – –

1899 9.56 8.97 12.1 27.2 16.1 15.6 27.27 27.18 – – – – –

1900 8.61 9.02 9.5 25.4 10.5 15.0 27.80 27.27 – – – – –

1901 8.97 9.06 2.7m 26.0 9.0m 14.6 26.94 27.28 – – – – –

1902 8.76 9.05 5.0 28.4 9.5 14.4 27.80 27.23 – – – – –

1903 8.92 9.03 24.4 31.3 14.9 14.6 27.06 27.21 – – – – –

1904 8.90 8.97 42.0 33.9 14.6 14.9 27.05 27.16 – – – – –

1905 9.15 8.94 63.5M 36.0 18.0 15.6 27.95 27.02 – – – – –

1906 9.10 8.98 53.8 36.6 15.5 16.6 27.03 26.93 – – – – –

1907 8.75 9.01 62.0 36.7 19.1 17.2 26.69 26.90 – – – – –

1908 9.49 9.03 48.5 35.5 20.1 17.2 26.55 26.88 – – – – –

1909 8.50 9.07 43.9 32.7 20.1 17.0 26.19 26.90 – – – – –

1910 9.04 9.07 18.6 30.3 20.5M 17.0 26.13 26.90 – – – – –

1911 9.42 9.05 5.7 29.6 18.9 17.4 26.81 26.83 – – – – –

1912 8.84 9.04 3.6 31.9 11.8 17.8 27.28 26.78 – – – – –

1913 9.23 9.03 1.4m 35.6 11.6m 18.2 27.10 26.81 – – – – –

1914 9.46 9.02 9.6 38.2 13.9 18.7 27.56 26.91 – – – – –

1915 8.63 9.04 47.4 40.1 18.6 18.9 27.42 27.05 – – – – –

1916 9.13 9.10 57.1 42.1 22.8 19.0 26.13 27.09 – – – – –

1917 8.63 9.13 103.9M 43.6 21.2 19.5 26.64 27.06 – – – – –

1918 9.29 9.10 80.6 44.4 24.5 20.1 27.14 27.03 – – – – –

1919 8.55 9.06 63.6 44.9 25.4M 20.1 27.67 26.98 – – – – –

1920 9.42 9.04 37.6 45.1 20.5 19.9 27.28 26.93 – – – – –

1921 10.27 9.07 26.1 45.3 19.5 19.8 26.61 26.99 – – – – –

1922 8.56 9.11 14.2 43.9 21.7* 19.7 26.73 27.08 – – – – –

1923 8.89 9.12 5.8m 42.0 13.2 19.4 27.09 27.09 – – – – –

1924 8.95 9.13 16.7 42.0 13.1m 19.1 26.66 27.06 – – – – –

1925 8.88 9.13 44.3 41.9 16.0 19.5 27.25 27.06 – – – – –

1926 9.43 9.04 63.9 41.6 22.9 20.1 27.58 27.13 – – – – –

Table 1. Annual and 10-yma values of ASAT, SSN, Aa, N3.4, and MLCO2,

and selected percentages (continued).
7

Year ASAT 10-yma SSN 10-yma Aa 10-yma N3.4 10-yma MLCO2 10-yma P1 P2 P3

1927 8.99 9.02 69.0 41.2 19.5 20.1 26.99 27.19 – – – – –

1928 9.20 9.10 77.8M 41.0 20.6 20.4 27.00 27.17 – – – – –

1929 8.95 9.17 64.9 40.6 22.4 20.9 27.15 27.14 – – – – –

1930 8.90 9.23 35.7 39.8 31.5M 21.2 27.78 27.11 – – – – –

1931 9.05 9.23 21.2 40.2 19.7 21.1 27.51 27.08 – – – – –

1932 9.29 9.23 11.1 43.3 22.0* 21.0 27.06 27.06 – – – – –

1933 9.73 9.27 5.7m 47.1 19.3 21.5 26.44 27.04 – – – – –

1934 9.65 9.32 8.7 49.9 16.3m 21.9 26.57 27.01 – – – – –

1935 9.29 9.36 36.1 52.7 18.6 21.9 26.89 27.00 – – – – –

1936 9.15 9.38 79.7 55.6 19.2 22.0 27.17 27.03 – – – – –

