Rising Sea Levels and Their Impact on the Economy and You

How Rising Sea Levels Are Changing Your World

••• Walking through street flooded by seasonal high tides and rising sea levels in Miami Beach, Florida. Joe Raedle/Getty Images

Since 1880, sea levels have risen 8.9 inches on average. That doesn't sound like much, but they’re rising much faster than in the previous 2,700 years. One-quarter of the 8.9-inch rise change occurred since 2000.

The rate of change is also increasing. As the table below shows, seas levels rose almost 1 1/4 of an inch between 2000 and 2010. They rose another 7/8 of an inch between 2010 and 2015. At this most recent rate, by 2020 they'll have increased by 1 3/4 inch in just five years.

YearCumulative Increase (Inches)Increase per Decade (Inches)
1880   0       0
18900.4   7/16
19001.1 11/16
19101.3   3/16
19201.9 11/16
19302.1   3/16
19402.6   9/16
19503.6Almost one inch
19604.5Almost one inch
19704.7   3/16
19805.6Almost one inch
19906.2 11/16
20006.9 11/16
20108.11 3/16
20158.9    7/8 in five years
20209.91 3/4 

How Scientists Know Sea Levels Are Rising

Scientists accurately measure global sea level increases in three ways. Since 1992, NASA has collected data from satellites.

NASA also uses tide gauges in many parts of the world to get a global average. The gauges block out the impact of waves and tides to get an accurate reading.

The third method is reviewing rock formations. Scientists use this method to determine the sea levels millions of years ago. They look for fossils of ocean organisms, sedimentary deposits, and even the actions of waves.

Effects 

Rising sea levels affect the 40 percent of Americans who live in coastal counties.

Higher levels will affect the eight of the world's largest cities that are near a coast. A Harvard study found that a three-foot rise would displace 4.2 million people

The Union of Concerned Scientists predicts that 170 U.S. coastal cities and towns will be “chronically inundated” in 20 years. Those areas will see 10 percent of their area flooded at least twice a month.

 By 2100, more than half of the communities along the Eastern Seaboard and Gulf Coast will experience it.

By 2045, another study found that 300,000 coastal properties will be flooded 26 times a year. The value of that real estate is $136 billion.  By 2100, that number will rise to $1 trillion. At most risk are homes in Miami, New York's Long Island, and the San Francisco Bay area.

Rising sea levels worsen flooding in low-lying towns. Floods have hit U.S. coastal towns three to nine times more often than they did 50 years ago. 

In Miami, Florida, the ocean floods the streets during high tide. To cope, the City of Miami Beach launched a five-year, $500 million public works program. The city must raise roads, install pumps, and redo sewer connections to keep the ocean from flooding the streets. Flooding has already depressed real estate prices in the area.  

Harvard researchers found that home prices in lower-lying areas of Miami-Dade County and Miami Beach are rising more slowly than the rest of Florida. A study using Zillow found that properties at risk of rising sea levels sell at a 7 percent discount to comparable properties.

By 2030, Miami Beach homes could pay $17 million in higher property taxes due to flooding by 2030.

By 2100, that could rise to $760 million, according to the Miami Herald

Atlantic City, New Jersey, is vulnerable because it is on a barrier island with low, flat terrain. The town regularly floods when it rains. Since it's so low, a four-foot storm surge would flood 50 percent of it. A similar surge in a higher city, such as Boston, would only flood 7 percent. 

But Boston has another set of problems. It's close to the Gulf of Maine, the fastest warming body of water on Earth according to the National Oceanic and Atmospheric Administration. That puts it at greater risk of higher sea levels. Furthermore, Boston's newly renovated Waterfront District suffers more from any storm-related damage. Almost $8 billion worth of new construction was built in the past decade.

Annapolis, Maryland, also experiences flooding from high tide.

The city is putting vents in floors to drain floodwaters from historic buildings. If sea waters rise 3.7 feet, the U.S. Naval Academy will be underwater.

