We have a COMPLEX system between solar input and the response of Earth to that energy input because of different reasons: the coupled system of oceans and atmosphere, plus the variation of solar energy due to the tilt of the earth spin axis. The precession of the spin axis, the variation of the obliquity with time, and the variation of the location of perihelion (the point of closest approach to the Sun of a body orbiting the Sun).

As a simple example consider the amount of incoming solar visible radiation that is reflected back into space. Currently this is about 30% for Earth. That is to say, out of each 1 joule of visible radiation that the Sun pours down upon us about 30 % is reflected back into space. The amount is controlled by the area of land versus area of ocean and by the areal extent of glaciers. Ice has a very high reflectivity. So now let us imagine, because of astronomical forcing, the Earth grows a little colder and more ice forms. The response of the Earth system will be to increase the reflectivity and hence make the earth even COLDER!! This is a positive feedback; if the planet gets a little colder due to one effect, ANOTHER effect kicks in to amplify the first effect.

The reason why the issue of climate prediction is so difficult is because MANY SUCH feedbacks both positive and negative exist!!!!!

Hence understanding the real response is a complex summation of all these simultaneous effects. This is why we call the Climate and example of a COMPLEX system. Another example of a complex system with feedbacks is YOU!!!!!

You go outside on a warm or hot day and your body sweats. But because it takes energy to evaporate water, as your sweat liquid water goes to the gas, it removes heat from your body cooling you off!!!! This is an example of a negative feedback: the more you heat up and sweat the more cooling effect you get.

Complex systems all share this phenomena of positive and negative feedbacks.