Global warming ice-melt feedback effect?

[Donk]

I posted a couple of days ago about latent heat of fusion of ice, and it got me thinking. The melting of glaciers, the Greenland icecap and the Arctic must be soaking up a lot of spare heat. This would act as negative feedback - when temperatures go up, ice melts and absorbs heat; when temperatures go down, the ice freezes and releases heat. But we may be overwhelming the feedback system.

 

A quick back-of-the-envelope calculation seems to show that the heat energy absorbed in melting one cubic kilometre of ice is enough to cool 216,000 cubic kilometres of air by 1°C! Last year, Greenland alone lost around 240 cubic kilometres of ice - enough to cool 51.6 MILLION cubic kilometres of air. :eek2:

 

There doesn't seem to be much about it in the literature, but this looks to me like a highly significant effect. I'm wondering whether this has caused the temperature plateau since 1998? Taking a temperature reading isn't enough - we need figures on how much ice has been lost worldwide to see how much heat energy is being added to the system.

[modest]

Hello Donk,

 

Very good thread idea.

 

Before getting into the implications - my numbers came up pretty significantly different. I’ll just really sparsely show my work and maybe you’ll see where we’re differing.

 

[imath]\Delta H_{fus}[/imath] melting ice = 333.55 J/g

[imath]C_{AIR} [/imath] = 0.001297 [imath]Jcm^{-3}K^{-1}[/imath]

Energy needed to melt a cubic kilometer:

[math]\left( \frac{0.9167 g}{cm^3}\right)\left( \frac{1 \times 10^{15} cm^3}{1 km^3}\right)\left( \frac{333.55 J}{g}\right) = 3.06 \times 10^{17} J[/math]

Warms how much air one degree:

[math]\left( \frac{3.06 \times 10^{17} J}{}\right)\left( \frac{1 cm^3 \times K}{0.001297 J}\right)\left( \frac{1 km^3}{1 \times 10^{15} cm^3}\right) = 236,000 km^3K [/math]

 

So, where I have 23,700 236,000 you have 216,000. I think one of us has one extra or one too few order of magnitude is all. What do you think?

 

I think we're solid ;)

 

~modest

[Donk]

Here are my figures:

 

1 gram ice absorbs 333.548 joules in melting.

1 gram ice is approx 1.1cc

Density of air at atmospheric pressure and 0°C density is 1.39 g/L

Specific heat of air = 1.0035 J/g/°C

 

1 gram melted ice cools 333.548/1.39/1.0035 = (approximately) 240 litres air by 1°C.

 

1 gram (=1.1cc) melted ice cools 240 litres air by 1°C

1cc melted ice cools 216 litres air by 1°C

conversion factor is 1:216*10^3 (1000 cc in 1 litre)

= 1:2.16*10^5

 

1 cubic kilometre ice cools 216,000 cubic kilometres air by 1°C.

 

239 cubic kilometres ice cool 51.6 million cubic kilometres of air by 1°C.

 

As I was working with mass of air in grams/litre, I went via litres and scaled up from there. It's nearly 3am here, so my brain is shutting down... but shouldn't your first calculation show 3.08 x 10^17?

[modest]

I found it. I had 33.55 rather than 333.55 input. That gives me 236,000 km^3 now. Considering we have rather different computational methods, I think that's close enough.

 

~modest (editing my post above)

[modest]

:eek_big:

 

Wiki's Polar ice packs is a good source. It brings up a good point:

 

Sea ice has an important effect on the heat balance of the polar oceans, since it insulates the (relatively) warm ocean from the much colder air above, thus reducing heat loss from the oceans...

 

While the atmosphere swings temperatures rather drastically with Earth's tilt; seasonally, sea water at the poles keeps a pretty consistent temperature. I guess the ice packs help regulate that consistency.

 

~modest

[Donk]

I have to say that I'm glad to see anything that might be acting as a feedback mechanism to prevent warming going to far too fast. Though I expect if it proves to be the case, the do-nothing crowd will crow with delight and carry on polluting. They'll no doubt miss the point that all it does is maybe give us a bit of breathing space to sort things out in.

 

I said "warming" rather than "climate change". An Amazon's worth of ice water flowing into the Atlantic is likely to have some interesting effects on climate, wouldn't you think?

[modest]

I said "warming" rather than "climate change". An Amazon's worth of ice water flowing into the Atlantic is likely to have some interesting effects on climate, wouldn't you think?

