Some remarks on atmospheric levels of carbon dioxide (Andrew Kenny) South Africa

Some remarks about the carbon dioxide cycle in living organism, the atmosphere, oceans and land.

Andrew Kenny Independent Energy Commentator, Professional Engineer with degrees in physics and mechanical engineering See some of his articles on nuclear energy here and here, and on fossil fuels and carbon dioxide here.

South Africa

August 9, 2017

1. CO2 has averaged about 2,000 ppm since PreCambrian: Ideal level of CO2 now The graph below shows CO2 levels and global temperatures over the last 550 million years, roughly the period of multi-celled life. As you can see, CO2 has averaged about 2,000 ppm (parts per million) over this time but with huge fluctuations. Temperatures by contrast have been remarkably steady except for three periods of cold (when there was ice at the poles) and a period of semi cold. There is no correlation between the CO2 and the temperatures. During the first of these periods of cold, which was probably even colder than now, CO2 was at about 4,000 ppm - ten times higher than now.

The Cambrian was the golden age of life on Earth, seeing an astonishing proliferation of life forms (this is sometimes known as the "Cambrian Explosion"). CO2 during the Cambrian was sometimes over 6,000 ppm. All of the burgeoning life forms then, which are the grandmothers and grandfathers of everything since, including ourselves, flourished under very high CO2 levels.

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What is the ideal level for us now? I'd guess about 1,500 to 2,000 ppm. Our present level, 400 ppm, is much too low. The level in the 19th C, 280 ppm was dangerously low.

The lowest level in the ice ages, 180 ppm, was on the edge of catastrophe. (In the post script after this, I'll attempt an explanation for the two drops in CO2, each threatening massive extinct, each rescued by quite different saviours.)

2. CO2 as a toxin CO2 is a clean, safe, natural gas upon which all higher life forms are dependent. In plants it is a feedstock. In humans it is an essential part of our control metabolism.

Animal bodies cannot detect oxygen levels directly in the blood so they regulate breathing on CO2. When levels are high they breathe quicker or deeper. When we breathe out, we breathe out air with CO2 at about 40,000 ppm (4%). Newly born babies often have air with CO2 at 100,000 ppm injected into their lungs to stimulate breathing.

No toxic effects of CO2 below 15,000 ppm have been seen. 5,000 ppm is the level set for continuous exposure by the American Conference of Industrial Hygienists but this is just a guess for good practice, not based on any harm seen at this level Page 2

3. Plants benefit from CO2 above 1,000 ppm Horticulturalists routine inject CO2 into their greenhouses at levels of 1,000 ppm or higher. The plants thrive on it, producing better yields. If you go to www.co2science.org, you will see the test results of a huge variety of plants grown under enhanced levels of CO2. The results overwhelming show benefits of CO2 much higher than our present low levels of 400 ppm.

4. Solar changes not CO2 caused recent temperature changes Over the last 10,000 years, following the end of the last ice age, there has been a series of temperature rises and falls. These are closely correlated to changes in solar output and have very little correlation with CO2. When the Sun is active, we have warming; when the Sun is inactive we have cooling. Whether CO2 goes up or down makes little difference. During the Mediaeval Warm Period, approx 900 to 1200 AD, temperatures all around the world were rather higher than now while CO2 was lower than now. They were higher still in the previous Roman and Minoan warmings when CO2 was low. The key Solar activity is not total energy emitted but the emission of charged particles and the strength of the magnetic field.

Nuclear power is the only generation technology that can reduce CO2 emissions. Since I am strongly pro-nuclear, I wish I could use this as an argument in favour of it. But I cannot.

Postscript: Explanation of CO2 falls Fall 1. After the Cambrian, CO2 levels dropped towards disaster and then recovered.

The usual explanation is this. When plants arrived on land, there were micro-organisms that could metabolise their tissues when they died and so released their carbon as CO2.

But then woody plants evolved lignins for structural strength. Nothing could metabolise lignin. So its carbon could not be liberated and was sequestered as coal. Then along came the first saviour, white rot fungus, which could break down lignin and release its carbon into the air.

Fall 2. Over the last 50 million years, shell making marine organisms proliferated. They convert CO2 to calcium carbonate, which nothing can metabolise. So the carbon gets sequestered into chalk and lime and never returns to the air. This went on until very recently. The new saviour? Us! We burn fossil fuels and use calcium carbonate in cements kilns - and so we have saved the planet.

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