Sea levels have already risen by 8 inches (200 mm) over the last 100 years

Sea levels have already risen by 8 inches (200 mm) over the last 100 years. That might not sound like much, but as the oceans warm and glaciers melt, levels will continue to rise faster and faster. Before too long, many low-lying villages, towns, cities, and islands will be threatened by flooding.

The Sun heats the ocean and causes it to expand.

Rising temperatures melt the glacier and water runs off into the sea. 

Why have seas risen?

Since 1900, sea levels have risen about 0.08 inch (2 mm] every year. About a quarter of this rise is caused by melting mountain glaciers, and another quarter by oceans expanding as they warm. But this still leaves half the rise unaccounted for. This is called the sea level enigma, which scientists are still trying to understand. Some think the cause may be melting sea ice at the poles. 

Sea level enigma

4inches (100 mm] 

Ocean warming

2 inches (50 mm] 

Melting glaciers

2 inches (50 mm] 

Sea level in 1900

²/3 of the world’s biggest cities are in low, coastal areas.

Deep trouble The tiny islands of Tuvalu, right, are about halfway between Hawaii and Australia. Rising seas have already flooded many areas. People who live on these islands may eventually have to abandon them and move to higher land.

ShishmarefThe residents of the coastal town of Shishmaref, Alaska, have already felt the effect of rising sea levels due to global warming. Increasingly high tides are washing away the foundations of their houses, which then collapse.

How far will sea levels rise?

If sea Levels continue rising at their current rate, they will be around 19 inches (480 mm] higher by 2100, shown here as an orange line. But this is not certain, and additional warming and ice melting in Greenland or Antarctica could push this level up to 39 inches (1,000 mm) or higher (green line).

Wetter, drier

Changes in weather patternscan cause both heavy rains and severe drought. We are already experiencing the effects of changing rainfall as it increases in some regions and decreases in others. Some scientists predict that global warming will many wet regions even wetter dry regions  drier. And as sea temperatures rise, existing climate problems such as drought, desertification, and flooding may become more common and more destructive.

Effects of desertification

Desertification happens when desert sands slowly shift to cover neighboring areas. This can destroy fields and ruin villages. It is caused largely by changes in wind patterns. Droughts linked to climate change may make the problem worse in some areas. 

Dry down under Record high temperatures hit Australia in 2002, causing one of the most widespread droughts in its history. About 60 percent of the country had little rain for nine months of the year. The drying of Lake Burrendong in New South Wales (above and right] caused severe water shortages in nearby town:

The village is threatened by the shifting sands.

Wind moves the sand.

The farmers must move from their village to the town.

Sand dunes cover the fields and destroy crops.