That output is known to vary during the course of the 11-year sunspotcycle, as well as over the longer term, and although such changes have not been matched to temperature changes in the way that rises in the level of greenhouse gases have been, they may still be making a contribution.
Sunspot activity waxes and wanes on the sun in a 11-year cycle, and we are approaching the peak of sunspot activity, probably reaching it in 2013, according to Hesse.