Solar Minima, Earth's rotation and Little Ice Ages in the past and in the future: The North Atlantic–European case

Abstract

The past Solar Minima were linked to a general speeding up of the Earth's rate of rotation. This affected the surface currents and southward penetration of Arctic water in the North Atlantic causing “Little Ice Ages” over northwestern Europe. At around 2040–2050 we will be in a new major Solar Minimum. It is to be expected that we will then have a new “Little Ice Age” over the Arctic and NW Europe. The mechanism proposed for the linkage of Solar activity with Earth's rotation is the interaction of Solar Wind with the Earth's magnetosphere; the decrease in Solar Wind at sunspot minima weakens the interaction with the magnetosphere that allows the Earth to speed up, and the increase in Solar Wind at sunspot maxima strengthens the interaction with the magnetosphere that slows down the spinning of the Earth.

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Solar Minima, Earth's rotation and Little Ice Ages in the past and in the future
The North Atlantic–European case
Nils-Axel Mörner
Paleogeophysics & Geodynamics, Stockholm, Sweden
abstractarticle info
Article history:
Accepted 13 December 2009
Available online 25 January 2010
Keywords:
Solar Minima
Rotational deceleration
Solar Wind
Little Ice Ages
The Gulf Stream
The Future
The past Solar Minima were linked to a general speeding up of the Earth's rate of rotation. This affected the
surface currents and southward penetration of Arctic water in the North Atlantic causing “Little Ice Ages”
over northwestern Europe. At around 2040–2050 we will be in a new major Solar Minimum. It is to be
expected that we will then have a new “Little Ice Age”over the Arctic and NW Europe. The mechanism
proposed for the linkage of Solar activity with Earth's rotation is the interaction of Solar Wind with the
Earth's magnetosphere; the decrease in Solar Wind at sunspot minima weakens the interaction with the
magnetosphere that allows the Earth to speed up, and the increase in Solar Wind at sunspot maxima
strengthens the interaction with the magnetosphere that slows down the spinning of the Earth.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
The concept of geoid changes (Mörner, 1976) seemed to imply
that there would hardly be any order in the eustatic differentiation
over the globe. Despite this, I observed that there were some
regularities, viz. correlation and anti-correlation between certain
regions. Furthermore, those regions were strongly affected by ocean
surface currents. The Kuro Siwo Current and the Gulf Stream seemed
to beat in pace, and the Equatorial Current seemed to record an East–
West beat. This could, in my opinion, only be understood in terms of a
feedback interchange of angular momentum between the oceanic
surface currents and the solid Earth (Mörner, 1984, 1987, 1988, 1990,
1992, 1993). The Gulf Stream seemed to exhibit 16 major pulses or
beat within the Holocene (Mörner, 1984). In the climatic–eustatic
cyclicity diagram of Mörner (1973) there are 23 Holocene pulses
recording frequency-changes pulses ordered in three larger waves
fitting well with oceanic circulation pulses (Mörner, 1995a). The
concept is further analysed elsewhere (Mörner, 1995b, 1996a, 1996b,
2005). In this paper I will address the question of Solar Minima in
the last 600 years and the next one to be expected at around 2040–
2050.
2. Major frames and boundary conditions
Mass, energy and momentum —what I called “the holy trinity”in
terrestrial and planetary physics (Mörner, 1995b, 1996a)—are
usually all considered as “constant”. This is illustrated in Fig. 1 with
respect to our terrestrial situation. Earth's energy could be altered by
changes in Solar irradiance (Fig. 1, right). Despite the fact that the
variation during a sunspot cycle is small (e.g. Foukal and Lean, 1990;
Willson, 1997; Pap and Fröhlich, 1999), hypothetical larger Solar
irradiance variations on the decadal-to-centennial time scale have
been proposed in order to explain the terrestrial climatic changes
during the last centuries to millennium (e.g. Hoyt and Schatten, 1993;
Lean et al., 1995; Lean and Rind, 1999; Bard et al., 2000; Rind, 2002).
The present theory (Fig. 1, middle) implies an alternative explanation
to the solar–terrestrial linkage on a decadal-to-centennial basis.
We may “change”mass, energy and momentum, however, by
redistribution of relevant factors within the given “constant”ter-
restrial frames (Fig. 1, middle). For example; glacial mass redistribu-
tion (e.g. Ice Ages) generates changes in sea level, which in its turn
affects Earth's rate of rotation leading to redistribution of mass (air
and water) and energy (stored in oceans and transferred by winds).
As demonstrated before (Mörner, 1984, 1987, 1988, 1995b, 1996a)
this system seems to play a dominant role for the decadal-to-
centennial changes (what we may call Super-ENSO events).
