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Oceans are rising around the world, causing dangerous flooding. Why is this happening, and what can we do to slow this down?

¹ As humans continue to release greenhouse gases into the atmosphere, oceans have reduced the effect of global warming. The world's seas have absorbed more than 90 percent of the heat caused by these gases, but it is causing a problem for our oceans: the year 2018 set a new record for ocean heating.

² Many people think of “global warming” and “climate change” as synonyms, but scientists prefer to use “climate change” when describing the complex changes now affecting our planet’s weather and climate systems.

³ Rising seas is one of those climate change effects. Average sea levels have grown over 8 inches (about 20 cm) since 1880, with about three of those inches (7.6 cm) happening in the last 25 years. Every year, the sea rises another 0.13 inches (3.3 mm).

⁴ The change in sea levels is linked to three primary factors, all caused by global climate change:

• Thermal expansion: When water heats up, it expands. About half of the sea-level rise over the past 25 years is due to warmer oceans simply occupying more space.

• Melting glaciers: Large ice formations such as mountain glaciers naturally melt a little each summer. In the winter, snows, mostly from evaporated seawater, are generally enough to balance out the melting. Recently, though, frequently higher temperatures caused by global warming have led to greater-than-average summer melting as well as less snowfall due to shorter winters. That creates an imbalance between melt water and ocean evaporation, causing sea levels to rise.

• Loss of Greenland and Antarctic ice sheets: As with mountain glaciers, increased heat is causing the huge ice sheets that cover Greenland and Antarctica to melt more quickly. Scientists also believe that melt water from above and seawater from below is getting beneath Greenland's ice sheets, which helps ice streams to move more quickly into the sea. While melting in West Antarctica has received a lot of attention from scientists, especially with the 2017 break in the Larsen C ice shelf, glaciers in East Antarctica are also showing signs of breaking up.

Consequences

⁵ When sea levels rise as rapidly as they have been, even a small increase can have catastrophic effects on coastal habitats and farther inland, it can cause destructive erosion, wetland flooding, aquifer and agricultural soil contamination with salt and lost habitat for fish, birds, and plants.

⁶ Higher sea levels are happening at the same time as dangerous hurricanes, cyclones and typhoons that drop more rain, and contribute to more powerful storm surges. These can destroy everything in their way. One study found that between 1963 and 2012, almost half of all deaths from Atlantic hurricanes were caused by storm surges.

⁷ Already, flooding in low-lying coastal areas is forcing people to migrate to higher ground, and millions more are vulnerable to flood risk and other climate change effects. The prospect of higher coastal water levels also threatens basic services such as Internet access, since a lot of the underlying communication infrastructure lies in the path of rising seas.

Adapting to the threat

⁸ As a result of these risks, many coastal cities are already planning adaptation measures to cope with the long-term effects of higher sea levels, often at a very high cost. Building seawalls, rethinking roads, and planting mangroves or other vegetation to absorb water are all examples of current projects.

⁹ In Jakarta, Indonesia, a US$40 billion (OMR 15 and a half billion) project will aim to protect the city with an 80-foot-high (about 24 meter) seawall. Rotterdam, home to the Global Center on Adaptation, has offered a model to other cities that want to prevent flooding and land loss. The Dutch city has built barriers, drainage, and innovative architectural features such as a “water square” with temporary ponds. However, for some vulnerable communities, possible solutions may not be achievable (without the help of other nations) because they are just too expensive.

How high will it go?

¹⁰ Most predictions say the warming of the planet will continue and is likely to accelerate, causing the oceans to keep rising. This means hundreds of coastal cities face flooding. But forecasting how much and how soon seas will rise remains an area of ongoing research. The most recent special report from the Intergovernmental Panel on Climate Change (IPCC) estimates that the oceans will rise between 10 and 30 inches (26 to 77 centimeters) by 2100 with temperatures warming 1.5 °C. That is enough to seriously affect many of the cities along the U.S. East Coast. Another analysis based on NASA and European data focused on the higher end of that range, predicting a rise of 26 inches (66 centimeters) by the end of this century if the current trend continues.

¹¹ If all the ice that currently exists on Earth in glaciers and sheets melted, it would raise sea level by 216 feet (nearly 66 meters). That could cause entire states and even some countries to disappear under the waves, including the USA state of Florida and the country of Bangladesh. That’s not a future scientists think is likely, and it would probably take many centuries, but it could eventually happen if the world keeps burning fossil fuels without thought.

¹² In the meantime, scientists keep improving their models of sea-level changes. They also point out that if countries work together to limit the release of more greenhouse gases this may have a significant impact on how quickly and how much sea levels rise.

Note: The words in bold are assessed. See Unit 4 Vocabulary.

The words in italics are in the glossary below.