Miami is among the U.S. cities most vulnerable to rising seas due to climate change, and city officials estimate that they may have to spend at least $900 million in the coming decades to upgrade the city’s flood prevention and drainage systems to keep the Atlantic Ocean at bay.

City officials don’t know exactly where all the money will come from, but in November the city will ask voters to approve a $400 million general obligation bond—new property taxes that will start chipping away at the cost of shoring up the city against the ravages of climate change.

Like many coastal cities, Miami is grappling with more frequent high tide flooding and vulnerability to hurricane storm surges as the Atlantic intrudes into once-dry areas and percolates inland through porous bedrock. Like all cities planning for the effects of climate change, Miami is struggling with who will pay for the costly measures needed to protect its residents.

In California, three communities last month decided to sue a group of fossil fuel companies to pay for the impacts of sea level rise they charge are overwhelmingly driven by the burning of fossil fuels. San Mateo and Marin counties, along with the city of Imperial Beach, base their claims in part on the Carbon Majors Database, research that begins to tie the impacts of climate change to the specific companies producing the greenhouse gas emissions.

While California clearly has issues along its coast, South Florida is among the lowest-lying metropolitan areas in the U.S., with nearly 2.5 million people vulnerable to a hurricane storm surge of less than four feet. Flooding from major storms is expected to become more severe because Florida’s coast could see 10 or more inches of sea level rise by 2050, according to research by Climate Central.

The bond, which the Miami City Commission narrowly approved in a 3-2 vote in July to appear on the November ballot, will pay for water pumping stations and drainage and sewer system upgrades, among other improvements. It’s part of Mayor Tomás Regalado’s “Miami Forever” plan that also aims to improve Miami’s parks, housing and roadways, all of which are vulnerable to increased flooding risk.

Only about half of the $400 million will pay for specific sea level rise mitigation and flood prevention projects, but the plan’s housing and other improvements all include measures to make those facilities more able to withstand flooding from rising seas and storm surges, said Jane Gilbert, the City of Miami’s chief resilience officer.

As the Atlantic slowly inundates low-lying areas of South Florida, more neighborhoods will begin to flood during king tides, and the rising groundwater table will prevent the city’s stormwater drainage system from functioning with gravity alone, Gilbert said.

Drainage system pumps and many other measures will be needed for the system to work, she said.

Frank Castaneda, chief of staff for Miami City Commissioner Wilfredo Gort, who cast the deciding vote to put the bond on the November ballot, said community feedback on the measure has been positive so far, but as to how voters feel about the issue, he said, “Who knows?”

City Commissioner Francis Suarez said the drainage projects that the bond would fund may not adequately account for the impacts of sea level rise and warned that the costly projects have a high risk of failure, the Miami Herald reported.

Miami’s climate change challenges are urgent, but rising seas and the enormous costs associated with protecting communities from them will be felt by many coastal cities.

A 2014 study estimated the total costs of sea level rise adaptation for the East and Gulf coasts combined through the end of the century will be $990 billion in 2005 dollars—about $1.1 trillion today adjusted for inflation.

Bob Kopp, co-director of Rutgers University’s Coastal Climate Risk and Resilience Initiative, said a meter of sea level rise could lead to roughly $30 billion in annual storm-related flooding losses.

Who ultimately pays for protecting cities against those risks depends on the resources of each coastal community, its geology and many other factors, Kopp said.

Miami Beach is paying for climate-related infrastructure improvements through an increased stormwater fee for homeowners. The city increased the fee 36 percent in 2016.

Miami and Miami Beach’s efforts to turn to their tax base to pay for infrastructure improvements may not make sense for smaller towns along barrier islands, Kopp said.

For example, in New Jersey, where tidal flooding is becoming more common, small towns on barrier islands along the Jersey Shore may find it difficult to turn to property taxes to fund infrastructure improvements because property is eroding away as the sea rises, Kopp said.

“If sea level rise is eating away at your property tax base, it’s not a sustainable solution,” he said.

The smaller the community, the more it will need to turn to a higher level of government to help pay the cost of climate adaptation, he said.

“A lot of it scales with capacity,” Kopp said. “A small shore town in New Jersey has not been able to put as many resources into preparing as New York City has.”

New York City was severely flooded in 2012 by superstorm Sandy and has spent millions of dollars creating a climate resiliency plan. The city received federal funding to help recover from the storm and to help fortify lower Manhattan against the flooding from another Sandy-like storm.

Jim Murley, chief resilience officer for Miami-Dade County, said the key for cities to control costs and find new ideas for shoring themselves up against sea level rise is to partner with other governments that are facing the same challenges.

“Don’t go it alone,” he said. “You get with communities with similar problems and extract ideas that may not have happened (to occur) to you.”