The magnetosphere–magnetopause represent the interaction
between the heliomagnetic field and the terrestrial field, both of
which vary with time (Mörner, 1984,Fig. 2). The Solar Wind of the
heliomagnetic field is known to vary significantly with the sunspot
cycle. These variations affect the shielding capacity of the Earth's
magnetic field; when weaker more cosmic ray particles pass
increasing the
14
C production, when stronger less particles pass
decreasing the
14
C production (like the in-fall of
10
Be). This was
known since long (cf. Stuiver and Quay, 1980). The novel thing is that
it may also change the Earth's rate of rotation by causing a number of
Global and Planetary Change 72 (2010) 282–293
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terrestrial variables to change accordingly (Mörner, 1996a). This will
be further examined in this paper.
3. Solar variability
The 11-year sunspot cycle and its longer cycles are well known
phenomena. The search for those cycles in terrestrial variables has a
long and intense history, which lies beyond the scope of this paper,
however (e.g. Lean et al., 1995; Willson, 1997; White et al., 1997; Bard
et al., 2000; Rind, 2002). For the last 150 years, there seems to be a
good correlation between changes in the length of the sunspot cycle
and general changes in global mean temperature (Friis-Christensen
and Lassen, 1991), and for the last 250 years between a “combined
solar irradiance model”and the mean Northern Hemisphere changes
in climate (Hoyt and Schatten, 1993).
On the centennial basis, the Solar activity (instrumental, observa-
tion, aurora, aa-index,
14
C production, and
10
Be in-fall) exhibits cyclic
variations between Solar Maxima and Solar Minima (e.g. Stuiver and
Quay, 1980; Hoyt and Schatten, 1993; Lean et al., 1995; Cliver et al.,
1998; Lean and Rind, 1999; Bard et al., 2000; Bond et al., 2001). The
Solar Minima —the Dalton Minimum 1800–1820, the Maunder
Minimum 1645–1705, the Spörer Minimum 1420–1500 and the Wolf
Minimum 1290–1350 —have attracted special attention because they
have been proposed to correlate (e.g. Eddy, 1976) with cold periods or
Little Ice Ages (Lamb, 1979). In the west European records (Guiot,
1992), there are quite clear cold minima at 1440–1460, 1687–1703
and 1808–1821 (Mörner, 1996a), i.e. right within the last three Solar
Minima. Below, I will expand on this.
4. Earth's rotation
The Earth's spin rate (angular momentum) varies on the long-term
basis as well as on the short-term basis. It is usually measured and
expressed in changes in the length of the day (LOD). Changes in the
total angular momentum (like deceleration due to tidal friction) are
compensated within the Earth–Moon system (e.g. Marsden and
Cameron, 1966). Differential changes, on the other hand, imply the
interchange of angular momentum between the different layers and
sub-layers of Planet Earth (Mörner, 1984, 1987, 1996a); viz. between
the atmosphere and the solid Earth (e.g. Barnes et al., 1983; Rosen and
Salstein, 1983; Hide and Dickey, 1990; Rosen and Salstein, 2000;
Abarca del Rio et al., 2003), between the hydrosphere and the solid
Earth (Mörner, 1988, 1990), between the core and the mantle (e.g.
Rochester, 1984; LeMoûel et al., 1986) and between the inner core
and the outer core plus mantle (e.g. Mörner, 1991).
Changes in the Earth's rate of rotation due to Solar Wind changes is
a novel concept (Mörner, 1995b, 1996a; Gu, 1998) analysed in this
paper. It should be noted, however, that a correlation between
sunspot activity and Earth's rotation had been noted before (e.g.
Kalinin and Kiselev, 1976; Golovkov, 1983) as well as more recently
(e.g. Rosen and Salstein, 2000; Abarca del Rio et al., 2003). Fig. 2 gives
a plot of LOD vs. sunspot number for the period 1831–1995. There is a
Fig. 1. Left: The “holy trinity”in terrestrial and planetary physics, all regarded to be “constant”, hence giving the frames within which our theories and interpretations must be kept.
Middle: The dynamically effective terrestrial system and the interaction between actual changes in the distribution of mass, angular momentum and energy. Right: Changes in energy
from variations in Solar radiation, an explanation, may be possible, but no longer necessary for the understanding of the decadal-to-centennial changes in climate (cf. Fig. 13).
Fig. 2. Instrumental LOD data plotted against sunspot numbers for the period 1831–1995 substantiating the existence of a correlation between Solar activity and Earth's rotation
(though the LOD data are, in fact, affected by multiple different factors).
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correlation, despite the fact that LOD represents the integrated effect
of multiple affecting parameters.
5. The Gulf Stream beat
The Gulf Stream is a remarkable system bringing hot equatorial
water to higher latitudes. It implies the redistribution of mass
(affecting Earth's rotation as recorded in sea level changes) and
energy (as recorded in regional climate).
