The sun is the primary source
of heat for our planet.
The heat contribution
from Earth's core, mainly
heat transported by
mantle convection, and also
hydrothermal convection,
and a little heat from volcanoes
and earthquakes too, is believed
to be VERY small relative to
energy coming from the sun
( but of course scientists have
been wrong before ! ).
Planetary (Earth / sun) geometry
is a very good explanation
for why there are ice ages,
and peak glaciations,
that come and go,
at very long-term intervals.
Short-term climate variations
are the most puzzling ...
and get almost all the attention,
( except for all the wild guess
predictions of doom way
off in the future),
but the short-term variations,
over a century or two,
are harmless,
and not important !
( except for all the wild guess
predictions of doom way
off in the future),
but the short-term variations,
over a century or two,
are harmless,
and not important !
2018 Sun Observations:
The Solar Dynamics Observatory
reports that over 60% of the days
in 2018, so far, had no sunspots.
That's unusual.
Sunspot counts are a proxy for solar
activity -- more sunspots means
there is a more active, hotter sun.
NOAA (US Commerce Department)
posted its monthly solar cycle #24
update for March 2018
March was the least active
month for sunspots since mid-2009.
The Sunspot Index and Long-term
Solar Observations webpage (SILSO)
says there were only five days
in March 2018 when sunspots
could be seen on the visible
half (hemisphere) of the sun.
Perhaps that means solar cycle 24
is ending, and solar cycle 25
has already begun ?
If the solar cycle 24 minimum
has arrived, then cycle 24
would have been only ten years long,
which would be one of the shortest
solar cycles on record.
All past short solar cycles
were active cycles,
but #24 has been a weak cycle
(solar activity based on sunspot counts,
available since the 1700s.)
We know for sure
that the solar science community
failed to predict cycle 24,
because half of the scientists
predicted a strong maximum,
and half predicted a weak one,
so we already knew a decade ago
that half the predictions
were going to be wrong
( ignorance of the "experts" ) !
Past solar cycles tended to ramp down
slowly to the solar minimum, not quickly,
like cycle 24 has done (so far).
Perhaps we're heading
into a grand minimum,
which last happened
during the Maunder Minimum
-- an unusually cold period
from 1645 to 1715 ?
During the Maunder Minimum,
there were practically no sunspots.
But at the time, astronomers had no idea
that a lack of sunspots was unusual.
If solar energy variations were
a primary cause of climate change,
then common sense would say
we’d see three "solar signatures":
(1)
An 11-year solar cycle
would be visible in the
average temperature data,
which we don’t see ...
... and any grand minimum
should have:
(2)
An unusually cold temperature
(enough for people to notice), and
(3)
Temperature declining over the years,
as the grand minimum continues.
Temperature reconstructions
for the centuries before 1850
are not high accuracy, and the
only real-time measurements
available for the "Little Ice Age"
(LIA) were some temperatures
in England:
Assuming the temperature data
are good enough for any conclusion,
it appears that none of
the four LIA grand minimums
had the ideal “solar signatures”
of weak solar energy
( see (2) and (3) above )
The Maunder Minimum
was most likely the coldest
of the four LIA grand minimums.
The average temperature was cold,
during the maunder Minimum,
but there was a rising temperature trend
during the minimum, which is the opposite
of what one would expect
if the sun was important for climate change.
People living in Europe did complain
a LOT about the cold weather during the
Maunder Minimum.
And there were some famines in Europe
during that grand minimum.
The other three LIA grand minimums
were not so cold, at least in England,
except for the beginning of the
Sporer Minimum.
But during the Sporer Minimum,
the average temperature also went UP,
which makes no sense if solar energy
"controlled the climate".
There were also some cold LIA
decades between the minimums,
but they can't be blamed
on low solar energy
(low sunspot counts).
A focus on ONLY
the Maunder Minimum
is data mining.
I used to do that years ago,
caused by my confirmation bias
-- I assumed the sun HAD to be
important in climate change,
and the Maunder Minimum was
a LIA minimum that supported
my assumption.
Conclusion:
We really do not know,
nor do we have measurements,
that explain, the influence
of the Sun’s "11-year" solar cycles
on Earth’s climate.
Notes:
(1)
Sunspot cycles are said to average
about 11 years long.
People prefer to see a simple,
regular 11-year cycle, to bring order
and simplicity to their world,
so they usually ignore the fact that
solar cycles overlap -- each cycle
is actually 16 or 17 years long.
There is an overlap, because
each new solar cycle begins
years before the old cycle dies.
A "minimum" is usually defined
as the time where the sum of
the sunspot counts for the
two overlapping solar cycles,
both the old and new cycle,
are at a minimum.
A minimum is NOT the time
where a new solar cycle begins,
and the old solar cycle ends.
A grand minimum is a very long
period of time with unusually low
sunspot counts, meaning unusually
low solar activity.
(2)
When solar activity was declining
in the 20th century, there was
global warming, NOT global cooling.
In fact, solar activity and temperature
were NOT positively correlated
in the past 60 years.
Some people suspect there's a time-delay
between changes in solar activity and
changes in the the average temperature.
But when investigating that possibility,
the data still show NO correlation
in the past 60 years, when considering
time delays ranging from 1 to 15 years.
(3)
Start dates for solar cycles at Wikipedia:
Solar Cycle Start & Duration in years
Solar cycle 1 "starts" 1755 February, "lasts" 11.3 years
Solar cycle 2 1766 June 9.0 yrs.
Solar cycle 3 1775 June 9.3
Solar cycle 4 1784 September 13.6
Solar cycle 5 1798 April 12.3
Solar cycle 6 1810 August 12.8
Solar cycle 7 1823 May 10.5
Solar cycle 8 1833 November 9.7
Solar cycle 9 1843 July 12.4
Solar cycle 10 1855 December 11.3
Solar cycle 11 1867 March 11.8
Solar cycle 12 1878 December 11.3
Solar cycle 13 1890 March 11.8
Solar cycle 14 1902 January 11.5
Solar cycle 15 1913 July 10.1
Solar cycle 16 1923 August 10.1
Solar cycle 17 1933 September 10.4
Solar cycle 18 1944 February 10.2
Solar cycle 19 1954 April 10.5
Solar cycle 20 1964 October 11.4
Solar cycle 21 1976 March 10.5
Solar cycle 22 1986 September 9.9
Solar cycle 23 1996 August 12.3
Solar cycle 24 2008 December (in progress)