3 causes of sea level rise:
1) THERMAL EXPANSION: The oceans take up over 90% of heat trapped by greenhouse gases . This slows warming of the atmosphere , but it also causes sea level rise. Warmer water molecules push each other further apart, meaning warmer water takes up more space . This is called ‘thermal expansion’ and it has caused about a third of sea level rise so far .
2) MELTING LAND ICE: Ice sheets naturally partially melt and reform on a yearly cycle . Global warming is making more melt in summer and less reform in winter . When ice on land melts, water runs into the sea, causing sea level rise .
3) MELTING SEA ICE: Ice floating on the ocean is known as ‘sea ice’. Ice is less dense than liquid water, so 1kg of ice takes up more space than 1kg of water . This is why about 10% of an iceberg is above water . This suggests that when an iceberg melts, the water produced only fills up the space that the iceberg took underwater before – melting sea ice should not increase sea level . However, this is not quite true, because sea ice is freshwater (no salt), but the ocean is saltwater . So, when 1kg of sea ice melts it adds 1kg of freshwater to the ocean [17,19]. The freshwater has a larger volume than seawater, so sea level rises a little [17,18,19]. However, this accounts for under 2% of sea level rise .
Which regions cause sea level rise? GREENLAND: ice sheets and glaciers are on land [14,15], and so add to sea level rise . ARCTIC: is floating ice, so contributes very little to rise . ANTARCTIC: no clear trend of sea ice extent over the last decades , perhaps due to natural variability, independent of climate change . Parts of it are melting, such as the West Antarctic Ice Sheet [2,6]. In contrast, colder parts may gain ice , because as air warms, it holds more water vapor, so more snow can fall . In the long term, however, we may see huge ice loss from Antarctic land ice [16,8], causing significant sea level rise.
Melting ice also indirectly further warms the Earth, and puts animals like polar bears at risk – see future posts.
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