 

I do think so. I think it would be an interesting thing to model in order to find out just what the caps are doing for us now and what will be different when they're gone.

 

The freezing and melting of pack ice is cyclic, but I'm sure it has an overall effect of either lowering or raising the temperature of ocean water. I'm thinking it would be interesting to model all of the factors and figure out what that overall effect is considering all pack ice as well as the polar ice caps may soon be gone. Some consequences of the ice caps:

 

• Lessens the amount of light heating ocean water (and earth considering ice and snow have a higher albedo than water).
  
• Ice prevents evaporation.
  
• Insulates the water from the air and temperature above
  
• Sea ice freezes without salt. So, more ice means a saltier ocean.
  
• And, of course, Ice caps lower sea level.
  

 

Does anyone know of any models analyzing an environment without ice caps? I have a feeling the consequences might be more than a lot of people would think.

 

~modest

[LaurieAG]

There doesn't seem to be much about it in the literature, but this looks to me like a highly significant effect. I'm wondering whether this has caused the temperature plateau since 1998? Taking a temperature reading isn't enough - we need figures on how much ice has been lost worldwide to see how much heat energy is being added to the system.

 

Hi Donk,

 

Our past two winters in Eastern Australia have been much cooler than the previous 10 years of relatively hot weather. In the past two years large chunks of ice sheet have broken off Antarctica. I've read about Antarctic sea temperatures rising as a result of the ice sheets going and I just wonder if the melting ice would cool the ocean wherever it drifted?

[modest]

Hi Donk,

 

Our past two winters in Eastern Australia have been much cooler than the previous 10 years of relatively hot weather. In the past two years large chunks of ice sheet have broken off Antarctica. I've read about Antarctic sea temperatures rising as a result of the ice sheets going and I just wonder if the melting ice would cool the ocean wherever it drifted?

 

Mostly, I think the oceans (below a hundred meters or so) are the same temperature as an iceberg. When the ice melts, I would think its water sinks immediately to at least that depth considering water is densest at 4 C. I don't think, then, that surface temperature would change much (if at all) from adding cold melt water.

 

Then again... the energy needed to melt the berg would come from the surface water... humm... ;) I'll leave this in Donk's capable hands :D

 

~modest

[Flying Binghi]

And I thought the science was all done ? ;)

 

... Looks like we have barely scratched the surface of a very complex subject.

[Nitack]

I think Donk has brought up a very interesting aspect that is missing from the mainstream coverage of the global warming phenomenon. Temperatures may be stagnant but that may only be temporary if we are losing ice and heat is now being stored in that water. If temperatures are stagnant it would only be a temporary reprieve until the ice has absorbed as much heat as it can and turned to water. At that point we would see our temperatures start dramatically rising with out any medium to absorb the heat. Scary stuff. Stagnant for five years and then an average temperature spike of what, 5-10 degrees?

[Overdog]

...When the ice melts, I would think its water sinks immediately to at least that depth considering water is densest at 4 C. I don't think, then, that surface temperature would change much (if at all) from adding cold melt water.

 

As an ex-sonar technician who has taken hundreds of bathy-thermograph readings in oceans around the world, I can tell you that the mixing of deeper, cooler water with warmer surface water can be strongly affected by winds and sea-state...

 

There is a boundary between surface waters of the ocean and deeper layers that are not mixed. The boundary usually begins around 100-400 meters and extends several hundred of meters downward from there. This boundary region, where there is a rapid decrease of temperature, is called the thermocline. 90 % of the total volume of ocean is found below the thermocline in the deep ocean. Here, temperatures approach 0 degrees Celsius. So even though surface waters can be a comfortable 20 degrees Celsius (good for swimming in!), the majority of our ocean water has a temperature between 0-3 degrees Celsius (32-37.5 degrees Fahrenheit).

Temperature of Ocean Water

 

I've taken readings many times in rough waters where the thermocline starts right at the surface.

[freeztar]

Here's an interesting article abstract that discusses the latent heat issue and how this is affected diurnally:

SpringerLink - Journal Article

 

Here's a link to some math equations that deal with several factors (temperature, wind, coriolis effect, etc.) that influence ice pack:

Maths and climate change: the melting Arctic

 

And finally, here is a nice pdf'd powerpoint presentation from Goddard (lots of good figures and pictures in here):

http://neptune.gsfc.nasa.gov/pdf/Bindschadler_smithsonian_2005.pdf

 

Happy reading! :doh:

 

"The canary has died. It is time to start getting out of the coal mines." - Jay Zwally

[Donk]

You people have been busy...

