What's The Straight Dope on Sea Levels?

One of the claims made by global warming proponents, is that the melting of land-based ice sheets (glaies, ice caps) will rase the level of the worlds oceans.
Presumably, this should be a measurable effect, yet outside of anecdotal claims, thee seems to be little factual evidence to validate this.
Critics point to the case of the Maldive Islands (the land seems to be sinking)-but it is unclear what is responsible (hundreds of wells have been drilled on the islands , and the withdawal of fresh water has resulted in subsiding land levels).
So, what evidence supports the claim of rising sea levels?

LMGTFY:
Turns out Wikipedia is your friend.

Are you kidding? This statement can only be based on a nearly complete failure to look for information on the subject. Unless you contend that the information provided by the US Environmental Protection Agency and the IPCC is anecdotal.

Seriously, ralph, try to do at least minimal research on a subject before opening a GQ thread about it.

And are you suggesting that sea level change doesn’t happen at all, or are you merely rejecting the notion that it’s happening right now?

Are you questioning the change in sea level or the cause of that change? IOW, are there normal fluctuations in sea level?

Here’s a related question:

How do global warming deniers explain the rising sea levels? Where is the water supposedly coming from if not from the frozen parts of the world melting?

The Intergovernmental Panel on Climate Change is not without its critics.

Scientists who have served on the panel have stated that some parts of the reports have not been accurate.

But Climate Change “true believers” on this board and elsewhere, of course, call these scientists idiots and worse for daring to question Al Gore and the IPCC.

IPCC reports are gospel, completely accurate and are not political motivated. How dare you question them?!!

[Moderating]

Frankly, I’d rather not see this turn into a debate on global warming, and have to move it to GD (especially since there are already about seven global-warming related threads on the front page). Let’s keep the discussion focused on the basic question in the OP, that is, the evidence that sea levels have recently risen/are rising.

Colibri
General Questions Moderator

[Moderating]

And especially keep this kind of rhetoric out of GQ. Don’t do this again.

Colibri
General Questions Moderator

Just to address this common misconception, melting ice is not the primary cause of sea level rise. As the Wiki article linked to by Squink indicates, the main cause of rising sea levels is thermal expansion of the oceans. As ocean temperature rises, the water expands and takes up more volume, thus causing levels to rise.

Anyone who still doubts global warming should listen to the first segment of http://www.cbc.ca/quirks/archives/09-10/qq-2009-11-28.html. Anyone who doubts rising seas should listen to the first segment of http://www.cbc.ca/quirks/archives/09-10/qq-2009-12-05.html. The latter says that the sea level has risen by about 20 cm (8") in the last 150 years but the former opens the possibility that this might be accelerating. Briefly, an expedition to measure the permanent arctic ice didn’t find it. Now they searched in only one place and, in any case, the arctic ice could melt completely with no effect on the sea level (except the effect of warmer water expanding. But let Greenland and any significant part of the antarctic ice melt and the change could be measured in meters. (For the record, the reason is that the arctic ice is floating and its melting does not contribute to sea level change. But there is enough in Greenland and the Antarctic to raise the level by many meters. Goodbye New York City, most of New Jersey, the California coast, most of Florida, the Gulf Coast including New Orleans.)

The mass balance change to the Greenland ice sheet (obviously above sea level) is contributing a significant component, c. +0.7 mm a[sup]-1[/sup], to the current trend of +3 mm a[sup]-1[/sup]. During the past year it has shed approximately 273 gigatonnes of ice (1500 Gt since 2000; graph here), and this rate of loss is likely to increase further due to positive feedback mechanisms.

You are in some sense correct in this respect. Arctic summer sea ice is disappearing at a greater rate than the worst estimates outlined in the 2007 IPCC predictions.

That’s hilarious!

What, exactly, so funny?

Care to explain?

I gather this sounds implausible to you.

Consider the following:

the volumetric coefficient of thermal expansion of water is 207 parts per million at 20 degrees Celsius (it decreases closer to the freezing temp, but this will do for a back-of-the-envelope calculation).

[url=]The average ocean depth is 12,400 feet.

If the average ocean temp rises by one degree celcius, that results in a sea level rise of about 31 inches (=0.000207 * 12,400 * 12).

The real number could be less, since the coefficient decreases as you get closer to freezing, and much of the deep ocean is right around that temp. But it could also be more, if the temp rise is greater. In any event, you can see that a large sea level rise due to a modest water temp increase is not implausible.

I wasn’t intending it to be a debate. I was just wondering if any alternate mechanisms had been proposed to explain the sea level data. It may be debatable whether those explanations are correct or not, but asking about the details of alternate explanations seemed like a factual question.

:dubious: Isn’t water one of the only substances that expands upon cooling, not upon heating?

Edit: After Googling the thermal expansion properties of water, I see it acts “normally” above 4°C by expanding as it heats. Strange stuff.

[Moderating]

There wasn’t actually anything wrong with your question as such. However, using loaded terms like “global warming deniers” opens the way for responses like Mangosteen’s, and it would be better to avoid them.

Colibri
General Questions Moderator