Because Southeast Florida will be among the first regions to experience rising sea levels, across-the-board planning on how to adapt will be essential. That could include difficult options like steering investment for new public infrastructure away from vulnerable areas, or protecting the region’s underground water supply from saltwater intrusion by raising freshwater levels in drainage canals, which could produce more seasonal flooding in some areas.

Some 200 public agencies, advocates, business groups and academic institutions, including the region’s principal universities, have signed up for the effort. Any resulting plans are purely voluntary, and no town or agency is obligated to adopt any ideas it doesn’t like, planners stress.

Still, the process hit a roadblock in the northernmost county, Indian River. The county commission and the Vero Beach City Council voted to drop out after tea party-linked activists raised a public ruckus over their participation. The activists contend Seven50 is part of Agenda 21, a 20-year-old, nonbinding United Nations resolution that called for environmentally sustainable urban development, which they describe as a conspiracy to evict people from their homes and force them into dense urban housing.

Seven50 planners had to post a response on their website explaining they intend no such thing. Since then, the Stuart City Council, in Martin County, has voted to join Seven50. Other Indian River agencies remain as participants.

The two-year planning effort, led by a consortium established by the South Florida Regional Planning Council and the Treasure Coast Regional Planning Council, is funded by a $4.25 million grant from the U.S. Department of Housing and Urban Development.

The federal agency is encouraging local governments to engage in long-range planning under the sustainability label, which covers a range of strategies to foster development of pedestrian-friendly urban zones that put jobs close to homes and save energy by providing alternatives to auto transportation.