These past few weeks, we’ve seen uncharacteristically warm fall weather with multiple 80+ degree days followed by intermittent dips below 70. Last month was the warmest and driest September ever recorded in Minnesota. The delay in fall colors on campus and the inability to wear our typical fall outfits or properly enjoy chai lattes has been frustrating for many Oles. So, what is causing this difference in fall weather?

The primary reason for this deviation from typical weather is climate change. With a warming planet comes more intense weather cycles. We are seeing this now not only with the loss of chillier fall days at St. Olaf, but also with Hurricane Milton and exacerbated wildfires in California over the past few years. 

Our warmer winter last year was slightly different, as it was part of a typical weather pattern called El Niño. This pattern is caused by a warmer ocean surface temperature, weakening trade winds and changing the position of the Pacific wind jetstream. That being said, drastic differences in weather like this fall are characteristics of a warming planet that we’ve been expecting. 

Typically, shorter days and cooler weather are the main contributors to the fall color we know and love on the Hill. Colder temperatures and less intense sunlight signal to the trees that it’s time to stop photosynthesis. When this happens, the chlorophyll in the leaves break down and the other pigments in the leaves become visible. Orange and reds are caused by visibility of carotenoids, which absorb blue-green wavelengths in light. Carotenoids also give carrots and pumpkins their color. Darker colors like purple are caused by the pigment anthocyanins, which protect the tree from UV-B radiation.

Orange Sugar Maple Along Heath Creek

The wet summer that Minnesota experienced this year may also be contributing to the lack of fall color. More rain throughout the summer can cause trees to keep their green leaves further into fall. Additionally, some meteorologists suggest that more heat could be trapped in the midwest because of the big storms like Hurricanes Helene and Milton, keeping weather from circulating as usual. Big storms like these may block or disrupt jetstreams of air that strongly influence weather patterns.

Minnesota has significantly less fall color at this point in the year than we have in previous years, according to the Minnesota Department of Natural Resources. 

(From the Minnesota Department of Natural Resources)

Based on historical averages, we may be able to expect a peak in fall colors on campus between the 14th and the 20th, although we can’t be certain with this year’s unique weather patterns. Either way, cooler fall temperatures are on their way in the coming weeks, so be sure to grab a chai and take a walk through the natural lands for a fall walk sometime soon. 

Sources

https://mndaily.com/286062/city/hot-dry-deptember-delays-minnesotas-fall/

https://www.cbsnews.com/minnesota/news/predictions-for-fall-weather-is-out-looks-like-the-heat-isnt-going-away-anytime-soon

https://bringmethenews.com/minnesota-weather/la-nina-is-coming-what-does-it-mean-for-minnesotas-winter

https://www.carbonbrief.org/jet-stream-is-climate-change-causing-more-blocking-weather-events/

https://www.mprnews.org/episode/2024/09/25/an-update-on-fall-color-plus-the-latest-on-hurricane-helene

https://www.startribune.com/fall-foliage-minnesota-color-map/601150323

https://www.dnr.state.mn.us/fall_colors/index.html#

https://www.weather.gov/arx/fallcolors

https://www.noaa.gov/understanding-el-nino

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1082902/ https://biology.appstate.edu/fall-colors/hidden-colors-leaves-what-are-functions-those-yellow-and-orange-pigments-we-see-fall