I recently finished reading Nathaniel Philbrick’s excellent book, Bunker Hill, discovering (to my chagrin) how little I had known about that era in our nation’s history and the early days of Boston.

But it was a side-story that I gleaned from the book that was particularly surprising to me and has led to a lot of thinking over the past few weeks. I was struck by the realization that 250 years ago Boston was an island, connected by just a single landbridge. This fact played heavily into the historical role Boston played as a Loyalist enclave and relatively safe haven for British troops leading up to the start of the American Revolution.

Looking at the maps of Boston that were included in the book (poorly rendered in the Amazon Kindle version I read), I realized that there must have been a fairly massive effort to build the current land base of Boston. Might strategic landbuilding be an option for us as we are forced over the next century to address sea level rise as global warming melts the huge ice masses in Greenland and Antarctica?

I set out to discover how the landbuilding in Boston was conducted—to deterring whether this idea is even worth considering. I’ll get back to that, but first, some context on sea level rise.

The seas are rising faster than previously thought

Several reports in the past month argue that sea level rise is occurring faster than previously thought and it could speed up dramatically in the coming decades. A paper in the journal Proceedings of the National Academy of Sciences and a companion report by the scientific organization Climate Central provide clear evidence that sea level rise is a) occurring at the most rapid rate in the past 2,700 years, b) linked to climate change, and c) having an impact on the increasingly common tidal flooding that is occurring in low-lying cities today even in the absence of major storms.

According to these publications and a February 22, 2016 New York Times article on those studies, nuisance tidal flooding has been increasing rapidly since the mid-1950s. For the 27 locations for which detailed, long-term tide-gauge data is available, the increase in flooding that can be attributed to anthropogenic sea level rise is dramatic. In Annapolis, Maryland, for example, during the decade 1955 – 1964, just 32 days of flooding fell into this category, while in the decade 2005 – 2014, 394 days did so. In Charleston, South Carolina, the flooding days jumped from 34 to 219 per decade, respectively. Rising seas are making life increasingly difficult in low-lying portions of dozens of U.S. cities today.

Then in mid-March, the journal Nature Climate Change published a paper projecting the number of people in coastal regions of the U.S. who would be affected by sea level rise of 0.9 meters (3 feet) and 1.8 meters (5 feet). Unlike previous assessments of impact, this study considered not only current populations, but also projected population growth in these regions.

By the year 2100, U.S. residents affected by 0.9 m and 1.8 m sea level rise would total 1.46 million and 3.85 million, respectively. Factoring in projected population growth in these regions, however, the number of people affected increases to 4.31 million and 13.1 million, respectively.

Finally, a new paper, “Ice Melt, Sea Level Rise and Superstorms,” published in the European journal Atmospheric Chemistry and Physics by the retired NASA climate scientist Dr. James Hansen and a long list of coauthors, posited that far more rapid climate change and sea level rise could occur than previously believed. This could happen, they propose, if melting land ice in Greenland and Antarctica deposits a layer of relatively fresh water on top of seawater in polar regions—which, in turn, would slow down or even stop the main ocean currents, which currently distribute warmer water around the Earth and allows heat to dissipate. Without those ocean currents dissipating heat, much more rapid warming would occur, melting sea ice in Antarctica and the Arctic, rapidly raising sea levels. This is what occurred, the scientists claim, 120,000 years ago. The paper is summarized in a March 22, 2016 New York Times article.

What does this have to do with Boston 250 years ago?

Beginning fairly early in Boston’s history—certainly by the 1700s—there was a massive effort to fill in the tidal flats around Boston. These efforts ultimately created some 5,250 acres of new land in Boston, East Boston, and Charlestown (see map above). In other areas, the land was significantly raised with fill. The original peninsula of Boston, known as Shawmut by the Native Americans, was just 487 acres. Today, merged with surrounding land, it is many times that size.

All this is laid out in great detail in the wonderful book by Nancy Seasholes, Gaining Ground: A History of Landmaking in Boston (MIT Press, 2003). Early photos of Boston, and many dozens of maps—both old and new—explain the landmaking that occurred over several centuries in Boston.

The earthmoving in Boston began in the 1700s with picks, shovels, and hand-pushed carts. In 1805, a small pulley-operated incline railroad in a Mount Vernon landmaking project used wooden rails and is recognized as the first “railroad” in the United States. The source of fill for Boston landmaking was initially the hills in Boston, including Beacon Hill and Fort Hill. Beacon Hill, once the middle and highest peak of “Tri-mountain” (now Tremont), was mined for fill so extensively that its height dropped by an estimated 60 feet and the Beacon Hill Monument had to be relocated in 1811.

