How the Climate Crisis is Impacting Fall

Climate change is profoundly impacting the fall season, altering everything from the visual spectacle of autumn leaves to the behavior of wildlife and the success of agricultural harvests.

The primary driver of these changes is a general warming trend, with fall temperatures rising across the United States. This warming is not just a subtle shift – it's delaying the onset of cooler weather and, in turn, extending the summer season into what was traditionally autumn.

Autumn Leaves

The vibrant colors of fall foliage are a delicate dance of chemistry and climate. The brilliant reds, oranges, and yellows that define the season are produced when trees stop producing chlorophyll—the green pigment used for photosynthesis.

This process is triggered by two key factors: shorter daylight hours and cooler temperatures. While the length of the day remains constant, rising autumn temperatures are throwing this process out of sync.

Warmer autumn temperatures delay the signal for trees to stop producing chlorophyll, causing leaves to stay green for longer. This shortens the window for “peak” foliage.

Additionally, if the weather is too warm or dry, trees can become stressed and may shed their leaves early, or the colors may be muted. The best fall foliage occurs after a summer with adequate rainfall, followed by cool nights and sunny, clear days. As climate change leads to more extreme weather events like droughts or excessive rain, these ideal conditions are becoming less common, potentially leading to less vibrant displays.

This shift in timing and vibrancy has significant economic consequences, especially for regions that rely on fall tourism. The “leaf-peeping” industry, a major economic driver in places like New England in the US, faces increasing unpredictability as the timing of peak colors becomes less reliable.

Disruptions to Wildlife

For many animals, fall is a critical period for preparing for winter. The warming climate is interfering with these natural cycles, creating a mismatch between environmental cues and the biological needs of wildlife.

Many migratory birds and insects, like monarch butterflies, time their journeys south based on temperature rather than just the shortening of daylight. With warmer temperatures lingering later into the fall, some species are delaying their migration.

This can be problematic if their food sources along the way—like insects or flowering plants—have already been affected by the shifting season, or if they arrive at their destination out of sync with other species they rely on. In some cases, warmer winters are even causing some birds to shorten their migration routes or not migrate at all.

Animals such as bears and squirrels, need to consume a large amount of food in the fall to build up the fat reserves necessary to survive the winter. A shorter autumn can mean less time to forage, potentially jeopardizing their survival.

The timing of their hibernation is also being affected by warmer temperatures, which can confuse their natural rhythms.

Warmer falls are also extending the active season for insects, including pests and disease-carrying vectors like ticks and mosquitoes. This prolongs the risk of diseases like Lyme disease and West Nile virus later into the year, and can also lead to larger populations of agricultural pests.

Agricultural and Human Impacts

The lengthening of the growing season due to warmer falls has a mixed impact on agriculture and human life.

While a longer growing season may seem beneficial, it can be a double-edged sword. It can allow for multiple harvests of certain crops, but it also increases the risk of damage from extreme weather events.

The unpredictability of these events makes it difficult for farmers to plan and manage their crops.

For millions of people, a longer fall also means a longer and more intense allergy season. The ragweed season, in particular, is extended by warmer autumns, leading to prolonged suffering for those with respiratory issues.

A warmer, drier fall can also extend the wildfire season, especially in the Western United States. This increases the risk of destructive fires, harms air quality, and puts communities and ecosystems at risk.

What You Can Do

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