PARK CITY: It’s no stretch to say that snow is the key to success for Jon Lillis.

The reigning world champion in aerials skiing is also a restaurant owner in Park City, and business at his hotpot eatery increases by more than 100 percent when nearby ski resorts are open.

So, when winters grow warmer and ski season starts later — Park City, and Vail in Colorado are among the Western resorts to push back openings by about a week in each of the last two years — not only does it affect Lillis’ ability to train and, as is the case this year, prepare for the Winter Olympics, it also affects the bottom line at his business.

“We expect to do 70 percent of our annual revenue while the ski resorts are open,” Lillis said. “So, the longer they’re not open, and it seems to be getting later and later every year, the window where we’re making all that money gets smaller. In ski towns, it’s the tourism market that keeps business alive.”

A study commissioned by the Natural Resources Defense Council and the athletes’ group Protect our Winters found that the 23 million people who participate in winter sports added an estimated $12.2 billion each year to the U.S. economy; restaurants and bars contribute about 31,600 jobs and $942 million in economic value.

But as ski seasons grow shorter, all those numbers have declined — about $1.07 billion gone between 1999 and 2010 — and bad ski years take a significant toll on most every business in a ski town such as Park City, Vail or Snowmass. In Colorado, the NRDC found that “low-snow” winters caused an 8 percent decline in skier visits, which resulted in a $154 million decrease in revenue.

Under a worst-case-scenario, where winter temperatures increase 4 to 10 degrees by the end of the century, the NRDC predicts snow depths in the American West could decline between 25 to 100 percent, and the length of the snow season in the Northeast could be cut in half. One troubling sign this season: A late-autumn warm spell across the country left only 3.5 percent of the 48 contiguous states with snow cover on Nov. 26, the lowest that figure has been since record-keeping began in 2003.

“If ski resorts can’t stay open for a certain number of days per year, then there’s a chance the skiing sport won’t be around in 20 years,” Lillis said.