How much of the Earth is covered by water?

About 70 percent of the surface area of the Earth is covered by water. The other 30 percent of the Earth is land located primarily in the Northern Hemisphere. If you look at a globe, you'll notice that the Southern Hemisphere has a great deal of ocean.

How much is the sea level rising?

Recent estimates show the sea level has increased 7 to 12 inches (20 to 30 centimeters) during the twentieth century.

What countries are threatened the most from rising sea levels, and may cease to exist in the twenty-first century?

Low-lying island nations of the Pacific and Indian Oceans are most at risk, most notably Tuvalu and the Maldives. Other candidates for severe flooding and reclamation of coastal land by the impending sea include Bangladesh, India, Thailand, Vietnam, Indonesia, and China, affecting the lives of hundreds of millions of people.

How much land disappears when the sea level rises?

Scientists believe that as the sea water rises by 0.04 inches (1 millimeter), the shoreline disappears by 4.9 feet (1.5 meters). This means that if the sea level rises by 3.28 feet (1 meter), the shorelines will extend another 1 mile (1.6 kilometers) inland.

How does the hydrologic cycle work?

The movement of water from the atmosphere to the land, rivers, oceans, and plants and then back into the atmosphere is known as the hydrologic cycle. We can pick an arbitrary point in the cycle to begin our examination. Water in the atmosphere forms clouds or fog and falls (precipitates) to the ground. Water then flows into the ground to nourish plants, or into streams that lead to rivers and then to oceans, or it can flow into the groundwater (underground sources of water). Over time, water sitting in puddles, rivers, and oceans is evaporated into the atmosphere. Water in plants is transpired into the atmosphere. The process of water moving into the atmosphere is collectively known as evapotranspiration.

Where is all the water?

Over 97 percent of the world's water lies in the oceans and is too salty to drink or to irrigate crops with (except when the water is cleaned through a desalinization plant, which is not done very often). About 2.8 percent of the world's water supply is fresh water. Of that 2.8 percent, about 2 percent is frozen in glaciers and ice sheets. This leaves only about 0.8 percent of the world's water that is accessible through aquifers, streams, lakes, and in the atmosphere. The water that we use primarily comes from this 0.8 percent.

What is evapotranspiration?

Evapotranspiration is the combination of water vapor being evaporated from the surface of the Earth (such as from lakes, rivers, or puddles) into the atmosphere, and transpiration, which is the movement of water from plants to the air.

What is an aquifer?

An aquifer is an underground collection of water that is surrounded by rock. The creation and filling of an aquifer is a very slow process, as it relies upon water to percolate through the soil and rock layers and into the aquifer. An aquifer lies above a lower layer of rock that holds the water in place and keeps it from moving further underground.

What is the Oglala Aquifer?

The Oglala Aquifer is a huge aquifer that spans an area from Texas to Colorado and Nebraska. The oldest water deposited in the aquifer is over one million years old, and only a very small amount of water is added each year. The Oglala Aquifer is being pumped rapidly by the farms in the region, causing a reduction in the amount of water in the aquifer. Consequently, wells have to be continually deepened so that they can continue to pump water.

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