Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: geo driver on 18/11/2009 16:57:53

Title: If the ice at Earth's poles melted, would the planet's spin axis be affected?
Post by: geo driver on 18/11/2009 16:57:53

ignoring catastophic tales of doom

if all the ice melted would the be a change of the degree of axis the earth revomves around.

or could we be like mars which every 20000 years or so rotates 90° of axis


[MOD EDIT - PLEASE ENSURE THAT YOU PHRASE YOUR THREAD TITLES AS QUESTIONS, WHICH IS THE FORUM POLICY. THANKS, CHRIS]

Title: Re: If the ice at Earth's poles melted, would the planet's spin axis be affected?
Post by: raptorguy on 18/11/2009 22:24:40

No or almost no difference. Pole ice is perhap 1/250,000 the total mass of the Earth....and even some of that is already below sea level. the Earth is a spinning object and all types of physics come into play but the moment of intertia for the spinning ice would be less than a millionth the angular monentum of the planet.

 What happens on the surface of the Earth needs perspective. The Earth is about 8000 miles in diameter....the highest point of land about 5.5 miles in altitude. We'll round that off to a 1/1500 ratio.  Unlike a globe that provides 'relief' when displaying the mountain ranges etc...a globe with accurate ratio of relief relief would feel as smooth as a balloon.  You wouldn't be able to feel the Himilayas, Andes, Rockies, etc. the Earth is REALLY big and the surface relief (including polar ice) just about insignificant as far as mass is concerned.

Title: If the ice at Earth's poles melted, would the planet's spin axis be affected?
Post by: chris on 18/11/2009 23:47:29

The melting of the ice at the poles will also have a more dramatic effect than would be predicted on the basis of sea-level rise secondary to melting alone.

The ice over Antarctica, because it is on land not floating (and hence already displacing its own weight), adds mass locally, which boosts gravity and attracts water to the polar region.

But if this ice melts this gravitational pinning effect will be lost and the watery bulge around the pole will be lost, redistributing the water worldwide and raising sea-levels by a significant amount:

http://www.thenakedscientists.com/HTML/content/news/news/1615/

Chris

Title: If the ice at Earth's poles melted, would the planet's spin axis be affected?
Post by: raptorguy on 19/11/2009 03:31:09

 Discover Dave: "Is there a springiness to this depressed ground, or is this depression permanent?"

There would be a rise of land but the amount and time frame an unknown. At the same time there would be other geologic activity going on. The deposition of sediment patterns could change  and 'other stuff' that , for example, might alter continental divides... causing even further change in sediments, etc.  Straits can open or close...ocean patterns change...this starts ice ages...etc. so much stuff going (on a geologic time scale) that it's all speculation built on a house of cards.

 But... Antarctica, Greenland aren't going to be doing much for a long time. (a lot of so-called 'journalists' confuse sea ice with continental ice mass.) 

Title: If the ice at Earth's poles melted, would the planet's spin axis be affected?
Post by: geo driver on 21/11/2009 10:41:10

yeah i was just thinking that if you got somthing balanced and then you take away a weight like the antartica ice sheet wouldnt things go off kilter,  and now you have more water being thrown around else where, i just thought that a wobble might happen speculating out loud

cheers for the answers

Title: If the ice at Earth's poles melted, would the planet's spin axis be affected?
Post by: litespeed on 21/11/2009 18:57:13

GEO

I believe normal ocean tidal forces are so much stronger, that a bit of extra water distributed from the poles towards the equator would not even be measurable as any sort of force at all.