In the central North Atlantic, the Gulf Stream (North Atlantic
Current) splits into individual branches (Fig. 3); the main NE-branch
(the North Atlantic Drift with Irminger Current, branches into the
North Sea and the Norwegian–N. Cape Currents), an E-branch towards
the Bay of Biscay and another major E-branch (the Azores and
Canaries Currents) towards Gibraltar and S-wards back to the
equatorial region. The distribution of water masses along the different
branches varies with time. When more water goes to the NE, less goes
to the East, and when more water goes to the East, less goes to the NE.
This mechanism was proposed 20 years ago (Mörner, 1984), later
improved (Mörner, 1988, 1995b, 1996a) and is in this paper shown
also to apply for the changes between Solar Maxima and Minima.
Kerr (2000) talks about “a slow, multidecadal climate pulse that
beats the Atlantic Ocean”(his AMO) and notes that already Bjerknes
(1964) talked about “a surge of warm water up the Gulf Stream”in
order to explain the early 20-century's warm climate over Northwest
Europe. Similarly, the North Atlantic changes recorded by Levitus
(1990) had to be related to changes in the strength of the Gulf Stream
(Greatbatch et al., 1991; Kushnir, 1994; Häkkinen, 1999). Further-
more, the major shifts in climate and sea level recorded over the last
150 years in Northwest Europe correspond with the major shifts in
LOD (Mörner, 1988, 1995b), indicating an interaction between
rotation and Gulf Stream beat on the decadal time scale. Recently,
Lund et al. (2006) have shown that, in the Florida Straits, the water
masses transported by the Gulf Stream have varied significantly
through the last millennium with a general lowering of about 3 Sv (i.e.
3×10
6
m
3
s
−1
) during the “Little Ice Age”; in their chronology dated
at about 770–150 years BP. Significantly, actual short-term variations
in the Gulf Stream transport have also been measured by sea level
variations along the east coast of United States (Ezer, 2001). What I
am here discussing, is a similar decadal-to-centennial beat in the Gulf
Stream transport and distribution of water masses (northeastward or
eastward; Fig. 3) also recorded in the spatial variance in Holocene sea
level changes (Mörner, 1984). Therefore, it seems significant that van
der Schrier et al. (2002), when extending the sea level analysis over
the last millennium, found agreements between the changes in steric
sea level and Solar irradiance. On the decadal-to-century basis, it is
not only steric changes, but rather changes in water volume due to the
differential distribution of the water masses along the different
branches of the Gulf Stream system (Fig. 3;Mörner, 1984).
Also the changes in the ice edge position in the Nordic Seas (e.g.
Divine and Dick, 2006) and polar front migrations may be seen as a
function of these changes. The shifts in sailing routes to Greenland are
an indication of this (Pettersson, 1913; Mörner, 1995b,Fig. 4).
6. Climatic changes: N–S along West Europe
The St. Jérôm database (nowadays known as the European Pollen
Data Bank, EPDB) of annual climatic changes over the last 900 years in
a grid of every 10° Long. and 5° Lat. (Guiot, 1992) was kindly put at my
disposal. The database is built on pollen records from land and sea
cores. The conversion into temperature is achieved by the transfer–
function methodology of Peyron et al. (1998, 2006; cf. Guiot, 1990)
implying that the values obtained are not true temperature values but
relative average values with error bars. The temperature values are
given in centigrade above and below a local mean. Consequently, the
individual temperature records used here are relative. Therefore, no
absolute values are given in Figs. 4–7. In this study, however, I am not
using the individual values, but their temporal and spatial distribution
over northwestern Europe at selected grid-points.
Fig. 3. The Gulf Stream and its sub-branches, viz. the main branch to the NE (NB), the side-branch towards the Bay of Biscay (NB 1) and the main southern branch (SB) with a sub-
branch towards southern Iberia, Gibraltar and northern Africa (SB 1). Any irregularities (or beat) in the transport of water masses along the Gulf Stream system will affect rotation.
Similarly, changes in rotation will affect the distribution of water masses along the various branches (cf. Fig. 11).
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For this study, I selected 8 grip-point stations consisting of an E–W
profile along Lat. 55° N at (1) 20° E, at (2) 10° E and at (3) 0°, and a
main N–S profile from the North Sea down to the Gibraltar region
consisting of stations at (3) 0° Long and 55° Lat., at (4) 0° Long and 50°
Lat., at (5) 10° W Long and 45° Lat., at (6) 10° W Long. and 40° Lat., at
(7) 10° W Long. and 35° Lat., and at (8) 0° Long. and 35° Lat. (Fig. 8).
