Scientific Review By Eli Ginsburg
When we think of autumn, our mind is usually filled with the brilliant red, orange, gold, and yellow leaves of the trees. In fact, stunning colors of autumn leaves drive a huge tourism industry from Vermont to the Carolinas. Unfortunately, environmental factors like air quality, droughts, and climate change could change all of that. Is it possible that autumn leaves will become a thing of the past?
Understanding the Colors of Autumn Leaves
On a basic level, the leaves of a plant appear green because of a green pigment called chlorophyll. Chlorophyll in leaves absorb light from the sun, crucially capturing the energy needed for the photosynthesis process, whereby trees and plants manufacture the food (carbohydrates and sugars) that they need to live and grow. During the spring and summer, chlorophyll is regenerated as a result of certain chemical processes that occur with warmer weather and longer exposure to sunlight.
During the spring-summer period, trees maintain high levels of chlorophyll causing the leaves to remain green. Yellow and orange pigments are also present, but they are hidden by the intense green color.
In autumn, as the weather cools, the leaves start to receive less sunlight. Less sunlight triggers the breakdown of chlorophyll in leaves, which is not replenished by the plant as the season progresses. The green color fades as chlorophyll in the leaves breaks down. The yellow, orange, and gold colors of autumn leaves are then visible in all their glory. The red and purple leaves, caused by other chemical processes, are also prompted by colder weather and shorter days.
This is why certain broad-leaved trees remain green year round in the southern states, where temperatures are warmer throughout the fall and winter.
Do Warmer Autumns Mean Shorter Fall Foliage Seasons?
The eight warmest Octobers on record were experienced in the Northern Hemisphere between 2014 to 2021. According to the National Oceanic and Atmospheric Administration (NOAA) monthly US climate report, in 2022, “the average October temperature across the contiguous U.S. was 55.3 °F (12.9 °C), 1.2 °F (0.7 °C) above the 20th-century average.”
Famous for fall foliage, the Northeastern US is actually warming at a faster rate than other areas of North America. Based on the science behind why leaves change color, it seems that warmer fall temperatures may be extending the growing season, keeping leaves greener for longer and delaying the autumn foliage season. Later fall foliage is also linked to warmer temperatures, lack of precipitation in the fall, and earlier spring bud burst.
Light levels stay consistent each year – so while longer growing seasons may be keeping leaves greener longer, it doesn’t necessarily mean they won’t shed at the same time they usually do. There are also other factors, like droughts, that have scientists seeing fewer days of fall colors. For example, a shorter fall season can be caused by a hot summer followed by a wet fall.
Scientists from George Mason University tracked maple trees in central and North Eastern United States from 1826 and 2016. The research found that the first appearance of colored leaves has shifted 0.26 days later each year, leading to a delay of more than a month in fall foliage since 1880.
Will Climate Change Dull Vibrant Fall Colors?
There isn’t just evidence that colorful autumn leaves will display for a shorter time each year; the brightness and array of autumn leaf coloring may also be affected by climate change. Dry conditions, and droughts in particular, cause leaves to be brownish rather than their usually vibrant fall colors.
A NOAA report reveals that year-to-date for 2022, total precipitation in the U.S. is 2.17 inches below average. And with about 62.8% of the continental United States (excluding Alaska) being in drought at the end of October, we can expect to eventually see the effect on trees and their autumn colors if droughts persist.
When trees are stressed by a drier spring and summer, the quality of colors of autumn leaves can diminish. And during continuous years of drought, the leaves skip the colorful phase altogether, turning brown instead and quickly shedding.
Like us, trees are susceptible to air pollution, impacting their health – and color of their leaves. Fossil fuel pollution can turn leaves white or brown before autumn, this can put the entire tree at risk. Additionally, poor air quality can lead to holes, as well as black and brown spots and edges. Decreasing air pollution will not only improve our health, it will also protect trees and preserve autumn leaf coloring.
