Experts studying the issue agree that sea level rise in coming decades could pose an enormous threat to San Francisco Bay’s shoreline. So perhaps it’s no surprise that there’s now talk of looking into an equally enormous response. Why not build a barrier to keep rising tides outside the Golden Gate? Researchers in the past have dismissed this seemingly straightforward concept on environmental grounds. Engineers are skeptical, too. But the enormity of the challenge has some Bay Area leaders saying it should at least be studied.