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Q & A: Global warming and the polar ice caps

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Most recent answer: 09/18/2013
Q:
How does Global Warming effect the polar ice cpas?
- Natalie (age 14)
St Michaels, Chorley
A:
This is a very important question! Global warming may have significant impacts on our environment over the next century, and many say that it is currently responsible for changes in weather and climate patterns already. The short-term variability of the weather makes it very hard to base decisions on only a few years’ observations, but the long-term trends (measurements over a hundred years) do indicate that we are on a warming trend.

Changing the average temperature on the Earth by even a few degrees is enough to upset delicate climate patterns. How these patterns are upset and by how much and how long it takes are matters we do not know for certain, but we do have ranges of predictions. We expect that even a small increase in the average temperature will melt large amounts of ice near the poles.

Much of this ice is in contact with water. At the South pole, gigantic ice shelves float on water, and at the North pole, there is no land and the ice floats on water. Much of the ice has a temperature very close to that of the nearby water, and so is ready to melt. There is a steady-state situation where snow falls around the poles, packs into ice, flows down in glaciers, and melts in the sea -- this process is extremely slow. Increasing the water temperature will increase the heat flow rate into the melting process, and reduce the equilibrium amount of ice at the poles.

Today there was an interesting on CNN’s website which claims that the snowfall rate on the poles may actually increase as the Earth warms. The argument is that with higher temperatures comes more evaporation of water from the oceans, and this must fall as precipitation somewhere, and that some of that precipitation increase may be found as snow near the poles.

This may not be enough to increase the amount of ice and snow around the poles. Most glaciers around the world have shrunk over the last century, even if the precipitation rate has gone up in some places. The precipitation rate may even go down in some places (like areas that are already deserts).

Tom

One question you may also be wondering about is how the melting ice caps would affect the sea level. When you melt an ice cube in a glass, the water level doesn’t change. However, the South Pole ice and the Greenland ice are not floating but sitting on land. As they melt, the sea level will rise. The sea level would also rise as the ocean temperature goes up, because most of the ocean is at temperatures for which water expands when it warms.
Mike W.

(published on 10/22/2007)

Follow-Up #1: antarctic ice packs

Q:
I was reading a post you replyed to about global warming from a girl named Natalie of St. Michaels, Chorley dated 07/18/06.

You made this statement..."Much of this ice is in contact with water. At the South pole, gigantic ice shelves float on water,"
Then at the end you make this statement..."However, the South Pole ice is not floating but sitting on land."

Those two statements as is, actually contradict each other which I am sure you did not mean it to come out that way.

Could you clarify how much ice is on land and how much ice is floating at the south pole?
Thanks, Shannon.
- Shannon
Alaska
A:
We’ll update this when I can scrounge the figures, but for now here’s a partial answer.

You’re right that the Antarctic ice  includes a huge amount over land but also extends out to sheets that rest on water. I think that most of the volume is on land, but will check that. In the near future, the parts that are melting or breaking away are the parts over water, so they don’t contribute to raising sea levels. Melting of the Greenland ice is a more near-term problem. In the long run, the fate of the land-based Antarctic ice is the biggest unknown in estimating how much sea levels will rise.

Mike W.

I found a web site

that gives a lot of facts on ice in the antarctic.  During the winter months the surface areas of the continent and the sea ice pack are comparable.  During the summer, the sea ice pack shrinks to about 1/6 of its winter size. The total volume of the continental ice, about  30 million cubic kilometers, is 1000 times greater than that of the winter sea ice pack.

LeeH

(published on 01/23/2008)

Follow-Up #2: melting Arctic ice

Q:
I just happened to come upon a explanation that has intrigued me. If the arctic ice is melting the sea level should actually 'decrease'. For example you you have two beakers of the same amount of water. One is frozen and its volume increases(water expands) and the other should stay the same. When put in the other beaker, the water level should decrease as its volume is decreasing. Is this right or is it due to the fact that some amount of the ice is submerged in the water and it decreases as it melts thus keeping the water level the same.
- Donkeychee (age 34)
Greenland
A:

It's the later- the melted ice is just the right volume to repace the part of the ice that was underwater, so the water level doesn't change. Archimedes figured that out. You can check it with a glass of icewater. 

As your Greenland ice melts, sliding off land into the ocean, the ocean levels go up.

Mike W.


(published on 09/18/2013)

Follow-up on this answer.