In Louisiana, rising sea levels are flooding the Mississippi delta. Louisiana is losing one acre an hour of wetlands. These areas nourish fisheries and protect New Orleans from hurricanes.

Rising sea levels combined with sinking land will flood many areas around San Francisco by 2100. The land is sinking because of groundwater pumping. Parts of the airport, as well as large sections of Union City, Foster City, and Treasure Island would be underwater.

Rising sea levels worsen damage from hurricanes. Seventeen of the 20 most destructive U.S. storms in history occurred after 2000. Three of them occurred in 2017. 

  • September 20, 2017. Hurricane Maria was a Category 4 storm when it devastated Puerto Rico. It cost $90 billion in damage. 
  • September 10, 2017. Hurricane Irma was the most powerful Atlantic hurricane in recorded history. Damage was $50 billion. AccuWeather estimated the total cost to the economy at $100 billion. It was the first time in 100 years that two storms Category 4 or larger hit the U.S. mainland in the same year. Hurricane Irma's power was fed by ocean temperatures of 86 degrees Fahrenheit.
  • August 25, 2017. Hurricane Harvey was a Category 4 storm that hit Texas. Damage was $125 billion.
  • October 29, 2012. Hurricane Sandy was a tropical storm that hit New York and New Jersey. Storm surges were 12 1/2 feet higher than normal at Kings Point, Long Island. The storm damaged 650,000 homes, and 8 million people lost power. It forced the New York Stock Exchange to close for two days, the first such closure due to weather since 1888.
  • August 29, 2005. Hurricane Katrina was a Category 5 storm that flooded New Orleans in 2008. It cost $108 billion and killed 1,836 people. 

The future impact of hurricanes could be worse. The Congressional Budget Office estimates that 1.2 million Americans live in coastal areas at risk of “substantial damage” from hurricanes. Most of this densely populated area lies less than 10 feet above sea level, according to the National Hurricane Center. A 23-foot storm surge would flood 67 percent of U.S. interstates, including 57 percent of arterial highways. Such a massive surge would cover almost half of the rail miles, 29 airports, and almost all ports in the Gulf Coast area.

Local governments are making costly investments in an effort to prepare. San Diego County in drought-stricken California is building the largest seawater desalination plant in the western hemisphere. The MIT Technology Review reports that the plant will cost about $1 billion.

In September 2016, the Center for Climate and Security released a report warning of the impact of sea level rise on military preparedness.  The U.S. military has 1,774 sites on 95,471 miles of coastline. Those sites are at risk of flooding from sea level rise. More than 30 sites in the continental United States are already suffering from sea level rise. More frequent and powerful extreme weather events will affect all bases, but especially those in the Pacific region. These bases are often hubs for disaster relief efforts.

Rising sea levels will increase migration. Residents from coastal areas in emerging market countries will have to move. They don't have the ability to erect barriers or install pumps. Some atoll island nations, such as the Maldives and Seychelles, will be completely underwater. By 2050, 17 percent of Bangladesh would be flooded, displacing 18 million people. Their residents will have to migrate to other countries.

Jakarta, Indonesia, is home to 30 million people. Forty percent of the city lies below sea level. Climate change is only part of the problem. The city is sinking as residents drain the aquifer upon which it rests.

Saltwater leaches into underground aquifers and the soil. It disrupts the chemical balance of estuaries. Saltier water destroys oyster beds and bird habitats. Increased salinity in Bangladesh, Vietnam, and other South Asian coastal countries threatens rice production. 

Sea levels threaten tourism and historical sites. On Easter Island, the famous Moai statues will be destroyed if the sea rises six feet. The Marshall Islands are disappearing already. They are less than six feet above sea level. But changing sea winds have raised sea levels a foot over the past 30 years. The nation's 70,000 residents will probably emigrate to the United States, thanks to a 1986 agreement.

