How can you say that?
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The nature of your question is splitting hairs. In the context of a cosmological and astronomical time frame 20 years is not significant. At least when when claimants are declaring global climate changes, IMO. When one wants to discuss nuclear fusion in the evolution of stars and its effects on planets over ten billion years is an entirely different matter. Be assured that the Mt. St. Helens eruption did more to affect an atmospheric change in 6 hours than the nonsensical statement:
"He says that the increased solar brightness over the past 20 years has not been enough to cause the observed climate changes, but believes that the impact of intense sunshine on the ozone layer and cloud cover could be affecting the climate more than the sunlight itself."
Duh. So we can conclude from the article that 'sunlight could affect the climate less because of sunlight in an ozone layer and clouds were the sunlight hits.' It is a poorly written article.
We know the sun has sunspot cycles. 11 years or 22 years depending how you look at it. This is cyclical variability. While the sun is no doubt evolving like any star, there would be no reason to assume it would evolve perfectly smoothly with no burps, but the evolution would have to be smooth within some limits or we wouldn't be here now.