by Jenna Lang

figures by Hannah Zucker

At some point during my lifetime, Harvard’s campus will flood.  The waters of Boston Harbor will rush around the Charles River dam and surge onto the Harvard Business School campus on one side of the swelling river and onto the Harvard College campus on the other side.  Winthrop House, where my sister will live starting next year, faces the Charles River and will be the first house affected by the overflow. Nearby Eliot House and Kirkland House (my own house) will next be damaged in the wake of the overflowing Charles River (Figure 1).

The waters will eventually recede back into the river, students will dry their wet shoes, and class will continue as usual. 

However, the waters will not stay away for long.  Climate change is causing coastal flooding to become more intense and more frequent in the coming decades. The increase in flooding is due to the combination of a rise in sea level and an increase in severe storms. 

Rising sea levels pose a threat

In recent decades, the sea level has started rising globally due to melting ice in the Arctic and Antarctic regions.  Changes in ocean current patterns have led to additional sea level rise in areas such as the Eastern United States.  Normally, the Gulf Stream current brings water from the Gulf of Mexico up the Eastern coast of the U.S. into the Arctic.  However, as Arctic ice melts and releases large quantities of freshwater into the Northern Atlantic, the Gulf Stream is slowing down, causing water to build up along the Eastern U.S and raise local sea levels.  In the Boston area, the sea level has already risen 10.4 inches since 1922, significantly above the global average. 

While 10.4 inches may not seem like an alarming amount, the next few inches are going to foreshadow our watery future.  On January 4th, 2018, the high tide was three inches higher than usual due to a storm offshore.  These three small inches created a record-breaking high tide and brought significant coastal flooding throughout the Boston area.  What is particularly frightening about this flood was that it occurred during a typical winter storm.  What used to be 100-year floods are now occurring during non-extreme weather events.  Storms such as the one in January 2018 occur regularly, and the city’s rising seas mean that more of these typical storms will cause severe flooding.  In addition to increasing the number of flood days, a rising sea level also means that when extreme weather events do occur, the flooding will be even higher than floods during storms in the past. 

Extreme weather events exacerbate the issue

Unfortunately, climate change is also resulting in more intense and more frequent extreme weather events.  If the storm on January 4^th had been more powerful, centered on the coast, remained for multiple tide cycles, or brought more precipitation of its own, the flooding and damage could have been significantly worse.  Unusually extreme storms like this are occurring more often and are only going to become more common in the coming decades.   

The increase in extreme weather events is partially due to changes in the North Atlantic Oscillation, a periodic variation in two pressure systems: a high pressure system over the Azores, west of Portugal, and a low pressure system over Iceland.  When these two pressure systems are both in their strong phase, New England has stormier weather compared to when the pressure systems are weaker.  As the climate changes, the pressure systems are more often in their strong phase, causing more storms on the East coast.    

Another factor that increases extreme weather in the Boston area is the slowing of the jet stream.  The jet stream is an air current in the atmosphere that circles the Northern Hemisphere and keeps the cold air of the Arctic contained there.  However, as temperatures in the Arctic increase and become closer to the warmer temperatures just outside the Arctic, the jet stream slows and weakens, allowing cold air and Arctic winter weather to leave the Arctic and settle over the northeastern United States, causing more extreme winter storms than Boston would typically experience.  A slower jet stream also slows the movement of storms, resulting in storms lasting longer over one area and causing more damage (Figure 2).

The reality of the threat

The combination of more extreme storms and sea level rise will cause unprecedented flooding in the Boston area.  The city is currently ranked 8^th in the world for flood risk.  While “flood risk” may make flooding sound like a future problem or like something that may never happen, we will soon see the effects firsthand.  In the next thirty years, Boston is projected to experience a five-foot flood, and there is a 50/50 chance that it will occur in the next ten years.  This flood will cover significant parts of seven Boston neighborhoods, with sections up to four feet underwater.  As Boston floods, the Charles River will bring the waters of Boston Harbor into Cambridge. 

After each flood, the waters will recede, but they will leave significant damage behind.  Our buildings, cars, houses, underground public transportation, and tunnels were not built to withstand flooding. As floods become more common, our city’s land and infrastructure will become increasingly less able to support our daily lives.  When the same piece of land floods 26 times or more per year, it is said to be in a state of chronic inundation.  Land in chronic inundation is no longer usable for its original purpose. 

If global carbon emissions continue to rise, by 2100, over half of Cambridge is projected to be in chronic inundation.  If we are able to curb global emissions and they begin to decline by 2050, between 25-50% of Cambridge will be in chronic inundation.  Of course, either scenario will occur gradually over the next 80 years, and there will be areas of higher elevation that are spared from flooding. 

If we greatly decrease our carbon footprint, we may be able to keep Cambridge on the lower end of these projections.  City projects such as raising streets and building large barriers are expensive but could prevent some of the flood damage. Other climate engineering projects such as reflecting some of the sun’s rays to lower temperatures and removing carbon dioxide could help keep Cambridge dry by limiting the effects of climate change in the first place.  However,  we cannot stop it all, and we must prepare for the reality that the first place the waters hit will be Harvard University.

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Jenna Lang is an undergraduate at Harvard College studying Cognitive Neuroscience and Global Health.

Hannah Zucker is a Ph.D. student in the Program in Neuroscience at Harvard University.

For more information:

• Learn more about flooding risk estimates in Boston and Cambridge
• Check out this SITN piece for more information on climate change
• Here’s a piece from the Washington Post about rising seas in Boston