From the Ars Technica article:
Sun-clouds-climate connection takes a beating from CERN | Ars Technica
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More careful looks at the connection between incoming radiation and cloud cover generally found no correlation at all; meanwhile, temperatures kept rising even as solar activity dropped. Plus clouds have a complex relationship to climate, reflecting sunlight or insulating the planet, depending on their location and structure. Finally it was never entirely clear that radiation could drive cloud formation in the first place.
That last point is where CERN, the people who built the Large Hadron Collider, stepped in. They're very adept at creating radiation in a controlled environment and figured they could get to the bottom of how that radiation could influence cloud formation. Preliminary results looked promising, but it later turned out that
the presence of even trace chemical contaminants could completely swamp the influence of the radiation.
Now, the same team is back with a follow-up paper that delves into the big picture of cloud formation. After
years of testing, the team had exposed water vapor to a variety of conditions: different temperatures, the presence of various chemicals like sulfuric acid and ammonia, and the presence or absence of radiation. In each condition, the number of particles that water condensed on
were measured."
