When an ice cube melts in a glass of water, the water level in the glass doesn’t rise, right? If so, then why is there so much talk about the ocean levels rising if the polar ice caps melt?
The ice on the South Pole is not floating, like your ice cube, it is on land; so if it melts, there is more water in the oceans and levels rise.
The ice caps aren’t entirely floating (at least Antarctica isn’t…not sure about the North Pole). As a result, if all the ice melted off of Antarctica, it would run off the land underneath the ice and into the ocean so sea levels would rise.
The ice caps of Greenland and Antarctica are resting on land. The Antarctic cap is also connected to a lot of floating sea ice. Here is a link about the Greenland cap: http://www.greenland-guide.dk/gt/images.htm
And here is one about the Antarctic cap: http://www.st-agnes.org/~dcrank/student/megan~2.html
So how much of the polar ice caps are displacing water anyway, and how much would have to melt to submerge coastal cities?
It has been my understanding, although you rarely hear it mentioned, that the bulk of the sea level rise due to global warming would be attributed to the expansion of water as its temperature increases. The actual volume of water from the melting ice caps added to the ocean would be much less than the volume increase due to the water expansion. I always wondered why this was always glossed over in discussions about sea level rise and ice cap melting. I guess the end result would be the same (flooding) but it still seams an important distinction.
I don’t have time to find a cite right now but I’m sure I have heard this in a couple of talks over the years.
Is Orbit saying that when the ice cube in the proverbial glass of water melted and then warmed up, it would overflow because the water expanded? If he is, then is he correct?
Nope, not for any forseeable temperature increase. Melting ice on antarctica and Greenland is the major effect.
However, a reality check is required. Antarctica is Increasing it’s ice mass, not decreasing.
Antarctica is the worlds driest continent. Less H20 falls there on average than in the Sahara.
What is happening is that the warming cycle of the past few hundred years is causing more and more ice to accumulate on the antarctic ice-cap, due probably to changes in circulation patterns. The warming cycle is unrelated to global warming and has been in place since the little ice-age of the 1600’s. This contrasts to the prior warm period peaking around the 10th - 12th century when Greenland was Green and Iceland was Icy
The story about the ‘collapse’ of the antarctic ice-shelf is interesting but irrelevant to the major processes at play in the antarctic region.
If the current antarctic accumulation processes increase more, the world sea levels will start dropping, not rising.
jezzaOZ might want to provide some citations to back up the oft-stated claims made in the last post.
Yesterday’s story about the collapse of part of the ice shelf along the Antarctic Penninsula noted that, while the collapse of the shelves would not raise the level of the sea, if the shelves were to collapse in significant degree, it would allow the ice mass that rests on land to slowly slide off the land mass into the ocean, much like the glaciers do in Alaska and elsewhere. Apparently, the ice shelves act as coffer dams, keeping the ice mass of the continent from flowing down off the land. See the story in yesterday’s The (Toledo) Blade.
No, I don’t think he is correct. Remember, water is one of the very few things that actually gets bigger when it turns into a solid. Most substances as they cool off contract with their solid form being the smallest they get (without compression). I don’t see water expanding as it warms being anywhere near as significant a contributor to overall volume as does the size increase water experiences as it turns into a solid.
I relaise it’s not as authoratitive as The (Toledo) Blade but how about the IPCC second report ? http://www.grida.no/climate/ipcc/regional/046.htm#ice
Argh, browser crashed, hope this isn’t a double post.
Another effect to consider is the rebound of the continent after the weight of the ice is removed. I believe North America and Europe are still rising (a little) from the loss of the weight of the glaciers from the last ice age.
The rebound has two effects on the sea level. Usually the rebound raises the land faster than the global sea level rises from the melt water. So locally, it would appear as if the sea level is going down. But globally, the rising continent reduces the area of the ocean, effectively raising the overall sea level. I think this effect is much smaller than the increase in volume due to melting ice.
Also, about the increase in ocean volume due to increase in temperature: this is included in the more sophisticated ocean models. For a gross estimate: say 1 deg increase in temperature causes a 0.01% increase in volume (a WAG). If the mean ocean depth is 1000 m (another WAG), that means a net increase in sea level of 10 cm. That’s not insignificant (although still a smaller effect than melt volume).
What you’re missing is that this is a classic physics riddle. You have a glass filled to the rim with water, and a chunk of ice floating in it such that some of the ice is protruding above the top of the glass. The glass is so full that even one more drop added will cause a drop to spill over the side. What happens when the ice melts? Does the extra volume of the ice that’s sticking up have to flow over when it melts?
The answer is no, because of the fact that water is denser than ice, it will reduce its volume in such a way that the glass will still be exactly full. The original post was saying that since the glass will be at the same water level, wouldn’t the oceans be at the same level if all the polar ice melted? That answer is no, because the ice on Antarctica and Greenland is resting on land.
The water in a glass riddle is similar to the toy-boat-in-a-bucket riddle. If you have a toy boat floating on water in a bucket, and it spontaneously springs a leak and sinks, will the water level in the bucket go up, down, or stay the same? It’s a surprising answer (to me, anyway, although I was able to figure it out).
To me the water level would go down with the boat sinking in the bucket.
As to the other bit I guess Orbit is correct. As the ice melted the water level would remain the same and then as it warmed the water level would rise.
I knew the bit about the ice cube just described…I’m not sure what I was thinking when I wrote my post (apparently I wasn’t thinking).