Bob wrote:

Yeah, come 2020 when the Sunspots become minimum, and things begin to
cool off, we will all sit back and have a laugh at the Chicken Little
Global Warmers of the day! I wonder how many of them are hold outs of
the Y2K fear mongering that went on at the turn of the century?

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Sunspot cycle

Sunspots have a diameter of about 37,000 km and appear as dark spots
within the photosphere, the outermost layer of the Sun. The photosphere
is about 400 km deep, and provides most of our solar radiation. The
layer is about 6,000 degrees Kelvin at the inner boundary and 4,200 K on
the outside. The temperature within sunspots is about 4,600 K. The
number of sunspots peaks every 11.1 years.

There is a strong radial magnetic field within a sunspot, as implied in
the picture, and the direction of the field reverses in alternate years
within the leading sunspots of a group. So the true sunspot cycle is
22.2 years. There is also a superimposed fluctuation with a period of 25
months, i.e. a quasi-biennial oscillation.

Sunspots were observed in the Far East for over 2000 years, but examined
more intensely in Europe after the invention of telescopes in the 17th
century. In 1647 Johannes Hevelius (1611-87) in Danzig made drawings of
the movements of sunspots eastwards and gradually towards the solar
equator. In 1801 William Herschel (1738-1822) attempted to correlate the
annual number of sunspots to the price of grain in London. The 11-year
cycle of the number of sunspots was first demonstrated by Heinrich
Schwabe (1789-1875) in 1843.

There have been several periods during which sunspots were rare or
absent, most notably the Maunder minimum (1645-1715), and less markedly
the Dalton minimum (1795-1820) (Fig 2.8 in the book). During the Maunder
minimum the proportional concentration of radio-carbon (14C) in the
Earth?s atmosphere was slightly higher than normal, causing an
underestimate of the radio-carbon date of objects from those periods. By
means of the premise of excess 14C concentrations in independently dated
material (such as tree rings), other minima have been found at times
prior to direct sunspot observations, for instance the Sporer minimum
from 1450 to1540. Data from 8,000 year-old bristle-cone pine trees
indicate 18 periods of sunspot minima in the last 7,800 years (1). This
and other studies have shown that the Sun (as well as other stars)
spends about a quarter of its time with very few sunspots.

There is another well-known, super-imposed variation of annual sunspot
numbers, of about 85 years. This irregular variation affects the length
of the sunspot cycle, ranging from 9.8 to 12.0 years. Maxima of
sunspot-cycle length occured in 1770, 1845 and 1940.

Sunspots and climate

Incidentally, the Sporer, Maunder, and Dalton minima coincide with the
colder periods of the Little Ice Age, which lasted from about 1450 to
1820. More recently it was discovered that the sunspot number during
1861-1989 shows a remarkable parallelism with the simultaneous variation
in northern hemisphere mean temperatures (2). There is an even better
correlation with the length of the solar cycle, between years of the
highest numbers of sunspots. For example, the temperature anomaly was -
0.4 K in 1890 when the cycle was 11.7 years, but + 0.25 K in 1989 when
the cycle was 9.8 years. Some critics of the theory of man-induced
global warming have seized on this discovery to criticize the greenhouse
gas theory.

All this evokes the important question of how sunspots affect the
Earth's climate. To answer this question, we need to know how total
solar irradiance received by the Earth is affected by sunspot activity.

Intuitively one may assume the that total solar irradiance would
decrease as the number of (optically dark) sunspots increased. However
direct satellite measurements of irradiance have shown just the opposite
to be the case. This means that more sunspots deliver more energy to the
atmosphere, so that global temperatures should rise.

According to current theory, sunspots occur in pairs as magnetic
disturbances in the convective plasma near the Sun's surface. Magnetic
field lines emerge from one sunspot and re-enter at the other spot.
Also, there are more sunspots during periods of increased magnetic
activity. At that time more highly charged particles are emitted from
the solar surface, and the Sun emits more UV and visible radiation.
Direct measurements are uncertain, but estimates are that the Sun's
radiant energy varies by up to 0.2%% between the extremes of a sunspot
cycle. Polar auroras are magnificent in years with numerous sunspots,
and the ?aurora activity? (AA) index varies in phase with the number of
sunspots. Auroras are faint and rare when the Sun is magnetically
quiescent, as during the Maunder minimum.

The periodicity of the sunspot number, and hence that of the circulation
in the solar plasma, relates to the rotation of the Sun about the centre
of gravity of whole solar system, taking 11.1 years on average.
Sometimes the Sun is up to a million kilometres from that centre, and
sometimes it more or less coincides, leading to different conditions of
turbulence within the photosphere. The transition from one condition to
the other affects the number of sunspots.

Not only does the increased brightness of the Sun tend to warm the
Earth, but also the solar wind (a stream of highly energetic charged
particles) shields the atmosphere from cosmic rays, which produce 14C.
So there is more 14C when the Sun is magnetically quiescent. This
explains why 14C samples from independently dated material are used as a
way of inferring the Sun's magnetic history.

Recent research (3) indicates that the combined effects of
sunspot-induced changes in solar irradiance and increases in atmospheric
greenhouse gases offer the best explanation yet for the observed rise in
average global temperature over the last century. Using a global climate
model based on energy conservation, Lane et al (3) constructed a profile
of atmospheric climate "forcing" due to combined changes in solar
irradiance and emissions of greenhouse gases between 1880 and 1993. They
found that the temperature variations predicted by their model accounted
for up to 92%% of the temperature changes actually observed over the
period -- an excellent match for that period. Their results also suggest
that the sensitivity of climate to the effects of solar irradiance is
about 27%% higher than its sensitivity to forcing by greenhouse gases.

Sunspots and climate prediction

We do not know why the Sun spends part of its time in a magnetically
quiescent state, and whether the sunspot minima occur with a regularity
that is sufficient to predict when the next quiescent episode might occur.

At present there is no concern about another Little Ice Age. Recent
satellite measurements of solar brightness, analyzed by Willson (4),
show an increase from the previous cycle of sunspot activity to the
current one, indicating that the Earth is receiving more energy from the
Sun. Willson indicates that if the current rate of increase of solar
irradiance continues until the mid 21th century, then the surface
temperatures will increase by about 0.5? C. This is small, but not a
negligible fraction of the expected greenhouse warming.

The relationship between cycle length and Earth temperatures is not well
understood. Lower-than normal temperatures tend to occur in years when
the sunspot cycle is longest, as confirmed by records of the annual
duration of sea-ice around Iceland. The cycle will be longest again in
the early 2020's.

http://www-das.uwyo.edu/~geerts/cwx/notes/chap02/sunspots.html

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I’m Mr. green Christmas
I’m Mr. Sun.
I’m Mr. Heat Blister
I’m Mr. One Hundred and one
They call me Heat Miser
Whatever I touch
Starts to melt in my clutch.
I’m too much!

http://www.youtube.com/watch?v=2C3bHVefvTo&feature=related

Mr. 101

http://www.myspace.com/greenxmas