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Author Topic: Why will melting ice cause rising sea levels?  (Read 716 times)

Offline thedoc

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Why will melting ice cause rising sea levels?
« on: 03/08/2016 14:23:01 »
Ruth Lewis asked the Naked Scientists:
   If a glass containing water is overloaded with ice, when the ice melts, it does not cause the water to run over the lip of the glass because Ice displaces more space than water.  Why is it that these global warmers say "Global Warming" will "flood the seacoasts?
What do you think?
« Last Edit: 04/08/2016 20:33:56 by chris »


 

Offline agyejy

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There are two distinct ways in which climate change impacts ocean levels. The first is the melting of any ice that is currently on land. You are right that icebergs (and most of the ice at the north pole) melting don't really cause sea level change. Basically any ice that is floating can melt without doing pretty much anything to sea level. The problem is a large amount of ice is actually on land in both Greenland and Antarctica. If this ice melts and the water runs into the ocean than that is new water that wasn't there before which is more like waiting for the ice to melt in the ice tray and then pouring it into a full glass of water.

The second way is that at temperatures higher than a few degree above freezing water does begin to increase in volume with temperature. This means that if the average temperature of the oceans increases all the ocean water expands and takes up more space and there is no where to go but up. When heating water in a pot the change isn't really noticeable but scale it up to the size of all the oceans and it becomes noticeable on a human scale.
 

Offline Tim the Plumber

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The second way is that at temperatures higher than a few degree above freezing water does begin to increase in volume with temperature. This means that if the average temperature of the oceans increases all the ocean water expands and takes up more space and there is no where to go but up. When heating water in a pot the change isn't really noticeable but scale it up to the size of all the oceans and it becomes noticeable on a human scale.

Yes but the amount of energy required to achieve this temperature change on a colum of water as deep as the oceans is so vast that just by increasing the temperature above the top of the colum by a couple of degrees will not be noticed by the water 2km down for many many thousands of years if ever.
 

Offline agyejy

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Yes but the amount of energy required to achieve this temperature change on a colum of water as deep as the oceans is so vast that just by increasing the temperature above the top of the colum by a couple of degrees will not be noticed by the water 2km down for many many thousands of years if ever.

1) Even the top couple hundred meters of the world's oceans is still a heck of a lot of water and even if just that was heated it would still be noticeable. Climate scientists do in fact model the impacts of different depths of the ocean warming differently. (Also you don't even need a couple of degrees of change to have a noticeable change in ocean levels.)

2) The amount of excess thermal energy going into the oceans right now is massive.

For example: http://e360.yale.edu/feature/how_long_can_oceans_continue_to_absorb_earths_excess_heat/2860/

Quote
The ocean has been heating at a rate of around 0.5 to 1 watt of energy per square meter over the past decade, amassing more than 2 X 10^23 joules of energy the equivalent of roughly five Hiroshima bombs exploding every second

To emphasize the point I will reiterate that right now the oceans are on average absorbing thermal energy equal to 5 Hiroshima sized bombs each and every second.

3) Last but not least the sea level rise has been measured: http://climate.nasa.gov/vital-signs/sea-level/



https://www.skepticalscience.com/sea-level-rise-predictions-intermediate.htm <- A more comprehensive look at the impacts of climate change on the oceans
 
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Offline evan_au

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Quote from: Tim the Plumber
increasing the temperature ... by a couple of degrees will not be noticed by the water 2km down for many, many thousands of years if ever
Oceans do not just warm by conduction, they also warm by global convection. Water that is heated by passing below a warming atmosphere reaches a higher temperature than previously. These warm currents flow on the surface from the equator towards the poles, where they cool, become denser, sink and flow back towards the equator. These convection currents "bury" warmer surface waters in the deep ocean, and it is happening already.

It is not just temperature that is affecting the oceans, but also salinity (saltiness). If more fresh water from Greenland and Antarctica flow into the ocean, it makes the water less dense, and less likely to sink. If these global-scale currents shut down, warm currents heating the UK and the east coast of Australia could shut down, and lead to localized cooling despite a generally warming planet.
- Imagine the UK with the same climate as Newfoundland (they are at similar latitudes)!
- The heat which currently heats the UK would stay closer to its origins in the Gulf of Mexico, and lead to more frequent hurricanes like the one that devastated New Orleans.
- The warm water which makes Sydney beaches famous would stay near the equator, and lead to more coral bleaching
See: https://en.wikipedia.org/wiki/Shutdown_of_thermohaline_circulation#Thermohaline_circulation_and_fresh_water

Most of our knowledge of sea temperatures is at the surface. Submarines no doubt take measurements of water temperatures, but can't release any data as it would reveal where they normally hide.
This is changing with the use of long-duration civilian research vehicles to sample the ocean waters at many depths:
https://en.wikipedia.org/wiki/Underwater_glider
 

Offline Tim the Plumber

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Water sinks to the deep ocean when it reaches 4c. This is the point at which water reaches maximum density. Water is strange stuff and the coldest water will float above warmer layers and then freeze from the top. As we all know.

The volume of water flowing across the oceans in the great currents is vast. The volume of ice melt coming of Greenland etc is tiny in comparison. Hype about any inpact on ocean currents is drivel.

The Gulf stream/North atlantic convayor moves 540 cubic kilometers of water per hour. Even in the breif 4 week summer of Greenland it's alleged extra melt rate of 200 cubic km is about 1/2000 of the flow rate of the ocean current it's supposed to stop.

I say alleged because if it's been melting at the rate the doomsayers would have it, 200 km3 per year for the last 20 years or so, where is the 4,000km3 gap where there used to be ice.

Sometimes the bleeding obvious trumps any number of papers published in Nature.
 

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