Solar activity – climate relations: A critical Review.
P. Stauning
Danish Meteorological Institute, Copenhagen, Denmark, (pst@dmi.dk / Phone: + 45 39157473)
Abstract. The presentation of solar activity-climate relations is extended with the most
recent sunspot and global temperature data series. The extension of data series
shows clearly that the changes in terrestrial temperatures are related to sources
different from solar activity after ~1985. Based on analyses of data series for the
years 1850-1985 it is demonstrated that, apart from an interval of positive deviation
followed by a similar negative excursion in Earth’s temperatures between ~1923 and
1965, there is a strong correlation between solar activity and terrestrial temperatures
delayed by 3 years.
Reid’s approach to solving the causality problem
“Solar variability and its implication for the human
environment” by Reid (1999) is one of the key papers
on the relation between solar activity characterized by
the sunspot numbers and Earth’s climate characterized
by global temperatures at land and in the oceans.
Fig.3
All time series are subjected to
corresponding 11-years running
averages. The smoothed curves
for sunspot numbers and
temperatures are exceptionally
alike.
A regression analysis between solar activity represented by the cycle-average
sunspot number, SSNA, and global temperature anomalies, ΔTA , averaged over the
same interval lengths, but delayed by 3 years, provides the relation ΔTA ~ 0.009
(±.002) · SSNA . Since the largest ever observed SSNA is ~90 (in 1954-1965), and the
smallest possible value is ~ 0, then the total solar activity-related changes in global
temperatures could amounts to no more than ±0.4°C over the past ~400 years where
the sunspots have been recorded.
The shortcomings of the solar-cycle length model and of the cosmic radiation-cloud
model are discussed. It is suggested that the in-cycle variations and also the longer
term variations in global temperatures over the examined 135 years are mainly
caused by corresponding changes in the total solar irradiance level representing the
energy output from the core, but further modulated by varying energy transmission
properties in the active outer regions of the Sun.
At a first view the figures appear
very convincing. The oceanic
temperatures
are
very
consistent in all three major
ocean
basins
and
also
consistent with the global seasurface temperatures (SST).
Fig.3 Sunspot numbers and ocean temperatures.
(from Reid, 1999)
The major rise in solar activity
starts before year 1900, well
ahead of the rise in temperature
starting just after 1900, to reach
maximum amplitude (now at
~1945) before the middle of the
century well before the global
temperatures
reach
their
maximum level (now ~1955).
However, the polynomial fitting “adjustments” serve to disguise – and not explain – the
causality problem.
Fig.1
Relations between solar cycle length and climate.
Instead of using the sunspot number as an indicator
of solar activity, it was suggested by E. FriisChristensen and K. Lassen in 1991 to use the length
of the solar cycle as a parameter to measure the solar
feature of importance for the changes in Earth’s
climate characterized by the terrestrial temperatures.
The correlation between sunspot no. and cycle length
is shown in Fig. 4 at different delays (cycle shifts).
Fig.5a
Question: Are suggested solar activity – climate relations real ?
Fig. 1 spanning 1850 to 2010 presents recently updated global land/sea-surface
temperature data (upper field) to represent Earth’s climate and sunspot numbers (lower
field) to represent solar activity. The blue temperature and sunspot curves presents
yearly averages. The red curves connect points representing min-to-min (square dots)
and max-to-max (asterisks) average values over complete solar cycles. The straight
lines represent coarse (subjective) trends.
From the presentation in Fig.1 we may conclude that the development in global
temperatures after ~1985 is controlled by drivers other than solar activity represented
by the sunspot number. Hence, we should exclude these years from the present
analysis, which is not considering resent possible anthropogenic global warming
scenarios.
The main obstacle for a credible solar activity-climate relation is the causality problem
since the sunspots lag the global temperatures by ~15 years. In many past publications
the problem has been disguised, among other, by the use of excessive smoothing.
Fig.2
The alleged temperature effect relies on the assumed net decrease in the
energy available near the surface of the Earth as the result of the reflection
of solar energy by the additional cloud cover created through nucleation at
ions generated by the cosmic radiation. The reflection of solar energy is
supposed to dominate over the restraining effects on the energy balance
from the excess cloud cover.
