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Rising sea levels are expected to force millions from their homes.

Sea level rise due to global warming set to cause 200 million climate refugees by 2050

Scott Sutherland
Meteorologist/Science Writer

Monday, November 17, 2014, 2:51 PM - Rising sea levels are a growing concern, specifically around the island nations of the world, which stand to lose the most, and whose people may be forced to abandon their homes and become environmental refugees.

Although extreme weather or ocean acidification often take centre stage when it comes to showcasing the hazards of climate change, a potentially more serious threat is the slow but steady rise in sea levels - not only in the future, but the rises we're already seeing now.

Sea levels are rising, and they will continue to rise, due to two very basic reasons:

  1. More water is being added to the oceans, and

  2. The water itself is taking up more space.

The extra water is mostly coming straight from melting glaciers, such as those in Greenland and Antarctica. Since these glaciers sit on land, all the ice contained in them has had very little, if any, influence on sea level so far, but as the ice melts the water is pouring into the oceans. Melting sea ice also adds more water, and although the weight of the ice was displacing the water, which offsets most of the resulting rise, there is still some rise from this process too (see below).

RELATED: Eastern Antarctic ice melt could lead to sea level rise of up to four metres

As for the water taking up more space, that's based on two processes, both of which affect the density of the water. The first is that ocean temperatures are rising, and since warmer water is less dense than colder water, the warmer water takes up more volume. The second is that all the fresh water being added - in this case from both melting glaciers AND melting sea ice - is diluting the salt water, and less salt means lower density, which results in higher volume.

Philippe Rekacewicz, UNEP/GRID-Arendal

There are some ways that nature acts to balance these effects - increased water temperature results in more evaporation from the ocean, thus raising salinity and density - however nature can only do so much to counter the pace that these changes are taking place at.

RELATED: Here's what rising sea levels look like

The end result is that the ocean basins are filling up to higher levels than they've been through most of human history so far.

Current projections put sea level rise at close to 1 metre by the end of this century, but this isn't just a future concern.

So far, since the mid-1800s, the Mean Sea Level has gone up by about 10 to 20 centimeters. While that may not seem like much, this is causing shorelines to retreat inland, tides are becoming higher and storm surges are having a greater impact than they did in the past. 

It's also impacting on the availability of drinking water, especially for island communities, as sea water intrudes farther inland, polluting natural freshwater resources.

This is causing a lot of concern for the future in island nations, of course, but given estimates of more than a billion people in the world living in low-lying coastal communities, this is all really a global concern.

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