However, the UTM biology professor doesn’t think that a warm autumn has any negative impact on the formation of fall colours because the sequence of events starts with the breakdown of chlorophyll — the green leaf colour, which slowly degrades and then actually makes all the carotenoids visible.
“Carotenoids are the yellow and orange pigments in the leaf that are all [there] during the summer, and they only become visible in the fall when the chlorophylls have been broken down,” said Ensminger. “It’s not that they were late in the fall, like many people think, that they all of a sudden are being produced. They have only been masked by the chlorophylls to that point.”
As a result, Ensminger doesn’t think our changing climate will necessarily alter the sequence of the events.
WATCH: Stunning aerial of the leaves changing in Toronto
However, if the trees experience droughts or a very hot summer, what climate change will “probably do” is modify the fall schedule to a “much, much larger” extent than just warm autumn temperatures, he said.
“The reason for that is this senescence process…where leaves are actually determined to be set at one point and where they’re no longer useful for the tree, that’s something that is accelerated during hot temperatures and drought, [when] the trees experience stress,” said Ensminger.
Historical data at Algonquin Park shows ‘consistency’
Using Algonquin Park as a source, Birrell said historical data from the park over several decades indicates a “point of consistency” when comparing autumns and leaf changes, even during the warmer and cooler summers.