BOSTON (AP) — A harbor barrier to protect Boston from rising seas and increased flooding due to climate change could cost nearly $12 billion and take more than 30 years to complete, according to a new analysis from the University of Massachusetts-Boston.

The researchers cautioned city leaders from pursuing the barrier idea. Instead, they recommended the city continue to make investments in relatively cheaper and quicker "shore-based" protections, such as temporary flood walls and berms that already are being tried in some low-lying neighborhoods.

Boston could revisit the barrier idea in a few decades, when the impacts of those cheaper alternatives could be measured and technological advances might make a harborwide barrier more feasible, Paul Kirshen, the UMass-Boston professor who led the project, said in an interview ahead of the report's release Wednesday.

"We're confident that shore-based solutions can get us through to 2070 or 2080," he said. "So the earliest we might need a barrier system is near the end of the century."

The report is being released as part of "Boston Harbor for All," a summit focused on protecting Boston's booming harborfront from the impact of climate change. The study was prompted by the city's 2016 Climate Ready Boston report , which recommended studying the feasibility of a harbor barrier to protect the city from coastal flooding.

The team, which also included researchers from the Woods Hole Oceanographic Institution and other organizations, looked at two possible designs for a gated harbor barrier.

The smallest would run about 1 mile (1.6 kilometers) from Logan International Airport to the Seaport area of South Boston and cost about $6.5 billion to $8.7 billion. A larger one stretching about 4 miles from Winthrop to Hull —two coastal Boston suburbs — could cost $8 billion to $11.8 billion and would also be the largest such barrier in the world.

Each would take at least until 2050 to build and not cause major negative impacts to the harbor ecosystem, the report found.

But the barriers would not mitigate tidal flooding that sometimes affects the city and could prove disruptive to maritime traffic, as the barrier gates would likely have to be closed more frequently as sea levels rise, the report concluded.

The researchers argued that berms and other cheaper landscaping alternatives, on the other hand, could help address tidal flooding problems as well as provide other community benefits, such as the creation of more public spaces and parkland.

"We really can improve the quality of life of people living on the shore," Kirshen said. "You don't get those amenities with a barrier system."