Test your knowledge of sea level and its relation to climate change and our quality of life.
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Over long geological timescales, changes in the shape of the ocean basins and in land/sea distribution affect sea level. During the past few million years' ice age cycles, sea level has varied by more than a hundred meters.
Melting sea ice cannot raise global sea level since the ice is already floating. (Think of an ice cube melting in a glass full of water.) However, Arctic sea ice is thinning and the long-term summer average has decreased by 34 percent since 1979. Ice from glaciers and ice sheets, which form on land, does add water to Earth's ocean when it melts and does contribute to sea level rise.
As the ocean warms, it expands and sea level rises, accounting for about a third of the approximately 20-centimeter sea level rise seen in the past century. Water released by melting glaciers and melting ice sheets contributes the other two-thirds of sea level rise.
Water resists changes in temperature; it is slow to heat up and slow to cool down. In scientific terms, water has high heat capacity. This means that, so far, Earth's ocean has been able to absorb and hold a majority of the heat from Earth's atmosphere.
El Niño is a natural Earth system phenomenon and is not directly associated with, or caused by, global warming. El Niño, marked by episodes of warm water in the eastern Pacific, is associated with regional and global changes in precipitation and ocean circulation patterns and has been occurring for hundreds of years or more. However, climate change might be influencing its frequency and intensity.
Very cold and very salty water sinks to become deep water in Earth's polar regions, while warm water tends to remain on the surface in tropical waters. Fresh water freezes at 0°C, but sea water freezes at colder temperatures because it contains salt.
Compared to today, sea level was three to six meters higher during the last interglacial period (the warm interval between ice ages) about 125,000 years ago.
According to the World Resources Institute, in 1995 2.2 billion people, or 39 percent of the world's population, lived on or within 100 kilometers of a seashore. Recent studies reveal that up to 600 million people live in Low Elevation Coastal Zones and 200 million people live within coastal flood plains.
During the last ice age, a significant portion of Earth's water was frozen into large ice sheets that extended away from the North and South Poles, just as they do today, but they covered a much greater area. In fact, much of North America was covered by ice at that time. Because so much water was locked within glaciers, sea level was lower.
Tuvalu, a small island nation in the Pacific Ocean, is only 4.5 meters above sea level at its highest point. Rising sea level and high tides could submerge it entirely. Bangladesh is affected by yearly monsoonal flooding in addition to sea level rise. Venice becomes inundated because the land is gradually sinking by about 10 centimeters per year, an effect exacerbated by sea level rise.