Balance is important!

Carbon dioxide (CO2) is a fertiliser because it carries one of the 16 essential nutrients (carbon, C) required for plant growth.

Plants acquire this essential nutrient in the form of CO2 via a process called photosynthesis. The rate of plant growth is directly related to concentration of CO2 in the atmosphere, all other things being equal.

I can recall as a young scientist in the then Ministry of Agriculture much talk about a new special glasshouse being constructed at the Levin Horticultural Research Station.

It was special because it was sealed so that plant growth - in this specific case, tomatoes - could be enhanced by increasing the concentration of CO2 in the atmosphere!

There is now a large body of research quantifying this effect. From this data it is predicted that if atmosphere CO2 was increased by 300ppm - and this, some say, is possible given current emissions - plant growth will increase by about 30-40%. A fertiliser indeed!

Satellite images have captured this fertilising effect. The planet is becoming greener, and this effect is most discernable in arid areas. Why should this be?

The "skin" - the outer layers of the plant leaf - have little openings called stomata through which gases can enter (e.g. CO2, water) and leave (oxygen and water) the plant.

As the CO2 increases, the number and the size of these stomatal "holes" decreases and consequently the plant becomes more efficient at using water.

The rule of thumb is that if you double the CO2 concentration, the amount of water required by the plant is halved. These, I emphasise, are not trivial effects!

These scientific facts about the important role of CO2 are immutable and therefore we should be very careful how we use words like "pollutant" and "decarbonise" when talking about CO2.

That "stuff" that you see pouring out of industrial chimneys cannot be CO2 for the simple and sufficient reason that the gas CO2 is colourless. That acrid smog hanging over our large cities is not CO2 because CO2 is odourless. The pollution - the smog, if you like - that you can see is largely due to micro-particles suspended in the air, not CO2.

So, can we agree to stop calling CO2 a pollutant?

Similarly, some balance is required when talking about the negative effects of CO2, especially in the context of agriculture. Sure, farmers need to be informed if their district is likely to become more arid because of global warming. But equally they should be informed that pastures will grow much faster, and they will be more drought resistant!

The whole narrative around 'climate change' has become clumsy and if we are to make progress in controlling the beast, we need to remain balanced.

Dr Doug Edmeades spent 20 years as a soil scientist at Ruakura. In 1997, he established his own science consulting business which has evolved into agKnowledge.