Other Impacts of a Changing Climate
Just like us, trees need to rest. The disturbance of processes leading up to leaf shedding and thereafter could have serious effects on the trees’ ability to cope and adapt. Acadia National Park in Maine is known for its brilliant fall foliage, and is an example of a forest where the effects of climate change can already be seen. The park has experienced an increase in temperature of 3.4 °F/1.9 °C over the last century. This has played a part in an increase in pests and diseases, unexpected tree deaths, the disappearance of 1 of every 6 plant species, non-native plants becoming more abundant, fewer birds and native animals, and more intense storms, all since the park was founded in 1919.
If the local climate continues to change at such a rapid pace, certain species of trees may be unable to adapt and thrive at the same rate. They may also be more vulnerable to infestations and wildfires. This may mean that trees could die out and stop growing altogether in certain areas; and possibly begin growing in new, more suitable environments. This could negatively impact industries, like leaf-peeping tourism and Vermont’s maple syrup production, as the maple trees with their bright, beautiful red leaves “migrate” northwards to Canada.
What Does All of This Mean for Us?
Long before BreezoMeter took it upon ourselves to educate people about air pollution, trees have been working to improve the air we breathe. Trees and plants are the original protectors of the atmosphere, and we can’t live without them.
The photosynthesis process removes carbon dioxide (CO2) from the atmosphere and converts it to oxygen. Together trees and soil store & sequester CO2 from the atmosphere, helping to maintain Earth’s carbon balance. When they die from pests and unsuitable environmental conditions, the carbon is released back into the atmosphere.
Central Park alone removes roughly 1 million pounds of carbon from New York City’s air each year, so you can imagine the impact large forests have on carbon sequestration (capture & long-term storage of CO2).
However, wildfires are also more likely to occur due to the effects of climate change, threatening forests and greatly impacting the air we breathe. Read more about this in our article: Are Wildfires Getting Worse Due To Climate Change?
Deforestation and the threat wildfires pose to trees and their health, means the release of carbon into the atmosphere and fewer trees to combat greenhouse emissions, leading to climate change – creating a vicious cycle.
Why are Forests Important for Mitigating Climate Change?
Given that carbon dioxide is a main contributor to climate change and the amount of CO2 emissions the world is putting into the atmosphere every year, forest carbon sequestration has become increasingly important. While reducing human-made emissions and greenhouse gases is important for combating climate change, we have to remember that forests are our single largest source of atmospheric carbon dioxide reduction.
Trees could actually be our best bet for mitigating climate change. Scientists even found that certain species of trees are growing faster and bigger due to the increase of CO2 levels – this is called “carbon fertilization.” It should be noted that some researchers do point out that this effect can plateau as time goes on, remarking that any positive benefits of carbon fertilization should be seen in context of the overwhelming negative effects of adding more CO2 to the atmosphere.
Although planting new trees can’t hurt, when considering a forest and climate change, it is the more mature trees that remove significant levels of carbon dioxide from the atmosphere. Protecting our forests will not only ensure autumn leaf coloring remains full and vibrant, it will give us a chance against rising CO2 emissions. And it’s not just the Amazon and Indonesia where forests are threatened by industry, a substantial loss of forest canopy is occurring in the Southeastern US. Unfortunately, older forests are far and few between in the US (less than 7% of US forests are over 100 years old).
Many of us love colorful autumn leaves, and while protecting our forests will keep us awe-inspired each fall, it is a far more important endeavor toward mitigating climate change.
Technology to the Rescue
Everything from satellites to drones to smartphone cameras are being used to collect data and provide actionable insights to help protect and restore our forests. For example, real-time satellite imagery of the earth is helping governments and organizations to identify and stop illegal deforestation; a pilot project in Indonesia is placing old solar powered smartphones on trees to detect suspicious sounds like trucks and chainsaws; and drones are being used to replant trees in hard to reach places, allowing forests to be replanted at a lower cost and a lot faster.
Advances in technology are making it easier to study, understand, and build solutions to combat climate change and protect our forests. As we’ve seen in the world of air quality, being able to access a comprehensive visualization of our environment helps people, organizations, corporations, and governments take appropriate action.
Hopefully this will lead to real change around forest preservation and ensure we have a bright future ahead of us to enjoy breathtaking autumn leaf-peeping.