In this paper, I confine the analysis to the periods of the last three
Solar Minima with short comparative analysis of the period of the so-
called Medieval Optimum and the 20th century. The periods will be
discussed below in chronological order.
Fig. 5. Period 1070–1300 with the mean trend plotted of stations 3, 6 and 8. The records
show (in relative temperature) a clear anti-correlation between the North (stations 3
and 6) and the South (station 8). Period 1070–1150 was warm in the South and cold in
the North. A rapid transition occurred in the period 1150–1200. Period 1200–1290 was
warm in the North and cold in the South. This period corresponds to the so-called
Medieval Warm Optimum.
Fig. 4. The eight stations in the St. Jérôm (EPDB) database selected for the present analysis of temporal and spatial changes in the distribution of warmer and colder areas (i.e. relative
temperature). The stations are marked with black dots and numbers. Temperature is given in centigrade; it refers to the local mean of the station and is relative. Black squares refer to
the core sites of Bond et al. (1997) and of Bianchi and McCave (1999), here labelled B1, B2 and BM3, respectively.
Fig. 6. Period 1428–1464 with temperature curves for all eight stations. Vertical scale
gives relative temperature of 1 °C above and below local mean. There is a strong cooling
event 1440–1456 with its maximum in the North Sea (station 3). Cold water penetrated
all the way down to station 6, even reaching station 7 at the later part of the period. In
the South there was a warming, at least up to 1448. This period coincides with the
Spörer Minimum.
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6.1. AD 1070–1300 and The Medieval Optimum
The Medieval Optimum was coined by Lamb (1979), dated at
around AD 1250 and likely to correlate with the Solar Maximum at
about 1100–1250 in the Solar irradiance curve of Bard et al. (2000).
Much discussion has been devoted to this period both locally and
globally. In this paper, I confine myself to a short analysis of the
situation as recorded in the St. Jérôm database. Fig. 5 shows the
variations in mean temperature for three grid-points. It reveals that
the temperature changes do not agree in N–S direction. The Medieval
Warm Optimum may be recorded in a temperature rise in the 13th
century in the North (stations 6 and 3), whilst —at the same time —
there was a temperature drop in the South (station 8). In the period
1070–1150, the situation was the reversed; warm at station 8 and cold
(a “Little Ice Age”) at stations 3 and 6. This N–S anti-correlation is
important.
6.2. AD 1428–1464 and the Spörer Minimum
Analysing the data for the 15th century, it was easy to see that
there was a drastic climatic change in Europe in the middle of the 15th
century. In Fig. 6, the records of the period 1428–1464 are plotted for
the 8 stations studied. In the years 1440 to 1956–1460 there is a major
climatic event. Cold conditions spread from the North all the way
down to station 6. The period is three-parted; (1) in years 1440–1444,
there was a cooling in the North (stations 1–6) with a warming in the
South (stations 7–8), (2) in the years 1445–1448, there was a warm
pulse from the South to the North, and (3) in the years 1449–1456
there was strong cold pulse reaching all the way down to station 7
(maybe, even 8) with a continuation up to 1460 in stations 5–7. The
northern cooling is a “Little Ice Age”. It correlates well with the same
event of Lamb (1979) dated at about 1430–1460, and the Solar
Minimum at 1440–1460 in the Solar irradiance curve of Bard et al.
(2000). The simultaneous warm peak (we may call it a “Little
Interglacial”) in the Gibraltar and North African region in years 1436–
1444 gives evidence of the character of the climatic change in Europe;
viz. not general but opposed regional.
6.3. AD 1672–1708 and the Maunder Minimum
The 17th century is especially interesting because it is the time of
the famous Maunder Minimum and the main “Little Ice Age”. In the
data set, there is a very clear and obvious signal within the period
1676–1704 (Mörner, 1995b). Fig. 7 gives the records from the
8 stations from 1672 to 1798. In 1676 a warming begins in stations
5–8. From 1677 to 1679, there is a short cooling event in the North
with a clear East to West decrease. From 1687 to 1703 there is a
drastic cooling in the North. The maximum values are in the North Sea
(station 3). This fits well with Lamb's (1984) statement that “the
ocean surface between Iceland and the Faeroe Islands seems to have
been about 5 °C colder”. It falls within the Solar Minimum at 1660–
1710 in the Solar irradiance curve of Bard et al. (2000). Obviously this
is the “Little Ice Age”event of the 17th century (Lamb, 1979). In the
South (station 7 and especially 8), there is a distinct warming event,
however. There is an initial warming phase 1676–1687 centred over
stations 5–7 and a main warming phase 1676–1706 confined to
stations 7–8 with the strongest signal at station 8. The North–South
anti-correlation is striking.
