Rise in Sea Levels

Why Are Sea Levels Rising?

Warm temperatures raise sea levels in two main ways. First, ocean water expands as it warms. This causes the level to rise. But expansion accounts for only part of the increase.

Warmer temperatures are also melting ice caps and glaciers. Three-fourths of Earth’s freshwater is stored in these ice formations. Satellite observations show that ice cover is shrinking worldwide. Runoff from mountain glaciers finds its way to the ocean. Major ice sheets in Greenland and West Antarctica are melting and slowly sliding into the sea.

Melting ice accounts for a large part of recent increases in sea levels. Melting will increase if temperatures continue to rise.

What Are the Dangers?

As sea levels creep higher, coastal areas face growing risks of flooding. The danger is greatest in low-lying areas. Such areas range from the Louisiana coast to the river deltas of Africa and Asia. Small islands are also at great risk. Many people live in these areas.

Rising sea levels also erode beaches. They flood coastal wetlands. And they raise the salt level (salinity) of rivers and bays. This affects wildlife. Coastal wetlands are home to many plants and animals. They also serve as “nurseries” for the young of many ocean species.

Continued warming could bring huge changes to the coasts. Large areas of land would be lost to the sea. If all the Greenland ice were to melt, sea levels would rise almost 23 feet (7 meters). Much of coastal Florida would be under water. So would most of the nation of Bangladesh. Some small island nations might disappear completely. Cities from London to Los Angeles would face flood risks.

What Can Be Done?

Scientists are not sure how much or how quickly sea levels will rise. That will depend on the speed of global warming. But some increases in sea level seem certain.

People are preparing. Some coastal areas are restricting new building. Hurricane-devastated New Orleans is a prime example. City planners have begun to restrict building in the most flood-prone areas. In other areas, they are requiring that builders take precautions to prevent flooding problems.

Others are requiring building designs that can better withstand floods. Some cities are planning floodgates and other systems to keep out rising seas. For example, the Thames Barrier protects London by blocking high tides that move up the River Thames from the sea. It has operated since 1984. Now a second, larger set of floodgates is proposed.

People in high-risk areas are also campaigning for cuts in emissions of carbon dioxide and other greenhouse gases. That is the surest way to reduce the warming trend. That, in turn, should reduce the rising of sea levels.