BEARTOOTH MOUNTAINS, Wyoming — Jim Halfpenny, an ecologist and teacher, didn’t know where the snow went. He had taken a group of students to see the ancient snowfields of Wyoming’s Beartooth Mountains, but the vast white expanses had vanished.

“My stomach dropped. I couldn’t believe it,” said Halfpenny. “Last year I was inside that snowfield. It was 20 feet thick, and we were walking up tunnel mazes made by meltwater.”

For the first time in recorded history, the ancient Beartooth snowfields near Yellowstone National Park melted.

“That snow is the water bucket that is providing the liquid nourishment for our breadbasket, the grain fields of North America,” said Halfpenny. “It will never come back.”

Permanent snowfields like the ones in the Beartooth Mountains fill an important environmental role: They regulate water flow year round by preserving winter snows late into the summer and providing a steady, dependable source of water. Their disappearance is part of a larger pattern of climate change that experts attribute to humans, and the permanent snowfields’ departure means the West will have another factor to consider when dealing with vanishing water supplies.

“Without this, we can’t have a commercial food industry that’s working,” said Halfpenny. “The timing of the flow and the amount, it’s going to have direct impact on our production of cereal-type products — grains, wheat.”

It also means that forest fires may start earlier in the year and last longer, nesting birds will have less food for their young in the late summer and snowmelt-fed fishing habitats like the Yellowstone River may be hit hard.

“We’re going to have fewer trout,” said Bruce Farling of Trout Unlimited. “We’re going to have more warm-water species. We’re going to have more diseases and parasites that are harmful to trout.”

Because the snowfields provide a steady stream of cold water, he said, some local native species of trout that are intolerant of warm temperatures may face extinction. Those sorts of changes would also have big effects on the economy. Fishing brings in hundreds of millions of dollars each year to the area’s economy.