Ah, fall — the wonderful transition from the sticky heat of summer into the crisp air of autumn. The leaves begin to turn, the scarves come out, and the scent of saccharine Pumpkin Spice wafts through the air, signaling to all residents of the Northern Hemisphere that summer is waning and winter is coming.
Or at least that’s how it used to be, before climate change came along and ruined fall for everyone.
It should go without saying that, in the grand scheme of things, the loss of autumn as we’ve come to know it might be one of the more manageable consequences of global warming. Climate change is a massive problem that will have devastating consequences that reverberate on a global scale, causing mass migrations and displacing millions of climate refugees.
Still, not all consequences of climate change will loudly announce themselves — so on the first day of autumn, it’s worth taking a look at just how climate change could forever reshape fall as we know it.
One of the most iconic harbingers of fall are the brightly colored leaves that seem to blanket the deciduous forests of the Northern Hemisphere during autumn. Leaf tourism, or leaf peeping as its known in New England, has even become big business, contributing an estimated $3 billion to New England’s economy during the fall months.
But the months-long spectacle of vermilion and crimson hues might not be around for much longer if climate change continues apace. As Howard Neufeld, a professor of physiological plant ecology at Appalachian State University, wrote in a 2014 piece for The Conversation, an increase in atmospheric carbon dioxide might actually intensify the color of fall leaves, making the colors brighter, but it will also likely lengthen summer and shorten fall, meaning that there is considerably less time for leaf peepers to enjoy the autumn leaves.
Changes in global temperature might also impact the changing of leaves by disrupting the synchronization that occurs between different species of trees. Right now, most species of trees change their colors at roughly the same time — but as temperatures continue to increase, more sensitive species will likely respond differently than other species, and the changing color of tree leaves could become patchier, with some trees turning while other trees remain green. What’s more, as temperature increases, bacteria, fungi, and pests that thrive in lower latitudes might begin make their way northward, introducing another threat for trees.
An increase in atmospheric carbon dioxide might actually intensify the color of fall leaves, making the colors brighter, but it will also likely lengthen summer and shorten fall.
And while an increase in carbon dioxide might intensify leaf color, other consequences of global climate change could actually make colors less intense. On one hand, an increase in precipitation — which the National Climate Assessment projects will take place across New England and much of the Midwest if greenhouse gas emissions aren’t drastically reduced — makes leaf colors less brilliant. Clouds cut down on the amount of light that can reach the leaves, thereby limiting the production of anthocyanins, the colorants responsible for those famous fall colors. On the other hand, drought — which New England has been suffering through this summer — can cause trees to lose their leaves prematurely, effectively cancelling the leaf peeping before it has even begun.
In the Southeastern U.S., climate change might mean those crisp fall days are replaced by smoggy fall days. That’s the conclusion of a study published last month in the Proceedings of the National Academy of Sciences, which found that drier, warmer autumn days — which scientists expect will be more common in the Southeastern United States due to climate change — will increase the likelihood of smoggy days.
As the incidence of hot, dry days increases… fall might mean smoggy weather for parts of the United States.
According to the researchers, that’s because on dry, hot days, trees and plants send the molecule isoprene into the air, to help protect their leaves from drought conditions. When isoprene is exposed to sunlight and reacts with human-made nitrogen oxides — which come from things like vehicle emissions and coal plants — it turns into fine particulate matter, or smog. And as the incidence of hot, dry days increases — and as those days become more common further into autumn — fall might mean smoggy weather for parts of the United States. That’s a problem for farmers, whose crops can respond poorly to smog conditions, and also a problem for smog-sensitive groups like the elderly and young children, who are more susceptible to health problems associated with smoggy air.
Beyond messing with fall leaves and creating more smoggy days, climate change is set to mess with our traditional picture of fall in a major way: by making pumpkins more difficult to grow.
Last year, Libby’s Pumpkin — which supplies the vast majority of the canned pumpkin sold in the United States — announced that it was facing serious yield shortages. That’s because Illinois, which grows ninety percent of the pumpkins in the U.S., experienced an unusually rainy late-spring and early-summer, a precipitation change consistent with what scientists project will occur with climate change.
And while those weather patterns aren’t directly tied to the fall season, their impact is far-reaching: Libby’s announced that they had to end their pumpkin harvesting at the beginning of October, cutting their harvest season short by nearly a month. In total, the rainy weather cost Libby’s half of their expected yield, and meant that after they released their final shipment in early November, there was no more Libby’s canned pumpkin until August of 2016.
Illinois wasn’t the only state to have its pumpkin crops impacted by unusual weather. In Oregon, Rogue Brewery had to release its seasonal pumpkin beer five weeks early due to unseasonably warm summer temperatures.
So enjoy the brilliant fall leaves, crisp fall mornings, and pumpkin-spiced-everything while they last — the fall of the future looks considerably warmer, hazier, and less brightly colored.