Now I am not a dyed in the wool believer in global warming but:
The above is some 20 years of my tracking the first bloom date of a set of species of Hemerocallis. The bloom date is measured in days from the first of the year. It does not take much to see what is happening, the slope is very much downward. In fact this year is the earliest ever, by a lot. Compared to the early 90s we are down tens of days, and that is substantial.
Just an observation. The details are in my garden web blog.