Later, as railroads emerged, thousands of train car loads of fill were brought in from extensive gravel deposits in Needham.

Boston’s well-known Back Bay region was originally the back bay of the Charles River—an extensive estuary on the western side of the Shawmut Peninsula. The Fenway and Fenway Park (the Boston Red Sox’s home stadium) get their names from the fens or bogs in the area. It was only after extensive filling that building here was possible.

Logan Airport was open water in the 1930s. Today it is part of the extensive new land in East Boston.

I haven’t seen estimates of the amount of fill been used in Greater Boston over the last three centuries. If one assumes an average fill of six feet over the 5,250 acres of made land, that would total roughly 1.4 billion cubic feet or 50 million cubic yards.

Raising elevation of low-lying areas

I was particularly intrigued to learn in Gaining Ground that not only was new land made on the tidal flats of Boston, but in some places the elevation of existing land was raised. In the Church Street and Suffolk Street Districts (new Bay Village and Castle Square), sewage back-up was a problem in the mid-1800s, because there wasn’t enough pitch to the sewers (which no doubt dumped into the Bay).

The solution was to elevate the land and the buildings that were located there. In the 1860s, the City decided to raise the grade of the entire District. They would fill basements and abandon them, elevate buildings on cribbing and build new foundations beneath them.

On Church Street, starting in July 1868, the City hired contractors to bring in more than 150,000 cubic yards of fill and elevate 296 brick buildings by as much as 14 feet and 56 wooden buildings by as much as 17 feet. Remarkably (by today’s standards), this work was virtually completed by October 1869—ahead of schedule and under budget.

A similar project was carried out in the Suffolk Street District starting in July 1870 and being completed by the end of 1872. Nearly 250,000 yards of fill were brought in, and 600 buildings were elevated—also under budget.

Boston isn’t alone in having seen extensive landmaking over the centuries. In Manhattan, several thousand acres of land were created using fill, and more than 3,000 acres were created in Chicago. But nowhere in the U.S. has the landmaking been as extensive as in Boston.

A solution to rising sea levels?

What this suggests about our long-term response to rising sea levels is that we shouldn’t rule out the idea of raising the grade in our most important cities. I was astounded to learn just how significant the earthmoving was centuries ago; with today’s equipment and engineering prowess, one can imagine raising a low-lying city by tens of feet.

Of course, there would be huge challenges and tremendous costs with such an initiative, not to mention environmental risks. Our buildings are bigger than those in Boston were in the 1860s; they are closer together and more complex. Our infrastructure—streets and highways, bridges, sewers, power grids, pipelines—are tremendously complex. And, we’re much more conscious of ecological damage today than we were 150 years ago.

But consider the alternative. Are we ready to abandon cities like Boston, New York, Philadelphia, and Charlestown? It could well be easier to raise a city than to move it. And we will have to figure this out before the end of this century. I don’t know if raising the elevation of our low-lying cities will make sense, but I think we should begin that discussion.

We can start by looking at past experience, and Gaining Ground provides a good starting point in doing so. In some cases, it may be possible to fill in basements, compacting the fill to equalize the pressure on the outside of those walls, and turn first floors into basements—essentially eliminating an occupied floor of a building.

In other cases, entire buildings may have to be elevated and new foundations built on compacted fill 15 or 20 feet higher. Streets would have to be covered and rebuilt on fill. Very challenging will be the need for such modifications to be coordinated on a neighborhood-by-neighborhood basis. You can’t raise one building 20 feet and not do anything with the building next door.

This would be an extraordinarily complex process in terms of phasing, implementation, and environmental protection.

But it’s time to take sea level rise seriously and begin looking at our options. Raising land mass may be one such option.

A source of fill that helps to mitigate climate change?

As for where all that fill would come from, that’s another challenge. I expect that much would come from the ocean. With all the beach restoration that we’ve done in recent years, the Army Corps of Engineers knows how to move an awful lot of sand very quickly! But such projects can wreck havoc with ecosystems.

There’s another source of fill that we might want to consider: producing synthetic limestone from power plant emissions. This is a technology being perfected by the California company, Blue Planet.

If we, as a society, start requiring power plants to remove carbon dioxide, I believe we will discover that it makes more sense to sequester that gas as calcium carbonate (limestone) than to try to inject it into the ground, as is commonly proposed today. We’ve learned in the Los Angeles Basin recently that when you inject gases into the ground, they sometimes leak back out—but that’s another story. We would have a ready repository for all that limestone aggregate in elevating our coastal cities.

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Along with founding the Resilient Design Institute in 2012, Alex is founder of BuildingGreen, Inc. To keep up with his latest articles and musings, you can sign up for his Twitter feed. To receive e-mail notices of new blogs, sign up at the top of the page.