California’s fabled beaches are shrinking, with waves and tides eventually expected to slosh over thousands of coastal homes and businesses. That’s the entirely plausible prediction from scientists studying climate change and rising ocean levels linked to hotter temperatures. In less than 30 years, rising waters will flood about 20,000 homes along the state’s shoreline. A warmer ocean is expanding and polar ice sheets are melting, pushing up sea levels here by nearly 2 feet. And it’s coming faster than ever, with lapping water noticeable by 2035 and the serious trouble a decade later.