Rising Sea Levels
Sea level rise, as eloquently explained by NASA’s Global Climate Change webpage, is caused by two factors. One of these is the amount of water added to the oceans by melting ice, while the other is the expansion of seawater as it gets warmer.
The graph below shows how global sea levels have risen since 1900. According to the US government’s National Oceanic and Atmospheric Administration (NOAA), there has been a mean global sea level rise of about eight to nine inches (twenty-one to twenty-four centimeters) since 1880.
Regionally, differences in sea level rise happen due to natural variability in the strength of winds and ocean currents that influence where and how much heat is stored in the deeper layers of the ocean.
This matters because numerous communities—including eight of the ten largest cities in the world—are located near an ocean shoreline, according to the UN Atlas of the Oceans. In the US, almost 30% of the population lives in a densely populated coastal area.
Melting Ice Caps and Sea Level Rise
The Arctic ice cap covers the North Pole and consists wholly of floating sea ice that is constantly shifting. Some of this ice forms and melts according to the polar seasons, while the remainder persists as ice throughout the year.
In the South Pole, only part of the Antarctic ice cap consists of sea ice. It melts completely and reforms on a seasonal basis, thus the seasonal decrease of sea ice is greatest in the Antarctic. The remaining portion of the Antarctic ice cap consists of ice sheets covering land, ice shelves, and glaciers.
Of the two ice caps, it is the Arctic that plays the larger role in regulating the climate, according to current thinking. It does so by regulating the exchange of heat, moisture, and salinity in the polar oceans.
The thickness of Arctic sea ice and the area it covers can vary significantly and change rapidly. In late winter, sea ice tends to cover an area of fourteen million to sixteen million square kilometers (8.5 million to 9.9 million square miles). In late summer, this falls to around seven million kilometers (4.3 million square miles).
In contrast, in Antarctica, the ice is around seventeen million to twenty million square kilometers (10.5 million to 12.4 million square miles) in late winter. By late summer, this shrinks to between two million and four million square kilometers (1.2 million to 2.4 million square miles).
According to a 2012 study on passive microwave satellite data, winter Arctic sea ice has decreased by about 3% per decade since 1979. Other evidence—compiled by scientists from satellite data, data from earlier ice charts, and other observations to form a chronological record from 1900 onward—shows that the area covered by sea ice in the Arctic has been declining since at least the early 1950s.
A recent article by Chris Mooney of The Washington Post cites a study published August 29 in Nature Climate Change. The study shows that the largest source of potential sea level rise is due to the melting of the Greenland ice sheet, which is one to two miles thick. The rate at which this ice is melting has accelerated since 2000 because temperatures in the Arctic are rising faster than anywhere else in the world.
Temperatures in the Arctic are rising faster than anywhere else in the world.
This potentially unstoppable melting suggests that the global sea level could rise by nearly 10.8 inches even if humanity stopped producing greenhouse gases instantly. This prediction is also viewed as a low estimate: If there are years in which there is a greater amount of melting, such as in 2012, this could mean a sea level rise of thirty feet. Indeed, many scientists agree that if all the ice on Greenland were to melt, it would cause a sea level rise of twenty feet.
“We have caused the ice sheet to go out of equilibrium,” said David Bahr, co-author of the study and a University of Colorado Boulder glaciologist, speaking to USA Today. “We’re melting it faster than the ice can move downstream and replenish areas that are melting.”
There’s no indication yet of when this world-changing sea level rise may occur, but scientists suggest that most of it will have occurred by 2100. However, another scientist, Ted Scambos, who did not contribute to the study, argues that a longer time frame is probably more accurate.
Whenever it happens, sea level rise will have “huge societal, economic and environmental impacts” across the world. Low-lying island nations and countries with coastal and delta areas—a common feature in the developing world—will be more adversely affected than nations with higher topographies.
Even a small amount of sea level rise can have disastrous effects on wildlife habitats, due to erosion, flooding of wetlands, and salt contamination of aquifers and agricultural land.
Moreover, sea level rise is suspected of influencing the behavior of hurricanes and typhoons—pushing storms toward the extreme end of the Saffir-Simpson Hurricane Wind scale, or affecting their speed or rainfall. Fiercer storm surges force people to move to higher ground while threatening basic services for people who remain behind.
In response to increasing sea level rise, many coastal cities are already planning to implement a range of adaptation measures. These include building higher sea walls, rerouting roads, and other transport corridors, and planting vegetation in threatened areas to stem the incoming sea water.
A global network of city mayors, called C40 Cities, has published a guide explaining how cities can respond to sea level rise. The first stage is to understand the local topography and how it affects the community’s vulnerability to sea level rise. This could involve examination of a risk map and production of a climate change risk assessment.
Towns and cities can follow this up by collaborating with other settlements in the region—sharing monitoring and alert systems, for example. A regional board can be established to coordinate action in the area.
Improving coastal flood defenses generally consists of two options, which can be employed in collaboration with each other. One is the reconstruction and strengthening of natural barriers through restoration of habitats and ecosystems, such as coastal wetlands, coral reefs, marshes, and mangroves.
The second option is building physical synthetic features, such as sea walls, dikes and levees, and flood barriers.
As with other climate change predictions, an extreme sea level rise could become a “new normal.” This makes it all the more important for communities to be forward-thinking and start planning and implementing measures to protect against sea level rise right now.
*Robin Whitlock is a freelance journalist based in the Southwest of England, UK. A correspondent for Renewable Energy Magazine since 2011, he specializes in environmental issues, climate change, and renewable energy, and also follows transport issues, particularly rail, bus, and coach, and green motoring.