 

Our past two winters in Eastern Australia have been much cooler than the previous 10 years of relatively hot weather. In the past two years large chunks of ice sheet have broken off Antarctica. I've read about Antarctic sea temperatures rising as a result of the ice sheets going and I just wonder if the melting ice would cool the ocean wherever it drifted?

Mostly, I think the oceans (below a hundred meters or so) are the same temperature as an iceberg. When the ice melts, I would think its water sinks immediately to at least that depth considering water is densest at 4 C. I don't think, then, that surface temperature would change much (if at all) from adding cold melt water.

 

Then again... the energy needed to melt the berg would come from the surface water... humm... :doh: I'll leave this in Donk's capable hands ;)

 

~modest

Firstly, my hands are a lot less capable than many other people here. I gave up my science job almost 40 years ago - two of us with two incomes were about to turn into three of us with one I went into industry at 70% more pay.

 

I've always been able to make connections, and I've tried to keep up with my reading, but I'll leave scientific rigor to the professionals - I prefer to play

 

Melt water wouldn't "sink immediately". Yes, cold water is heavier than warm, but not that much heavier: a litre of water at 20°C masses 998.2g, as against 1000g at 4°C and 999.9g at 0°C. Additionally, the melt water would start out fresh, which is lighter than salt water.

 

So yes, I'd say the surface waters would get colder, upsetting Laurie's winter weather. Obviously there would be other factors involved, but Latent Heat needs to go into the pot as well.

 

Thanks for the links, Overdog and Freeztar - that's me sorted out for the evening

[modest]

Additionally, the melt water would start out fresh, which is lighter than salt water.

 

This is a very good point that I didn't consider. Water @ 20 C with 35 ppt salinity is 1025 kg/m^3 while 4 C with roughly no salinity is 1000 kg/m^3. So it has no immediate inclination toward sinking. Climatologists are, indeed, well aware of this as they worry about less-dense water disrupting the oceanic "conveyor belt".

 

Melting Arctic Sea Ice and the Global Ocean Conveyor

 

Good call Donk

 

~modest

[Donk]

From last night's research, a few musings :eek_big:

 

I'm trying to understand exactly how ice melts, down at the molecular level. I'll say what I think is happening in layman's terms, and hope there's an expert or two here to sniff it over and tell me how close I am to being right.

 

This is probably where I get egg all over my face :hyper:

 

I'm visualising the surface of the ice as an array of water molecules. Where does any molecule get the energy it needs to suddenly change state from solid to liquid?* It's a lot of energy to gain in one hit. My intuition is that it gains it from the surrounding molecules. The bandit ice molecule robs its neighbours and promotes itself to water. It's still at 0°C, but its neighbours have gone down to perhaps -10°C or less. They get their act together and steal the energy back, turning the rogue molecule back to ice and bringing their temperature back to 0°C. It looks static at the macro level, but at the molecular level it's seething with activity.

 

Now bring in another factor. A wind passing over the ice. The suddenly subzero victims have a new source of energy, and pull some heat from the air. Now they aren't cold enough to rob the bandit molecule of its ill-gotten gains, and it stays liquid. The other molecules carry on pulling heat from the air until they're back to 0°C.

 

The upshot of all this is that ice at 0°C, on the point of melting, might be able to cool air faster than ice at -5°C. So the Arctic and Greenland exerted a small but insufficient cooling effect while they were safely subzero. When they reached melting point (1998 maybe?) the effect multiplied, helping to keep global temperatures constant.

 

All the interesting stuff seems to be subscription-only, so I'm using educated guesswork. I might be horribly wrong - but what can you expect from someone with a jackass for an avatar?

 

* I'm assuming a sudden state change. Can the molecule gain energy gradually? I don't see how: it would imply an intermediate state between solid and liquid - a quantum leap looks more feasible.

[Overdog]

The sea state data seems kind of sparse...

 

There is evidence that the North Atlantic Ocean grew considerably rougher between the 1960s and 1980s, during the age of the ocean weather ships, at least at a few isolated stations (Bacon and Carter, 1991). Is this natural variability or global warming? A new perspective is brought by analysis of satellite data.

WAVE STUDIES

 

But if at the same time as the ice was reaching the melting point, the warming was also increasing sea states around the world, then the increased mixing of warm surface water with cooler deep water might also have contributed to the temperature plateau since 1998...