Causes 

Did global warming cause the rise in sea levels? A Rutgers University study found that warming air temperatures contributed to half of the increase. How much has it warmed? Over the past century, the earth's air temperature has warmed by 1.00 degrees Fahrenheit. Researchers found that 2017 was the warmest year on record. As a result, the upper 2,300 feet of ocean warmed by 0.18 degrees Fahrenheit. Like your swimming pool, the water in the ocean warms more slowly than the air. 

A warmer ocean causes sea level rise in two ways. First, warm water takes up more space. About half of the sea level rise in the past century is because of this effect.

Second, warmer temperatures melt the ice sheets covering Greenland and the polar ice caps. Over the winter, snowfall rebuilds the ice. But shorter winters mean less time for water to evaporate and turn into snow. As a result, more water stays in the ocean and the glaciers aren’t rebuilt. At the same time, more water enters the ocean from the melting ice.

Melted water combines with seawater below the ice sheets. It creates a river under the glaciers that ferries them more quickly into the ocean. Higher sea temperatures combine with higher air temperatures to melt the ice sheets from both the top and the bottom at the same time.

Between 2002 and 2016, Antarctica lost 125 gigatons of ice per year. It contributed 0.013 inches of sea level rise per year. Most of this loss occurred in the West Antarctic Ice Sheet. Antarctica holds 90 percent of the world's ice. If it all melted, sea levels would rise 200 feet.

The rate of ice sheet melting is accelerating. Between 2010 and 2016, the grounding line has receded 600 feet per year. The grounding line is the last place where the ice meets bedrock. A receding line means warmer ocean water is melting the underside of the glacier while warmer air temperatures attack the top layers. It reinforces concerns about a worst-case Antarctic meltdown that raises sea levels another 10 feet by 2100. It's enough to put FDR Drive and 1st Avenue on the Upper East Side in Manhattan underwater.

A 2018 study found Antarctic ice is melting at an ever-faster rate. Between 1992 and 2017, Antarctica shed 3 trillion tons of ice. It increased sea levels by three-tenths of an inch. But 40 percent of that occurred during the last five years, from 2012 to 2017.

Surprisingly, it's tripled since 2007. At that rate, it will increase sea levels another six inches, or 15 centimeters, by 2100. Andrew Shepherd, a professor of earth observation at the University of Leeds, said that translates into flooding in Brooklyn around 20 times a year.

During the same period, Greenland lost 280 gigatons of ice per year. It's melting at the fastest rate in at least the past 450 years. The melting ice added 0.03 inches each year to rising sea levels. The worst losses occurred along the West Greenland coast. If the Greenland ice sheet melts completely, it would raise sea levels by 16 feet to 23 feet. That's enough to put New Orleans, Miami, and Amsterdam underwater.

Sea Level Rise Predictions

Scientists estimate that, if climate change isn't arrested, average sea levels will rise between one and two feet by 2100. The Intergovernmental Panel on Climate Change is an international group of hundreds of climate experts. They don't make recommendations or policies. They simply state observations about the facts they find. The Panel published this forecast in 2007. 

In 2018, Potsdam researchers demonstrated that timing is critical. A five-year delay would increase sea levels by another 7.8 inches. That's almost the 8.9-inch increase that's already occurred since 1880. 

In February 2018, a NASA study reported that sea levels are rising faster than the IPCC forecast. It predicts sea levels will be 26 inches higher by 2100. It based this on recent measurements of melting ice in Greenland and Antarctica. The scientists warn this is a conservative estimate.

This two-foot rise would flood tens of millions of people living in low-lying areas. It's enough to swamp many U.S. East Coast cities. 

A 2010 North Carolina study predicted that ocean levels will rise three feet by 2100. That would flood 50,000 residents of the state. It would also damage tens of thousands of expensive beach-front properties. 

