Seawater - CO2 -
Antti Roine January 30, 2010
Carbon Dioxide Cause or Effect?
Fig 1: Our climate has never been stable. Carbon dioxide may increase temperature or vice versa. Both are valid conclusions based on currently available experimental data.
Mainstream science and the media believe that the main reason for climate change is the man-made carbon dioxide content increase in the atmosphere (AGW). The truth may, however, be the other way round. Ice cream consumption increases at warm weather in the summer time, but still the ice cream is not the cause or the reason of the warm weather.
Several times within the past million years the seawater temperature has began to rise BEFORE a similar growth in atmospheric carbon dioxide and methane concentrations. Recent analysis show that CO2 lags warming and cooling of climate by 200 - 800 years, this may be the time which is needed to reach the steady-state within the oceans and atmosphere.
The latest evidence shows that the Earth's climate is constantly changing, as continuous change seems to be the normal state of nature, Fig. 1. These changes have created and destroyed huge empires within the history of mankind. In fact, we should be talking about the temperature change of the oceans, because they control the climate - and there is 260 times more seawater than air on our planet, Fig. 2.
Fig 2: There is some 260 times more seawater on the Earth than air. The amount of seawater is roughly 1.35E+21 kg. The amount of air is 5.15E+18 kg, which equals 3.99E+18 Nm3.
Carbon Balance of Earth
Fig 3: Carbon balance and storages. In practice the limestone is the "final destination" of the carbon. The organic carbon returns back to the atmosphere due to respiration. Bacterias and fungus decompose and oxidize organic material into the methane and CO2. In this respect plants are only temporal carbon sinks.
(Sources for data, see appendix.)
Manmade emissions are quite small compared to the natural carbon cycles. Oceans are the main carbon sink, they have harvested huge amounts of carbon into limestone within the millions of years. Actually also biofuels increase emissions, but it is still better to burn organic waste materials and utilize their energy content than just let them form methane in the dumping place.
Carbon dioxide emissions of oceans increase along with surface temperature of the oceans. This is a fact which have been verified experimentally and can also be verified by chemical equilibrium calculations. Hot areas of oceans emit and cold areas absorb carbon dioxide.
There are three key questions in the climate change discussion:
1) Carbon dioxide content has increased rapidly many times within the history and every time this increase has reversed and turned to decrease, Fig. 1. If the carbon dioxide really is the main cause of the climate temperature increase then - why this effect has not autocatalytically increased the temperature and evaporated oceans? Which effect has stopped down the temperature increase in spite of the high carbon dioxide content.
2) Why the temperature has usually started to increase first and then after few hundred of years carbon dioxide content has started to rise? The same delay seems to exist also when temperature starts to decrease. In normal industrial process the cause always happens first and just before the effect and response. Why this not true with the climate?
3) Why Climatic Research Unit (CRU) has heavily underestimated the effect of towns on the global temperature date? Why it has even modified the raw data in order to get the temperature rise, and why the original data has been deleted?
We may try to find answer to these questions using chemical equilibrium calculations.
Chemical Equilibrium Calculations
One important question in the climate change discussion is the effect that carbon dioxide has on the temperature. A lot of different models with a huge number of fitting and tuning parameters have been created to estimate the effect of CO2 on the global temperature. These parameters have been needed to make the models agree with the CRU made global temperature data.
However, far fewer calculations have been made to estimate the effect of temperature on the equilibrium pressure of the CO2 over the seawater. This effect may be estimated using the HSC Equilibrium module (See appendix), Fig. 4. This module do not use any tuning parameters, all the results are based on basic thermo chemical properties of the chemical species. These calculations are based on chemical equilibriums of theoretical aqueous solution models.
Fig 4: Air - seawater - limestone chemical system specification in the HSC Equilibrium module. All the amounts have been divided by 1E+18 just to make the figures more readable. N.B! This does not have any effect on the results.
Fig 5: Effect of temperature on the activity coefficients in the seawater.