1937 9.20 9.39 114.4M 57.9 22.0 22.6 27.07 27.04 – – – – –

1938 9.75 9.39 109.6 59.4 26.5 23.2 26.60 27.02 – – – – –

1939 9.41 9.40 88.8 60.0 26.1 23.9 26.87 27.05 – – – – –

1940 9.25 9.45 67.8 59.9 26.5 24.1 27.80 27.05 – – – – –

1941 9.17 9.50 47.5 60.4 27.9 24.7 28.17 27.01 – – – – –

1942 9.25 9.51 30.6 62.9 24.7 25.4 26.61 26.98 – – – – –

1943 9.90 9.51 16.3 66.1 28.8M 25.7 26.55 26.99 – – – – –

1944 9.59 9.55 9.6m 69.7 20.7 25.6 26.96 27.00 – – – – –

1945 10.29 9.59 33.2 72.8 19.3m 25.5 26.44 26.90 – – – – –

1946 9.32 9.58 92.6 74.7 28.3 25.7 26.85 26.76 – – – – –

1947 9.15 9.55 151.6M 75.9 28.1 26.2 26.80 26.72 – – – – –

1948 9.71 9.52 136.3 75.8 25.5 26.3 27.14 26.78 – – – – –

1949 10.33 9.50 134.7 75.4 24.1 26.1 26.57 26.80 – – – – –

1950 9.17 9.44 83.9 75.4 27.3 26.1 26.00 26.74 – – – – –

1951 8.96 9.40 69.4 78.1 31.7M 26.1 27.19 26.68 – – – – –

1952 8.82 9.44 31.5 82.5 30.8 26.2 26.88 26.69 – – – – –

1953 9.87 9.46 13.9 86.8 25.1 26.4 27.38 26.74 – – – – –

1954 9.16 9.44 4.4m 90.5 20.2m 26.8 26.48 26.79 – – – – –

1955 9.49 9.45 38.0 93.1 20.5 27.4 25.88 26.86 – – – – –

1956 9.38 9.49 141.7 93.7 27.6 27.2 26.20 26.89 – – – – –

1957 9.84 9.52 190.2M 93.3 29.3 26.2 27.55 26.87 – – – – –

1958 9.45 9.45 184.8 94.3 28.4 25.6 27.49 26.86 (315.23) – – – –

1959 10.21 9.41 159.0 95.3 30.1 25.2 27.05 26.87 315.98 – – – –

1960 9.44 9.39 112.3 94.4 32.8M 24.7 26.97 26.96 316.91 – – – –

1961 9.58 9.36 53.9 88.5 22.3 23.9 26.87 27.10 317.64 – – – –

1962 8.77 9.33 37.6 79.0 21.4 22.9 26.73 27.11 318.45 – – – –

1963 8.57 9.30 27.9 70.2 21.2 22.1 27.42 27.05 318.99 318.99 – – –

1964 9.49 9.23 10.2m 63.6 17.1 21.3 26.52 27.05 (319.20) 319.81 – – –

1965 8.82 9.16 15.1 60.5 14.0m 20.2 27.66 27.07 320.04 320.68 – – –

1966 9.38 9.16 47.0 60.8 17.3 19.4 27.29 27.02 321.38 321.56 – – –

1967 9.40 9.17 93.8 63.0 19.7 19.3 26.68 27.04 322.16 322.44 – – –

Table 1. Annual and 10-yma values of ASAT, SSN, Aa, N3.4, and MLCO2,

and selected percentages (continued).
8

Year ASAT 10-yma SSN 10-yma Aa 10-yma N3.4 10-yma MLCO2 10-yma P1 P2 P3

1968 9.32 9.20 105.9M 65.0 22.5 19.5 27.04 27.04 323.05 323.42 – – –

1969 8.93 9.21 105.5 66.8 19.9 20.4 27.62 26.97 324.63 324.51 – – –

1970 9.29 9.23 104.5 68.0 19.9 21.6 26.71 26.87 325.68 325.62 – – –

1971 9.72 9.27 66.6 66.3 20.0 22.3 26.13 26.77 326.32 326.71 – – –

