By the end of the century, a white Christmas could be just a dream even for California's highest mountain communities, and this has the ski industry sweating.

Climate models almost unanimously predict decreasing snowpack for mountainous regions across the globe, including the western United States.

"It's a big issue for us," said Bob Roberts, executive director of the California Ski Industry Association.

And California's ski resorts may have even more reason to worry than their Rocky Mountain neighbors.

"It's typically not as cold in the Sierra Nevada range and the Cascades as in the Rockies," said geologist Lisa Sloan of UC Santa Cruz..

The Rockies have the benefit of higher altitude, which means colder temperatures. Most of California's 34 ski resorts have a base altitude between 6,500 and 7,500 feet, whereas resorts in Utah and Colorado typically have their base above 8,000 or 9,000 feet.

Warmer air can hold more moisture, but whether that moisture becomes rain or snow depends on the temperature. Today, winter temperatures at the Sierra resorts tend to hover near freezing, so even a small bump up in temperature could be a big problem.

"I would think the Sierra Nevada is going to be faced with the transition to golf and mountain biking sooner than other areas," Sloan said.

In moderate future scenarios, snowpack in the Sierra Nevada is projected to drop between 30 percent and 70 percent from 1961-90 levels by the end of the century, depending on which climate model is used and whether greenhouse gas emissions are curbed significantly in the future, according to a study in the Proceedings of the National Academy of Sciences in 2004.

This translates to a ski season that starts three to five weeks later and is seven to 15 weeks shorter. Resorts would struggle to open by Christmas and would be forced to close as early as mid-March.

And when the worst case scenario of unabated future emissions is paired with a highly sensitive climate model, snowpack is down 90 percent by 2100, and never reaches the minimum 2 feet of depth needed for most ski slope operations.

So what's an industry to do?

"Most of the resorts are really upping their investment in snowmaking," Roberts said. Even Kirkwood and Mammoth, the highest resorts in the state, have started beefing up their snowmaking capabilities.

Many resorts, including Kirkwood, are also hedging their bets by refashioning themselves as not just ski resorts, but also destinations with many options. Shopping, ice skating and spas are cropping up at the base of resorts. The hope is that as snow becomes less reliable, people will still be able to book their trips in advance with the confidence that they will have something to do, regardless of the weather.

And some resorts are thinking beyond adaptation strategies and trying to lead by example by using alternative fuels such as biodiesel, wind and solar, aggressively recycling, and offsetting their carbon emissions..

"We're acutely aware of the fact that California has to change its ways and the world has to change its ways," Roberts said. "This is a problem that we're not going to eliminate, but that we can mitigate."

In 2005, Sugar Bowl became the first ski resort in the country to offset 100 percent of its energy use by purchasing green energy credits from wind farms..

The resort still gets its energy from the electrical grid, but it also pays extra to renewable energy companies that put an equivalent amount of energy into the electrical grid somewhere in the country. The idea is to increase demand for green energy and reduce the need for fossil fuels.

Alpine Meadows and Heavenly have followed suit by offsetting 100 percent of their energy use as well. Dozens of other resorts in the country are doing the same, or planning to, for at least some of their energy.

"In our little way, our little industry could be a catalyst on this issue," Roberts said.

Betsy Mason covers science and the national laboratories. Reach her at 925-847-2158 or bmason@cctimes.com.