Doug Edmeades: Carbon dioxide - friend or foe?

There's an upside to increasing C02 in the atmosphere, argues Doug Edmeades.

Over the last 30-odd years Earth has been getting greener as a consequence of the increasing atmospheric CO2 concentration.

Over the last 30-odd years Earth has been getting greener as a consequence of the increasing atmospheric CO2 concentration.

OPINION: One of the talks I enjoy presenting to farmers is my Soil Fertility and Pasture Nutrition 101. It centres on the simple and elegant fact that plants need 16 nutrients. These are referred to as the "essential nutrients", meaning they are required for the plant to grow and complete its reproductive cycle.

Some, the macro-nutrients, are well known; nitrogen (N), phosphorus (P) potassium (K) sulphur (S) and magnesium (Mg). Some trace elements, for example molybdenumn (Mo) and copper (Cu), will be familiar. We need not concern ourselves with all of them at this stage.

What surprises most farmers – and this applies I have no doubt to the great unwashed, is the realisation that carbon (C) is also an essential nutrient and that its source as far as plants are concerned is carbon dioxide (CO2). In this sense atmospheric CO2 is a fertiliser.

What are the properties of this particular fertiliser? Carbon dioxide is colourless and odourless. Those white plumes of gas you see belching from factory chimneys are therefore not CO2, despite the implication that the viewer is generally invited to take in this "man-induced-climate-change" world.


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The atmosphere contains about 0.03 per cent CO2 (about 390ppm). Plants take up carbon dioxide from the atmosphere by photosynthesis, converting it initially into sugars from which the complex carbohydrates that form the structure of the plant, are 'built'. Pasture plants typically contain about 40 per cent carbon and have a carbon:nitrogen ratio of 10:1.

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As with all fertilisers, plant growth increases as the concentration of the essential nutrient increases, at least up to some point. So, too, with the fertiliser CO2. Indeed, hundreds of scientific studies have quantified the effect that increasing CO2 concentration has on plant growth.

I can recall back in my MAF days that considerable money was spent at the then Levin Horticultural Research facility sealing a glasshouse so that they could experimentally modify the 'atmospheric' CO2 concentration to study its effect on plant growth – getting those tomatoes off to the market sooner?

Dr Craig Idso, the founder of the CO2 Science website ( has compiled a list of 45 crops which make up about 95 per cent of the world's food production. He then calculates, based on this scientific literature, the likely increase in production for each of these crops, as a consequence of increasing the CO2 concentration by 300ppm. Depending on the crop, the range is from 13 to 77 per cent and typically 30-40 per cent.

From this information he calculates the increase in dollar value of these crops worldwide, assuming an increase in CO2 from 280ppm (the 1961 concentration) to 390ppm (the 2011 concentration) and then from 390ppm to 700ppm (the estimated CO2 concentration in 2050).

The estimated annual value of these crops for the 50 years (1961 to 2011) increased from US$18.5 billion in 1961 to $140b in 2011. The sum of the annual benefits over this period was US$3.2 trillion. The accumulated increase in the value of the 45 crops from 2012 to 2050 was estimated to be $9.8t. As I tease famers, "no one has gone broke putting on fertiliser."

This is not, I assure you, pie in the sky. There is now evidence, derived from satellite imaging, that over the last 30-odd years Earth has been getting greener as a consequence of the increasing atmospheric CO2 concentration. This is of course consistent with the science above and indeed was predicted many years ago. The figures are: 25- 50 per cent of the vegetative land on earth is now 14 per cent greener (measured by leaf area index) and that 70 per cent of this effect is due to CO2, as distinct from solid fertiliser use or improving climatic conditions.

We could crudely apply some of this logic to New Zealand's pastoral sector. This sector currently earns about NZ$28 billion annually in exports. Assume that the CO2 will increase by 300ppm from now to 2050 and that this will increase pasture production by about 30 per cent. Thus, the predicted increase in annual export earnings for this sector will be about $8b, give or take a little.

In other words by 'deliberately' increasing the concentration of carbon dioxide in the atmosphere the pastoral sector would easily meet the Government's aspirational goal for the sector to increase productivity by 20 per cent by 2025.

These large financial benefits which arise from increasing the concentration of fertiliser CO2, need to be offset against the predicted costs of increasing CO2, assuming it causes global warming. This is how Wikipedia summarises the state of knowledge:

"Many analyses, such as that of the Stern Review presented to the British Government, have predicted reductions by several per cent of world gross domestic product due to climate related costs such as dealing with increased extreme weather events and stresses to low-lying areas due to sea level rises. Other studies by independent economists looking at the effects of climate change have found more ambiguous results around the range of net-neutral changes when all aspects of the issue are evaluated, though the issue remains intensely debated."

So there you have it folks. The certitude of the agronomic science versus the uncertainty of climate and economic models. "Old King Coal was (is?) a merry old soul …. You choose.

Dr Doug Edmeades, MNZM, is an independent soil scientist and managing director of agKnowledge. He is happy to hear from readers:

 - Stuff


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