With the Sun and Solar Flares currently in the news, i thought i’d update my blog by adding chapter S from my book The A-Z of Global Warming, which discusses the Sun’s impact of global warming, and gives some facts and figures on Earth’s nearest star…
Bear in mind the book was written in 2008 – but mentions the increase in Solar activity now in the news…
The sun is a star, which is located at the centre of our solar system.
It is only one of about 100 billion stars in our own galaxy, the
Milky Way, which in turn is one galaxy of literally billions in the
universe, each containing billions and billions of stars.
Our sun has been in existence for about 4,600,000,000 years,
and it will provide life support for planet Earth for another 5–
6,000,000,000 years, until it transforms into a red giant gas star
and finally dies.
The energy from our sun, in the form of sunlight, supports
life on Earth and is responsible for the Earth’s weather and climate
systems. The sun cannot be ignored in the context of global warming.
Earth’s power supply
The surface of the sun has a temperature of about 5,500°C (9,932°F),
and it’s even hotter on the inside! As you might expect, being
the only source of heat in our solar system, its effects on Earth’s
climate and temperature will be significant.
The total amount of radiant energy emitted by the sun that
reaches Earth is termed the total solar irradiance or TSI, and it
is measured in watts per metre squared.
Energy from the sun is measured both at the top of the Earth’s
atmosphere, called the solar constant, and at the surface of the
Has the sun caused or contributed to global warming?
This is the question many scientists are trying to answer. NASA
satellites have measured total solar irradiance since 1978. Six
overlapping satellites have monitored TSI since 1978, and the first
records came from the Nimbus 7 Earth radiation budget (ERB)
experiment from 1978–1993. NASA’s ACRIM 1 satellite, which
is an acronym for Active Cavity Radiometer Irradiance Monitors,
also studied the sun, from 1980–1989, and ACRIM 2 from 1991–
2001. Finally ACRIM 3 from 2000–2005.
These satellites produced a wealth of information about the
sun. Richard Wilson, a researcher affiliated with NASA’s Goddard
Institute for Space Studies and Columbia University Earth Institute
in New York, compiled TSI records over the twenty-four-year
observation period by piecing together the records.
The results showed a 0.05 per cent decade upward trend of
TSI measured in watts per metre squared between solar minimum
solar cycles, 1978 to the present (solar cycles twenty-one to twenty-three).
What are solar cycles?
The sun goes through cycles, called solar cycles, every eleven years.
During this period the sun goes through a period of increased
magnetic and sunspot activity, called the solar maximum, when
solar-energy output increases, followed by a quieter period, called
the solar minimum, and back again. During a solar cycle, the
number of sunspots also varies with solar minimum and solar
maximum, with peak sunspot activity occurring at the solar
What are sunspots?
Sunspots are basically dark and relatively cooler regions of the
sun, caused by concentrated magnetic fields. Sunspots can cause
decreases in TSI by about 0.2 per cent during say a week-long
passage of a large sunspot group across the ‘Earth facing’ surface
of the sun. These changes are insignificant however to the sun’s
total output of energy, but still equivalent to all the energy
mankind produces and consumes in one year!
So, when the sun is at solar maximum, irradiance and magnetic
activity are at their highest, which is proportional to solar activity.
Sunspot numbers are representative of the general level of solar
At present the sun is just coming out of a quiet period, which
is solar minimum of solar cycle twenty-three. The last solar
maximum was in about the years 2000–2002 (cycle twenty-three).
NASA scientists have recently discovered a new technique,
‘helioseismology’, which works in a similar way to ultrasound,
but in the case of the sun, not part of the human body!
The sun’s magnetic fields, plasma flows and magnetic
signatures left by fading sunspots are looked at by NASA’s solar
and heliosphere observation satellite (SOHO). This has led the
NASA team to predict that the sun’s next solar cycle will begin
with an increase in solar activity in late 2007 or early 2008, and
this will be thirty to fifty per cent more intense than the current
cycle, reaching its peak in about 2012 (cycle twenty-four).
This could affect space satellites and any technology that relies
on them, as the sun’s energy output increases together with
perhaps a temporary increase in the Earth’s temperature during
Has the sun affected the Earth’s climate in the past?
While NASA satellites have been monitoring sunspot activity and
TSI since 1978, scientists and astronomers have been looking at
the sun through telescopes for almost 400 years, since shortly after
the telescope was invented.
As we know from Chapter H, the Earth entered a cooling period
about 1350–1850, which was termed the Little Ice Age. Temperature
drops around the globe were noticeable. Glaciers in the Alps
advanced, canals in Holland regularly froze and the Thames in
London would freeze over every twenty years or so.
During the coldest part of the Little Ice Age, between about
1645 and 1715, very low sunspot activity was observed.10
This period is called the Maunder Minimum, after the English
astronomer who made the observation.
Scientists now consider there is a link between the Little Ice Age
and the low level of sunspot activity recorded during that time.
So, it would seem that from scientific studies of the sun so far
that the sun’s irradiance may be slightly increasing by 0.05 per
cent each decade, which may have an effect on climate change
over timescales of 100 years or more.
The sun’s energy output may be responsible for causing or
contributing to the Little Ice Age, as very low sunspot activity
was observed for seventy years during the coldest part of this
Is it the sun, yes or no?
While there is little doubt about the fact that global temperatures
have increased during the last 100 years, there is continuing
scientific debate in respect of the sun’s contribution to current
According to the 2007 IPCC report, changes in solar irradiance
since 1750 are estimated to have caused a radiative forcing of 0.12
(+0.6 to +0.30) watts per square metre.
This is compared to a total net anthropogenic (manmade)
forcing of 1.6 (+0.6 to +2.4) watts per square metre.
Manmade radiative forcing is therefore much greater than the
effect the sun has had warming the Earth since the year 1750.
Radiative forcing is basically the change in the balance between
radiation entering the Earth’s atmosphere and leaving it. Positive
forcing will warm the Earth and negative will cool it.
It seems therefore that while the sun does of course have an
effect on the Earth’s climate, and therefore potentially global
warming, such effects are nowhere near as great as those of
anthropogenic or manmade causes, the burning of fossil fuels etc.
However, much longer studies will have to be made, it seems,
to determine the answer for sure!
➢ Light energy emitted from the sun, solar
irradiance, has increased by about 0.05 per cent
each decade from 1978, which could affect Earth’s
climate over the long term.
➢ The sun goes through solar cycles, which occur
every eleven years.
➢ Sunspot numbers represent the general level of
solar activity, with peak sunspot activity occurring
during solar maximum.
➢ During the coldest part of the Little Ice Age,
sunspot activity was observed to be at its lowest.
➢ While the sun does of course have an effect on
Earth’s climate, solar irradiance has had a radiative
Interested in reading more? Try the book…