Is climate change affecting fall foliage in western WA? Here’s what the latest data says

Colorful foliage is as much of a fall staple as Halloween, apple cider and Thanksgiving. But as the climate warms , will it have an effect on fall leaves?

According to climate science nonprofit Climate Central , the climate can impact everything from the color of autumn leaves to when they begin to fall from the trees.

How climate change can affect fall foliage

According to Climate Central, trees "use cues from the environment" to start preparing for winter. These include shorter days, cooler temperatures and an increase in rainfall. As a result, early arrival of summer heat and drought are linked to leaves beginning to fall earlier in the year. Warm fall nights and high temperatures in October, meanwhile, have been linked to the leaves of fall starting later in the year.

Weather extremes, also believed to be impacted by climate change, can contribute as well. Wildfires, drought and extreme heat can cause leaves to dry up and fall earlier, while heavy storms can knock the leaves off of a tree.

The color of fall foliage is also impacted by the climate. During the fall, sunny days and cool nights lead to more vibrant, colorful leaves, while summer heat, drought and early frost can all dull the color of foliage. Climate Central analyzed data from 243 U.S. locations and found that 87% had seen their fall nights warm since 1970, with an average increase of 2.7 degrees Fahrenheit.

Fall climate in western WA

So how does this impact Washington? With some effects of climate change causing earlier leaf fall and some delaying it, experts are torn on whether or not autumn foliage is arriving earlier.

Washington has seen a rise in temperatures since the late 20th century, according to National Weather Service data , but the extent of the change varies depending on the month and the location.

In western Washington, summer weather has arrived slightly earlier in recent years. According to the NWS, the average June high temperature in Olympia across the 1980s was 71.2 degrees Fahrenheit, while that number rose to 73.2 degrees over the past ten years. While the earliest NWS available for is from 1982 for Tacoma and 1985 from Bellingham, both have seen June's average high temperature rise since the '80s, but by less than half a degree.

The difference isn't as pronounced in the fall. In Olympia the average October and November high temperature jumped by 0.1 degrees and 0.8 degrees, respectively between the '80s and the past ten years. Bellingham saw its average October highs rise by 0.2 while its November highs rose by two degrees, while actually Tacoma saw October averages drop by 0.6 degrees and November average rise by the same amount.

So the state has seen earlier summers and hasn't particularly seen warmer falls. But what about fall nights, which experts say have an outsized impact on foliage?

Bellingham saw average low temperatures in October and November that were within 0.3 degrees of its averages in the '80s. In Tacoma, October lows have risen by 2.8 degrees between the '80s and the past ten years, while November lows have risen by just under a degree. And farther south, Olympia's average October lows have risen by nearly two degrees, but November lows actually fell by a third of a degree.

So when will fall foliage peak in WA?

SmokyMountains.com, a site dedicated to travel in and around its namesake national park, maintains an interactive map of estimates for when fall foliage will peak in each region of the country.