The GCR level is to some extent controlled by the combined shielding
effect of the solar magnetic field extended into the interplanetary space by
the solar wind and the Earth’s own magnetic field.
In-cycle sunspot and temperature variations.
Fig. 14 presents the superpositions of the yearly averages of sunspot numbers in the lower part and
global temperatures in the upper part of the figure. All data are plotted relative to the mid-cycle year.
The heavy red lines denote averages over cycles 10 to 21 of the sunspots and the temperature
anomalies, respectively. The blue lines marked by dots display the sunspot numbers and the
temperature anomalies during the largest ever recorded solar cycle #19 (1954-1965).
Fig.14
The plot in Fig.15 presents the time-history of the
deviations of the global temperature anomaly from
the regression line (0.0090 deg/ssn) defined in
Fig. 1. Note in the figure that the positive and
negative excursions during cycles 16-19 are about
equal and each has the Hale cycle length (22
years for a complete solar magnetic cycle).
Fig.8
Fig.7
Fig.15
Fig.8
The initial relation between cloud cover and depression of GCR is displayed
in Fig. 7 while the correlation between cloud cover and GCR is shown in Fig.
8 (from Svensmark and Friis-Christensen, 1997)
The cosmic ray level always return to the
Fig.10
quiet level (Fig. 9). Hence the behaviour
does not comply with the requirements to
the main forcing process but might
contribute to the small variations observed
at the peak of the individual cycles (Fig.10).
Fig.9
Discussions.
From the regression displayed in Fig.1 it appears that there is a strong correlation between the
global temperatures and the sunspot numbers. However, during the course of the individual
cycles, as presented in Figures 10 and 14, there is little indication of a large cyclic variations in
temperatures from sunspot minima to maxima during the cycle. Hence, the temperature variations
could not easily be coupled to parameters that vary in concordance with the sunspot numbers
without imposing excessive smoothing related, for instance, to the inertia in the global system.
However, such inertia would also have the effect of causing an added delay between the longterm changes in the solar activity characterized by the average sunspot number and Earth’s
climate characterized by the global temperatures. Thereby, the causality problem in the
displacement of the peak in sunspots to around 1958, i.e. ~15 years after the peak in global
temperatures at ~1943 would be further exaggerated.
Fig.5b
Here we suggest that the major part of the long-term variations in global temperatures observed
over the 135 years from 1850 to 1985 are caused by corresponding long-term changes in the total
energy output from the Sun, mostly through variations in the total solar irradiance (TSI).
Fig. 5 (a) Sunspot numbers (+) and NH temperatures (*), (b) solar cycle length (+)
(inverted) and NH temperatures (*) (from Friis-Christensen and Lassen, 1991, FCL91).
From Fig. 5a (left) it is clear that the rise during 1930-1960 in solar activity as
characterized by the cycle-average sunspot numbers occurs well after the rise in
temperatures during 1910 (1890) to 1940. There is, it seems, a delay of 15-20 years
between the two otherwise similarly-looking characteristic features, which should
exclude the temperature rise from being caused by solar activity.
However a way around this problem was found by using the cycle length instead of
sunspot number as a parameter to characterize solar activity giving a ~0.5 cycle shift.
The Gleisberg (1-2-2-2-1) smoothed cycle length used in the display in Fig. 5b (right)
gave another ~0.5 cycle shift to provide a resulting nice fit. It is still unclear even now,
two decades later, which physical parameter should be related to the cycle length.
Fig. 6 displays a replot of FCL91Fig.2 with recent temperature and
solar cycle length (SCL) data
included. The blue curve represent
NH surface temperatures averaged
over solar cycles. The black curve
connects recently estimated min-tomin and max-to-max cycle lengths,
while the red curve presents 1-2-2-21 averages of SCL.
