The ocean is rising and Monterey is deciding between building seawalls or retreating.

Portions of Monterey’s busiest road could be submerged within 10 years, according to the latest projections of sea level rise. Eventually, tides and storms would flood not only Del Monte Avenue but also the Lighthouse Tunnel; the water would overtake El Estero Park.

Even if greenhouse gas emissions were to be drastically cut, much of the swelling of our oceans and melting of the polar ice caps is already locked in by past emissions.

Monterey officials, like those in other cities located up and down California’s coast, are studying how they might respond to this threat. A newly published report lays out two general courses of action – and both come with tens of millions of dollars in costs. One option is a managed retreat from the lowest-lying part of the coast. The other is to build walls to block the rising seas. Retreat would mean ceding 30-45 developed acres around Lake El Estero and allowing the water to push inland and create a new bay. Del Monte Avenue could be raised onto a viaduct bridge as part of a $300 million public works project, or traffic could be rerouted through streets like Pearl or Fremont at a lower cost.

The alternative, building a seawall up to 17 feet high, would preserve buildings and streets for a while, but the view of the ocean would be blocked. This option is projected to cost up to $88 million, depending on the type of wall.

The decision between the two strategies will be made over time by the city of Monterey and its residents. A presentation on the new report will be given on Zoom at a meeting of the city Planning Commission at 7pm on Tuesday, Dec. 8. Members of the public are encouraged to weigh in.