Background
Lastovicka (2006), in broadly summarizing recent advancements in the field, has recently written that "new results from various space and ground-based experiments monitoring the radiative and particle emissions of the sun, together with their terrestrial impact, have opened an exciting new era in both solar and atmospheric physics," stating that "these studies clearly show that the variable solar radiative and particle output affects the earth's atmosphere and climate in many fundamental ways."

What was done
In a review of this broad area of research, Bard and Frank consider "changes on different time scales, from the last million years up to recent decades," and in doing so "critically assess recent claims that the variability of the sun has had a significant impact on global climate."

What was learned
"Overall," in the judgment of the two researchers, the role of solar activity in causing climate change "remains unproven." However, as they state in the concluding sentence of their abstract, "the weight of evidence suggests that solar changes have contributed to small climate oscillations occurring on time scales of a few centuries, similar in type to the fluctuations classically described for the last millennium: the so-called Medieval Warm Period (900-1400 A.D.) followed on by the Little Ice Age (1500-1800 A.D.)."

What it means
The measured judgment of Bard and Frank seems to us to be right on mark. The subject they treat is so complex that most theories of solar forcing of climate change must be considered to be as yet "unproven." It would also be well for climate alarmists to admit the same about the role of rising atmospheric CO2 concentrations in driving recent global warming, especially in light of Bard and Frank's conclusion that "solar fluctuations were involved in causing widespread but limited climatic changes, such as the Little Ice Age (1500-1800 A.D.) that followed the Medieval Warm Period (900-1400 A.D.)," for if it is fairly certain that the sun was responsible for creating these multi-centennial cold and warm periods, it is clear it could easily be responsible for the global warming of the past century or so, which has yet to return the earth to the level of warmth experienced during the Medieval Warm Period, when there was 100 ppm less CO2 in the air than there is today, which CO2 deficit - according to the climate-alarmist way of thinking - should have made it even more difficult to sustain the higher-than-current temperatures of that earlier warm period.

Reference
Lastovicka, J. 2006. Influence of the sun's radiation and particles on the earth's atmosphere and climate - Part 2. Advances in Space Research 37: 1563.