Fig. 2 displays cycle-average temperature anomaly values plotted against the average
sunspot no. The intervals of temperature averaging have the same length as the
interval used for sunspot averaging, but displaced 3 years (after sunspots). A least
squares regression line, ΔTA (°C) = 0.0090 · SSNA - 0.70 has been calculated and
plotted in the diagram. There is a high correlation (R = 0.77) , but the causality
problem documented in Fig. 1 remains to be explained.
Fig.4
The Cosmic Ray – Climate theory.
The effects of the galactic cosmic radiation (GCR) on the climate through
its control of the cloudiness (e.g., Pudovkin and Veretenenko, 1995;
Svensmark and Friis-Christensen, 1997; Svensmark, 2000) also fail to
comply with the recorded temperature changes.
The diversion of the temperature and
SCL curves after ~1980 is evident
here in contrast to the coincident
final upturn in FCL91 (marked by an
ellipse in Fig.5b), which was based
on incomplete data (e.g. Laut and
Gundermann (2000), Damon and
Laut (2004)).
Fig.6
The effects of the shielding by the Earth’s
own magnetic field is evident in the
variation in GCR level at the different
stations in Fig.9.
Over the past 400 years the core field has
decreased considerably. The increase in
the GCR level is shown in Fig. 11. Thus,
according to the GCR-Climate theory, the
global
temperatures
should
have
decreased since ”The little Ice age”.
It is further suggested that the cycle-average sunspot number is a fair indicator of the solar energy
output level for slowly varying changes such as those seen in cycles 9 to 15 and 20 to 21. During
faster changes in the solar energy output level such as those inferred from the global temperature
variations during cycles 16 to 19 the solar energy output is possibly modulated by varying energy
transmission properties in the deep solar convection region.
Fig.11
An even more striking rejection of the theory is provided by Nigel March and
Henrik Svensmark (2000). Their Fig.1 (here Fig.12) displays the cloud anomaly
for high, middle, and low clouds and the GCR (red line) intensities.
Fig.12
The positive relation exists only for the
low clouds, and the variation is only ±
0.6% (not ± 2% as in Fig.7) and only in
the low clouds. Their Fig. 2a (here Fig.
13a) displays the GCR-Temperature
correlation, which is close to 0 for most
regions and not 0.5-0.9 as in Fig 8.
Fig.13
Thus, the energy transport from the core (Fig.16-1) via
the radiation zone (2) and the interface layer assumed
to carry the currents that generate the solar magnetic
fields and further through the convection zone (3) to
the photosphere (4) is a little faster during cycles 1617 with relatively weak magnetic fields and impeded
(slower) during cycles 18-19 with strong solar
magnetic fields. Being related to transmission
properties the positive and negative excursions should
balance each other in the end like it is seen in Fig. 15.
Thus the apparent violation of basic causality
principles during cycles 16-19 is removed.
Fig.16
Conclusions. Several of the previously published reports on postulated close relations between
solar activity and Earth’s climate are based on clever data manipulation and neglect basic causality
principles in the relations between solar activity and Earth’s climate as well as the finer details in
the modulation of global temperatures with respect to cyclic solar activity variations.
• We suggest a steady variation in cycle-average global temperatures, ΔTA, = (0.009 ±
0.002)·SSNA with solar activity represented by the cycle-average sunspot number, SSNA. Further,
we suggest that the solar activity-related global temperature variations are caused by variations in
total solar irradiance of ~1 W/m2 over the solar cycle and 2-3 W/m2 in the longer run during the
past ~150 years.
It is quite conceivable that the solar cycle length is
an indicator of solar output, i.e., total solar irradiance
(TSI), but the 1-2-2-2-1 smoothing applied only to
solar activity, not to temperature, is inconsistent .
• During slowly varying conditions the cycle-averaged sunspot number provides a fair
representation of solar energy output while during strong variations internal energy transmission
properties modulate the solar energy output rate.
• After ~1985 the possible solar activity-related global temperature variations (0.009 deg/ssn) are in
the wrong direction to explain recent global temperature enhancements.
Reference: Stauning, P., Solar activity-climate relations: A different approach, J. Atm. Solar-Terr. Phys. 73, 14 pp., 2011.
doi:10.1016/j.jastp.2011.06.011.