SANDSTONE (AP) — Peter Lenz felt a little guilty ice climbing recently. The weather was disturbingly nice.

With the sun shining and Pine County temperatures hovering in the mid-30s, it was beautiful out — and chilly enough to keep conditions safe for the Sandstone Ice Festival.

For Lenz, though, it just didn’t feel like January, and it sure didn’t feel like a normal Minnesota winter. “Ice climbing should be cold,” he said to Minnesota Public Radio News .

Sandstone’s ice cliffs offer a practical lesson in the problems of climate change and how Minnesotans must increasingly adapt. The cliffs attract climbers and business, but it’s getting harder to keep the scene going as winter temperatures moderate.

Sometimes, it’s even impossible.

“We had to cancel (the festival) in 2016,” said Lenz, who sits on the board of the Minnesota Climbers Association, which organizes the event. “It was just too warm to make ice. And we had to push it back to the first weekend in January just because of warming temperatures.”

The festival, which just completed its 14th year in Sandstone’s Robinson Park, used to be held in December. But temperatures proved to be too reliably high.

Ice climbing requires big sections of solid, vertical ice. Climbers wear boots with crampons and carry ice tools, which are like hammers with sharp metal picks on the ends. They use a harness and rope to protect themselves in case they fall.

At Sandstone’s Robinson Park, the ice runs down rock walls left behind from an old mining operation. Some of the ice forms naturally; much of it is man-made.

A few years ago, the city ran a water line out toward the park so the climbers group could build an ice-farming system. A band of volunteer climbers installed a series of pipes, misting devices and low-flow showerheads to run water down the cliff.

Now, if conditions are right — somewhere around 25 degrees, Lenz said — perfect slabs of ice forms from the system.

“It’s really dependent on the temperatures, and we’ve struggled this season already with finding weeks that have those good temperatures,” he said. “In December we had to not farm for two weeks just because it was too warm.”

The trendline is worrisome for Sandstone and its climbing crew. Historical temperature data show the city’s Decembers and Januarys trending several degrees higher over the past 120 years.

Across the state, winters are getting shorter and warmer, about 1 degree every decade. It’s changing ecosystems and affecting economies, especially in outdoor recreation — you can’t ski or snowshoe without snow.

The ice-farming system uses an estimated 65,000 gallons of water each year, said climbers association president James Loveridge. Water use varies depending on the year’s weather conditions.

“This year hasn’t been that cold, so we probably used a bit more water than we wanted to,” Loveridge said.

Sandstone doesn’t charge the climbers group for the water, Loveridge said. If it did, he added, the nonprofit couldn’t afford the bill on its shoestring budget.