Thursday 14 August 2014

An average temperature?


One temperature?


The temperature differences which are producing higher CO2 could be quite subtle.
As previously discussed, while you can manufacture an “average” global ocean temperature, averaged over a huge number of situations even over one day and across a planet and seasons, even years, no actual place has that temperature. It is like a stopped clock being right twice a day. It does not mean it is working.
The idea of an average temperature for the planet or the earth or the sky or the oceans may not be enough to explain what is happening on a smaller scale at which thing actually happen. The world result is the sum of a lot of local results with local conditions. For example and as previously shown, CO2 will be higher at ocean hot spots and presumably lower over cold spots. Who knows what is going on in a storm?
No it is possible that a shift upwards of even 1 degree in say the cooler parts of the ocean would produce a 50% increase in CO2. You would hardly notice this in a world average.
The other aspect of the exchange depicted by Henry’s law is that this law is about laboratory situations where the air is stationary, the water is stationary without waves on the surface or currents below and the pressure is constant in the liquid and the gas. None of these conditions are met in a storm or even on a nice day. The air is generally a quite different temperature to the water. The water pressure varies dramatically from one atmosphere to 400 atmospheres as you go down. So Henry’s law is only a guide to idealized conditions, not real life. I guess I am saying when you x50 because the gaseous CO2 dissolved in the oceans is 50x as much in the air, it does not take much disturbance in temperature anywhere to have a dramatic effect, even if the notional average is unchanged.

Estimate the change in CO2 from simple ocean warming. 

However there is another way to calculate the impact, without Henry's law.  WIthout any laws as such, just the observation of the solubility of CO2 in water, something well known to lemonade manufacturers.

From graphs of the solubility of CO2 vs temperature and pressure and a reasonable 8 degrees and a 1 degree change in the temperature of the water.

A change from say 8 degrees to 9 degrees  produces a solubility reduction from 0.2492 to 0.2403 gm CO2 per 100mm of H20.    

This does not seem like much, 3.6% reduction in solubility as CO2 leaves the ocean.     However consider that 98% of the world's free gaseous CO2 is dissolved in the ocean.  If you applied this to a reservoir which is 50x as big as the atmosphere, that would increase atmospheric CO2 by 3.6% x 50 or 180%!    Conversely to get a 50% increase in 100 years, you would need a rise of only about 0.25 degrees C.


A typical solubility table as below.  

Aqueous Solubility of CO2 at 101.3 kPa (1 atm) partial pressure[9]
Temperature
Dissolved
CO2 volume
per volume H2O
grams CO2 per
100 ml H2O
0 °C
1.713
0.3346
1 °C
1.646
0.3213
2 °C
1.584
0.3091
3 °C
1.527
0.2978
4 °C
1.473
0.2871
5 °C
1.424
0.2774
6 °C
1.377
0.2681
7 °C
1.331
0.2589
8 °C
1.282
0.2492
9 °C
1.237
0.2403
10 °C
1.194
0.2318
11 °C
1.154
0.2239
12 °C
1.117
0.2165
13 °C
1.083
0.2098
14 °C
1.050
0.2032
15 °C
1.019
0.1970
16 °C
0.985
0.1903
17 °C
0.956
0.1845
   
Temperature
Dissolved
CO2 volume
per volume H2O
grams CO2 per
100 ml H2O
18 °C
0.928
0.1789
19 °C
0.902
0.1737
20 °C
0.878
0.1688
21 °C
0.854
0.1640
22 °C
0.829
0.1590
23 °C
0.804
0.1540
24 °C
0.781
0.1493
25 °C
0.759
0.1449
26 °C
0.738
0.1406
27 °C
0.718
0.1366
28 °C
0.699
0.1327
29 °C
0.682
0.1292
30 °C
0.655
0.1257
35 °C
0.592
0.1105
40 °C
0.530
0.0973
45 °C
0.479
0.0860
50 °C
0.436
0.0761

It is interesting that the change in solubility is vastly greater in colder water, say 4.5% per degree at 0C.   At 20C, it is only 3%.    This also has an impact on averages as higher values are overrepresented in an average against the median.  

To use this table to show why an 'average' temperature is a silly thing, if say the cooler waters are warmed by 1C while the warmer waters are cooled by 1C, the notional average does not move but the CO2 from cooler waters is substantially increased over the increased absorption of CO2 in the warmer waters, giving a nett effect of an increase in CO2 of 4.5/3 of 50%.
Averages are deceptive.   For example if you answer the question whether the sun was up, using light as your sole measure, you could say on average it was a bright day (with average half light intensity).   It would be a lie.



No comments:

Post a Comment