Routine flooding from rising sea levels could threaten $80B worth of real estate in Boston. The World Bank declared the city the eighth most vulnerable in the world to real estate damage from higher waters in coming years, and officials are intent on solving the problem. However, the solution could be one of the costliest infrastructure projects in city history, the Boston Globe reports.

The Boston Planning & Development Agency has advised developers on climate change since 1996 with Article 80 of the city’s zoning code. The guideline asks builders to go through a climate impact checklist with their developments, but changes are happening more quickly than the rule predicted. The city’s Climate Ready Boston report anticipates sea levels to be three feet higher in 2070 than they were in 2000. A report by the National Oceanic and Atmospheric Administration envisions a more dire scenario: seas 8.2 feet higher by 2100.

Environmental teams at City Hall are looking to build a sea barrier of some form across Boston Harbor to protect the city from high tides and cresting stormwaters. An environmental consultant estimates the four-mile outer harbor proposal would cost tens of billions of dollars; however, he believes water damage would average $1.4B/year if the barrier is not built. At $5B, a 1,200-foot similar project in Venice has cost twice as much as projected and is still one year away from being finished. For comparison, the MBTA’s 4.3-mile Green Line Extension will cost $2.3B.