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The effects of solar irradiance on climate is just recently being investigated. We know that sun spots vary week to week and also follow an eleven year cycle. It is now accepted that sun spot activity is connected to solar output (irradiance).

The changes in solar irradiance over the long term is not known yet, because irradiance data has only been available for the last 20 years. Even the method of measuring the changes in irradiance have only recently been agreed upon. What is beginning to be understood is the huge effect of these relatively small changes in solar output on precipitation and ultimately, climate.

We do have long term historical data about sun spot activity. If the correlation with sunspots is true, then by using the historical information about sun spots, we can look at climate changes. For example, between 1945 and 1715 there is record showing low sun spot activity. During this period, there was record low temperatures on the earth. Since that mini ice age, the earth has been on a 300 year warming trend. Sun spot activity has gone through a similar increase with the peak in 1960.

Solar irradiance levels go through relatively small fluctuations. How can such small changes affect climate in such big ways? Absorption of solar energy by the tropical oceans create ocean-temperature anomalies that are transported by ocean currents over a period of time to locations where the ocean temperature can modify the North American jetstream in position and strength. Such action in turn determines precipitation patterns. This influence on the jetstream is the key to the climate change. Only recently is the jetstream being understood in its role in climate change and global warming. When it is fully understood all the influences affecting the behavior of the jetstream we may then find that the human impact is not really the culprit. So far we are finding that the primary influence on the jetstream points more and more to the natural fluctuations of the sun's output; something that man has little control.