COLUMBUS, Ohio (WCMH) – Central Ohio’s fall colors are late to the season.

As the calendar turns to November, autumn leaves across most of the state are just now hitting their peak, and colors around Columbus are appearing 2-3 weeks behind normal.

“This year and a number of years in the past couple of decades, we have peaked during the last week of October or the first week of November,” said NBC4 meteorologist Ben Gelber, who has been tracking central Ohio weather and climate for more than 40 years.

Fall colors have historically peaked in central Ohio in the third week of October, but many local trees this year waited until this week – the first of November – to reach their peak change. The latest weekly map published Thursday by the Ohio Department of Natural Resources shows central Ohio state parks just now peaking.

ODNR fall foliage map Nov 4 2021
Ohio fall color progress report, Nov. 4, 2021. (Ohio Dept. of Natural Resources)

“Today through next week will likely be this year’s peak condition for most of the state before leaf drop,” ODNR fall color forester David Parrot said in the agency’s Thursday update.

Warmer Octobers mean later and stranger changes

Three things factor into when the leaves change color after summer: sunlight, temperature and rainfall. When days get shorter, there’s less sunlight, so leaves stop producing chlorophyll – the substance that makes them green – revealing the yellow, orange, red and purple hidden pigments.

The change in sunlight happens on time every year regardless of the weather thanks to Earth’s rotation around the sun. But it’s the second factor – temperature – that’s messing most with leaves’ timing.

As human activity emits heat-trapping gases like carbon dioxide into the atmosphere, air temperatures are warming. A 2015 analysis by Boston University researchers in the journal Annals of Botany found October temperatures are the biggest factor in when leaves change color, and those color changes have been delayed over time in the U.S. as average temperatures warm.

“The perfect combination is bright, sunny days followed by chilly nights,” Gelber said. Unfortunately for the leaves, 2021 saw some of the warmest October nights in local history.

This year set an October record for average daily minimum temperature at Columbus’ main National Weather Service station, where recordkeeping goes back to 1878. The average low temperature for an October date this year in the capital city was 53.9 degrees Fahrenheit, 9.1 degrees above normal.

Ohio city°F increase in daily low temp. in Oct. ’21Rank (Years of records)
Akron+9.9°1st (129 years)
Zanesville+9.5°1st (75 years)
Columbus+9.1°1st (144 years)
Mansfield+8.4°1st (101 years)
Youngstown+8.4°1st (94 years)
Findlay+8.2°1st (77 years)
Toledo+8.2°2nd (149 years)
Cincinnati+7.7°6th (150 years)
Dayton+7.2°2nd (129 years)
Cleveland+6.6°1st (147 years)
Source: NOAA. For cities with multiple weather stations, station with longest history chosen.

Many October days, too, felt like an extension of summer at a time when leaves look for cues to stop producing their green chlorophyll. Columbus’ average daily temperature in October was 62.2 degrees, which tied as the city’s 3rd-warmest on record at 7.1 degrees above normal.

“It’s normal to have a mix of above and below average temperatures,” Gelber said, which is just a typical seasonal pattern. But when so many autumn days are warmer than normal week after week, “that has certainly played a role in slowing down the seasonal change in fall colors.”

Warmer temperatures in early autumn also push trees out of sync with each other, Gelber added. Some turn on time, like maples, but others stay green longer, like oaks. “So, you get splashes of color but not in unison,” he said, “and that diminishes the overall effect.”

More rain, storms wash out colors

As the effects of climate change push back leaves’ color transition, the colors that do show may appear less vibrant.

“There is a tendency in recent decades to have both warmer nights and wetter autumn seasons,” Gelber said, “both of which counteract the ideal conditions that we’re looking for.”

More rain in the fall prevents that perfect combination of sunny days and crisp nights, diluting the color changes. Every season in Ohio has seen more precipitation since the mid-20th century, Gelber said, because a warmer atmosphere can hold more moisture, and more of that water vapor falls as rain.

October in Columbus, he added, is one inch wetter on average – and September a half-inch wetter on average – compared to the second half of the 20th century.

Storms also knock leaves off trees. Over the past two decades, Gelber said, there has been a greater tendency for tropical storms, hurricanes and their remnants to come farther northwest to Ohio and “bring heavy to excessive rainfall in September and October.”

“Even as they weaken over land, they still bring copious rains and gusty winds, both of which can diminish the fall colors and bring the leaves down prematurely,” he said.

Gelber also noted warmer autumn weather is accompanied by higher humidity, which is more conducive to strong thunderstorms and has made fall tornado outbreaks more common this century.

On Oct. 21, for example, the National Weather Service office in Cleveland issued a record 11 tornado warnings for a single event. Similar conditions spawned six tornadoes in south-central Ohio five days earlier in a rare nighttime October outbreak.

Fall foliage in a warmer future

Autumn in Columbus has already risen 2.8 degrees since 1970, according to researchers at Climate Central, resulting in more days above normal like Ohio saw last month.

If current emissions trends continue, a scenario modeled by researchers at the Union of Concerned Scientists in 2019 found 90-degree heat index days would more than triple in Columbus by the middle of this century. Along with a scorching summer, that trend would likely also heat up early fall, further delaying and desynchronizing the leaves’ annual changes.

And even with realistic emissions reductions, the UCS study found that 90-degree heat index days throughout the year would nearly triple.

Although temperatures continue to warm from to climate change, Gelber said, there will always be a limit, “because even in a warmer climate it’s still going to get cold at some point.”

The bottom line, though, is that climate change is still “shortening the period of peak colors,” he said. And those famous fall colors that do manage to shine through the treetops will be “less vibrant and less synchronized.”