We can put all the oceans, atmosphere, and lot of calcite into a single chemical reactor unit and run equilibrium calculations. This chemical system specification is shown in Fig. 4. The amounts and compositions of gas and water phases correspond to the average amounts and composition of the atmosphere and seawater. Calcite has been assumed to consist mainly of CaCO3.
The equilibrium calculations may be carried out at different temperatures and CO2 amounts in the air. The Equilibrium module calculation routine uses the Gibbs Energy Minimization method, which determines the phase amount, and the composition combination where the Gibbs free energy of the chemical system reaches its minimum. This method automatically takes into account all the possible chemical reactions that may occur in this system.
The enthalpy, entropy, and heat capacity data for the pure chemical compounds shown in Fig 4. are based on the extensive HSC 7 thermo chemical database. The non-ideal behavior of the water solution is calculated using the HSC Aqua module, Fig. 5, which uses an extensive aqueous solution database. The amounts and compositions of the air and seawater are based on average values available in public encyclopedias and Internet sources.
The current average CO2 content of the atmosphere is some 383 ppm. The average temperature at sea level is 15 °C. The equilibrium pressure of CO2 above the seawater in these conditions is only 157 ppm. This is the thermo chemical explanation of why the oceans are the most important carbon sinks, see Fig. 3 and 6.
The chemical potential and activity of the carbon dioxide is lower in cold seawater than in air, and this is the chemical explanation of why carbon goes to the sea in cold areas. If the chemical potential of carbon dioxide were higher in seawater, then seawater would release much more carbon dioxide into the air in hot areas, however, we are lucky and this is not the situation.
On the other hand, at high surface temperatures, like 25 - 35 °C, the oceans may release carbon dioxide because the equilibrium pressure increases rapidly along with the temperature, Figs. 6 and 7. The sun may easily warm up a thin surface layer of the sea and this is enough to increase CO2 emissions. At medium surface temperatures this layer may behave as a barrier which prevents the CO2 dissolution to the seawater.
Figures 6 and 7 also shows the explanation why the CO2 content in the atmosphere within the last 800 000 years has never been lower than 160 ppm, Fig. 1.
The carbon dioxide pressure and chemical potential difference decrease along with an increase in temperature. This simply means that the driving force for carbon dioxide absorption and accumulation in the sea is decreasing radically, Fig. 6. This always happens if the temperature of the oceans increases for any reason. Seawater emit CO2 when surface temperature of seawater is high, because carbon dioxide pressure is higher in seawater than in the atmosphere.
The sea can easily absorb large amounts of carbon dioxide. Figure 7 shows what happens if we change the amount of CO2 in the atmosphere. The result is that if we remove carbon dioxide from the atmosphere, then the sea will release CO2 until the CO2 content reaches 140 ppm. On the other hand, if we double the CO2 amount in the atmosphere, then sea will absorb CO2 until the CO2 level in atmosphere reaches 180 ppm. Of course, in the long-term, the conditions of the whole chemical system will change, but this calculation illustrates the direction of the chemical reactions.
Actually the total CO2 absorption potential of seawater is very high because the equilibrium partial pressure of CO2 decreases along with pressure, see Fig. 8. Ie. carbon dioxide dissolution into seawater increases along with pressure. This promotes formation of limestone, because seawater is generally supersaturated in calcite, CaCO3. The shells of marine organisms made of calcite can form limestone sediments, because calcite do not dissolve into seawater. The limestone is the most important destination for the carbon, Fig. 3.
However, at very high pressure also calcite starts to dissolve into seawater, usually this happens about 4500 meters below sea level. This depth is called carbonate compensation depth (CCD) or lysocline. Below this depth limestone sediments may dissolve.
Fig 6: The effect of temperature on the carbon dioxide equilibrium pressure over seawater at steady-state with homogenous phases. The average temperature is assumed to be 15 °C and the CO2 content 383 ppm in the atmosphere. The difference between the equilibrium curve and 383 ppm level creates the driving force of CO2 absorption.
