Rising Sea Levels

Sea level rise comes from warmer temperatures both directly and indirectly. Firstly, warmer temperatures cause a phenomenon called thermal expansion. The ocean absorbs more than 90% of the heat trapped by the greenhouse effect, warming the upper part of the ocean. Since warmer waters expand their volume, sea levels rise as oceans warm. 

Secondly, warmer temperatures cause snow and ice to melt on land, particularly in the Arctic and Antarctic. These areas have ancient glaciers which contain enormous amounts of frozen water. Land snow and ice are split into two categories: ice sheets and glaciers which are outside of those ice sheets. Warmer temperatures cause these ice sheets and glaciers to melt into the ocean. There are two ice sheets today: the Greenland ice sheet and the Antarctic ice sheet. These ice sheets are massive, spanning thousands of square kilometers. If Antarctica's entire ice sheet were to melt, it would raise the sea level by almost 190 feet (just over 24 feet for Greenland).

If we limit warming to 1.5ºC (which would need major solutions immediately to do), then researchers estimate ice melting would raise sea levels by five inches. But if we stay on our current emissions trajectory (no change in how we act), then it would be double that by 2100 – ten inches. That's a frightening amount because even ten inches will result in much worse coastal flooding.

However, Antarctica is different. Most of the sea level rise is coming from Greenland and glaciers. Antarctica is poised to reach a "tipping point" when warming is between 2ºC and 3ºC (scientists are unsure of when exactly). At this tipping point, a lot of the Antarctica ice sheet will collapse, raising sea level by an additional six inches by 2100.