Rising seas will bring big changes to Boston, and sooner than you might think. Climate change is expected to raise average global sea levels between two and six feet by century’s end, and a recent US Geological Survey study suggests that the waters around the Hub and other East Coast cities are rising even faster than the global average.

To put that in perspective, if seas rise just 2.5 feet, a strong Nor’easter could put much of Back Bay, East Boston, South Boston, Chelsea and Cambridge under water. Hundreds of billions of dollars of real estate and vital infrastructure, from sanitation, sewer and water systems to highways, tunnels and Logan Airport, are at risk.

Faced with these dire predictions, some progress has been made to boost Boston’s resiliency. East Boston salt marshes are being restored for better flood control. Waterfront structures are being elevated, including the new Spaulding Rehab Center in Charlestown, which was raised two feet to prevent flood damage. Like the New England Aquarium, it also installed electrical systems on its roof. Developers investing in the city’s waterfront Innovation District are being required to take similar steps.

The Mayor’s Green Ribbon Commission, on which I serve, is also working to build private sector support for efforts to adapt to climate change. One group in particular has been feeling the effects of climate change for several years – insurers. Insurers often carry the costs of climate risk, but by managing that risk, they can bring enormous leverage to bear on whether and how cities and developers prepare for the consequences of rising seas.

There’s no doubt that the stakes are high: “Stormy Future,” a new report on the insurance sector from my organization, Ceres, indicates that 2011 was the second costliest year ever for insured losses from natural catastrophes globally. In the US alone, extreme weather events cost property/casualty insurers more than $32 billion in losses. The science is clear: Climate change increases the risk of extreme weather. Extreme weather increases potential losses. If insurance companies hope to protect their clients—and their business models— they must adapt.

In hurricane zones, insurers are already catching on to the value of preparation. Before Hurricane Katrina, Rhode Island insurer FM Global invested an average of $7,500 per site in hurricane loss-prevention at Louisiana properties it insured. When the storm struck, it reduced its clients’ losses by 85 percent compared to properties without such preparations.

To reduce risks even further, insurers can also work directly with government officials on several key initiatives. First, they must attack the root of the sea rise problem by acting on carbon pollution, the primary driver of a warming world. Boston has set a goal to reduce carbon emissions by at least 25 percent by the year 2020 and 80 percent by the year 2050. Other communities—and corporations—must join this effort to prevent further climate impacts.

Second, cities need lasting changes to building codes and land use planning, and with the right policies, insurers stand to benefit. The Aquarium and Spaulding Rehab are already implementing best practices that should become requisites for new development projects.

Next, updated and improved flood mapping are essential. City planners rely on flood maps from the Federal Emergency Management Agency and other resources to determine zoning and building codes. Insurers use them to set rates from Cape Cod to Florida, but much of the available information is now out-of-date. It is imperative that flood maps be updated soon to reflect the new reality, including new projected flood lines.

Other cities are looking at more elaborate solutions. After Hurricane Irene triggered New York City’s first mandatory evacuation last year, officials are now considering building solid storm barriers across the harbor to be deployed during storms. Such a barrier might protect runways at the city’s three major airports (including Newark) and other vital infrastructure, but it comes with a nearly $10 billion price tag.

With other adaptation initiatives already underway, Boston’s leadership is right in thinking we can’t wait for big pie-in-the-sky solutions like multi-billion dollar barriers. Those inevitably lead us to endless debate over a mega-project’s merits, while distracting us from the problem at hand.

To adapt to rising seas, planners and insurers must act today with the tools we have now. Or else, grab a bucket and start bailing.

 Mindy Lubber is President of Ceres, a Boston nonprofit group advocating for sustainability leadership from businesses and investors