6.4. AD 1800–1833 and the Dalton Minimum
In the early 19th century data, there is a clear signal coinciding
well with the Dalton Minimum (around 1800–1830 in the Solar
irradiance curve of Bard et al., 2000). Fig. 8 gives the records from the
Fig. 8. Period 1800–1833 with temperature curves for all eight stations. Vertical scale
gives relative temperature of 1 °C above and below local mean. A cooling event is
recorded 1808–1821. It represents the “Little Ice Age”of the Dalton Minimum. This
time, the cooling reached all the way down to station 7, implying that even the sub-
branch towards the Gibraltar (SB 1) suffered diminishing.
Fig. 7. Period 1672–1708 with temperature curves for all eight stations. Vertical scale
gives relative temperature of 1 °C above and below local mean. There is a strong cooling
event at 1687–1703 with maximum cooling in the North Sea and with cold water
spreading all the way down to station 6. This is the cold event or “Little Ice Age”of the
Maunder Minimum. In the South (stations 7 and 8), there was a warming. At 1676, a
distinct warming begins in stations 5–8 reaching a maximum in 1689–1691 in station 6
and lasting up to 1686. A short cooling is registered in the North around year 1677.
Obviously more hot water was now flowing along the sub-branch towards the Bay of
Biscay. The anti-correlation between the “Little Ice Age”of the North and the “Little
Interglacial”of the South is striking.
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8 stations for the period 1800 to 1833. A strong cooling event is
recorded in stations 1–7 with maximum values in the coastal sites
(stations 3–6) for the period 1807–1821. Obviously, we here have a
record of the “Little Ice Age”of the 19th century. In this case, all the
sites along the coast, from station 3 down to station 7, record the
cooling event. There is no opposed warming in the south. This implies
that even the southeastern branch of the Gulf Stream (Fig. 3)
decreased giving a cooling event at station 7.
6.5. AD 1924–1958 and the cooling event around 1940
The general picture of temperature changes on a European as well
as global scale is that temperature rose from the Mid-19th century up
to 1930–1940 after which temperature fell and kept lower from about
1940 to 1970. In Fig. 9, the records of three northern stations (1–3) are
compared with those of two southern stations (7–8). The warm
optimum in the 1930s in the North corresponds to a cooling in the
South. The terrible war-winters in the North (stations 1–3) anti-
correlate with a warm period in the South (station 7 and, less clear, 8).
The proposed global cooling event around 1940 is here recorded as a
drastic cooling in the North at the same time as there was a
simultaneous significant warming in the South; i.e. once again
evidence of a N–S anti-correlation (also recorded in the European
Climate Assessment database by Klein Tank et al., 2002).
7. Discussion
At all the three Solar Minima, the temperature signal in Europe was
quite clear (Figs. 6–8); viz. a cooling event spreading, with a maximum
in the North Sea, down along the coast of Europe all the way to central
Portugal (station 6). At the same time, the South Iberian and North
African region (stations 7–8) experienced warming during the Spörer
and Maunder Solar Minima. This can only be understood in terms of a
shift in the main flux of the Gulf Stream (Fig. 3)andasouthward
penetration of Arctic water, or rather southward spreading of a
significant SST cooling, as illustrated in Fig. 10 (cf. Mörner, 1995b,
1996a). The Maunder Minimum climatic event is most expressive as it
includesa stepwise displacement of the Gulf Stream from (1)a “normal”
northern dominance, via (2) an intermediate dominance along the
eastern branches towards the Bay of Biscay (stations 4–6) and Gibraltar
(stations 7–8), to (3) a dominance confined to the southern branch
(stations 7–8), and then back (4) to northern dominance again
(Fig. 10B). During the Dalton Minimum even the sub-branch towards
Gibraltar diminished Fig. 10C).
The forcing function must, in my opinion, be a speeding up of the
Earth's rate of rotation deflecting the Gulf Stream to southern regions
at the same time as cold Arctic water is drawn down along the Atlantic
east coast. So far, the observational records here presented. The
excellent drift-ice records of Bond et al. (1997, 2001) seem directly to
add on to this picture, however. Cores form both sides of the North
Atlantic (off Newfoundland and off Ireland) record cyclic peaks in ice-
rafted material from drift-ice (IRD), indicating cyclic alternations
between two modes: (1) low IRD, warmer SST and a circulation as
today, and (2) ice-rafting events with peaks in IRD, colder SST and a
significant southward advection of colder and fresher water. As a
consequence, the thermohaline circulation was reduced as recorded
in NADW by Bond et al. (1997) and in ISOW by Bianchi and McCave
(1999). This is consistent with the present model (Mörner, 1995b,
Fig. 2), where the surface water circulation affects the deep-water
circulation, not vice versa, as often claimed. Furthermore, this
southwards shift of colder, ice-bearing surface water far into the
sub-polar North Atlantic had an ocean surface circulation, which was
coupled with the atmospheric circulation over Greenland (Bond et al.,
1997). Consequently, we can safely assume that the observed cooling
events recorded far down along the European coasts (Fig. 10) also
extended over the central and western parts of the North Atlantic (as
recorded by the drift-ice events).