1972 8.74 9.25 68.9 61.3 20.5 22.6 27.84 26.80 327.45 327.84 – – –

1973 9.33 9.22 38.0 57.3 26.7 22.7 26.41 26.83 329.68 329.05 – – –

1974 8.94 9.18 34.5 59.1 30.3M 23.0 26.12 26.81 330.25 330.28 – – –

1975 9.70 9.15 15.5 64.1 23.7 23.1 26.02 26.81 331.15 331.54 – – –

1976 9.34 9.11 12.6m 70.3 22.2 23.2 26.98 26.88 332.15 332.88 – – –

1977 8.92 9.11 27.5 76.3 20.2m* 24.1 27.56 26.92 333.90 334.24 – – –

1978 9.21 9.17 92.5 80.1 25.5 25.0 26.88 26.98 335.51 335.58 – – –

1979 8.36 9.21 155.4M 82.1 22.4 25.0 27.25 27.05 336.85 336.94 0.602 0.848 0.906

1980 9.11 9.17 154.6 82.8 18.5m 24.9 27.20 27.07 338.69 338.39 0.603 0.846 0.903

1981 9.09 9.08 140.4 83.0 24.7 24.8 26.87 27.10 339.93 339.88 0.601 0.842 0.901

1982 9.44 9.05 115.9 83.1 33.9M 24.6 27.98 27.15 341.13 341.38 0.596 0.838 0.897

1983 9.77 9.08 66.6 83.6 29.5 24.4 27.51 27.14 342.78 342.93 0.597 0.835 0.894

1984 9.29 9.19 45.9 84.1 28.8 24.6 26.34 27.05 344.42 344.53 0.598 0.833 0.891

1985 8.70 9.32 17.9 83.6 22.5 25.4 26.35 27.00 345.90 346.11 0.597 0.830 0.887

1986 8.57 9.38 13.4m 83.3 21.1 26.3 27.15 27.04 347.15 347.67 0.595 0.825 0.883

1987 9.07 9.39 29.4 82.4 18.9m 26.5 28.29 27.07 348.93 349.21 0.595 0.822 0.879

1988 9.66 9.37 100.2 80.8 22.1 25.9 26.04 27.05 351.48 350.69 0.598 0.820 0.877

1989 10.07 9.35 157.6M 79.4 30.3 25.8 26.27 27.11 352.91 352.12 0.596 0.816 0.873

1990 9.94 9.43 142.6 78.5 26.6 25.8 27.24 27.20 354.19 353.59 0.594 0.812 0.870

1991 9.43 9.54 145.7 78.3 34.2M 25.6 27.66 27.21 355.59 355.12 0.594 0.810 0.869

1992 9.45 9.64 94.3 77.6 27.3 25.4 27.69 27.18 356.37 356.63 0.592 0.807 0.866

1993 9.27 9.72 54.6 75.5 25.5 25.2 27.50 27.24 357.04 358.13 0.592 0.806 0.865

1994 9.38 9.75 29.9 70.4 29.4* 24.7 27.44 27.28 358.89 359.66 0.594 0.806 0.865

1995 10.23 9.75 17.5 66.1 22.0 24.2 27.04 27.21 360.88 361.19 0.597 0.807 0.866

1996 9.23 9.76 8.6m 63.2 18.6 23.6 26.69 27.11 362.64 362.73 0.600 0.807 0.867

1997 10.33 9.80 21.5 61.9 16.1m 22.8 28.25 27.06 363.76 364.34 0.601 0.807 0.867

1998 10.09 9.88 64.3 62.9 21.0 23.1 27.14 27.05 366.63 366.11 0.606 0.809 0.869

1999 10.18 9.96 93.3 63.9 22.2 23.4 25.97 27.04 368.31 367.96 0.609 0.810 0.870

2000 9.93 10.00 119.6M 65.0 25.4 23.1 26.19 27.04 369.48 369.82 0.610 0.810 0.871

2001 9.58 10.06 111.0 66.0 22.4 23.1 26.73 27.07 371.02 371.72 0.613 0.810 0.871

2002 10.20 10.13 104.0 65.6 22.7 22.9 27.65 27.00 373.10 373.67 0.616 0.811 0.873

