A case for the 400ppm CO2 limit

If you read my comment on Belitte's blog a while ago, you know that I made a case why burning of fossil fuels will NOT bring the atmospheric CO2 to beyong 400 ppm. It's very simple, we have a limited amount of fossil fuel left. When you calculate how much extra CO2 it may contribute when all the fossil fuel we have left is burned, it actually does not make it up to 400 ppm, from the current level of 375 ppm atmospheric CO2.

Belitte tried to make a bet with me regarding whether human will contribute enough CO2 to raise it to 400 ppm, in 20 years. I did not response. I feel that his level of intelligence is just too low to warrant a response at that point. The amount of usable fossil fuels left on earth, and how much we burn per year, is a definite number. The corresponding CO2 you can generate by burning the fuels, is also a definite number well defined by the calculation. If one believes he can burn one kilogram of fuel and obtain 2 tons of CO2 out of it, he has not learned the basic physics that matter and energy are conserved. Do the calculation. And if the actual observed atmospheric CO2 increase is much more than what you calculated from fossil fuel, than only means the natural carbin cycles play a much bigger role than human consumption of fossil fuel.

I spotted this web page called Burning buried sun shine. I think I can actually use some of the numbers provided, to get a good estimate how much fossil fuel we have left.

According to Jeff Dukes, who explains the formation of fossil fuels from plantation. Only 9% of the carbon in the plantation goes into the coal, and only 1/10750 of the carbon forms the petroleum. So we can assume, out of the original carbon, about 100%-9%, 91%, eventually escape back to the atmosphere, and 9% remain underground. Out of this 9%, only 1/10750 eventually turn into petroleum, and all the rest turn into other forms of carbon within the rocks. So that is a convertion efficiency of 1/10750 divided by 9%, which is 0.109%.

The atmosphere contains 200,000 ppm of O2 (20%) in volume. Prior to origin of life, that was supposed to be 200,000 ppm of CO2 instead. Plantations essentially turn virtually all of the CO2 into O2, and capture the carbon into biomass, and some of it, let's say half, turn into petroleum at 0.109% efficiency.

You can calculate how much carbon there was, in the 20% CO2 atmosphere, using the know atmospheric pressure and the surface area of the earth. You arrive at 4.46x10^17 kg of carbon originally in the atmosphere. Convert half of that to petroleum, at 0.109% efficiency. That's 2.43x10^14 kg of carbon in petroleum.

Further using Dukes's data, one litre of patrol contains 1.1 kg of carbon. 3.785 litres is one gallon. And 42 Gallon is one barrel. So one barrel of oil contains 175 kg of carbon. Using the above figure of 2.43x10^14 kg carbon in petroleum. The total reserve of petroleum is 1.4x10^12 barrel. i.e., 1.4 trillion barrels.

This figure is essentially right. The world had a total ot 1.4 trillion barrel recoverable petroleum. We have burned half and there is only half left, 700 billion barrels. The official figure is actually 1200 billion barrels left but consider that the official number is fishy, 700 billion is a more realistic estimate.

Now, if you burn the 700 billion barrel remaining petroleum, that would generate 122.5 trillion kilogram of carbon in CO2. Should that CO2 all stay in the atmosphere, that would increase the CO2 concentration in the atmosphere by about 55 ppm (in volume). However not all CO2 will stay, some will be re-absorbed by plantations, so the actual increase will be less than 55 ppm.

Let's use some number BeLette used. He claimed that the measured CO2 is increasing 15 ppmv per decade, i.e., 1.5 ppm per year. Let's take that number as correct. We know the world is burning 85 million barrels of oil per day, or 31 billion barrel per year. So each 31 billion barrel of petroleum burned results in 1.5 ppmv increase of CO2. We have 700 billion barrels left, so that gives 33 ppmv at most. Adding 33 ppmv on top of the current 375 ppmv, the final atmospheric CO2 may reach 408 ppmv, so it could be a little bit more than 400 ppmv, but only by a very small amount.

Belitte argued that at 1.5ppmv increase per year, the atmospheric CO2 could easily surpass 400 ppmv in just 20 or 30 years. What he does not realize is that our remaining petroleum underground, if burned at current speed, hardly last us more than 20 years at most!!! And after that we no longer have any oil to burn!!!

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