In 2017, researchers led by the University of Melbourne, Australia predicted sea levels could rise as much as six feet by 2100. As Antarctica melts, it will reach the larger sheets that are more inland. Their weight will make them melt faster than smaller ice sheets have in the recent past. A six-foot rise would put Atlantic City underwater.

The National Oceanic and Atmospheric Administration provides an interactive viewer that shows this and other impacts of sea level rise on coastlines. The website ShortList also shows simulations of how major cities would look.

The Speed of Today's Sea Level Rise Is Unprecedented

How do recent sea level increases compare to the past? During the last Ice Age, the sea level was 400 feet lower than it is today. That was about 26,500 years ago. It was after the Neanderthals went extinct (40,000 years ago) but before Homo sapiens learned how to farm (12,000 years ago). Massive ice sheets extended as far south as New York and the Rockies. Great Britain, Germany, and Poland were also covered in ice. Lower sea levels exposed the Bering land bridge from Siberia to Alaska, allowing the ancestors of Native Americans to migrate to the Americas.

The Ice Age ended when the earth's orbit wobbled closer to the sun. Sunlight hit the northern ice masses, which had grown so large they had become unstable. When they melted, fresh water poured into the ocean, reversing the ocean currents that carry warm water north from the equator. Warm water flowed south, melting the Antarctic and changing the polar winds. This chain reaction released carbon dioxide from the Southern Ocean by 100 parts per million over thousands of years. It's about the same amount that's been released in the last 200 years.

The last time the oceans were this warm was 100,000 years ago. Neanderthals lived in Europe. Homo Sapiens lived in Africa, where droughts reduced them to no more than 10,000 adults. But sea levels were 20 to 30 feet higher. Why were sea levels higher, when carbon dioxide wasn’t warming the climate? The earth had shifted on its axis closer to the sun. Higher levels of radiation had been heating the earth's atmosphere and oceans during the past 4,000 years.

Recent greenhouse gas emissions have heated the earth the same amount, but in only 150 years. Warming has happened so fast that the ice hasn't melted yet. It's like putting an ice cube in hot coffee. Once the hotter temperatures from the earth's atmosphere have had time to melt the polar ice caps, sea levels could rise another 20 to 30 feet. 

Solutions

Rising sea levels are Americans' second-biggest worry when it comes to climate change. A Pew Research Study found that 17 percent of Americans said rising sea levels are the effect that concerns them most. 

Governments have begun addressing the immediate impacts of sea level rise. Coastal cities are installing drainage systems and building up seawalls. Island populations are moving. Tourists are flocking to visit popular vacation spots, like the Maldives, before they are underwater.

In Boston, developers are planning ahead. Skanska Commercial Development constructed an elliptical office tower designed to withstand fierce wind storms. The building's electrical infrastructure is located 40 feet above the 100-year floodplain. It also has a 40,000-gallon water reclamation tank, and a raised ground floor. 

Between 1978 and 2015, there were 30,000 homes that flooded multiple times. The federal government bought out fewer than 9 percent, according to the Natural Resources Defense Council. The buyouts that do occur take two to three years. They only pay 75 percent of the home's value. Federal disasters funds are designed to help people rebuild their existing homes in the same spot. 

Other federal programs make selling these homes difficult. In 2012, Congress passed a bill that phased out subsidies for federal flood insurance. The subsidies disappear entirely for any new homebuyer. That makes it too expensive for many homeowners

The only permanent solution is to slow or reverse global warming. The amount of greenhouse gases emitted into the earth's atmosphere need to be reduced or eliminated. Those gases act like a blanket over the earth's atmosphere. They prevent the earth's natural heat from radiating out into space. Instead, the blanket sends it back to Earth. The oceans can absorb the heat without much rise in their temperature. Instead, they expand. But when they've absorbed all they can, their temperatures rise. That began to happen at the beginning of the 20th century. 

Once limits are firmly set, carbon emissions trading can reward businesses that adhere to the cap. Carbon taxes can punish those that do not.