2003 10.02 10.13 63.7 61.8 37.1M 22.5 27.30 26.88 375.64 375.60 0.620 0.813 0.874

2004 10.21 – 40.4 – 23.1 – 27.43 – 377.38 – 0.623 0.814 0.875

2005 10.24 – 29.8 – 23.2* – 27.10 – 379.67 – 0.627 0.815 0.876

2006 10.43 – 15.2 – 16.2 – 27.16 – 381.84 – 0.619 0.815 0.877

2007 10.59 – 7.5 – 15.0 – 26.50 – 383.55 – 0.632 0.816 0.878

2008 9.78 – 2.9 – 14.2 – 26.35 – 385.34 – 0.635 0.817 0.880

Table 1. Annual and 10-yma values of ASAT, SSN, Aa, N3.4, and MLCO2,

and selected percentages (continued).
9

Year ASAT 10-yma SSN 10-yma Aa 10-yma N3.4 10-yma MLCO2 10-yma P1 P2 P3

Mean 9.24 9.20 56.0 56.4 21.4 21.4 26.95 26.97 345.04 344.18 – – –

sd 0.54 0.33 43.8 18.2 5.6 3.5 0.57 0.15 21.24 17.17 – – –

 Note:m means minimum value.

m* means alternate minimum value in vicinity of sunspot cycle minimum.

M means maximum value.

M* means alternate maximum value during decline of sunspot cycle.

*means alternate maximum value closer to sunspot cycle minimum.

Aa refers to the Aa–geomagnetic index, increased by 3 nT for years prior to 1957.

N3.4 refers to the HadSST value for the Niño 3.4 region.

MLCO2 gives CO2 in parts per million by volume as measured at Maun Loa Observatory in Hawaii <http://cdiac.ornl.gov/ftp/trends/co2/maunaloa.co2>; 

 annual means for 1958 and 1964 are based on 10 and 9 mo, respectively.

Figure 2 displays the inferred bivariate fit of ASAT against Aa and MLCO2 for the common interval 1963–2003. The inferred correlation is extremely strong, having r=0.948 (inferring 

that nearly 90% of the variance in ASAT can be explained by the combined variations of Aa and 

MLCO2) and se=0.11 °C. The occurrences of significant volcanic eruptions are across the top of the 

chart (those having a volcanic explosivity index (VEI) ≥4), strong El Niño (EN) events (those having 

an anomaly 1.5 °C or warmer using the Hadley Sea Surface Temperature (HadSST1) dataset), and 

strong La Niña (LN) events (those having an anomaly –1.5 °C or cooler using the HadSST1 dataset), where the EN and LN event occurrence year is determined as the year when the anomaly was 

at greatest strength.20 Table 2 provides a convenient listing of significant volcanic eruptions21 and 

table 3 identifies the occurrences of strong EN and LN events22 for the expanded interval 1870–2003. 

A bivariate fit using N3.4 and MLCO2 does not improve the correlation as compared to the singlevariate fit of using MLCO2 alone.

Figure 3(a) depicts the estimated 10-yma values of MLCO2 using the inferred bivariate fit 

(B1) identified in figure 2 for the expanded interval 1873–2003. Since ASAT and Aa are both known, 

one can estimate MLCO2 using the fit. Also plotted are the observed MLCO2 values for the interval 

1963–2003 and the occurrences of significant volcanic eruptions and strong EN and LN events (taken 

from tables 2 and 3). Certainly, the observed and estimated MLCO2 values are in reasonably close 

agreement for 1963–2003, with slight discrepancies possibly being associated with the occurrences of 

significant volcanic eruptions and/or strong EN southern oscillation (ENSO) events. Even the values 

prior to about 1925 seem somewhat reasonable to the unaided eye, if one ignores the values between 

1925 and 1965, suggesting an exponential rise in MLCO2, but one that possibly is steepening with 

the passage of time. It is the anomalous interval between 1925 and 1965 that proves troublesome. 

