Global Climate Destabilisation

[Little John]

http://www.climatecentral.org/news/anta ... ears-20451

No going back

[emordnilap]

LJ, it's a hoax. The people we vote for say so. We're not so stupid as to put them in power are we?

Here's a nice f'rinstance (see no. 2 especially).

[emordnilap]

Question for those more knowledgeable than I:

If all or a significant amount of the ice caps melt, will the shifting weight of water across the planet have an affect on tectonic plates and their movement?

[Little John]

Bound to.

In fact, I recall asking that very question here a year or two back and wondering out loud if it might, in turn, cause a rise in earthquakes and volcanoes. Lo and behold, I read, a couple of days back that is exactly what scientists are now suggesting is happening.

[clv101]

Question for those more knowledgeable than I:

If all or a significant amount of the ice caps melt, will the shifting weight of water across the planet have an affect on tectonic plates and their movement?

Yeah. Firstly the ice-caps have non-trivial gravitational fields of their own. That's one reason why if you were to melt Greenland totally, raising average sea levels by ~7m, the sea level near to Greenland would actually go down as the ice-sheet's gravitational field would no longer be pulling the ocean towards it. It would go up by more than 7m elsewhere to compensate. One little known fact is that most coastal cities can expect more sea level rise than the average (that is most often presented/discussed) due to their locations.

Secondly they weigh a lot and depress the Earth's crust - look at a map of Greenland and you see the edges are above sea level, the centre of the island is depressed below sea level. As the ice melts there's an instant elastic response (the rock actually does go down in the winter with the weight of additional snow and rebounds up in the summer as it melts, this can be measured with GPS!) and a much slower viscus response.

Whether these factors can be said to cause a rise in earthquakes and volcanoes is an open question but melting ice-sheets certainly influences the lithosphere.

[Little John]

http://europe.newsweek.com/nepal-earthq ... 6017?rx=eu

[emordnilap]

Question for those more knowledgeable than I:

If all or a significant amount of the ice caps melt, will the shifting weight of water across the planet have an affect on tectonic plates and their movement?

Yeah. Firstly the ice-caps have non-trivial gravitational fields of their own. That's one reason why if you were to melt Greenland totally, raising average sea levels by ~7m, the sea level near to Greenland would actually go down as the ice-sheet's gravitational field would no longer be pulling the ocean towards it. It would go up by more than 7m elsewhere to compensate.

By how much? The idea that ice-caps have 'non-trivial' gravitational fields is a little hard for most people to swallow, you have to admit!

[clv101]

It's enough gravitational attraction that even if you add enough water to the oceans to produce an average 7 m of sea level raise, the loss of Greenland's gravitational attractions means the local sea level falls.

This is the key image:

On the left, Greenland, on the right, West Antartica. The scale is normalised, it's the proportion of average that you see. So for Greenland, for every 1m of average sea level rise, the area around Greenland (and Iceland) actually sees a drop of ~0.4m. But Cape Town for example will see ~1.2m rise. The reverse is true for West Antartica.

The upshot of this is that here in the UK, we have relatively little to fear from Greenland's melting!

You can measure changes to the gravitational field from space, it's one way to measure changes to the ice-sheet's mass. You have a pair of satellites on a polar orbit, with a radar link between them measuring the exact separation. As they fly over Greenland the increased gravitational field affects the separation. Over months and years you can measure mass changes; both the season cycle and the long term trend.

[careful_eugene]

Question for those more knowledgeable than I:

If all or a significant amount of the ice caps melt, will the shifting weight of water across the planet have an affect on tectonic plates and their movement?

Yeah. Firstly the ice-caps have non-trivial gravitational fields of their own. That's one reason why if you were to melt Greenland totally, raising average sea levels by ~7m, the sea level near to Greenland would actually go down as the ice-sheet's gravitational field would no longer be pulling the ocean towards it. It would go up by more than 7m elsewhere to compensate. One little known fact is that most coastal cities can expect more sea level rise than the average (that is most often presented/discussed) due to their locations.

Secondly they weigh a lot and depress the Earth's crust - look at a map of Greenland and you see the edges are above sea level, the centre of the island is depressed below sea level. As the ice melts there's an instant elastic response (the rock actually does go down in the winter with the weight of additional snow and rebounds up in the summer as it melts, this can be measured with GPS!) and a much slower viscus response.

Whether these factors can be said to cause a rise in earthquakes and volcanoes is an open question but melting ice-sheets certainly influences the lithosphere.

Absolutely fascinating, thanks for sharing this.

[emordnilap]

I started typing 'fascinating' too, c_e.

[Potemkin Villager]

I had always thought that when you were in a hole it generally was not wise to dig deeper. These "can do" folk certainy believe deeper digging is the answer.

http://gizmodo.com/this-giant-straw-wil ... 1700743879

[Blue Peter]

It's enough gravitational attraction that even if you add enough water to the oceans to produce an average 7 m of sea level raise, the loss of Greenland's gravitational attractions means the local sea level falls.

On the left, Greenland, on the right, West Antartica. The scale is normalised, it's the proportion of average that you see. So for Greenland, for every 1m of average sea level rise, the area around Greenland (and Iceland) actually sees a drop of ~0.4m. But Cape Town for example will see ~1.2m rise. The reverse is true for West Antartica.

Just to make sure I have this right. If we measure everything relative to where sea level is now (call it zero, 0m). If Greenland melts than average sea levels are +7m, but the average sea level round Greenland is less than 0 i.e. some negative metres?

The gravitational effect is that great!? Wow!


Peter.

[clv101]

Yep.

And the unfortunate thing is that most of the big coastal cities are in areas that will see more than average sea level rise.

[emordnilap]

It's enough gravitational attraction that even if you add enough water to the oceans to produce an average 7 m of sea level raise, the loss of Greenland's gravitational attractions means the local sea level falls.

On the left, Greenland, on the right, West Antartica. The scale is normalised, it's the proportion of average that you see. So for Greenland, for every 1m of average sea level rise, the area around Greenland (and Iceland) actually sees a drop of ~0.4m. But Cape Town for example will see ~1.2m rise. The reverse is true for West Antartica.

Just to make sure I have this right. If we measure everything relative to where sea level is now (call it zero, 0m). If Greenland melts than average sea levels are +7m, but the average sea level round Greenland is less than 0 i.e. some negative metres?

The gravitational effect is that great!? Wow!


Peter.

It's not easy to take in; in fact, the idea would be met with great skepticism down the local pub, which in turn chain-links to people not really caring much.

[Catweazle]

This is a very informative thread. Top marks.