There is a possibility that maybe the majority of the climate variations observed since 1750 have been caused by amplification of the solar radiation received by the atmosphere/Earth system. The argument begins with the noticeable correlation between sunspot numbers and the long record of central England temperatures. Possible causes come later
This diagram shows the monthly average temperature record for central England and it is noticeable that the graph from 1900 mirrors quite well the global temperature record. The other plot is the number of sunspots noted monthly.
There is a suggestion of correlation; the maxima and minima of both records show the same pattern. Just how and why sunspot activity should be connected with climate is a matter of intense debate. The IPCC only report that the measured output of the sun varies only slightly with time and could not possibly be connected with climate change on a basis of radiation intensity hitting the top of the atmosphere changing. In that respect they are correct; the amount of solar radiation incident upon the atmosphere is actually known as the solar constant [342 W m-2 on average over the Earth's surface] although it does vary with the seasons by about 3% because the Earth's orbit around the sun is elliptical.
One mechanism for sunspots affecting the climate is connected with the solar wind; the stream of atomic particles that is ejected from the sun and which is dependent upon the intensity of sunspot numbers. The Earth's magnetic field forms the charged particles into a shield for cosmic rays that originate from all parts of the universe so the majority do not penetrate the atmosphere. If the solar wind is intense as would be the case for a large sunspot number, the shielding of the Earth from cosmic rays is efficient. Few of the particles get through and those that do penetrate the atmosphere participate in the nucleation of clouds. If the sunspot numbers are low the corresponding solar wind is less intense and the shielding is not so efficient. This allows more cosmic particles to penetrate the atmosphere and this results in a cloudier Earth system. More cloud implies that a smaller fraction of solar radiation pentrates the atmosphere to cause warming; the Earth is cooler under these circumstances.
This mechanism is currently being investigated experimentally at the CERN facitily in Switzerland.
But what causes the sunspots to appear with such regularity in cycles of around 11 years, or is it 22 years or even 179 years?
The Table below contains some data about the planets.
|Planet||Mass [Earth = 1]||Orbital period [Earth years]|