The correlation by Bond et al. (2001) between periods of increased
drift-ice and periods of reduced Solar activity (as recorded by
cosmogenic nuclides which, in fact, refers to Solar Wind activity)
calls for a re-examination of the Holocene Gulf Stream pulses
previously interpreted in terms of differential rotation (Mörner,
1984, 1988, 1995b), because they may represent the same mechanism
as here proposed; the Solar Wind effect on the Earth's total rate of
rotation.
Fig. 11 gives four possible stages in the intensity and distribution of
the Gulf Stream and its sub-branches; viz. (1) an equal distribution in
all sub-branches, (2) a dominance along the main northern branch on
the expense of the eastern (southern) branches, (3) a dominance
along both the eastern branches on the expense of the northern
branch, and (4) a dominance restricted to the southern branch on the
expense of both the others, and with a simultaneous penetration of
Arctic water all the way to central Portugal. Stage 2 represents periods
of low rate of rotation, and stage 4 periods of high rate of rotation.
Consequently (and this is a main novel conclusion), Solar Minima
represent periods with a speeding up (acceleration) of the Earth's rate
of rotation (stage 4), whilst Solar Maxima represent periods of
slowing down (deceleration) of the Earth's rate of rotation (stage 2) as
illustrated in Fig. 12.
If this is correct, there should be a correlation between sunspot
activity and Earth's rotation. This is exactly what has been observed
(above: Section 4). Previously, the reason for this correlation
remained obscure, however.
The interpretation for this causal correlation must be searched in
the variability in the Solar Wind and its interaction with the
magnetosphere. At strong Solar Wind during Solar Maxima, the
interaction is strong leading to a strong shielding capacity (as
recorded) but also to a slowing down of the Earth's rate of rotation
(as here proposed). At Solar Minima, the Solar Wind is weak and the
interaction with the magnetosphere weak with a low shielding
capacity (as recorded) and with a speeding up of the Earth's rate of
rotation (as here proposed and demonstrated by the ocean circulation
changes at the Spörer, Maunder and Dalton Solar Minima).
8. Solar Wind and Earth's rate of rotation
Having noted that all the three major Solar Minima in the last
600 years coincided with the Gulf Stream stage 4 situation of Fig. 11,it
seemed logical as a driving force to infer a general acceleration of the
Earth's rate of rotation; in this case, not an interchange of angular
Fig. 9. Period 1924–1958 with temperature curves of the three northern stations (1–3)
and the two southern stations (7–8). The warm peak in the mid-30s in the northern
stations corresponds to a cold period in the southern stations. Similarly, the cold war-
years in the North correspond to a warm period in the South. The N–S anti-correlation is
striking.
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momentum between the hydrosphere and the solid Earth (e.g.
Mörner, 1988), but a speeding-up of the entire Earth.
Knowing that the Solar Wind beats with a tremendous force
between Solar Maxima and Minima, varying its flow rate between 900
and 300 km s
−1
, interacting with the Earth's magnetosphere, altering
its radius by 1 Earth radius, etc., it seemed obvious the these changes
had to affect the Earth's rate of rotation, hence explaining the
correlations observed between Solar activity and LOD on the short-
term (Fig. 2) as well as the centennial basis. A Solar Wind increase
(during a Solar Maximum) would lead to a deceleration, whilst a
decrease during a Solar Minimum would lead to an acceleration just as
inferred from the observed oceanic changes in circulation and SST,
and land surface temperature during the Spörer, Maunder and Dalton
Minima over western Europe and adjacent parts of the Atlantic.
This theory was presented at the IUGG meeting in Boulder in 1995,
at a climatic meeting in Rio (Mörner, 1996a) and more extensively at
the IUGG meeting in Birmingham (Mörner, 1999). The physical
mechanism, however, was not further explored. Krymsky (1995) had
discussed a possible mechanism of transferring impulse moment from
the Solar Wind to the magnetosphere. Later, Gu (1998) gave a detailed
account on the mechanism of transferring rotational energy from the
Solar Wind to the magnetosphere and the Earth. He proposed that this
Fig. 11. Four stages in the distribution of hot equatorial water along the Gulf Stream system: (1) equal distribution over the whole system, (2) dominant distribution along the
northern branch on the expense of the eastern (NB 1) and southern branches, (3) dominant distribution along the eastern and southern branches on the expense of the northern
branch (as was the case 1676–1686), and (4) dominant distribution along the southern branch on the expense of the northern branch, including the eastern sub-branch, and strong
southward penetration of cold Arctic water all the way down to station 6 (as was the case during all the three Solar Minima here analysed), not only along the eastern side of the
North Atlantic but also in the central and western parts judging from the drift-ice records of Bond et al. (1997, 2001).
