And yet, I doubt that you scoff about the 11-year sunspot and geomagnetic storm cycle, linked to solar activity - that trend has been observed for more than 200 years (~20 cycles) and is a strong and regular signal.

Tides and weather occur on a schedule linked to the moon, yet are subtly variable day-by-day. Weather is linked to daily and annual patterns of solar irradation, yet is subtly unpredictable.

There are two issues here:

1) No specific "cause" has been shown for the cycle. This doesn't mean we should doubt the effect. Before tides were shown to be due to the gravitrational gradient of the moon, they were well-accepted. We still don't have "proof" of the mechanisms behind the 11-year solar cycle, but we make plans to protect sattelites against its consequences.

2) The signal is weak. That's why long-term records like tree-ring chronologies and sediment cores are important as proxies for palaeoclimate going back thousands or even tens of thousands of years. A weak signal can reliably emerge from the noise, given a long enough data series. DOn't ridicule these methods. They callibrate the radiocarbon chart (which is non-linear due to - guess what? - variations in solar activity over time), and they inform our understanding of geomagnetic field reversals and other long-term Earth processes, so the methods are not hokum.

In a sense, it's like listening to a motor run and telling from the sound (the pattern of vibrations, something about the health of the engine, and its micro-scale future behaviour)

Having said which, the signal is STILL weak, and may not be statistically significant. Other things in our realm of purview are also weak signals over time. The idea of a 26 million year periodicity in extinction events is at the limit of detectability. It sounds plausible, but it isn't the sort of thing to have you running for your tin hat because the sky will fall tomorrow (unless you're easily excited and let these things go to your head, EP). Therefore it may, or may not be real. What is undeniably true is that solar output varies slightly with time, like a gently flickering candle. Life on earth depends not for its survival, but for the quality of life, on those flickers of warmth and cool (remember the little ice age of the late middle ages?)

Even if true, it only accounts for 5% to 20% of recent planetary warming, so it is a minor player. No reason to change our policy on greenhouse gas, whatever that might be, although some will seize on this as "evidence" that anthopogenic emissions are irrelevant. They aren't, but they might also not be as "evil" as they are portrayed by some factions, either...