DETROIT – With autumn comes Michigan’s beloved color change, when foliage transitions from greens to reds, oranges and yellows.
The timing of the transition is different for each region, occurring earlier in the season the farther north you go. But climate change is threatening to confuse that timeline even further.
Why do leaves change color?
Leaves are green from spring to summer. That green is the color of chlorophyl, which turns sunlight into food for the tree.
Then two things happen in the fall that causes chlorophyl to break down: diminishing sunlight and colder temperatures. This is a natural process and is part of the tree’s transition to winter mode. As the chlorophyl breaks down, the leaves morph into other colors.
Diminishing sunlight in the fall is a constant, it happens at the same pace every year. But temperature is not a constant -- and changes to our October temperature regime could change the timing of when the leaves turn.
Impact of climate change
In a chart in the video above, you can see that the peak color change in Michigan starts up north by early October, then works its way downstate to Metro Detroit, where it usually peaks during mid-to-late October.
October temperatures in North America have been warming up over the past 25 years, which is consistent with what we are seeing due to climate change. Warmer temperatures would tend to delay the color change a bit.
Other factors brought on by climate change could also have an impact on the timing of Michigan’s fall color show.
Factors like drought -- which we had this past spring -- and floods -- which we had over the summer -- stress trees, causing them to drop their leaves quicker and develop less vibrant color. Extreme heat can also stress trees, and we’ve seen some high temperatures this year. It is a documented fact that these types of extremes are happening more often and becoming worse due to the warming climate.
Climate change will undoubtedly impact our fall color change in the years ahead. In some years, the impact may simply be a change in the timing of the transition. But in other years, there will be increased stress on trees, which will have a significant impact.
Special section: Forecasting Change