Presuming the veracity of the bivariate fit, one is led to conclude either that the ASAT or Aa values might be in error during the interval or that the atmospheric CO2 concentration unexpectedly 

rose steeply, reached a plateau, then fell prior to the 1963–2003 rise. Indeed, values of Aa have been 

slightly increased by 3 nT prior to 1957, to account for relocations of the magnetometers used to 

derive the Aa values,12 which has improved certain correlations related to Aa but does not appreciably alter the estimated MLCO2 values. Likewise, ASAT during this timespan is well-calibrated 

and agrees with anomalies as depicted in the Goddard Institute for Space Studies surface temperature analyses,23 in other European temperature records,24 and in sea-surface temperature trends,25

Table 1. Annual and 10-yma values of ASAT, SSN, Aa, N3.4, and MLCO2,

and selected percentages (continued).
10

1960 1970 1980 1990 2000

B1

B1= 4.00727 – 0.06973Aa + 0.02049MLCO2

r = 0.948

ASAT

10.510.0

9.59.08.58.0

Year

C) ° 10-yma Temperature (

Strong LNStrong ENSignicantVolcanic Eruptions(VEI≥4)

Figure 2. The bivariate fit of 10-yma values of ASAT using Aa and MLCO2 

for the interval 1963–2003.
11

Table 2. Significant volcanic eruptions (VEI ≥4).

Year Month Day Name Location VEI

1872 11 3 Merapi Java 4

1877 6 25 Cotopaxi Ecuador 4

1883 8 26 Krakatau Indonesia 6

1883 10 6 Augustine Alaska-SW 4

1886 1 11 Tungurahua Ecuador 4

1886 8 31 Niuafo’ou Tonga-SW Pac 4

1888 7 15 Bandai Honshu-Japan 4

1899 11 13 Dona Juana Columbia 4

1902 5 7 Soufriere

St. Vincent

W. Indies 4

1902 5 8 Pelee W. Indies 4

1902 8 30 Pelee W. Indies 4

1902 10 24 Santa Maria Guatemala 6

1911 1 27 Taal Luzon-Philippines 4

1913 9 - Novarupta Alaska Peninsula 6

1914 1 12 Sakura-jima Kyushu-Japan 4

1919 5 19 Kelut Java 4

1929 6 17 Komaga-take Hokkaido-Japan 4

1933 12 24 Kuchinoerabu-jima Ryukyu Is 4

1937 5 29 Rabaul New Britain-SW Pac 4

1943 2 20 Michoacan-Guanajuto Mexico 4

1947 11 2 Hekla Iceland-S 4

1951 1 15 Lamington New Guinea 4

1955 7 26 Carran-Los Venados Chile-C 4

1956 3 30 Bezymianny Kamchatka 5

1963 2 19 Agung Lesser Sundra Is 4

1965 9 28 Taal Luzon-Philippines 4

1966 4 26 Kelut Java 4

1966 8 12 Awu Sangihe Is-Indonesia 4

1966 8 14 Lengai, Ol Doinyo Africa-E 4

1974 10 10 Fuego Guatemala 4

1980 5 18 St. Helens US-Washington 5

1982 3 28 El Chichon Mexico 5

1982 4 4 El Chichon Mexico 5

1982 5 17 Galungung Java 4

1982 5 27 El Chichon Mexico 4

1990 2 10 Kelut Java 4

1991 6 15 Pinatubo Luzon-Philippines 6

*Adapted from National Geophysical Data Center
12

1900 1950 2000

1875 1900 1925 1950 1975 2000

Est. MLCO2 = (ASAT – 4.34035 + 0.06831Aa + 0.00312SSN)/0.02007

Estimated Observed

400

350

300

250

Year

10-yma MLCO2 400

350

300

(a) 250

(b) 10-yma MLCO2

Strong LN

Strong EN

Significant

VEI≥4

Est. MLCO2 = (ASAT – 4.00727 + 0.06973Aa)/0.02049

Estimated Observed

Figure 3. Estimated 10-yma values of MLCO2 for the interval 1873–2003, using (a) bivariate 

and (b) trivariate fits, and significant volcanic eruptions and occurrences of strong 

EN and LN events.
13

Table 3. Strong EN and LN events.

