climate change math

[mopinko]

is anyone here familiar enough with climate change models to take a stab at a wildly speculative question?
i was listening to a guy on npr today, talking about climate change, and mentioning the unexpected rise in ocean temps- 6 degrees so far. i had just been having a conversation with my geek son about using the temperature differential of the ocean to generate electricity. this seems pretty simple, and doable. he mentioned some guy with an island, doing all kinds of energy stuff, including this.
here is the question- can you estimate the scale that something like this would require to make a dent in ocean temp? obviously, the oceans are large, i know that. but just curious about the order of magnitude of this kind of thing. any other new energy technologies that are even being evaluated in terms of direct effect on warming? seems like all things being equal, taping the actual warming would be kind of a two-fer.
or am i just crazy?

[Dead_Parrot]

1. Sounds like insane fun

I'll try and get within a few orders of magnitude :)

According to google, we've got 510 million km² of ocean: and for the sake of argument we'll assume we're talking about the top 10 metres warming up, so that's 5.1x10¹⁵ m³ of water, or 5.1x10¹⁸ kg.

The heat capacity of water is 4186 J/kgK, so the extra heat energy in the water would be 5.1x10¹⁸ x 4186 x 6, or 1.23x10²³ J - roughly enough to replace all our current energy (gasoline included) for 500 years. As a solution, though, we'd have to work out how to pull it out fast enough.

(And before anyone says it, yes I am assuming 100% energy conversion, and yes I have heard of entropy :silly:)

So no, you're not totally crazy - it's actually a nice idea (doubt it'll work, but nice :D).

[mopinko]

2. well. "work"

no, i don't suppose it would solve the problem. but i just got to wondering about the ability of new technologies to do more than just not add to the problem. especially considering that things seem to be accelerating much faster than was predicted.
what started me down this road was listening to the numbers on water temperature and hurricanes. i got to wondering if a small increase in the surface temp of the gulf could increase the intensity of storms so much, could a heat exchange system that used the heat in those waters to make electricity could actually reverse this. i mean, a foot of surface water in the gulf is a much smaller order than the whole oceans. so maybe this is not outside reality.
after all, we never thought human actions could affect the planet, now did we.

[Dead_Parrot]

3. I guess it might have posibilities for the Gulf of Mexico

I have no idea what the temperature gradient is like, but certainly off the edge of the continental shelf it gets quite deep, so there should be scope there for a string of OTEC plants (Interestingly, the first OTEC plant was built in Cuba.)

The amount of energy you'd need to extract, even to reduce the surface by .1K, would be formidable but it certainly wouldn't do any damange and might just knock some wind (ahem) out of the hurricanes...

I think I need to mull this over some more. :)

[Dogmudgeon]

4. Air Conditioners. Giant, enormous Air Conditioners.

Since temperature changes always cause more wind, we could use wind power to run them. That way, they would be self-powering!

And with activated charcoal filters, they would leave the air smelling springtime-fresh.

--p!
Doom? Gloom? Moi?

[skids]

5. Problem is the "sink" is also warming.

Most ocean heat proposals are based on warming cooler lower waters. Not so sure we want to be doing that. Waste heat ejected into water bodies from thermoelectric plants are already a problem.

There are a lot of crazy proposals out there that don't seem to have researched their potential impact on local biosphere heat budgets.

Now if the idea would be to run it in reverse -- e.g. at night or in the winter transfer heat from the surface waters to the atmosphere, then that's an idea, but keep in mind that the atmosphere gets warmed, too -- and it's the temperature differential that matters most, not the absolute temperature.

Other than tidal or wave, the only other ocean proposal I'm inclined to be enthusiastic about in the salinity-based electricity generation, whereby fresh river water that is going to mix into the sea anyway is forced to mix through a proton exchange membrane, generating electricity instead of the heat that is normally released.

[mopinko]

7. no, no, not just cooling the water

extracting electricity from the water with heat exchanger type technology, returning it slightly cooler, win, win.
i am big on wave generators for a personal reason. my dad was kind of crazy, and he had a lot of ideas, one of which was wave turbines for electricity. this was back in the 60's. he built a model, and talked to physicists at the university of chicago, he was convinced this was a great idea. so, i am very happy to see this is happening, just like he said it would. too bad he wasn't a little more paranoid. he would have seen what we were up against.
seems to me that wave turbines in hurricane prone areas ought also to diminish the intensity of storms at some point, as well. might be hard to make them hurricane proof, tho.

[skids]

9. The amount of power we can use...

...is miniscule compared to the amount of excess heat energy that is there. Now I suppose that if we turned it into high frequency light and beamed it off the planet, or used it to sequester carbon, we could possibly do so usefully in respects to global warming. However, where the heat that we cannot turn into electricity goes is a big problem (heat pollution of cold sinks), and given the very small temperature differential, you would only be able to extract a very small percentage of the heat.

I am very leary of strategies that involves injecting waste heat into the lower waters. Noone knows what this will cause WRT killing organisms that live down there (likely it would be a scenario like red tide where an algae or something takes over.)

(You do know, by the way, that you cannot operate a heat exchanger without warming up your cool sink, right? Though the total amount of heat left in the result is reduced, your cool sink would still be warmed up.)

As far as shielding from hurricanes, wave and tidal probably won't unless we were to integrate them into a barrage system that doubled as a levy, which would help with the surge. Enough windmills might sheild a small area behind them from surface winds, though.

[phantom power]

6. There is a guy who wants to generate electricity from that gradient.

He's got a prototype somewhere in Hawaii. His method actually pumps cold water from the depths, up to a surface generating station. It should be possible to induce thermoelectricity directly, but I assume his approach has some advantage.

[mopinko]

8. i think this is the guy my son was talking about

he has all kinds of stuff going out there.