[timr]

> A 1,200 year time series.. that's definitely in the climate area.

Superficially, sure, but this is not a good dataset for any climate related argument. Cherry trees live about 100 years under optimal conditions, so you’re talking about multiple generations of trees here, with significant adaptation and selection along the way (humans heavily influenced the development of these trees, and the current “standard” tree for cherry blossoms in Japan is actually a hybrid first created in the 1700s). In short, even if you set aside measurement reliability and consistency over time, this dataset is heavily confounded.

As an aside, you’ll note that the primary change is that the lagging tail of the distribution is pulling forward (i.e. the distribution is getting narrower) not that the distribution overall is shifting forward. You can find trees blooming “this early” many hundreds of years ago, just not as often as now.

[adriand]

But wouldn’t that be true for all periods in the dataset? You see ups and downs over the centuries, and in each of those centuries I’m sure humans heavily influenced their evolution. Then you see a pronounced upward trend that just happens to also coincide with what we know to be serious, sustained and highly unusual planetary-wide warming.

[timr]

Sure, but it doesn’t matter. Confounding means that there’s an uncontrollable factor in the analysis. You can’t just assume that the uncontrollable factor is the same over all measurements in the dataset.

Just to illustrate the point, the trend you’re describing (which you haven’t correctly described, but I digress) could be due to warming, or it could be due to selection in favor of earlier blooming varieties in the last generation. You can’t know which explanation is true, so you can’t draw conclusions.