The sun's activity waxes and wanes on a cycle that averages roughly 11 years, though cycles as short as nine years and as long as 14 years have been observed. Chinese astronomers were already tracking the sun's activity using sunspots more than 2,000 years ago; the modern record of solar output starts in 1755, with cycle 1, and runs through cycle 24, which began in late 2008. Generated by intense magnetic fields, sunspots have proven one reliable indicator of the sun's overall output and its production of solar storms.
However, the current cycle (with its relative quite period) is "weak". Sunspots are predicted to be their lowest in 200 years. Thus, to the extent that solar activity influences Earth's climate, the impact is at a minimum. A weaker solar cycle is accompanied by a slightly dimmer sun, which changes the average temperature on Earth. That generality being said, the sun's brightness did not hit an all-time low during the past solar minimum, even though the sun was unusually quiet. So, although it can be said that the influence of Earth's climate will be less than when a solar maximum is reached, it cannot be stated with certainty the full extent to which a solar minimum will mean a truly dimmer sun.
Nonetheless, the decline in solar brightness from 2002 to 2008 as solar activity dwindled probably countered the warming on Earth that would otherwise have occurred due to greenhouse gases over that period. Thus, as solar activity now increases, it can be expected that this mitigating effect will diminish or cease.
All this implies that the relationship between GHG concentrations and temperature that have been the focus of so much chatter the last decade is probably skewed toward the low side of temperature response. As solar activity grows in the next cycle this "relationship" will be seen to be inaccurate and too conservative.
The assessment of the solar cycle can be found at http://www.nature.com/nature/journal/v471/n7336/full/nature09786.html