Football fans on their way into Rice-Eccles Stadium on Saturday night weren’t seeing things. There, on the hill next to the block U, illuminated in red and white, was a second U — in purple.

Yes, purple is a combination of BYU blue and Utah red, the colors of the teams facing off on the field. But it was intended as something more than that — a call for action on global warming.

“This is a bigger issue than the football game going on tonight, but a lot of people are paying more attention to that,” said Madison Marichuch, a senior at the University of Utah who’s majoring in environmental studies. “Climate change is going to affect everyone.”

“This is something that really matters to us,” said Kaleb Christensen, a Brigham Young University student who organized this year’s effort. “And it comes just a day after the federal government released its new report on climate change.”

That report warned of a continued rise in temperatures that will, among other things, precipitate more wildfires and more hurricanes.

“This is an urgent issue that we need to address,” Christensen said. “Particularly here in Utah, we need to do something about this air. We’re hoping this helps inspire change.”

Christensen, a senior from Bountiful who’s majoring in biology, is a member of the Citizens’ Climate Lobby, but most of those participating were concerned students who banded together informally.

He pointed to successful student-led efforts to persuade the Utah Legislature to pass a bill recognizing the effects of climate change, “but there’s so much more to do. My hope is that this will be one in a couple [of] efforts that will lead to passing future legislation that will help mediate the effects of climate change.”

“I’m hoping to bring a little more awareness and public support to the issue,” said Casey Mullen, a doctoral student in sociology at the U. “I hope people realize we don’t have to be divided on this. We should work together.”

A group of BYU and Utah students created a purple block Y in Provo during last year’s Utah-BYU game; Christensen was determined to repeat the feat this year in Salt Lake City.

“This isn’t a stunt. This isn’t a fad. We’re not going to go away,” he said. “It’s people of our generation who have to do this for the world we’re going to live in — for our future.”

U. officials turned down a request by the informal group to change the lighting on the permanent block U to purple (with cellophane); BYU officials rejected the same request for the block Y a year ago. And Utah also denied a request for the climate activists to distribute purple flowers to students at the game during halftime.

“I wasn’t too upset about it,” said Christensen, who learned that the land next to the block U is public — so the plan changed to gathering people to form a U and hold powerful, purple flashlights.

The bigger problem turned out to be the timing of this year’s BYU-Utah game during a holiday weekend. Last year, the game was played Sept. 9 and between 50 and 60 Utah and BYU students turned out; on Saturday, about 30 turned out.

“It’s hard this year, just because of the fact that it’s Thanksgiving and so many people went home for the weekend,” Christensen said. “We had to change the expectations. I’m sure we’d have more than we had last year if it was any other weekend.”

The students — along with some of their friends and family members — said they turned out on a cold, damp night to make a statement.

“My hope is that this will inspire students, the government and the general populace,” Christensen said. “I’m hoping it helps inspire change.”