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Comment by mamon | Hacker News Reader

Dumb question: if all the ice melts, especially in Arctics shouldn't the see level fall down as volume of water is smaller than volume of ice? And with increased temperature there is also increased vaporization and world's average humidity - another reason for sea levels to fall down.

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There are no dumb questions :-), but no, this is not what will happen. For one thing, the ice that floats around in sea displaces exactly as much water as ice (uses the same 'water volume') as it will as water. (Almost, because the water volume per mass will actually increase with increasing temperatures, which is quite a significant effect). However, a large amount of ice is on land, where it doesn't contribute to ocean volume. If it were to melt that would be a major contributor to sea level rise.

Also, the average humidity is quite stable on earth, and any excess water that evaporates into the atmosphere quickly rains out again. Furthermore, the amount of water in the atmosphere is very small in comparison to the amount of water in the oceans. (See e.g. here: http://water.usgs.gov/edu/watercycleatmosphere.html). So it is very difficult to imagine that an increased humidity would have a significant effect on the sea level.

The fear of ice melt is not from the arctic but from land. There is a significant amount of water trapped on the tops of mountains and in glaciers not in the water. Those melt and the sea will rise.

http://linkingweatherandclimate.com/ocean/figs/density2.png

Look at this graph. By having the ice melt you'll have more salty water. Even if it is all fresh, the density maximum is close to 5 degrees Celsius. Ocean water is warmer in most of the oceans.

Water vapor is a greenhouse gas - more water vapor will mean even higher temperatures, which would lead to more melting.

The other people have already answered this, but I just wanted to clarify that this is why people talk about the Greenland and Antarctic ice sheets in this context, because those rest on land.

The Arctic ice is important for albedo reasons, it reflects a lot of sunlight that would otherwise go into warming the water, but as you correctly point out, the melting of that particular ice won't contribute to sea level rise directly.

Watch Fox new much? Climate deniers love this argument. Jon Stewart answers your question here:

https://youtu.be/lPgZfhnCAdI?t=459

While looking for the clip I found this gem: https://www.youtube.com/watch?v=cjuGCJJUGsg

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