Atmospheric carbon dioxide and base-load electricity

Some of this heat will be absorbed by the oceans. Given the enormous mass and high specific heat of the oceans, there will be a long lag time for temperature to rise. This indicates that the annual anthropogenic derived combustion of CO₂ has a minor effect on atmospheric heating but it is cumulative, year on year and as emissions increase so does its effect.

The Earth's Energy Balance and Emission Windows

There is a constant flow of energy from the Sun to Earth and from the Earth to Space, resulting in a steady state energy flow balance at equilibrium. At steady state equilibrium there is an equal amount of energy arriving from the Sun as is leaving the planet, albeit with different spectral values, the radiation emitted by Earth being of longer wavelengths than that emitted by the Sun (Stefan-Boltzman) due to the lower temperature of the Earth compared to the Sun.

The atmosphere is essentially transparent to incoming solar radiation while it is partly opaque to the outgoing longwave radiation (OLR) due to absorption at these longer wavelengths by minor gases in the atmosphere. This absorption causes the atmosphere to be warmer than it otherwise would be (the Greenhouse Effect). Water vapour is the principal source of the absorption. Other minor gases involved are CO₂, CH₄ and O₃. For water vapour there is a particularly good transparent window approximately between 8 and 14 µm. CO₂ has its highest absorption finger around the higher wavelengths of this window, around 15 µm.

Although this steady state energy balance obeys the basic laws of physics and is easy to understand, the actual internals of the system itself are seriously complex. To name a few: the incident solar radiation is subject to a 24 hour cycle, the angle of incidence of the solar radiation varies from perpendicular near the Equator to essentially zero at the Poles, there are discernible layers of the atmosphere, the complex role of H₂O in its various states (ice, water and vapour) and there are oceanic and terrestrial surfaces and circulations and possible feedback loops.

CO2 and the Outgoing Longwave Radiation (OLR)

Carbon dioxide has strong absorption around 15µm wavelength of EM radiation (infrared). Spectrophotometry of the outgoing longwave radiation (OLR) from the Earth from such as the Mars Global Surveyor Spacecraft at a distance of 4.8x10⁶ km from Earth shows the deviation from the thermal radiation emitting curve due to this absorption, indicating that atmospheric CO₂ causes heating.

The 15 µm band is absorbed in less than 10 m from the surface (1/0.095) and at the tropopause it is absorbed in less than 27 m (1/0.038).

On being absorbed the energy is then partly re-radiated in all directions as well as by conduction and convection. At a far enough distance away from the surface the 15 µm band can escape when the pressure and therefore concentration of CO₂ is low enough, giving rise to the characteristic OLR of the Earth with a big deviation around 15 µm area. This follows from the First Law of Thermodynamics and Reciprocity between absorption and emitted wavelengths. The intensity of this radiation will depend upon the temperature at the emission layer (Stefan-Boltzman).

The Earth's OLR may be seen as a 'summary' or end result of all the complex known and unknown thermodynamic processes that occur on the Earth's surface and has the utility and certainty of being a direct measurement.

By comparing the area under the complete body curve to the area deviation by CO₂ at 15 µm, from the spectrograph from the Mars Global Surveyor Spacecraft, a calculated figure of 8.5% contribution to the Greenhouse effect can be attributed to CO₂. Given that CO₂ has approximately doubled since the Industrial Revolution, then 4.25% can be considered anthropogenic. If we assume Earth surface temperature would be -18⁰ C without Greenhouse and now it is 15⁰ C (33⁰ C the difference) then 0.0425x33=1.40 C increase in temperature, so approximately 1.5 degrees C can be attributed to anthropogenic causes.

However the mass and specific heat of the oceans are gigantic compared to that of the atmosphere Ratio of heat capacity of ocean to atmosphere 1.35x10¹⁸ x3.850/5.2x10¹⁵ x0.70 = 1,428 so that it will take a long time to reach equilibrium at the 1.5 C figure as the ocean acts a heat sink. However changes to climate can possibly emerge earlier as the thermodynamic equilibrium of the surface of the planet is being disturbed. As well, unfortunately anthropogenic CO₂ will not stay stationary at the present level without cessation of emissions and so, as time goes on, the temperature rise will be even greater if there are no significant reductions in emissions forthcoming and it would be cumulative.