LOS ANGELES — California is defined by its scenery, from the mountains that enchanted John Muir to the wine country and beaches that define its culture around the world.

But as scientists try to forecast how global warming might affect the nation's most geographically diverse state, they envision a landscape that could look quite different by the end of this century, if not sooner.

Where celebrities, surfers and wannabes mingle on Malibu's world-famous beaches, there may be only sea walls defending fading mansions from the encroaching Pacific. In Northern California, tourists could have to drive farther north or to the cool edge of the Pacific to find what is left of the region's signature wine country.

Abandoned ski lifts might dangle above snowless trails more suitable for mountain biking even during much of the winter. In the deserts, Joshua trees that once extended their tangled, shaggy arms into the sky by the thousands may have all but disappeared.

"We need to be attentive to the fact that changes are going to occur, whether it's sea level rising or increased temperatures, droughts and potentially increased fires," said Lisa Sloan, a scientist who directs the Climate Change and Impacts Laboratory at the University of California, Santa Cruz. "These things are going to be happening."

Among the earliest and most noticeable casualties is expected to be California's ski season.

Snow is expected to fall for a shorter period and melt more quickly. That could shorten the ski season by a month even in wetter areas and perhaps end it in others.

Whether from short-term drought or long-term changes, the ski season already has begun to shrivel in Southern California, ringed by mountain ranges that cradle several winter resorts.

"There's always plenty of snow, but you may just have to go out of state for it," said Rinda Wohlwend, 62, who belongs to two ski clubs in Southern California. "I'm a very avid tennis player, so I'd probably play more tennis."

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Because California has myriad microclimates, covering an area a third larger than Italy, predicting what will happen by the end of the century is a challenge.

But through a series of interviews with scientists who are studying the phenomenon, a general description of the state's future emerges.

By the end of the century, temperatures are predicted to increase by 3 to 10 degrees Fahrenheit statewide. That could translate into even less rainfall across the southern half of the state, already under pressure from the increased frequency of wildfires and relentless population growth.

Small mammals, reptiles and colonies of wildflowers in the deserts east of Los Angeles are accustomed to periodic three-year dry spells. But they might not be able to withstand the 10-year drought cycles that could become commonplace as the planet warms.

Scientists already are considering relocating Joshua tree seedlings to areas where the plants, a hallmark of the high desert and namesake of a national park, might survive climate change.

"They could be wiped out of California depending on how quickly the change happens," said Cameron Barrows, who studies the effects of climate change for the Center for Conservation Biology in Riverside.

Farther north, where wet, cold winters are crucial for the water supply of the entire state, warmer temperatures will lead to more rain than snow in the Sierra Nevada and faster melting in the spring.

Because 35 percent of the state's water supply is stored annually in the Sierra snowpack, changes to that hydrologic system will lead to far-reaching consequences for California and its ever-growing population.

Some transformations already are apparent, from the Sierra high country to the great valleys that have made California the nation's top agricultural state.

The snow line is receding, as it is in many other alpine regions around the world. Throughout the 400-mile-long Sierra, trees are under stress, leading scientists to speculate that the mix of flora could change significantly as the climate warms. The death rate of fir and pine trees has accelerated over the past two decades.

In the central and southern Sierra, the giant sequoias that are among the biggest living things on Earth might be imperiled.

"I suspect as things get warmer, we'll start seeing sequoias just die on their feet where their foliage turns brown," said Nate Stephenson, a U.S. Geological Survey ecologist who is studying the effects of climate change in the Sierra Nevada. "Even if they don't die of drought stress, just think of the wildfires. If you dry out that vegetation, they're going to be so much more flammable."

Changes in the mountain snowpack could lead to expensive water disputes between cities and farmers. Without consistent water from rivers draining the melting snow, farmers in the Central and Salinas valleys could lose as much as a quarter of their water supply.

Any drastic changes to the state's $30 billion agriculture industry would have national implications, since California's fertile valleys provide half the country's fresh fruits, nuts and vegetables, according to the Union of Concerned Scientists' study.

"Obviously, it's going to mean that choices are going to be made about who's going to get the water," said Brian Nowicki, a biologist with the Center for Biological Diversity in Tucson, Arizona

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Among the biggest unknowns is what will happen along California's coast as the world's ice sheets and glaciers melt. One scenario suggests the sea level could rise by more than 20 feet.

Will the rising sea swamp the ports of Long Beach and Los Angeles, the nation's busiest harbor complex, turning them into a series of saltwater lakes? Will funky Ocean Beach, an island of liberalism in conservative San Diego County, become, literally, its own island?

Among the more sobering projections is what is in store for marine life.

The upwelling season, the time when nutrient-rich water is brought from the ocean's depths to the surface, nourishes one of the world's richest marine environments.

That period, from late spring until early fall, is expected to become weaker earlier in the season and more intense later. Upwelling along the Southern California coast will become weaker overall.

As a result, sea lions, blue whales and other marine mammals that follow these systems up and down the coast are expected to decline.

The changing sea will present trouble for much of the state's land-dwelling population, too. A sea level rise of 3 to 6 feet would inundate the airports in San Francisco and Oakland. Many of the state's beaches would shrink.

"If you raise sea level by a foot, you push a cliff back 100 feet," said Jeff Severinghaus, professor of geosciences at the Scripps Institution of Oceanography in San Diego. "There will be a lot of houses that will fall into the ocean."