Fig. 10. Ocean circulation models explaining the temperature changes observed for the Spörer Minimum (A), for the Maunder Minimum (B) and for the Dalton Minimum (C). At all
three Solar Minima, the northern branches of the Gulf Stream diminished allowing cold Arctic water to penetrate down along the coasts all the way to station 6, probably even down
to station 7 at the Dalton Minimum (cf. Fig. 11, stage 4).
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mechanism could explain the difference between the observed
deceleration (∼1.5 ms per century) and that deduced from tidal
friction (∼2.4 ms/cy).
This opens an alternative, or parallel, way (Fig. 13) of explaining
correlations between variations in Solar activity and variations in a
number of different Earth surface variables and related propositions of
“solar forcing”and “solar–terrestrial interaction”(cf. Fig. 1).
9. The Future Solar Minimum
The Solar activity follows cyclic patterns. Consequently, what
happened in the past will also happen in the future. The combination of
cycles can be done in different ways. Originally, I used a combination of
the Gleissberg and De Vries cycles for the past 600 years and extended
into the Future giving a new Solar Minimum at around 2040–2050
(Mörner, 2005, 2006a, 2006b). In this paper, I use the Solar Irradiance
curve of Bard et al. (2000), noting that this curve, in fact, rather should
be labelled “a Solar Wind Curve”as it is constructed from the variations
in cosmogenic nuclides controlled by the variations in shielding
capacity of the Earth's geomagnetic field (Fig. 13). Along this curve
(Fig. 14), I have marked the changes recorded between Gulf Stream
stage 2 (above) and 4 (below) situations. In the middle of this century
(at about 2040–2050), we should, by cycle extrapolation, have a fist
Future Solar Minimum when the past Gulf Stream situation should
repeat; i.e. we would have a new stage 4 situation with “Little Ice Age”
conditions in Europe and in the Arctic.
This is in sharp contrast to the predictions by IPCC (2001) and ACID
(2004), which predict a unidirectional continued warming leading to
the opening of the Arctic basin within this century. This prediction is
based on modelling excluding the effects of the Sun, however.
Personally, I am convinced that we need to have “the Sun in the
centre”(Mörner, 2006a, 2006b), and having this, we are indeed facing
a new Solar Minimum in the middle of this century. Whether this
minimum will be as the past three once were (Fig. 14), or it will be
affected by anthropogenic factors, is another question.
10. Conclusions
All of three last Solar Minima (Dalton, Maunder and Spörer)
correspond to periods of significant changes in surface heat distribu-
tion over Western Europe and the adjacent part of the North Atlantic.
At the same time, the area of Gibraltar and Northwest Africa
experienced periods of warming. The origin must predominantly be
temporal and spatial changes in SST, and the driving mechanism for
this has to be the changes in intensity and distribution of the transport
of warm, saline water along the Gulf Stream system in the North
Atlantic (Fig. 1). Any irregularity in the transport of mass (in this case
water masses) from southern to northern latitudes will inevitably
have to affect Earth's rotation (Mörner, 1984, 1988). Therefore, it
seems highly likely that the changes recorded during the Solar Minima
were all driven by the spinning-up of the Earth's rate of rotation
(Mörner, 1995b, 1996a).
The recording by Bond et al. (1997) of a strong southward
advection of drift-ice during cooling periods, including the main Little
Ice Age period (Bond et al., 2001), fits perfectly well into the present
theory of an Earth rotational acceleration during Solar Minima.
Fig. 12. The relations among Solar activity, Earth's rotation and switches between Gulf Stream 2 and 4 stages.
Fig. 13. Variations in Solar activity lead to changes in the Solar Wind and in Solar
irradiance, both of which may affect Earth's climate. The variations in irradiance are
known to be small or even minute. The variations in Solar Wind are large and strong, via
the interaction with the Earth's magnetosphere, it affects Earth's rate of rotation, by that
forcing several different terrestrial variables like the Gulf Stream beat in the North
Atlantic. Simultaneously, the shielding capacity affects the concentration of cosmogenic
nuclides (Bard et al., 2000), like the aa-index (Cliver et al. (1998). At any rate, there are
two different ways for how changes in Solar activity may affect Earth's climate. In the
present case, it is the left line that operated.
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From the cyclic repetition between Solar Maxima and Minima, one
can infer that there will be a Future Solar Minimum in the middle of
this century (Fig. 14) when it is most likely that climatic conditions
similar to those of the Little Ice Ages (Figs. 6–8) will re-appear.