Fig 7: Seawater may effectively buffer temporal CO2 variations in the atmosphere. The calculations have been carried out by changing the amount of CO2 in the atmosphere.
Fig 8: Effect of sea depth on the partial pressures of carbon dioxide and water vapor. The CO2 absorption potential of seawater increases rapidly when total pressure increases. CO2 dissolution to seawater increases along with pressure. However, at very high pressure also calcite starts to dissolve also into seawater and this prevents the precipitation of the limestone. Usually this happens when the depth is more than 4500 m.
Most of the carbon in seawater is in deep areas, Fig. 3. Theroretical chemical calculation results in Fig. 8, are in nice agreement with this experimental fact.
All these results are based on theoretical aqueous solution data. These thermochemical models could also be used inside climate models to calculate the dependence between the climate temperature and carbon dioxide content of the atmosphere. Then of course some calibration parameters should be used to fix these results more exactly with the experimental data.
Effect of Sun on Earth's Climate
The primary reasons for the global temperature changes are the solar activity changes and variations in Earth's orbit, rotation and axis. See, for example:
These very preliminary and brief chemical equilibrium calculations show that carbon dioxide may not be the only reason for the increase in the temperature of the Earth’s climate. In fact, it seems that a temperature increase may be the cause and the carbon dioxide content increase in the atmosphere is the natural effect of the climate change processes. Most likely, carbon dioxide contributes to global warming, but it is hardly the primary reason for global warming.
These preliminary and simple equilibrium calculations prove that we should invest much more effort on atmosphere and ocean chemistry research. We have to improve basic data of the equilibrium calculations and take into account also kinetics, temperature, pressure and concentration gradients, as well as validate the calculation models experimentally.
We have also to remember that we must find sustainable, low cost, new energy sources and solve the extensive environmental and emission problems, because energy costs and recycling are the key issues if we want to improve worldwide welfare. This is a fact, whether climate change is due to human activity or not.
The basic ideas of this paper may be summarized in the following conclusions:
1) The oceans are and has been the most important and pre-eminent carbon sinks, Fig. 3.
2) The effect of humans is much less than 5% of the natural carbon cycle.
3) Huge amounts of CO2 are released from the sea, when sun heats up the thin surface layer of seawater, Fig 6. There are delays in this process due to diffusion and convection.
4) In cold areas oceans absorb huge amounts of CO2, Fig. 6. There are delays in this process due to diffusion and convection.
5) Deep oceans contain gigantic amounts of carbon, because carbon dissolution into seawater increases along with the pressure, Fig. 8.
Comparison to Experimental Data
Fig 9: Annual mean sea surface dissolved inorganic carbon. The cold red areas absorb much more carbon than the blue hot ones, ie. the arctic seas are CO2 absorbers. This experimental result is in nice agreement with current calculated results given in Fig. 6.
Fig 10: Annual CO2 Flux Estimated from Air-Sea Difference in CO2 Partial Pressure. The red areas may emit and the blue ones absorb CO2.
Fig 11: Partial pressure of CO2 may be very high at sea surface at higher temperatures like 26 °C. In these conditions seawater cannot absorb CO2 at all. The average CO2 partial pressure in homogenous seawater is some 150 - 200 ppm, Fig. 6, but on sea surface it may be much higher due to slowness of the diffusion and convection.
Actually the total CO2 absorption potential of seawater is very high because the equilibrium partial pressure of CO2 at deeper levels is very low, see Fig. 8.
Fig 12: Experience curve relating actual atmospheric carbon dioxide levels with actual global average sea surface temperature. It is not a time scale, just the simple relation between two physical parameters independent of time. The line shown is just the sequence of actual plotted points for each end month of the two moving averages. References (prof. Lance Endersbee):
Appendix / Carbon cycle references:
Appendix / CO2 effects may be estimated using the HSC Equilibrium module: