Environmental Engineering Reference
In-Depth Information
ocean waters would take up more space. Increased hurricanes also could cause seasonal swelling of the oceans.
Oceans cover approximately 70 percent of the Earth's surface, and the sea level is currently rising at a rate of
1⁄10 inch per year. Due to the CO
2
already in the atmosphere, the sea level is projected to continue rising for
many centuries.
The impacts of a rising sea level include loss of coastal ecosystems, flooding of cities (such as New Orleans
and Venice), disappearing islands, disappearing wetlands, displacement of coastal inhabitants, and increased
vulnerability to storm surges because coral reefs and barrier islands, which protect the coastland, may be sub-
merged. Some of these effects could be magnified if the frequency of severe storms increases. Bangladesh, for
example, is an impoverished nation that is projected to lose 17.5 percent of its land if the sea level rises 40
inches. Louisiana would lose its freshwater wetlands. Economic challenges of a rising sea include decreased
tourism and reduced local agriculture.
El Niño and La Niña
El Niño and La Niña patterns also have been altered by global climate change. El Niño events produce in-
creased warming of the Pacific Ocean every two to seven years, while La Niña events produce cooling of sur-
face waters near the equatorial region of the Pacific Ocean every two to seven years. During the last several
decades, the frequency of El Niño events has increased while the frequency of La Niña has decreased. Studies
of historic data show that the recent increase in the El Niño variation is most likely linked to global warming.
However, these cycles are still not fully understood, so future changes in these cycles are difficult to predict.
For example, stronger El Niño events may occur in the early stages of global warming but may become weaker
as the lower layers of the ocean get warmer. Some scientists believe these patterns will stabilize on their own.
Melting Glaciers
Over time, in areas where more snow falls than melts, the accumulation of snow compresses the lower layers
into glacial ice. This ice slowly slides toward lower elevations like an ice river, and at a certain elevation, the
ice starts to melt. Many people worldwide depend upon melting glaciers for survival. However the warming
Earth means that over the past century, Earth's glaciers have increased their melt rate, decreasing in total land
coverage by 50 percent. Glacial melting in areas unaccustomed to water causes landslides, flash flooding, and
increased variation of water flows into rivers. Much of Asia relies on the waters from seasonal melting of the
glaciers in the Himalayan Mountains, where global warming has increased the overall flow of water, which
has, in turn, increased flooding and disease. Once the source glaciers are depleted, it is expected that the flow
of water to much of Asia will decrease, leading to droughts and decreased potential to produce hydroelectric
power.
Current estimates put the number of people living within 1 vertical meter of the coastline at about 150 million,
and current estimates predict a rise in sea level of between 0.5 and 1.5 meters by the end of the century. The
resulting worldwide flooding of islands and coastal areas will force these 150 million people to relocate.
Since the end of the last ice age 18,000 years ago, the sea level has risen 122 meters, most of that in the first
15,000 years. It is estimated that the rate of ocean rise for the 3,000 years prior to the Industrial Revolution had
slowed to about 0.2 mm per year. Since the Industrial Revolution, the pace of ocean rise has increased to about
3 mm per year.
If all the glaciers, the ice sheets, and the polar ice cap melted in the Northern Hemisphere, combined with the
thermal expansion of water, the sea level would rise 6.5 to 7.5 meters. If the ice cap and ice sheets in Antarc-
