Breaking from land and bobbing in the ocean for centuries upon centuries, icebergs are surely one of nature's most beautiful masterpieces.

Each year, hundreds of thousands of them crack off glaciers and slide into the sea from the northern and southernmost tops of the globe. Only ten per cent of an iceberg is visible from above the surface of the water, the rest of its mass lies beneath it.

Formed from snowflakes settling into land and being compressed over time before breaking away in lumps, some defiant icebergs started their lives more than 30,000 years ago.

Polar-Latitudes.com Glaciologist Robert Gilmore, who heads a pilgrimage to Antarctica every year with Polar Latitudes, tells MailOnline Travel: “They melt incredibly slowly. And they move slowly too, two knots at most depending on the current.”

You may have heard about global warming. It seems that in the last 100 years the earth’s temperature has increased about half a degree Celsius. This may not sound like much, but even half a degree can have an effect on our planet.

According to the U.S. Environmental Protection Agency (EPA) the sea level has risen 6 to 8 inches (15 to 20 cm) in the last 100 years.

Actually, over the past century, sea level has slowly been rising. This is in part due to the addition of water to the oceans through either the melting of or the “calving” off of icebergs from the world’s land ice. Many individual mountain glaciers and ice caps are known to have been retreating, contributing to the rising sea levels.

It is uncertain, however, whether the world's two major ice sheets-Greenland and Antarctica-have been growing or diminishing. This is of particular importance because of the huge size of these ice sheets, with their great potential for changing sea level.

Together, Greenland and Antarctica contain about 75% of the world's fresh water, enough to raise sea level by over 75 meters, if all the ice were returned to the oceans.

For some specialists’ perspectives, the higher temperature may be causing some floating icebergs to melt, but this will not make the oceans rise. Icebergs are large floating chunks of ice. In order to float, the iceberg displaces a volume of water that has a weight equal to that of the iceberg. Submarines use this principle to rise and sink in the water, too.

“However, in the fact, the rising temperature and icebergs could play a small role in the rising ocean level. Icebergs are chunks of frozen glaciers that break off from landmasses and fall into the ocean. The rising temperature may be causing more icebergs to form by weakening the glaciers, causing more cracks and making ice mo-re likely to break off. As soon as the ice falls into the ocean, the ocean rises a little.

If the rising temperature affects glaciers and icebergs, could the polar ice caps be in danger of melting and causing the oceans to rise? This could happen, but no one knows when it might happen.

The main ice covered landmass is Antarctica at the South Pole, with about 90 percent of the world's ice (and 70 percent of its fresh water). Antarctica is covered with ice an average of 2,133 meters (7,000 feet) thick. If all of the Antarctic ice melted, sea levels around the world would rise about 61 meters (200 feet). But the average temperature in Antarctica is -37°C, so the ice there is in no danger of melting. In fact, in most parts of the continent it never gets above freezing.

There is a significant amount of ice covering Greenland, which would add another 7 meters (20 feet) to the oceans if it melted. Because Greenland is closer to the equator than Antarctica, the temperatures there are higher, so the ice is more likely to melt.

But there might be a less dramatic reason than polar ice melting for the higher ocean level -- the higher temperature of the water. Water is most dense at 4 degrees Celsius. Above and below this temperature, the density of water decreases (the same weight of water occupies a bigger space). So as the overall temperature of the water increases it naturally expands a little bit making the oceans rise.

In 1995 the Intergovernmental Panel on Climate Change issued a report which contained various projections of the sea level change by the year 2100. They estimate that the sea will rise 50 centimeters (20 inches) with the lowest estimates at 15 centimeters (6 inches) and the highest at 95 centimeters (37 inches). The rise will come from thermal expansion of the ocean and from melting glaciers and ice sheets. Twenty inches is no small amount -- it could have a big effect on coastal cities, especially during storms.

Why is the Pine Island Glacier melting so quickly? Global warming is a serious threat. Emission of greenhouse gas, such as CO2 from coal combustion is one of the important reasons for global warming. It is no time to delay for carrying out Green Travel and emission reduction, otherwise our human and other creatures won’t survive.