Start Max End Type

1877-02 1878-01 1878-06 EN

1888-02 1888-11 1889-04 EN

1889-08 1890-01 1890-12 LN

1896-07 1896-12 1897-03 EN

1902-05 1902-11 1903-04 EN

1916-07 1916-12 1917-03 LN

1925-07 1926-01 1926-07 EN

1930-07 1930-11 1931-07 EN

1940-11 1941-04 1942-03 EN

1954-06 1955-11 1956-12 LN

1965-06 1965-11 1966-04 EN

1972-05 1972-11 1973-03 EN

1973-06 1973-12 1974-06 LN

1975-04 1975-12 1976-03 LN

1982-05 1983-01 1983-06 EN

1986-09 1987-09 1988-01 EN

1988-05 1988-11 1989-06 LN

1991-05 1992-01 1992-06 EN

1997-04 1997-11 1998-05 EN

1999-07 2000-01 2000-06 LN

2007-08 2008-01 2008-05 LN

*Based on HadSST1 dataset.

so ASAT is considered correct. The anomalous interval 1925–1965 corresponds to an interval of 

rapid growth in the strength of solar cycles (cycles 16–19, with cycle 19 being the strongest on record). 

Perhaps, an additional factor (SSN) might have to be included during this interval (e.g., 10-yma values of SSN rose from 40 to 95 between 1930 and 1959).

Figure 3(b) displays the estimated 10-yma values of MLCO2 for the interval 1873–2003, 

based on a trivariate fit for the interval 1963–2003, one that incorporates 10-yma values of Aa, 

SSN, and MLCO2. The trivariate fit has a slightly larger r (=0.952) and smaller se (=0.1 °C) than 

the bivariate fit, and is given as T=ASAT=4.34035 –0.06831Aa–0.00312SSN+0.02007MLCO2. 

The estimated MLCO2 values found using the trivariate fit are quite similar to that found using the 

bivariate fit, although slightly lower values are inferred prior to about 1945 and slightly higher values are inferred during the interval 1945 to about 1963. Consequently, the mystery remains. Is the 

inferred increase in atmospheric CO2 concentration real, or has the bump in ASAT during the mid 

20th century been caused by some other unknown effect? Observed values from 1963 to the present 

are closely approximated by both the bivariate and trivariate fits. Because 10-yma values of Aa and 

SSN probably will be decreasing in the near term before increasing due to strengthening of sunspot 

cycle 24, the 10-yma value of ASAT might level off or even slightly decline, unless, of course, the 

10-yma value of MLCO2 continues to increase unabated.
14

3. SUMMARY

Global warming is proving to be a rather pernicious problem, one that must be dealt with 

sooner rather than later, for its continued unabated rise will greatly alter ecological habitats and 

human lifestyle.9–11,26–28 Ten-yma surface-air temperatures, as recorded at Armagh Observatory, 

Northern Ireland, have documented the rise over the past 165 yr. Today (i.e., 2003, the last available 10-yma value), the temperature measures 10.13 °C, a value that exceeds the long-term mean 

by 0.93 °C. While the overall trend in Armagh 10-yma values can be fit linearly for the interval 

1883–2003 as ASAT=–5.251+0.00746t for r=0.792, the trend since 1982 has been much steeper 

(ASAT=–91.185+0.05059t for r=0.989), indicating a potential rise to 2 °C above the long-term 

mean in about the year 2024.

