I shall rephrase this question. Is the sun a major factor in causing climate change?
The answer is YES and I shall endeavor to explain the current thinking on the subject.
Global warming is now more commonly called "climate change", which can include global cooling. Also, I don't wish to blame the sun because it can't help doing what suns and planetary systems have to do, by virtue of their existence. Do we blame dogs for barking?
The correlation of sun spot activity to climate was first reported by Sir William Herschel in 1801 who noticed a relationship between solar activity and the price of wheat, from the data given in Adam Smith's book "The Wealth of Nations" published in 1776.
The radiation from our sun is the ultimate source of energy and warmth on earth. Our atmosphere and the earth's surface is continually bombarded by a wide range of electromagnetic radiation, protons, electrons and cosmic rays, which emanate largely from our sun but also from outer space. The intensity of this radiation varies with sun spot activity which are enormous electromagnetic storm regions that are observed to develop periodically on the surface of the sun.
Historical observation of sun spot activity has shown it to be roughly cyclical in nature, time wise. The interval between maxima is about 11 years and for the big solar cycle of 100 years there are 9 individual 11 year cycles. Why this should be so will be speculated upon later.
The actual variation of the sun's total flux of electromagnetic radiation is very small, only a few tenths of a percent which directly can not adequately account for global warming and cooling. There is not a uniform change with all wavelengths from UV, visible and IR radiation etc. Some wavelengths may be more effective than others. However, what is important is whether or not a "multiplier effect" exists and how it may work.
The degree and nature of cloud cover is thought to be very important in determining global and regional temperatures and so climate change. On the micro scale animals and humans automatically know this on hot, cloudless days, by seeking the cooler shade of a bushy tree or by staying in doors in our homes where the sun's warming rays can not penetrate directly.
On the macro scale, the same phenomenon seems to happen when high altitude cloud (cirrus) develops and persists. Cirrus cloud consists of highly reflective ice particles (temperatures ca minus 50 degrees C) and reflect the sun's heat away from the earth, thus promoting a cooling
effect. When there is no reflective cirrus cloud present the atmosphere receives the full brunt of the sun's radiation and the temperature rises.
Cloud formation is a function of the humidity of the atmosphere, or how much water vapor is present. No water vapor means no clouds. High humidity allows for much cloud formation which at low altitudes are aggregates of tiny liquid water particles, and at the cooler high altitudes, ice particles.
The mechanisms of cloud formation and dispersal and how it may be driven by sun spot activity has been the subject of much research.
The nucleation of clouds from water vapor is thought to be caused by cosmic rays which impinge on the earth from outer space. When sun spot activity is high the increased magnetic field of the sun deflects the cosmic rays from the earth thus causing a lower tendency for cloud formation. Also the greater the UV radiation from the sun results in evaporation of the high altitude ice particles and the cloud cover disappears. In general, periods of high sunspot activity are related to global warming and periods of low sun spot activity with global cooling.
The troposphere where our all our weather occurs ranges in thickness from 7 kms upwards at the poles to 20 km at the equator and averages about 11 kms. Globally it is divided up into major convective cells where the hot air over tropical regions rises and moves eventually to descend over the polar regions.
The Australian climate is very much correlated with the El Nino and La Nina events. El Nino is when there is when the tropical oceans receive maximum heating which causes increased evaporation and greater humidity. Colder periods are encountered when there is low sun spot activity and lower radiation flux which allows for more extensive high altitude cloud cover (1, 3).
The surface waters of the oceans are the major stores of heat, much more so than the atmosphere. The circulating ocean currents disperse heat from the tropics both northwards and southwards to be replaced by colder currents coming from polar regions. This is much slower than atmospheric movement. It takes about 6 months for the warm waters of the Gulf Stream to move from the Caribbean to reach Europe.
In the Pacific Ocean the cold Humboldt Current rich in nutrients flows northwards along the coast of South America to normally as far as Peru is stymied during an El Nino period and is replaced by a warm southerly flow here. This results in appreciable climate change. This natural climate
oscillation between La Nina and El Nino conditions takes place every 3 or 4 years and is of variable intensity. It has an appreciable effect on Peruvian fishing industry for sardine and anchovy. The Australian climate is effected too, and ranges from periods of drought (El Nino) to wetter with flooding (La Nina), thus effecting crop yields (3).
In summary, the primary drivers of climate are the variability of the sun's radiation and how it effects the earth's cloud cover, which determines the amount of warming and cooling of the oceans and land surfaces.
So what causes these sun spots and why do they fluctuate regularly in number over the years?
The pioneer of research on the sun's effect on climate was Rhodes Fairbridge, an Australian, who published extensively on his researches in the 80s and 90s, but received little recognition for its importance (4).
It is generally believed that the earth and other planets revolve around the sun. This is the simple picture and is not quite true. Our planetary system which includes the sun and all the planets revolve around a barycenter which may be within the sun but at times can be as much as two sun' diameters away. This is due to the gravitational effect on the sun of our wandering planets, especially the large ones, Jupiter, Saturn and Neptune. Sometimes they may be widely spaced but at other times their orbits bring them all to one side of the sun which causes gravitational tidal disturbances to the sun's fiery nuclear surface and promotes the formation of electromagnetic disturbances, or sun spots (5). It's a bit like stoking a coal fire to get more heat!
The gravitational effect of the moon on our earth as it rotates results in a tidal pull on the oceans. Locally, almost at my back door, the sea level changes by 1 to 3 meters. These tides happen with monotonous regularity, twice a day, and we are so familiar with them that we tend to forget their cause. May be periodic tides on the sun stir up its outer envelope of plasma gases, thus causing the sun spots, which are the ultimate cause of periodic short term climate changes on earth?
(1) "Illusions of Climate Science" by William Kininmonth
Quadrant Magazine, October 2008
(2) "Evidence of sun spot involvement in climate change compelling" by Kelvin Kemm
Tech Track: Engineering News - Online, 21 Nov. 2008
(3) "El Nino Warning" by Earl Happ
Wine Industry Journal, July/August 2008 (wwwwinebiz.com.au)
(4) "Rhodes Fairbridge and the idea that the solar system regulates the Earth's climate"
by Richard Mackay, Journal of Coastal Research, Special Issue 50, 2007
(5) "How Barycentric Orbits Influence Climate" by Jim Sprott
Lavoisier Group Inc., November 2008
Articles 4 and 5 are best accessed by going to the website of the New Zealand Climate Science Coalition (www.climatescience.org.nz/) and (1) from the website of the Lavoisier Group Inc., at (www.lavoisier.com.au).
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