The mechanism of how variations in the Solar Wind intensity
affect Earth's rotation is both simple (the more pressure, the slower
the rotation) and complicated (the physical transfer of impulse
moment and rotational energy). The variations in the magnetosphere
control its shielding capacity and this is easily measured by variations
in the in-fall of
10
Be and the production
14
C. Therefore, the temporal
variations of these nuclides (Bard et al. (2000) provide a measure of
the Solar activity; not irradiance (provided it is not causally linked, as
assumed by Bard et al., 2000) but Solar Wind emission.
This implies that we now have not one but two ways of how
changes in the Solar activity may affect the Earth's variables; one by
irradiance and one by rotation (Fig. 13).
The observed changes in Solar irradiance (e.g. Foukal and Lean,
1990; Willson, 1997; Pap and Fröhlich, 1999) are very small. It has
been a problem how these “extremely weak perturbations in the Sun's
energy output”(Bond et al., 2001) can cause the changes observed in
the decadal-to-century terrestrial climate variables. Accordingly,
Goosse and Renssen (2004) stated: “unfortunately it has been difficult
to propose a convincing mechanism that would imply an oceanic
amplification of the response of climate to solar forcing”.Bard et al.
(2000) used the “magnetic variability of the Sun as a proxy surrogate
for irradiance fluctuations”. Their curve for the last 800 years is excellent
Fig. 14. The main Solar cycle in the last 800 years and its expected extension into the future. At the three past Solar minima, NW Europe, the North Atlantic and the Arctic experienced
cold phases known as “Little Ice Ages”. It should be noted that the seven maps of past ocean circulation changes are observationally based records. The cyclic Solar activity record can
be extended forwards into the future (dotted line) and then gives a new Solar Minimum at around 2040–2050. This prediction “with the Sun in the centre”indicating a cooling in the
near future is opposed to the unidirectional warming and opening of the Arctic predicted by the models of ACID (2004) and IPCC (2001), which do not consider Solar variability
(Mörner, 2006b).
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as a measure of the Solar Wind interaction with the magnetosphere, but it
remains “a surrogate”as proxy for Solar irradiance.
The geomagnetic aa-index refers to the disturbance in the Earth's
geomagnetic field and hence provides a measure of the Solar Wind
interaction with the magnetosphere (besides a contribution, usually
subordinate, from variations in the Earth's own geomagnetic field).
Consequently, it seems most significant that Cliver et al. (1998) found
good correlations, for the last 120 years, among the cyclic variations in
aa-index and sunspot numbers, and between the base curve of aa
variations and the mean changes in climate. In the present analysis, it
seems obvious that it is the Solar Wind variations that affect the
Earth's rate of rotation (Fig. 13), which affects the ocean circulation by
that generation changes in climate (Fig. 12).
In the present study, I hope I have presented observational facts
indicating the effects of changes in Earth's rate of rotation driven by
variations in the Solar Wind. Whether this is the main line, or just an
additional line, in solar–terrestrial interaction (Fig. 13), is for others to
find out.
Acknowledgements
Professor Hugues Faure was an outstanding scientist. We met in the
late 60s and immediately became friends, a friendship which grew into
brotherhood within the years. Together, we draw up the lines for the
INQUA Neotectonics Commission and started the annual issuing of the
Neotectonics Bulletin (1977–1996). In 1979/80, we worked side by side
when I stayed at his institute in Luminy setting up a paleomagnetic
laboratory. It was a very creative and brainstorming period. Very early
did Hugues observe the differential sea level changes along the West
African coast (Faure, 1980), which meant much for me in the
formulation of the concept of geoid deformation (Mörner, 1976)and
of differential rotation with interchange of angular momentum
(Mörner, 1984, 1988). He noted the cyclic changes in African aridity
and published a very important paper challenging its future prediction
(Faure and Gac, 1981). When he started his remarkable carbon project,
he insisted that I should work with lithospheric degassing which led to
the paper by Mörner and Etiope (2002). It was a tragedy that his time
run out andthat he was not able tocontinue his carbonproject, whichhe
loved and spent so much efforts on. It was a true privilege for me to have
had the pleasure and benefit to work with Hugues for more than
30 years. And I am happy to dedicate this paper to his memory and
honour; and I bow my head in respect for this great man.
I thank Professor Guiot for providing me with the St. Jérôm
database, and I acknowledge a very nice and constructive collabora-
tion within INTAS project 97.3008 on “Geomagnetism and Climate”
(reported at the EGS–AUG–EUG meeting in Nice, 2003). Finally, I want
to thank my two reviewers for excellent comments and suggestions,
which significantly improved the paper.
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