Comparisons of ASAT against SSN, Aa, N3.4, and MLCO2 reveal strong correlation to 

exist against the solar cycle indices, in particular, Aa, especially for the interval prior to about 1980 

(ASAT=7.807+0.063Aa for r=0.762), weak correlation against N3.4, and very strong correlation 

against MLCO2 (ASAT=3.664+0.017MLCO2 for r=0.877). A bivariate fit using Aa and MLCO2 

is found to be even stronger (ASAT=4.00727–0.06973Aa+0.02049MLCO2 for r=0.948) and a trivariate fit using Aa, SSN, and MLCO2 is inferred to be stronger still (ASAT=4.34035–0.06831Aa

–0.00312SSN+0.02007MLCO2 for r=0.952).

Extrapolating the bivariate (or trivariate) fit backwards in time results in estimates of CO2

atmospheric concentration in close agreement with preindustrial levels (about 280 ppmv), although 

an anomalous peak in CO2 atmospheric concentration is inferred to have occurred about 1925–1965, 

indicating that CO2 levels were enhanced during this 40 yr interval, an interval associated with a 

strengthening of sunspot cycles (cycles 16–19). Extrapolation of the bivariate (or trivariate) fit forwards 

in time suggests that ASAT could be about 2 °C warmer than its long-term mean within about 20 yr 

(from 2003), using a 10-yma value of Aa= 17 (equivalent to that found for cycle 14, the smallest cycle 

in the modern record) and a 10-yma value of MLCO2=407 ppmv (from extrapolation of the exponential fit, log(MLCO2)=–0.971+0.00177t). If CO2 atmospheric concentration increases more rapidly, then the 2 °C threshold would be attained more quickly. Similarly, if emission levels of CO2 (and 

other greenhouse gases) can be quickly stabilized, then the effect on ASAT (and, hence, the inferred 

trend of global temperature) could be ameliorated. Certainly, it now appears that anthropogenic forcing due to increasing greenhouse gas concentration is the main culprit of the current trend in surfaceair temperature (i.e., global warming), in contrast to an earlier time when the solar cycle appeared to 

be more dominant. In fact, CO2 atmospheric concentration is higher now than at anytime in the past 

130 yr. 
15

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18

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Solar Cycle and Anthropogenic Forcing of Surface-Air 

Temperature at Armagh Observatory, Northern Ireland

Robert M. Wilson

George C. Marshall Space Flight Center

Marshall Space Flight Center, AL 35812

National Aeronautics and Space Administration

Washington, DC 20546–0001

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Subject Category 47

Availability: NASA CASI (443–757–5802)

Prepared by the Science and Exploration Vehicle Office, Science and Mission Systems Office

M–1275

Technical Publication

NASA/TP—2010–216375

Armagh Observatory, surface-air temperature, solar cycle forcing, carbon dioxide forcing, global warming, 

climatic change

01–03–10

UU 28

NASA

U U U

A comparison of 10-yr moving average (yma) values of Armagh Observatory (Northern Ireland) surface-air temperatures with selected solar 

cycle indices (sunspot number (SSN) and the Aa geomagnetic index (Aa)), sea-surface temperatures in the Niño 3.4 region, and Mauna Loa carbon dioxide (CO2) (MLCO2) atmospheric concentration measurements reveals a strong correlation (r=0.686) between the Armagh temperatures 

and Aa, especially, prior to about 1980 (r=0.762 over the interval of 1873–1980). For the more recent interval 1963–2003, the strongest correlation (r=0.877) is between Armagh temperatures and MLCO2 measurements. A bivariate fit using both Aa and Mauna Loa values results in 

a very strong fit (r=0.948) for the interval 1963–2003, and a trivariate fit using Aa, SSN, and Mauna Loa values results in a slightly stronger fit 

(r=0.952). Atmospheric CO2 concentration now appears to be the stronger driver of Armagh surface-air temperatures. An increase of 2 °C 

above the long-term mean (9.2 °C) at Armagh seems inevitable unless unabated increases in anthropogenic atmospheric gases can be curtailed. 

The present growth in 10-yma Armagh temperatures is about 0.05 °C per yr since 1982. The present growth in MLCO2 is about 0.002 ppmv, 

based on an exponential fit using 10-yma values, although the growth appears to be steepening, thus, increasing the likelihood of deleterious 

effects attributed to global warming. 

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