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Causes, consequences of a warming planet

Melting snow, ice raise sea level

From the Don Hofstrand series: Causes and consequences of a warming planet series
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Melting land ice and warming oceans are two significant causes of sea level rise. In this article we will discuss melting land ice. In the next article we will discuss the warming of the oceans.

Snow and ice floating in water, called sea ice, covers much of the Arctic Ocean. The Arctic sea ice has been melting rapidly in recent years. Although melting sea ice impacts the warming of the Earth, its impact on raising sea level is minimal.

To understand this, put an ice cube in a glass and fill the glass with water. Does the glass overflow when the ice cube melts? No, the water level in the glass is unchanged. That’s because the volume of water displaced by the floating ice cube (the amount of the ice cube below water) is equal to the amount of water contained in the ice cube.

Conversely, melting snow and ice on land does raise sea level. For example, if a chunk of the ice covering Greenland breaks off and falls into the ocean, sea level rises.

It is like dropping an ice cube into a glass of water. The water level in the glass will rise by the amount of water the ice cube displaces in the glass, possibly causing the glass to overflow.

Similarly, if a portion of the land ice on Greenland melts and the water flows into the ocean, sea level will rise. It like melting an ice cube and adding the water to the glass. The water level of the glass will rise.

A complete melting of the Greenland’s land ice would raise sea level by 20 feet. A complete melting of Antarctica’s land ice would raise sea level by 200 feet. Although this level of melting would take hundreds of years, it does show the potential impact of these land ice sheets on sea level.

Glaciers in other parts of the world are being impacted. Scientific studies have confirmed that most of the world’s glaciers are retreating. Most of the smaller ones are rapidly disappearing.

For example, in 1850 there were about 150 glaciers in what is now Glacier National Park. Today there are only 25. It is expected that the Park will become glacier-free sometime in the future.

Don Hofstrand is a retired agricultural economist from Iowa State University Extension. During the last few years of his work life, he focused on renewable energy and climate change. He and his wife live in Mason City.


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