Source of graphSkeptics ask whether global warming is due to changes in solar activity. The sun does fluctuate in its output on an 11-year cycle, which are shown above as sunspots. This variation does affect the weather patterns that we see, but the influence of solar variation is only 1/8th as strong as the influence of the greenhouse gases in the atmosphere.
Sometimes the sun is active for a longer period, and I personally expect that the Maunder Maximum of sunspot activity will be shown to account for at least some of the Mediaeval Warm Period.
Nobody claims that computerised climate models are perfect, but as the science progresses, they will become increasingly accurate. There are at least six variables that affect the earth's temperature. We can only modify one of them - our greenhouse gases. This we have got to do, and Copenhagen is the place to do it.