Somehow I missed Nir Shaviv’s comment about Jasper Kirby’s CLOUD experiment, read here: Shaviv writes (emphasis added):
Ok, so what do these results imply?
The first point was essentially pointed above. The results unequivocally demonstrate that atmospheric ionization can very easily affect the formation of condensation nuclei (CNs). Since many regions of earth are devoid of natural sources for CCNs (e.g., dust), the CCNs have to grow from the smaller CNs, hence, the CCN density will naturally be affected by the ionization, and therefore, the cosmic ray flux. This implies that ion induced nucleation is the most natural explanation linking between observed cosmic ray flux variations and climate. It has both empirical and beautify experimental results to support it.
Second, given that the cosmic ray flux climate link can naturally be explained, the often heard ‘no proven mechanism and therefore it should be dismissed’ argument should be tucked safely away. In fact, given the laboratory evidence, it should have been considered strange if there were no empirical CRF/climate links!
Last, given that the CRF/climate link is alive and kicking, it naturally explains the large solar/climate links. As a consequence, anyone trying to understand past (and future) climate change must consider the whole effect that the sun has on climate, not just the relatively small variations in the total irradiance (which is the only solar influence most modelers consider). This in turn implies (and I will write about it in the near future), that some of the 20th century warming should be attributed to the sun, and that the climate sensitivity is on the low side (around 1 deg increase per CO2 doubling).
Read it all here: http://www.sciencebits.com/CLOUDresults.
He says he’ll write more about this in the future. Hopefully he won’t keep us waiting too long, as many of us are looking forward to his expert assesssments.